109 - Bridge Preservation Strategies
Bridge Preservation projects include one of two types of bridge projects: Bridge Rehabilitation or Preventive Maintenance. Work on bridges tends to coincide with preventive maintenance, which is a cost-effective treatment for an existing roadway system that preserves the system; retards deterioration; and maintains or improves the functional condition. Bridge rehabilitation involves major work to restore the structural integrity of a bridge, widen roadways, and correct major safety defects.
Both preventive maintenance and rehabilitation strategies are described in Section 109. Preventive maintenance will include, but is not limited to, the following:
- Patching, repairing, and sealing concrete
- Bridge deck overlays and waterproofing membranes
- Repairing cracks in concrete
- Painting structural steel
- Sealing and replacing deck joints
- Improving deck drainage
- Power washing
Rehabilitation of culverts and retaining walls is included in Section 109 due to similarities in design and construction.
The Department evaluates several factors in the identification and prioritization of bridge rehabilitation candidates. These include:
- Bridge health index
- Structural sufficiency rating
- Historical significance
- Functional class
- Truck traffic volumes
- Bridge load capacity
- Fracture susceptibility
- Scour susceptibility
- Detour length
- Benefit/cost analysis considering lifecycle costs
All Delaware bridges in the NBI are inspected at least every other year to evaluate their condition. Bridges not on the NBI are inspected at least once every 4 years. Bridges not owned by the state are inspected by the Department, except bridges owned by the Delaware River and Bay Authority. Bridges must be inspected to be eligible for Federal-aid funds. Inspections are performed in accordance with the Department’s Bridge Inspection Manual (2011) and the NBIS.
NBI inspections provide an overview of the major bridge components—i.e., deck, superstructure, and substructure—as well as an appraisal of the structural adequacy and functionality of the bridge. Preventive maintenance is also eligible for Federal funding, according to a state and Federal agreement initiated in 2008, based on a FHWA Memorandum dated October 8, 2004.
Information from the inspections is entered into the AASHTOWare BMS, formerly known as Pontis™, by the Department’s Bridge Management Section. The BMS uses element-level inspections to determine the most cost-effective action for a given bridge element in a given condition state and generates a list of bridges with recommended maintenance, repair, and rehabilitation (MR&R) actions. This list of bridges is then ranked according to “deficiency points” using the Department’s Bridge Deficiency Formula for selecting bridge replacement, rehabilitation, or preventive maintenance projects.
Other sources of information used by the Department’s Bridge Management Section include:
- Bridge safety inspection file and structure data records (SDRs)
- Traffic counts from Division of Planning;
- Delaware’s Historic Bridges Inventory
- Paint Condition Index listing
The Bridge Management Section screens all the information collected for work that can be performed by the District’s forces or by their structure maintenance contracts. The remaining bridges are sent to the Bridge Design Section for investigation. Their investigation will include a review of the inspection reports and a field review. Based on their findings, a prioritized list of deficient bridges is added to DelDOT’s Bridge Design projects for funding approval. Most projects are then initiated through DelDOT’s Bridge Preservation Program through the Department’s Capital Transportation Program (CTP).
Bridge improvement projects may necessitate improvements to conform to new roadway geometry. It may be necessary to widen a bridge or add shoulders, sidewalks, railings, or other improvements to eliminate hazards at bridge sites, even though the bridge may not have a high deficiency rating. The designer should evaluate what is needed—rehabilitation or replacement—in accordance with Section 103.8 – Bridge Rehabilitation versus Replacement Selection Guidelines, giving full consideration to the deficiency rating, the condition of the bridge, its remaining service life, and the purpose and goal of the project.
Some bridges may have to be rehabilitated because of unforeseen emergency circumstances, such as fire damage, washouts, or structural damage from traffic. The priority given these emergency projects by the Department will depend on their impact on traffic, the ease of detouring traffic, and the severity of the deficiency. Eligibility for Federal funding will be determined on a case-by-case basis.
109.1.1 Bridge Inspections and Load Ratings
In-depth bridge inspections at the beginning of projects assist in making rehabilitation versus replacement decisions. In general, an in-depth bridge inspection shall be conducted by the designer as part of the scope of work to assess rehabilitation needs and perform load ratings. The inspection may include both destructive and nondestructive testing, as needed, and will enable detailed information to be gathered for the as-built and as-inspected load ratings, and for possible strengthening of particular elements of the bridge. The designer shall review the original design drawings, as-built drawings, and any rehabilitation drawings prior to the start of the work, and include field-verification of critical information. Load ratings are to be conducted in accordance with the AASHTO Manual for Bridge Evaluation (2013) using Part A – Load and Resistance Factor Rating (LRFR) procedures. Load rating should be considered in any rehabilitation versus replacement decision. If a recent rating is not available, the designer shall rate the structure using LRFR. All rehabilitated structures shall be load-rated using LRFR procedures upon completion of the design work.
109.1.2 Environmental Considerations
The Department encourages recycling materials obtained from the demolition of structures and roadways. However, the designer must be aware of the environmental aspects of bridge rehabilitation. Many older structures used materials in their construction that are environmentally unacceptable today. The designer must be aware of environmental permit requirements and conditions for removal and disposal of hazardous materials such as utility conduits containing asbestos, creosoted timbers (and surrounding soil), and lead paint, or their by-products.
For bridges eligible for Federal funding, the designer shall consult 23 U.S.C. 144 regarding use of debris from demolished bridges and overpasses, requiring that debris from the demolition be made available for beneficial use by a Federal, state, or local government unless such use obstructs navigation.
The designer must evaluate all demolition to be encountered on the project to ensure that removal can be performed using commonly accepted methods both safely and economically. Demolition methods are the responsibility of the contractor. The Department reviews proposed demolition and shielding plans in the course of pre-construction reviews and during construction.
109.1.3 Rehabilitation Design Criteria
Existing bridge ratings are to be considered when developing the scope of bridge rehabilitation by defining the desired load ratings. The basis of design for bridge rehabilitation is AASHTO LRFD. The resulting rehabilitated structure is to meet the desired load ratings specified by DelDOT. Refer to Section 108 – Bridge Load Rating.
For all widening, confirm that the available existing bridge plans depict the actual field conditions. Bring to the attention of the Bridge Design Engineer any discrepancies that are critical to the continuation of the widening design.
For existing bridges, assume the target service life is 75 years, unless a LCCA to rehabilitate any one primary component (i.e., substructure, superstructure, or deck) determines otherwise. For additional information, the designer should refer to the draft publication Design Guide for Bridges for Service Life, SHRP 2 Renewal Project R19A (TRB, 2013). The scope of a bridge rehabilitation project shall be developed to achieve the service life of the bridge. The target life for the rehabilitation work shall not be less than 30 years.
109.2 Material Testing
Several laboratory tests (Table 109‑1) are available for determining the properties of the existing concrete from core samples removed from bridge decks, structural beams, columns, etc. These tests, along with additional field tests, are typically performed when conditions warrant.
|Table 109-1. Laboratory Test Methods|
|Tests performed by DelDOT Materials & Research (M&R) Section|
|AASHTO T24 (ASTM C42)||Obtaining and Testing Drilled Cores and Sawed Beams of Concrete|
|ASTM C856 (Annex A only)||Petrographic Examination of Hardened Concrete|
|AASHTO T260||Sampling and Testing for Chloride Ion in Concrete and Concrete Raw Materials|
|ASTM C1583||Tensile Strength of Concrete Surfaces and the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by Direct Tension (Pull-off Method)|
|ASTM C457||Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete|
|Tests performed by Outside Agencies|
|ASTM C856||Petrographic Examination of Hardened Concrete|
|ASTM C876||Corrosion Potentials of Uncoated Reinforcing Steel in Concrete|
|ASTM C1202||Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration|
188.8.131.52 Compressive Strength
Concrete cores for testing should be at least 3.70 inches in diameter, or two times the nominal maximum size of the coarse aggregate, whichever is larger. The preferred length is twice the diameter; however, shorter cores may be used if there is insufficient member thickness, but minimum length-diameter ratio should not be less than 1. Obtaining, preparing, and testing of cores shall be performed in accordance with AASHTO T24 (ASTM C42).
184.108.40.206 Alkali-Silica Reaction Evaluation
Alkali-silica reaction (ASR) is the susceptibility of certain aggregates composed of various silica minerals to chemically react with alkalis such as sodium and potassium found in Portland cement to produce an expansive gel. The swelling form of the gel requires a minimum amount of calcium hydroxide to be present in the concrete.
If ASR is suspected, in accordance with ASTM C856, Annex A, a qualitative test can be performed by the Department’s M&R section using the uranyl-acetate indicator method to test for the presence of ASR. If ASR is determined to be present at high levels, then a petrographic analysis may be recommended.
Concrete core samples should be removed from suspected ASR-affected decks and concrete members for petrographic and stereo microscopic evaluation by a petrographer experienced in evaluating ASR-affected concretes, and tested to determine the extent of reactivity, strength, and modulus. Petrographic examination should be performed in accordance with ASTM C856. Refer to Section 220.127.116.11 – Petrographic Analysis, for additional information.
18.104.22.168 Chloride Content
Studies have shown that chloride contents above about 0.02 to 0.03 percent by weight of concrete (1.0 to 1.5 pounds per cubic yard), depending on the cement content, can promote corrosion of embedded uncoated steel in non-carbonated concrete (ACI 201: Guide to Durable Concrete ). Levels below this threshold can accelerate corrosion in carbonated concrete.
To determine chloride content of the concrete with depth, sample chlorides using 0.25-inch-thick slices of a 4-inch-diameter core centered at the following depths: 0.375 inch, 1 inch, 2 inches, and 3 inches. Test at lower depths if the 3-inch layer shows significant chloride contamination; or at the depth of the top steel reinforcement if it is deeper than 3 inches. Also, determine the background or baseline chloride concentrations using at least two samples from depths great enough that the chloride value is not affected by chloride penetration from the surface. This provides the chloride concentration in the as-mixed concrete. Plot the chloride content versus depth. Testing should comply with AASHTO T260, using procedures for determining water-soluble chloride content.
For bridge decks, chloride concentration levels tend to be higher in the upper layers and the gutter area than those in other parts of the deck. Consequently, different areas of the deck may require different actions. Generally, core sampling for non-overlaid decks should consist of one core per 2,000 square feet of deck area, but no less than three for chloride ion testing.
The resistance of concrete to damage from freeze-thaw cycles (e.g., surface scaling, spalling, crumbling) is significantly improved by the use of intentionally entrained air. As water in moist concrete freezes, it produces osmotic and hydraulic pressures in the capillaries and pores of the cement paste and aggregate. The hydraulic pressure is due to the 9 percent expansion of water upon freezing in water-filled cavities. The osmotic pressure typically develops in cement paste from differential concentration of alkali solutions, whereby water is drawn from lower alkali pores into higher alkali ones. Entrained air creates voids that act as empty chambers to allow the freezing and migration of water to take place.
The air content of hardened concrete and of the specific surface, void frequency, spacing factor, and paste-air ratio of the air-void system can be determined by microscopic examination of polished sections in accordance with ASTM C457. The spacing and size of the air-voids may be determined using Procedure A or B. The durability of the concrete may then be assessed by interpreting the results in accordance with the guidelines given in Appendix X.1 of ASTM C457.
22.214.171.124 Half-Cell Potential
A half-cell analysis measures the active corrosion and corrosion potential of embedded reinforcing steel. This is done by measuring the electrical potential between two points. Half-cell readings are usually taken on the concrete surface along a grid pattern at 4-foot intervals. As part of the half-cell analysis test procedure, one wire (+) of a high-impedance voltmeter is attached to the reinforcing steel. The second wire (-) is attached to a copper-sulfate half-cell electrode (CSE). This test procedure is conducted in accordance with ASTM C876.
By taking readings of half-cell potentials at multiple locations, an evaluation of the corrosion activity of the embedded reinforcing steel can be made. ASTM standard C876 states that there is a 95 percent probability of corrosion if the CSE half-cell potential is more negative than -0.35V, but that corrosion is uncertain when potentials are between -0.20 and -0.35V.
126.96.36.199 Petrographic Analysis
Petrographic analysis is a microscopic examination of a concrete sample. Examination of hand-specimen or thin-sections provides a great deal of information about the constituents of the concrete, features of deterioration, and details of the mechanisms producing deterioration such as voids, micro-cracking in coarse aggregate, and cracking or debonding between the aggregate and the cement grout. Petrography can also be used to determine original mix proportions, including cement and aggregate type, water/cement ratio, air content and chemical admixtures used, as well as other physical features.
Samples for examination should preferably be 6-inch by 4-inch in cross section if possible, but no less than 4 inches in diameter. Sampling and visual examination should be performed in accordance with ASTM C823. Petrographic examination should be performed in accordance with ASTM C856 by experienced personnel.
Only a few laboratory tests are typically necessary for determining the composition and properties of existing bridge steels. These tests, along with additional field tests such as hardness, are typically performed to better characterize critical steel components that may be nonredundant, cannot tolerate any crack growth, or be subjected to necessary field welding.
188.8.131.52 Chemical Analysis
Chemical analysis should be performed in accordance with ASTM A751 practices, with percentages determined for carbon, manganese, phosphorous, sulfur, and silicon, at a minimum. The wet chemical test methods used for quantifying the individual elements for bridge steels are described more fully in ASTM E350. Samples may be obtained from remains of test coupons or from ½-inch-diameter steel slugs from drilled cores removed in the field. The carbon equivalent (CE) shall also be determined from the results to assess the weldability of the steel.
184.108.40.206 Mechanical Properties
Tensile tests are to be conducted in accordance with ASTM E8 methods. Full-size plate-type specimens should be obtained from the field whenever practical; however, standard ½-inch- and small-size ¼-inch-diameter cylindrical specimens may also be used. Specimens should be tested with the rolling direction parallel to the load axis. Results should be reported for tensile strength, yield strength, percent elongation, and percent reduction of area.
Impact tests should be performed in accordance with ASTM E23 methods using Charpy V-notch (Type A) specimens. Full-size specimens should normally be used. Subsize specimens may be used if approved by the Bridge Design Engineer. The designer shall specify the preferred orientation for the specimens, as well as the array of test temperatures. If a sufficient number of specimens is available, tests should be carried out at 0, 40, 70, 100, 150 and 212 degrees Fahrenheit (°F). If there is a limited number of specimens, tests should be carried out at the AASHTO test temperature for the material.
If tensile test specimens are not used, laboratory hardness tests may be performed on remnants of Charpy V-notch specimens, or other specimens removed from the bridge, and results correlated to approximate tensile strengths in accordance with ASTM A370. Either Brinell or Rockwell hardness values may be determined, depending on the anticipated strength level of the steel. Yield-strength–to–tensile-strength ratios (YS/TS) for known bridge steels may then be applied to estimate a minimum yield strength level for design. Note that portable hardness testers meeting the requirements of ASTM E110 shall be used for field applications only. Ultrasonic Contact Impedance or Dynamic Impact (Leeb) testers shall not be used.
109.3 Concrete Bridge Decks
109.3.1 Condition Survey
In addition to performing concrete laboratory tests discussed in Section 109.2.1 – Concrete, the designer or the Department will conduct field activities for characterizing the condition of an existing concrete bridge deck. The decision of whether the designer or the Department conducts the activities depends on the particular contractual obligations agreed upon; however, in most cases, the Department will perform the work. These activities include:
- Visual inspection
- Delamination survey
- Reinforcing corrosion survey
- Deck coring
The designer must request the needed tests (except visual inspection) from the Materials and Research Section unless otherwise directed from the Bridge Design Engineer. Determination of the proper deck rehabilitation strategy is most effective when based upon a broad evaluation of multiple test results, and not based solely on the results of any one particular test.
220.127.116.11 Visual Inspection
Inspection of a concrete deck involves the assessment of five important conditions:
- Cracking is a linear separation of the concrete matrix that may extend partially or completely through the concrete deck.
- Spalling is caused by the separation and removal of a portion of the concrete, leaving a roughly circular or oval depression in the concrete.
- Scaling is the gradual and continuous loss of surface mortar and exposure of the coarse aggregate due to frost and de-icing salts.
- Wear or polishing is the loss of skid resistance due to heavy traffic volumes passing over the concrete surface.
- Efflorescence is a white, powdery substance (calcium carbonate) that appears on the surface of the concrete along cracks due to leaching of calcium hydroxide from the cement paste, subsequent evaporation, and carbonation.
Each factor should be evaluated to determine the percent of deck area in each span that exhibits these conditions, and documented on a plan. In addition, an overall percentage for each condition should be computed for the total area of bridge deck.
Both the top surface and the underside of the concrete deck should be visually inspected. Cracks are best observed when surfaces are drying from recent rain, because the differential drying highlights fine cracks. The presence of a bituminous concrete wearing surface will prevent the visual inspection of the top of the deck. In these cases, the wearing surface may be partially or totally removed and the deck inspected; or the top of deck evaluation may be based on the observed condition of the underside of the deck. Likewise, where SIP forms exist, small portions of the form may be removed, especially in areas where leakage or corrosion is present. Typically, the top of the deck will have a condition equal to or worse than the bottom of deck.
18.104.22.168 Delamination Survey
The designer should chain-drag and hammer-sound the deck surface, and document the location, size, and amount of the delaminations on a plan. On large decks, select areas that are typical, and that can be surveyed in detail and used to estimate the overall deck condition. Generally, 100 percent of the deck area should be surveyed. This would include the traffic lane experiencing the most damage or having the most heavy truck traffic or de-icing exposure, and include the pier and joint locations. If less than 100 percent of the deck area is permitted by the Bridge Design Engineer, the surveyed locations should be sufficiently balanced so that a representative picture of the bridge condition is obtained.
Pull-off tests are conducted by the Department. These tests follow the procedures given in ASTM C1583, whereby a test specimen is formed by drilling a shallow, 2-inch-diameter core. The core is left attached to the concrete, and a steel disk is adhered to the specimen and pulled upward until failure occurs. The failure load, mode, and nominal tensile stress are then determined. A nominal tensile stress greater than 200 pounds per square inch is considered acceptable bond strength.
GPR can also be used to detect delaminations in bridge decks, particularly if the delamination has resulted in a wide void in the deck. GPR can also be used to locate reinforcing steel. This technique requires expertise to accurately gather and interpret data. If data collected with GPR are available, any delaminations that are identified should be documented on a plan.
The impact-echo method may also be used to detect delaminations in bridge decks. This nondestructive method involves introducing mechanical energy, in the form of a short pulse, into a structure. A transducer mounted on the surface of a structure receives the reflected input waves or echoes from the discontinuities (flaws) in the concrete. By determining a propagation velocity, reflected waves can be analyzed with a Fast Fourier Transform analyzer to determine internal characteristics of the concrete. This method can detect the size and location of subsurface flaws such as honeycombing, overlay debonding, delaminations, and large subsurface cracks. In addition, the method can measure the thickness of the concrete deck. Areas showing delamination should be documented on a plan and investigated further by removing cores.
Infrared (IR) thermography can be used to detect concrete defects such as cracks, delaminations and concrete disintegration. IR is not to be used as a stand-alone method, but may be used in conjunction with other methods. IR cameras measure the thermal radiation emitted based on the thermal properties of various deck constituents or defects, and captures the regions with temperature differences. The three main properties that influence the heat flow and distribution in the concrete include the thermal conductivity, specific heat capacity, and density. When solar radiation heats up a deck, all the objects on the deck emit some energy back. This energy is then converted into an electrical signal, which is further processed to create a surface temperature map. Delaminated and voided areas filled with water or air have a different thermal conductivity and thermal capacity than the surrounding concrete; therefore, these areas heat up faster and cool down more quickly, and develop surface temperatures from 1 degree Celsius (°C) to 3°C higher than the surrounding concrete when ambient conditions are favorable. The method does not detect deep flaws, however; and the method is affected by surface anomalies and boundary conditions, such as when sunlight is used as a heating source, clouds and wind can affect the deck heating by drawing heat away through convective cooling.
22.214.171.124 Reinforcing Corrosion Survey
The designer should perform/request a half-cell survey of the entire deck if practical; if not, survey a sufficient number of typical areas to fully characterize its condition. The technician should note whether epoxy-coated deck reinforcing is present in the top mat only or in both top and bottom mats. The technician should also note if bar electrical continuity is present and if the half-cell measurements are reliably measured. Refer to Section 126.96.36.199 – Half-Cell Potential, for additional information.
Sufficient readings should be taken on a 3- to 5-foot grid pattern. Plot copper-copper sulfate potential values as contours, and identify area having potentials more negative than -0.35V on a contour map. Points of equal electrical potential are connected by iso-potential lines. Areas of high negative potential and large potential gradients can be readily identified. The areas having steep potential gradients may be better indicators of actively corroding locations than the fixed -0.35V criteria. Deck surfaces altered by carbonation, sealers, or membranes may affect the reliability of the half-cell values, and essentially shift the potential values to indicate less-active corrosion. Coring and visually inspecting the condition of the reinforcing steel in selected areas to verify corrosion activity is recommended. Coring in several “nonsuspect” areas is also suggested to verify bar conditions where corrosion is not predicted.
A pachometer survey or other approved non-destructive test methods shall be conducted to locate the top layer of reinforcing steel and depth of cover throughout the surveyed deck area. Reinforcing depth is necessary for interpreting the significance of the depth of chloride penetration into the deck as described in Section 109.3.2 – Deck Evaluation. Decks with bituminous concrete-wearing surfaces cannot be tested unless the bituminous concrete is removed. The unit shall be calibrated to known bar covers and sizes prior to use.
188.8.131.52 Deck Coring
Coring bridge decks allow the designer to evaluate the compressive strength and concrete quality of the deck. Typically, 4-inch-diameter cores should be taken from several locations on the deck. When determining the number of cores to be obtained, consideration should be given to how these cores will be used for subsequent testing. Generally, core sampling for non-overlaid decks should consist of a sufficient number of cores for carbonation testing and petrographic examination, for compressive strength testing, and for chloride analysis. The recommended minimum number of cores is given in Table 109‑2. Removal and testing shall be in accordance with AASHTO T-24 (ASTM C42) procedures. Core locations shall be sited to avoid existing deck reinforcement.
|Table 109-2. Recommended Coring for Deck Testing|
|Material Tests||Area of Bridge Deck (square feet)|
|< 6000||6000 – 18,000||>18,000|
|Carbonation and petrographic analysis1||2 cores||3 cores||4 cores|
|Compressive strength||2 cores||4 cores||5 cores|
|Chloride analysis||3 cores||6 cores||9 cores|
Alternatively, samples for chloride analysis may be taken from the bridge deck at selected depths using the “Pulverizing Method” in accordance with Section 4.1.3 of AASHTO T260, subject to approval by the Bridge Design Engineer.
The designer should also test the exposed surface of cleaned drilled holes for depth of carbonation. Carbonation is known to lower the alkalinity of concrete and reduces corrosion protection for reinforcing steel. Testing can be done by first rinsing the hole with distilled water and then spraying it with a 1 percent phenolphthalein solution. Noncarbonated concrete will turn a bright pink/purple color, while carbonated concrete will remain colorless. Good-quality, noncarbonated concrete without admixtures will usually have a pH greater than 12.5. Record the depth of carbonation in the hole.
The designer should review all the compressive strength test results to identify the high- and low-strength areas and the concrete variability throughout the deck. It may not be necessary to remove the concrete in the high-strength areas. Removal of higher-strength concrete is more difficult, and the designer must alert the contractor to the variability of the concrete strength, especially when hydro-demolition is used.
109.3.2 Deck Evaluation
A “Deck Characterization” process is used to identify the current condition of the deck, and forms the basis for deck repair, rehabilitation, or replacement decisions. The process is described more fully in Guidelines for Selection of Bridge Deck Overlays, Sealers, and Treatments 2009, prepared by Wiss, Janney, Elstner Associates as part of NCHRP Project 20-07 Task 234, and sponsored by AASHTO. This document will be referred to from here on as the Task 234 Guidelines.
The Deck Characterization process is driven by assessing the four following factors:
- Percent Deck Distress and Visual Condition Ratings. This is determined by the percent of non-overlapping area of patches, spalls, delaminations, and CSE half-cell potentials more negative than -0.35V, by the NBI condition rating of the deck, and by a separate condition rating of the deck bottom surface. The rating for the underside of the deck is assigned using the same 0 to 9 scale employed for the NBI condition ratings. The determination of deck distress based solely on the NBI of the top deck surface is not allowed. As an aid, the following shows the NBI rating codes with supplemental information developed for bridge decks provided in brackets “[ ].”
- 9 Excellent [No visible distress]
- 8 Very Good [No visible distress except minor areas or fine cracking]
- 7 Good [Less than 1 percent patches and spalls]
- 6 Satisfactory [Deck shows minor spalling or moderate cracking]
- 5 Fair [Less than 10 percent patches and spalls]
- 4 Poor
- 3 Serious [More than 35 percent deck distress]
- The “Percent Deck Distress” and the “Percent Deck Distress and Half-cell Potentials less than -0.35V” are calculated as follows:
- Percent Distress = non-overlapping areas of spalls + patches + delaminations, as a percent of area surveyed.
- Percent Distress + Half Cell = non-overlapping areas of spalls + patches + delaminations + deck area with half-cell potentials less than -0.35 V (CSE), as a percent of area surveyed.
- Depending on the general deck condition, areas having sound, well-bonded concrete patches should be omitted from the total area of distress.
- Estimated Time-to-Corrosion. This is expressed as the time until sufficient chloride penetration occurs to initiate corrosion of the reinforcing steel. If the Percent Distress for a bare deck (i.e., no overlay) is greater than 10 percent, or the Percent Distress + Half Cell is greater than 15 percent of the surveyed deck area, consider the corrosion “Ongoing.” If percentages are less than these values, the designer shall determine the estimated time-to-corrosion initiation, using information from the chloride content analysis, depth of concrete cover information following the “Simplified Approach” procedures outlined in the Task 234 Guidelines. The expected depth of the chloride threshold front shall be calculated as follows:
- Depth in 5 years = current depth + (rate of advancement x 5)
If this calculated depth exceeds the 20th percentile depth of cover obtained from the cumulative distribution curve (determined from the histogram of field data collected for depth of concrete cover from the pachometer survey), report the time-to-corrosion as “< 5 years.” Similarly, if the depth exceeds the depth of cover after 10 years, report the time-to-corrosion as “< 10 years.” If the time-to-corrosion is greater than 10 years but the carbonation front exceeds the 20th percentile depth of cover, report the time-to-corrosion as “< 10 years.” The rate of advancement shall be determined from the tables given in Appendix B of the Task 234 Guidelines.
- Deck Surface Condition. Certain deck surface conditions require improvements to the grade or quality of the riding surface. These conditions may include drainage problems, cross-slope or grade problems, uneven joints, concrete surface scaling, abrasion loss, or poor skid resistance. Decks requiring grade corrections or new surfaces are better candidates for overlays or structural rehabilitation than for routine maintenance. Surface scaling occurs when the air entrainment in the near surface is lowered by poor finishing practices. This deterioration will stop after the poorly air-entrained surface layer deteriorates and is worn away. Alternately, the affected surface concrete can be milled and grooved to restore ride quality.
- Concrete Quality. Concrete bridge decks can be seriously affected by internal deterioration mechanisms such as alkali-aggregate reactions or delayed ettringite formation (DEF). Inadequate air entrainment results in concrete that will deteriorate due to cyclic freezing. Low strength could cause premature deterioration of bridge decks.
Typically, DEF is not common on decks because most decks are cast-in-place, thin, and not heat-cured. Deterioration due to cyclic freezing, although not common due to the routine use of air-entrainment, does sometimes occur on bridge decks. The service life of decks having poorly air-entrained concrete in cyclic freezing locations usually can be extended by placing an overlay to keep the concrete protected and less saturated with water, but in many cases it may be best to replace the deck.
Alkali-aggregate reactions can be moderate to severe depending on the aggregate properties and cementitious components of the concrete. The presence of alkali-aggregate reactions is a major concern, because deterioration can cause serious loss of deck integrity, and extending the service life of affected decks is difficult. Moderately large areas of concrete can fall away from the deck without significant warning in advanced cases of alkali-aggregate reactions, leaving only the reinforcing steel to support traffic. Repair of concrete decks determined to exhibit ASR must be considered carefully, and any proposed deck overlay or rehabilitation decisions are subject to approval by the Bridge Design Engineer.
Based on the assessment of the four factors above, Table 109‑3 is used to rate the significance of each finding and to direct the user to the most appropriate repair category. One of the following repairs is then selected for the deck:
- Do Nothing
- Maintenance, which may include:
- Crack repairs
- Concrete sealer
- Protective Overlay
- Rehabilitation, which may include:
- Partial deck replacement
- Full-depth deck replacement
Each characterization factor and the resulting input for the decision process are illustrated below. Any individual factor can result in the need for a greater level of repair in the hierarchy from “Do Nothing” to “Rehabilitation.” The “Do Nothing” option is selected only if all the factors rate within the Do Nothing category. A repair category is selected based on the factor(s) that indicate the greatest level of repair; or based on engineering or value judgments.
|Table 109-3. Deck Repair Evaluation Matrix|
|Do Nothing||% Distress||< 1%||> 10 years||none||none|
|% Distress + half cell||< 5%|
|NBI deck rating||≥ 7|
|underside rating||≥ 7|
|Maintenance||% Distress||1 – 10%||> 5 years or
> 10 years
|% Distress + half cell||1 – 15%|
|NBI deck rating||≥ 5|
|underside rating||≥ 5|
|Overlay||% Distress||2 – 35%||Ongoing to
< 5 years
|% Distress + half cell||10 – 50%|
|NBI deck rating||≥ 4|
|underside rating||≥ 5|
|Rehabilitation||% Distress||> 35%||Ongoing||yes||yes|
|% Distress + half cell||> 50%|
|NBI deck rating||≤ 3|
|underside rating||≤ 4|
The Do Nothing decision is appropriate for a deck in satisfactory condition with little corrosion risk in the next 10 years, or for a deck that is programmed to be replaced in the near future. It is sometimes more cost-effective to allow an older deck in poor condition to deteriorate further prior to the scheduled replacement, delaying the need for expenses related to the bridge, however, safety still remains paramount.
The Maintenance option is best for decks showing little or no serious distress, and with little risk of deterioration in the near future. For decks subjected to de-icing chemicals, cracks should be sealed or repaired. Most visible cracks (widths > 0.010 inch) can allow de-icers to rapidly penetrate into the concrete deck and corrode reinforcement. If the deck has moderately to highly permeable concrete, a surface sealer can be an effective way to reduce the amount of chloride ingress into the concrete over time. Maintenance such as patching and sealing of decks with or without existing overlays is also done. Deep removal areas should be patched independently prior to placing an overlay.
A protective Overlay is often appropriate if the deck has little to moderate deterioration, but likely will have significant deterioration in the near future. Bonded overlays (as opposed to hot-mix asphalt [HMA] overlays) provide a new wearing surface so deck surface conditions—such as cross-slope and grade, joint transitions, drainage, abrasion resistance, skid resistance, or scaling problems—can be improved. Overlays also provide good protection to decks having many cracks because existing cracks rarely reflect through a newly bonded overlay. Overlays are well-suited for decks in very high traffic areas, where it is expensive and very disruptive to replace the deck using staged construction. Bonded overlays normally add structural capacity to the deck because the deck is thickened; however, such additional capacity shall not be considered in design. Overlays do add dead load, which can be reduced by using thinner overlays or by milling the concrete cover prior to placing the overlay. If a deck has been previously overlaid several times, and the concrete cover is a problem, a partial-depth deck replacement needs to be considered (see next paragraph). Refer to Section 184.108.40.206 – Low-Permeability Overlays for further information.
Rehabilitation of decks with moderate deterioration that require grade or slope corrections are candidates for partial-depth replacement. Partial-depth deck replacement includes removing the existing concrete deck to below the top mat of reinforcing, and replacing with low-permeability concrete in the upper portion of the deck. A minimum of 1 inch of clearance below the upper steel mat is required to allow for proper consolidation of the new concrete below the mat. Replacement of damaged and corroded top reinforcing is done before placing the new concrete.
Full-depth deck replacement is warranted if the bulk of the concrete deck is not adequately air-entrained to resist continued scaling and cyclic freezing damage; is spalled with exposed reinforcing on undersides of deck; or is seriously affected by ASR. If not replaced, the deck should be inspected annually until an estimate of the rate of deterioration can be established. Decks with cracking due to ASR may benefit from treatment with high-molecular-weight methacrylate (HMWM) resin to bond cracks, but service life may be extended only 2 to 5 years. Alternatively, the use of a lithium treatment for bridges meeting certain requirements may be beneficial. Refer to FHWA-HRT-04-113 Protocol for Selecting Alkali-Silica Reaction (ASR) Affected Structures for Lithium Treatment (2004).
109.3.3 Deck Removal Methods
Typical methods used for the removal of concrete, in whole or in part, for the repair, rehabilitation, or replacement of bridge decks include:
The edges of areas to be patched must be saw-cut 1 inch deep into squares or rectangles. Saw cuts must be stopped at the corners to prevent overcutting. The corners must be hand-chipped. The rest of the removal is performed with jackhammers, hydrodemolition, or hand-chipping.
Jackhammer. The size of the jackhammer must be appropriate for the amount of removal to prevent unnecessary damage to the deck or superstructure. For delicate work, 15-pound demolition hammers shall be used.
Sawcutting. This method is prone to cutting the top flanges of girders and causing delays. Therefore, transverse cuts directly over girder lines are prohibited unless the designer provides supplemental direction or remedial measures to the contractor via notes or sketches shown on the Plans.
Hydrodemolition. Hydrodemolition is the use of high-pressure water jetting on a large scale to remove deteriorated concrete from bridge decks. The extent of concrete removal is primarily determined by concrete strength, water pressure, type of nozzle, and equipment speed. The designer must consider the strength of the concrete and the capability of the equipment before specifying this method of removal. Sufficient deck-condition data must be obtained to evaluate the removal needs. The designer must specify the minimum depth of concrete removal in areas with high concrete strengths, and estimate the quantity of removal in all areas.
Excessive pressure or inappropriate machine speeds will result in the removal of an excessive depth of concrete. To prevent this, the contractor is required to perform a demonstration in a test section. The designer must determine the size and number of test sections. Multiple machine settings may be required to match the depth of removal with the levels of deterioration and concrete strengths.
The depths and limits of removal and the number of test sections must be shown on the Plans.
Milling. Milling is used to prepare decks for complete overlays, or as an initial step when hydrodemolition is performed. The weight of the milling machine must be considered when milling bridges constructed with low or highly variable deck concrete strengths. The depth of concrete cover should be determined from the pachometer data collected as part of the Reinforcing Corrosion survey in order to avoid damage to the deck reinforcing.
Milling can be used to remove deteriorated wearing surfaces and to remove chloride-contaminated concrete. At least ½ inch to 1 inch of original concrete cover over the reinforcing steel must remain to ensure bar encapsulation. If the top portion of the steel is exposed in a chloride-contaminated deck, rapid corrosion of the steel can result in premature bond failures. Milling to near the top reinforcing layer may make future overlays more difficult, because little concrete cover is left over the steel; and this shall be avoided. If the reinforcing steel is exposed during milling, the concrete should be removed to at least ¾ inch below the steel using 15-pound demolition hammers. In general, the depth of milling should be kept to a minimum, but should be decided based on the condition of the deck surface; the chloride contamination profile within the deck; dead load; and roadway elevation considerations.
Refer to Section 220.127.116.11 – Temporary Protective Shield for requirements.
109.3.4 Preventive Maintenance and Rehabilitation
Preventive maintenance of bridge decks is defined as crack sealing, surface sealing (using silanes and siloxanes), coating (using thicker polyurethanes and epoxy resins), and patching applied to the top surface of the deck. Rehabilitation consists of overlays, partial- or full-depth deck replacement, deck widening, and barrier reconstruction—exclusive of isolated repairs or barrier maintenance. For associated repair or replacement of deck joints encountered as part of these activities, refer to Section 109.7 – Deck Joints.
For proposed work involving new concrete or concrete repair material cast next to existing concrete, traffic in adjacent lanes shall be prohibited until the concrete strength has exceeded 0.5 f’c to mitigate possible effects of traffic-induced vibrations. These requirements shall be specified on the Plans.
Any change in roadway profile or widening shall require a complete bridge-deck drainage analysis to be performed to determine the need for scuppers. Analysis shall be conducted in accordance with the FHWA’s HEC-21, Bridge Deck Drainage (1993), the DelDOT Road Design Manual (2004) Chapter 6 – Drainage and Stormwater Management (updated July 2008), and Section 18.104.22.168 –The Rational Method.
Repaired or widened bridge decks shall be designed by the Traditional Method. All new longitudinal and transverse deck reinforcement should match size, spacing, and coating of the reinforcement to which it is spliced. Also, deck thickness shall match existing thickness. Additional reinforcement shall be added as necessary to satisfy railing impact loads. Refer to Section 22.214.171.124 – Barrier Reconstruction for additional information.
The method of patching depends on the depth of the deteriorated area. A shallow repair is used where the depth of concrete deterioration is typically less than 2 inches, and reinforcing is not exposed. Deep repairs involve removal of concrete below the top mat of reinforcing steel, cleaning the steel, supplementing deteriorated steel, and placing and curing the repair material. A full-depth repair involves removing the entire thickness of concrete deck, cleaning the steel, supplementing deteriorated steel, and forming, placing, and curing the repair material. Generally, Portland Cement Concrete is used for deep-and full-depth repairs. For shallow repairs, several proprietary cement-based repair materials are available; however, asphalt shall not be used. Patches shall be made square or rectangular in plan; and edges sawcut 1 inch deep. For typical repair details, refer to Section 301.03 – Concrete Repair Details.
All delaminated areas must be removed. All chloride-contaminated concrete must also be removed, where the chloride concentration is greater than 0.03 percent by weight of concrete (1.5 pounds per cubic yard) found above the top mat of reinforcing steel.
If a shallow repair and patching is performed, the top surface of the deck above the top mat of reinforcing steel is to be removed without debonding, damaging, or dislodging the reinforcing steel. Removal can be accomplished by milling, hand-chipping, or hydrodemolition.
All new or existing bare reinforcing steel should be evaluated for the benefits of passive cathodic protection measures (e.g., point anodes or “hockey pucks”). Patching material must be compatible with the selected overlay, if one is subsequently applied. The surface must be patched prior to any overlay so that a uniform thickness will result.
If anchored temporary longitudinal barriers are installed as part of a traffic control plan, all holes drilled into the concrete deck must be repaired. The designer shall specify that the holes be filled with grout, and that the contractor submit repair methods to the Department for approval.
126.96.36.199 Low-Permeability Overlays
The goal of a bonded overlay is to have a low-permeability surface material. A Portland-cement–based composition must meet the “Very Low” chloride ion penetrability given in Table 1 of AASHTO T277 (ASTM C1202). The Department currently permits only latex-modified concrete (LMC), which consists of cement mortar or concrete mixed with styrene-butadiene latex. LMC may be used for thin patches, which may be placed concurrent with the overlay. The minimum thickness of an LMC overlay is 1¼ inches. The maximum thickness for LMC overlays is 2 inches. A structural analysis is needed for any overlay that increases the dead load more than 10 percent or 25 pounds per square foot, unless load ratings or existing design drawings indicate that such an increase in dead load can be permitted.
The minimum total clear cover over the top mat of reinforcing steel is 2½ inches for an overlay. Surface preparation is necessary to ensure the required bond between the overlay and the deck.
The designer shall review the chloride content with depth data, and determine the optimum depth of concrete removal and thickness of the overlay. If chloride concentrations at most bar depths are less than the chloride threshold CT (taken as 0.03 percent by weight of concrete (1.5 pounds per cubic yard) for black steel, or 0.15 percent (7.5 pounds per cubic yard) for epoxy-coated steel), limit removal to only contaminated concrete areas where chloride concentration exceeds the threshold value. Cathodic protection shall be implemented for heavily contaminated decks where chloride-contaminated concrete cannot be removed by milling.
188.8.131.52 Widening and Partial-Width Re-decking
Compressive strength, unit weight, thermal expansion, and permeability of the new cast-in-place concrete or concrete repair material shall be compatible with existing, sound concrete properties.
Either precast deck panels or metal SIP forms may be used in lieu of a formed cast-in-place deck. The designer shall assume cast-in-place deck construction, but shall compute deflections separately for SIP forms based on an additional 15 pounds per square foot dead load, and provide either of the following: two camber diagrams, double table entries, or separate notes stating percent reduction for “Total DL” deflections with and without use of SIP forms. For spans greater than 350 feet, the Bridge Design Engineer shall decide whether this information is to be provided or not.
For determining live load force effects in the slab, approximate methods of analysis in which the deck is subdivided into strips perpendicular to the supporting beams may be used, per Section A4.6.2 – Approximate Methods of Analysis, provided the difference in beam stiffness between interior and new exterior beams is not more than 15 percent. Differences greater than 15 percent will require more refined methods of analysis, in accordance with Section A4.6.3 – Refined Methods of Analysis, using grid or finite-element models.
184.108.40.206 Barrier Reconstruction
Whenever barriers are to be reconstructed or replaced on an existing deck slab that is largely to remain, the supporting deck overhangs shall be analyzed for the applicable design forces, in accordance with Section A13.4 – Deck Overhang Design. If necessary, additional reinforcing steel and/or supplemental anchorages shall be designed to meet the specified test level for the traffic railing (barrier).
Existing barriers to remain must be analyzed to determine their equivalent crash-load resistance (i.e., performance test level), and compared to the capacity of the existing deck overhang, as described above. If necessary, additional reinforcing steel and/or supplemental anchorages shall be designed for the overhangs to exceed the crash-load resistance of the existing barrier to meet the test level required.
109.3.5 Concrete Deck Replacement
Any deck other than cast-in-place concrete or precast concrete must be approved for use by the Bridge Design Engineer. The Department uses epoxy-coated reinforcing steel in all new and replacement decks, barriers, and barrier anchorages unless approved by the Bridge Design Engineer. Galvanized bars should not be used to supplement uncoated reinforcing bars.
Structural steel exposed during a deck replacement shall be cleaned and primed, as prescribed in Section 220.127.116.11 – Paint Systems.
18.104.22.168 Cast-in-Place Concrete
Both normal-weight and lightweight concrete may be considered for deck replacement, but the deck must be all normal-weight or all light-weight. Normal-weight concrete is preferred. The designer will specify the unit weight of concrete assumed in design. The bridge deck is to be designed by the Empirical Design method in accordance with Section A9.7.2 – Empirical Design. The Traditional Design method may be used subject to approval by the Bridge Design Engineer, or if the required design conditions given in Section A22.214.171.124 – Design Conditions are not met.
126.96.36.199 Precast Concrete
Consideration should be given to the use of precast deck slabs or deck panels during preliminary design. Use of standard details from FHWA ABC initiatives may be used when demonstrated to provide economic or project schedule advantages. For preferences related to ABC construction, refer to Section 103.9 – Accelerated Bridge Construction.
Precast deck slabs are manufactured full thickness in segments for placement on the beams. A concrete overlay is required for the final roadway surface. Slabs are typically post-tensioned in the final deck configuration; however, use of UHPC has been shown to eliminate the need under certain conditions. The designer shall confirm adequate room for the post-tensioning as part of the deck design and staging analysis.
Precast, prestressed concrete deck panels are manufactured partial thickness (usually 3½ to 4½ inches), and are placed to act as SIP forms. The remainder of the deck is cast-in-place to form a full-thickness composite deck. Precast, prestressed concrete deck panels are not to be used where bridge skews exceed 30 degrees.
For deck slabs or panels, the designer shall consider the following, at a minimum, in the design and staging analyses:
- Composite action requirements
- Staged construction deflections and haunch provisions
- Staged construction load capacity
- Details for attachment of the slabs or panels to the superstructure
- Horizontal shear connection between the deck and superstructure
- Joints between slabs or panels
- Final roadway profile and surface
Refer to NCHRP Report 584: Full-Depth Concrete Bridge Deck Panel Systems (2008) and PCI State-of-the-Art Report on Full-Depth Precast Concrete Bridge Deck Panels (2005) for design of precast slabs.
109.4 Steel Grid Decks
Grid decks are only to be used on bridges where reducing deck weight is a primary design issue. Steel grids preferably will be filled (flush-filled), partly filled, or surfaced (overfilled) with either normal-weight or lightweight concrete, but may be open to meet weight or drainage requirements. A separate wearing surface may also be placed in addition to the concrete fill. As stated in Section 109.3.2 – Deck Evaluation, Task 234 Guidelines outlines the common steel-grid deck repairs used in the United States. Some common practices are to replace the concrete overlay with an asphalt-concrete overlay or polymer-concrete overlay, and/or to coat the open steel grid with a zinc-rich primer.
Both painted and galvanized grid decks are permitted and shall be evaluated based on the designer’s judgment and the specific project requirements. The designer is encouraged to evaluate and specify more stringent fabrication tolerances, such as squareness, camber, and sweep, and increased installation requirements, such as minimum size and frequency of attachments, for new grid deck on highway bridges. The galvanization process has the tendency to warp the deck panels and create difficulties with field welding. If a warped panel is forced into place and fastened to the superstructure, induced stresses can cause the grid, the support member, or the connections to prematurely fail.
109.4.2 Existing Steel Grid Deck Evaluation
The designer shall conduct field activities for characterizing the condition of an existing grid deck. There are generally four considerations to be evaluated during a field survey of a steel grid deck:
- Connections between grid deck and the superstructure
- Corrosion of the grid and/or supporting elements
- Delamination of the surface
- Reduced skid resistance of the surface
Existing deck conditions are typically assessed through visual inspection. Each item in the list above shall be estimated to determine the percent of deck area that exhibits these conditions. The inspectors shall document all deck deficiencies on a plan. The percentages are used to determine the scope of the repair/rehabilitation plan.
In open-grid deck cases, a visual inspection along the top side of the deck is generally adequate in assessing the four survey items. However, the presence of a concrete fill will inhibit the inspection of the grid deck and connections. In these cases, an underside inspection is warranted to assess the underside of the grid deck, the connections, and the supporting members. If this type of inspection is not possible due to access restriction, space constraints, or other factors, selective removal of concrete fill for means of top-side inspection is recommended.
The field survey is used to identify the current condition of the deck, and forms the basis for deck repair, rehabilitation, or replacement decisions. Similar to Section 109.3.2 – Deck Evaluation for concrete bridge decks, four repair alternatives are provided once the condition of the grid deck is assessed:
- Do Nothing
- Patchwork/Localized Repair
- Partial or Full Deck Replacement
Note that the deck condition rating system adopted in Section 109.3.2 – Deck Evaluation is modified slightly and used herein for quantifying the severity of the four failure criteria. In general, deck distress that encompasses more than 25 percent of the deck area (or total quantity in the case of connections) is considered a serious condition worthy of partial or full replacement. Note that this value is a rule of thumb; the designer should ultimately use his/her judgment in determining the severity of the deck condition.
The Do Nothing decision is appropriate for a grid deck in satisfactory condition with very few failures, as outlined in the subsequent section (<1 percent deck distress), or a deck that is programmed to be replaced in the near future.
The Localized Repair option is best for decks with a few localized failures (<10 percent) that are not deemed to have significant risk of future deterioration. This alternative mainly covers a small patchwork of concrete fill (typically less than 5 square feet), and/or individual connection repairs, whether they are welded or mechanical fastener repairs.
The Overlay option is best suited for decks with little to moderate failures (<25 percent) that are likely to experience significant deterioration in the future, whether due to frequent exposure to de-icing chemicals and/or heavy traffic. Note that this repair alternative applies mostly to grid decks with existing concrete fill, and/or with an overlay. However, an open grid deck may be protected post-construction as long as the designer determines that the deck and bridge structure have adequate strength to handle the increased dead load.
The Deck Replacement option, partial or full, shall be implemented when a large percentage of the deck (>25 percent) has experienced one or all of the failure conditions described herein. The decision between partial or full replacement is the judgment of the designer, based on factors such as safety, traffic disruption, and cost.
The following subsections present the four evaluation considerations in greater detail. The aforementioned evaluation tools outlined in this section shall be considered for each of the four items.
188.8.131.52 Connection Failure and Fatigue
Grid decks are typically connected to the superstructure either by welding or mechanical fasteners. The connections are subjected to forces caused by the interaction between the grid and its supporting elements. These forces stem from vehicle loads, including those forces introduced through braking or accelerating. These connections may fail over time because of fatigue and other time-dependent effects.
When steel grid decks are subject to many cycles of loading and unloading (from 20,000 to over 5,000,000), the metal may fatigue and develop cracks in regions of high and localized stress. Left unaddressed, fatigue cracking can ultimately lead to the complete failure of the deck, the attachment of the deck to the supporting member, or the supporting member itself. The designer shall evaluate the severity of the condition and the remaining fatigue life of the existing connections (welds or fasteners) in accordance with AASHTO LRFD. This is especially important for movable bridges where the deck may be lifted high above the approach spans, causing additional safety concerns.
The grid bars (and the supporting purlins, stringers, and connections in the case of open grids) are exposed to road chemicals, including de-icing salts, which cause corrosion to develop in the steel grid deck system. Open-grid decks are more susceptible to these effects, but concrete-filled grids and those with overlays that contain cracks and spalls can contain corroded steel, as well. The connections can be subjected to expansion forces caused by corrosion of the steel grid (“deck growth”) relative to its supporting elements, which may then fail over time.
184.108.40.206 Delamination of Surfacing
Filled and surfaced grids can also be subject to delamination between the riding surface and the grid. This is of particular importance for cases in which the concrete fill is used for its strength. Repair of the concrete fill and/or deck overlay may be required in these situations.
220.127.116.11 Reduced Skid Resistance
Both open grids and concrete-filled grids (flush-filled) without surfacing are subject to decreased skid resistance over time. Unsurfaced filled or partly filled grids can develop cupping or wear of the concrete between the grid bars, which exposes the grid to direct wheel loads. The surface then becomes similar to that of an open grid, and skid-resistance quality declines. This is dangerous in wet weather, because water is held in the cups. In freezing weather, the hazard increases due to ice formation. When new, the riding surface of the grid elements presents some resistance to skidding, but wear causes a reduction in skid resistance. Ultimately, it is up to the discretion of the designer to determine the severity of the grid and/or overlay wear, and which repair alternative is most prudent.
109.4.3 Design Considerations
Refer to Section A9.8.2– Metal Grid Decks for the design of steel grid decks. Additional information provided in this section supplements those design standards.
Welded and mechanically fastened connections are both permitted. For the replacement of existing grating, the designer is to evaluate and specify the method of removing existing connections and installing new grating, and select the method of making new connections. The corrosion resistance of connections is to match or be superior to that of the grating. Removing and reapplying the galvanizing or painting is to be accounted for by the designer for cost and schedule impacts.
Where welded connections are used, specify a minimum weld size of ¼ inch by 3 inches in length, or alternatively ¼ inch by 1½ inches on opposite sides at each main grating bar intersection with supporting steel. Effects of the welded details on the fatigue performance of the supporting members must be evaluated. Specify a minimum grid-deck thickness of 4 inches. The designer is to provide the minimum section properties required for the design of the grid-deck panels. The designer is to detail typical panel joints and panel support details around cut-outs or special conditions.
Replacement grid decks shall be shifted along the primary support member to preclude welding the grid at the same locations as the previous welds. Attachment of the grid to the superstructure is a critical detail and must be closely evaluated.
109.5 Timber Decks
For inspection and evaluation of timber decks, refer to Chapter 7 of FHWA’s NHI 12-049 Bridge Inspector’s Reference Manual (2012). For the design and maintenance of timber decks, refer to Timber Bridges: Design, Construction, Inspection, and Maintenance (Ritter 1990).
Timber decks are to be considered nearing the end of their useful lives when exhibiting a number of signs indicating that there are problems, including:
- excessive deflection under load;
- loose connections as a result of shrinkage;
- deterioration, such as checking, cracking, crushing, or rot; and
- wear of the timber deck evidenced by protruding nails.
When more than 25 percent of the members need replacement, the entire timber deck shall be replaced.
Timber decks should be replaced with precast, voided deck panels or reinforced-concrete slabs unless weight or aesthetic concerns (i.e., context-sensitive) justify replacement with timber. Structural composite lumber (SCL), stress-laminated panels, and glue-laminated panels may be used if approved by the Bridge Design Engineer. Following replacement, a new deck should not be cause for posting or load limits.
109.5.2 Design Considerations
Use pressure-treated lumber. All hardware shall be hot-dipped galvanized, including gang nails and clips used to provide bracing for supporting beams. The designer is to confirm preservatives specified are compatible for service with galvanized hardware.
Detail timber where practical to stagger panel and runway joints.
Contract documents shall indicate whether timber dimensions shown are nominal or actual, and are to be used consistently. Dimensional variations in rough or full-sawn timber are to be considered by the designer in developing design and details.
A bituminous concrete overlay should be considered for use over timber decks for rideability and to meet skid-resistance criteria. Both a leveling course and a surface course shall be used. A waterproof membrane is to be used for bituminous overlays over timber decks.
For timber bridge rail, see Railing Systems for Use on Timber Deck Bridges (Faller et al. 1999) and the FHWA “Bridge Railings” web page at https://safety.fhwa.dot.gov/roadway_dept/countermeasures/reduce_crash_severity/listing.cfm?code=long.
109.6 Safety Considerations
It is desirable for safety items in completed projects to meet current Department and AASHTO standards when a deck rehabilitation or replacement project is constructed. These items include:
- Barrier rail;
- Approach guardrails and attachments to the structure;
- Curbs and/or sidewalks; and
- Approach guardrail end treatments.
The Bridge Design Engineer must approve design exceptions, where safety items at the completion of a deck rehabilitation or replacement project will not meet current Department standards.
For all NHS bridges, longitudinal barriers shall consist of bridge rail meeting Test Level 3 or higher requirements given in AASHTO Manual for Assessing Safety Hardware (MASH) (2016). For non-NHS bridges having design speeds less than 45 miles per hour, barriers may consist of bridge rail meeting Test Level 2 requirements, at a minimum. Highway safety hardware accepted prior to the adoption of MASH using the criteria contained in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features (1993) may remain in place and continue to be manufactured and installed.
Temporary longitudinal barriers used in construction zones shall meet the performance requirements for Test Level 3, unless unusual traffic type and volume require a different level.
Pinned-down F-shape barriers that incorporate pin-and-loop connections between 12½-foot-long barrier segments, two guide holes aligned 40 degrees from the roadway surface per segment, and 1½-inch-diameter by 21¼-inch steel drop-pins with ½-inch-thick plate covers that extend 6¼ inches vertically into the deck may be permitted by the Department (Sheikh and Bligh, 2009). Pinned-down F-shape barriers are to be used for temporary applications only.
Precast barriers attached to the deck using adhesive anchors will not be allowed.
Free-standing, unanchored temporary longitudinal barriers placed adjacent to deck openings shall be sited to provide sufficient clear distance behind the barrier to the opening to allow for the anticipated barrier displacement (i.e., maximum dynamic deflection) documented by crash testing and approval of the barrier system plus 1 foot. Otherwise, the barriers shall be rigidly attached to the existing bridge deck to transfer crash loads.
109.7 Deck Joints
The designer shall attempt to eliminate or minimize the number of deck joints whenever deck rehabilitation involves a partial-depth or full-depth deck replacement.
Refer to Section 106.6 – Deck Joints for the types of joint devices that may be used in Delaware. The designer should attempt to use sealed deck joints whenever possible, or provide sloped neoprene troughs under finger joints or sliding plates to control roadway runoff, for any deck overlay or deck rehabilitation project.
The limits of concrete deck removal on each side of an existing deck joint needed to install a new expansion joint device shall extend beyond the thicker, haunched slab section and be sufficient to allow for the replacement of the existing bent steel reinforcement.
109.8 Approach Slabs
Approach slabs are to be included in the condition evaluation of a bridge deck. Approach slabs are to be repaired or replaced when repairing or replacing bridge decks. If the approach slab has been previously overlaid with bituminous concrete, replacement with Portland cement concrete should be considered so the bituminous overlay is not needed. This should be done in conjunction with deck overlay or replacement.
Where approach slabs are undermined, repair by filling voids using one of the following:
- Cement grout (pressurized)
- Flowable fill
- Expansive polyurethane
The cause of the undermining can be leaking joints, therefore, reseal joints to prevent recurrence.
Existing bridges that currently do not have approach, but would otherwise be required per Section 103.3.7 – Approach Slabs shall have new approach slabs incorporated into the rehabilitation work.
109.9 Slabs, Beams, and Girders
109.9.1 Reinforced-Concrete Slabs
Typical simple-span, reinforced-concrete solid-slab bridges in Delaware have span lengths (as measured along the centerline of roadway) less than 35 feet, and roadway widths that carry two to four lanes of traffic between curbs. Many of these bridges are skewed, and built prior to 1970. Common practice consisted of placing the main bottom steel parallel to the curbs, and another layer of bottom steel parallel to the supports. Slab thicknesses ranged from 12 to 24 inches.
The primary tests used to evaluate slab bridges are visual examination, sounding, and coring. Additional testing options are the same as those used for concrete bridge decks. Refer to previous Section 109.2.1 – Concrete, and Section 109.3.1 – Condition Survey. In addition, the designer must evaluate each bridge for collision or fire damage, if suspected. Refer to the Commentary following Chapter 8, Part 21.3 of the AREMA Manual for Railway Engineering, Vol. 2 (2015) for information regarding the evaluation of fire-damaged concrete structures.
The designer must evaluate the structural effects of repairs and modifications—particularly the effects of concrete removal—on the capacity of the reinforced concrete. The need for shoring and falsework is to be determined, and is to be incidental to the design of repairs.
Repairs to slab bridges shall generally follow the materials and methods outlined for reinforced-concrete bridge decks. Refer to Section 109.3.4 – Preventive Maintenance and Rehabilitation. A pigmented waterproofing sealer should be applied to the entire underside and sides of the slab bridge to create a uniform appearance upon completion.
18.104.22.168 Design Considerations
When rehabilitating slab bridges, typically the direction of maximum bending moment can be taken parallel to the longitudinal direction of the bridge for all straight and skewed spans up to 45 degrees. Bending moments due to dead load in skewed bridges having “normal” span lengths less than half their width may be determined the same as for straight bridges (i.e., 0.125 pa2) (Jensen and Allen, 1947). Note that the normal span length “a” is measured perpendicular to the supported edges.
Approximate methods of analysis for live load using equivalent strip widths, in accordance with Section A22.214.171.124 – Equivalent Strip Widths for Slab-Type Bridges, shall be used for determining longitudinal reinforcing steel (i.e., parallel to traffic) in slab bridges. For transverse reinforcing and edge support, refer to Sections A5.14.4 – Slab Superstructures and A126.96.36.199 – Edge Support, respectively. When necessary, the designer shall investigate shear forces at the corners caused by transverse curvature and skew effects using refined methods of analysis or simplified equations (Theoret et al., 2012). In addition, existing slabs that do not meet the minimum recommended thickness requirements specified in Table A188.8.131.52.3-1 shall be investigated for shear.
For all widening projects, closure pours shall be used between existing and new slabs. The thickness of new slabs should match the existing. The designer must take into consideration significant differences in elastic moduli and coefficient of expansion between existing and new slabs when such differences could result in significant variations in the distribution of live load. New slabs shall be cambered to match existing slabs.
New slab bridges joined to an existing are to be made integral by splicing of reinforcing. All new reinforcing steel shall match the existing size, spacing, and orientation; however, grade 60 reinforcing steel may be spliced with existing grade 40 steel. Stiffened edges need not incorporate an integral structural component, but shall be designed to support the full self-weight of the concrete barrier, in addition to other dead and live loads. In addition, stiffened edges shall incorporate C-shaped reinforcing bars along the outside edge to provide increased shear ductility.
Voided slabs are not allowed.
184.108.40.206 Repair and Strengthening
Repair methods for reinforced-concrete decks involving patching have been given previously in Section 220.127.116.11 – Patching and are considered equally suitable for slab bridges. The designer shall also consider alternative repair methods for slab bridges, which may include the use of pneumatically placed concrete (shotcrete) and/or epoxy injection of cracks when applicable.
Shotcrete. The designer shall select the most appropriate shotcreting method (wet or dry) based on recommendations given in ACI 506R: Guide to Shotcrete (2005) or ACI 506.1R: Guide to Fiber-Reinforced Shotcrete (2008). The designer shall incorporate the following into the design and contract documents:
- At all construction joints, the shotcrete shall be tapered to the edge to permit overlapping of later material. Square joints are not allowed.
- The thickness of each coat should not be greater than 1 inch, and should be placed so that it will neither slough nor decrease the bond of the preceding coat. Where a successive coat is applied on shotcrete that has set more than 2 hours, the surface must be cleaned and water-blasted.
- The final surface of shotcrete should be given a rubbed finish.
- No reinforcement is required for shotcrete encasement less than 1½ -inches thick.
- A layer of reinforcement for each 4 inches (3 inches overhead) of thickness shall be required. Each layer should be 3-inch by 3-inch – W 1.4 × W 1.4 welded-wire reinforcing.
- For thicknesses in excess of 4 inches (3 inches overhead), an additional two-way system of No. 3 reinforcing bars in both directions shall be used. Bars shall be wired to anchors spaced no further than 6 inches apart in any direction. The last layer of wire mesh shall be secured by wiring to the bars.
- Mesh extending around corners or reentrant angles shall be shown bent to a template. At corners, double-reinforcing mesh should be provided and extended a minimum distance of 6 inches beyond the intersection of the two planes.
- When splicing wire mesh, a lap of 1½ mesh spacings shall be shown, wired together at intervals of not more than 18 inches.
- Where reinforcement is required for structural strength, engineering calculations must be furnished.
Epoxy Resins. Epoxy injection of cracks is an acceptable repair method. Some cracks are active, while others are not; therefore, the designer must determine the cause of the crack before attempting to seal or repair it. The designer shall select the most appropriate type of epoxy resin and viscosity depending on the need for structural bonding or waterproofing, based on recommendations given in ACI 546.3R: Guide for the Selection of Materials for the Repair of Concrete (2014) and ACI RAP-1: Structural Crack Repair by Epoxy Injection (2009). Crack widths exceeding the limits given in ACI 224R Table 4.1, “Control of Cracking in Concrete Structures,” and accompanied by efflorescence and rust staining, shall be repaired.
109.9.2 Prestressed Concrete Beams
Types of prestressed concrete beams considered in this section include adjacent box beams, spread box beams, and I-girders (AASHTO or bulb-tee sections).
Bridge-widening projects shall match the aesthetic level of the existing bridge. Additions to existing bridges should not be obvious "add-ons." Use the same superstructure type and depth where possible. Avoid mixing concrete and steel beams in the same span. Bearing fixity and expansion devices should be the same in both the widened and existing bridges. Bridges composed of existing beams made continuous for live load shall have new beams designed and constructed in a manner similar to the original design details.
When redecking existing bridges composed of prestressed beams made continuous for live loads, continuity diaphragms shall not be removed below the top flange due to “locked-in” stresses.
When redecking existing bridges constructed with integral abutments, end diaphragms extending below the top flange shall not be removed due to “locked-in” stresses.
The designer must evaluate each bridge for collision or fire damage if suspected. Refer to the Commentary following Chapter 8, Part 21.3 of the Manual for Railway Engineering, Vol. 2 for information regarding the evaluation of fire-damaged concrete structures.
When evaluating damage from collision, employ the following concepts:
- Exposed strands pose no immediate danger to the integrity of the beam unless there is a substantial loss of concrete.
- A nick in three or less wires of seven-wire strand may remain in-service.
- Severed or sharply bent wires are to be analyzed for increased strand stress and fatigue, and strands repaired or beam replaced accordingly.
- Severance of more than two strands is to be considered cause for beam strengthening or replacement, based on analysis.
18.104.22.168 Design Considerations
Design all widenings and rehabilitations in accordance with AASHTO LRFD.
When evaluating existing beams or designing new beams as part of a widening project, the designer shall follow the requirements described in Section 106.9 – Prestressed Concrete Bridge Superstructures for prestressed concrete beam bridges.
When evaluating the shear capacity of existing beams, those that fail to meet the current shear provisions may be reanalyzed using the original design method to determine their capacity as long as it has been verified in the field there is no significant shear-related distress.
When detailing connections and selecting or reviewing construction methods, the designer shall consider the amount of differential deflection between adjacent beams (existing or new) that may occur prior to placing the new deck. Field measurements taken before and after any deck removal should be used to determine the elastic properties of an existing beam based on the rebound.
For composite bridge decks, decreases in camber between new and existing beams after deck has cured due to creep, shrinkage, and other prestress losses need not be considered due to increased stiffness of the overall composite system. Differences in stiffness between new and existing beams due to elastic moduli must be considered by the designer.
The designer is to take into account measures to maintain the stability of prestressed beams during redecking and/or widenings, including bracing, temporary erection towers, and measures necessary for erection in the staging and outages allotted for the work. The designer shall check the stability of the beams in the erected condition and calculate the bracing locations and forces required. For simple spans, evaluate both roll stability and service stresses, assuming full prestress losses have occurred for the following construction conditions (Mast, 1989 and 1993):
- Unbraced beam set on bearing pads with construction wind load acting;
- Braced beam set on bearing pads with design wind load acting; and
- Braced beam set on bearing pads with construction wind load and wet concrete deck loads acting.
The designer shall evaluate the exterior beams of the existing structure for construction conditions and the final condition; e.g., after attachment of the widened portion of the structure.
Whenever time-dependent prestress losses or elastic modulus for prestressed beams need to be determined more accurately than estimated methods, the designer should consult NCHRP Report 496: Prestress Losses in Pretensioned High-Strength Concrete Bridge Girders (2003).
The cause of cracking is to be understood and evaluated for possible effects and the practicality of rehabilitation. Loss of prestress force and fatigue shall be investigated. Shear cracks, flexure/shear cracks along the bottom flange greater than 0.009 inch wide, spaced less than 12 inches apart, and longitudinal cracks accompanied by efflorescence and rust staining, shall be repaired (AASHTO, 2011). Flexural cracks that are tight (< 0.004 inch) need not be repaired.
22.214.171.124 Repair Methods
The Department’s preferred repair methods for prestressed concrete beams are discussed below.
Spalls and Cracks. When conventional, superficial-type repairs are needed for prestressed beams, the designer shall consider the following guidelines in preparing contract plans and specifications:
All deteriorated concrete shall be removed to sound concrete using pneumatic hammers that do not exceed a nominal 15-pound class. The sound concrete must exhibit a minimum surface profile of at least 0.125 inch, or as recommended by the repair material manufacturer.
Repair material shall have a compressive strength equal to or greater than the original concrete (when known), but not less than 4,500 pounds per square inch and 5,500 pounds per square inch at 7 and 28 days, respectively. In addition, the repair material shall have minimum bond strength of 200 pounds per square inch achieved with or without a bonding agent.
For concrete repair areas that equal or exceed 3 inches deep and 12 inches in any direction, mechanical anchorage and repair reinforcing is to be detailed.
Preload, if used, shall be specified on the contract drawings, along with assumptions and loading parameters used in repair analysis.
Cracks are to be repaired by epoxy injection as outlined in Section 126.96.36.199 – Repair and Strengthening.
External Reinforcing. Only non-prestressed carbon-fiber-reinforced polymer (CFRP) is to be used for external reinforcing. The designer must develop a conceptual design and provide calculations that summarize the assumptions and parameters used for the CFRP system and performance specifications that are to be included in the contract documents. The final design of the CFRP system will be the responsibility of the contractor.
Design in accordance with NCHRP Report 655: Recommended Guide Specifications for the Design of Externally Bonded FRP Systems for Repair and Strengthening of Concrete Bridge Elements (2010); and refer to NCHRP Report 609: Recommended Construction Specifications and Process Control Manual for Repair and Retrofit of Concrete Structures Using Bonded FRP Composites (2008), as well as ACI 440.2R: Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures (2008) in preparing the conceptual design, contract drawings, and performance specifications.
The strengthening obtained by the CFRP system shall be limited to prevent sudden failure of the beam under sustained service loads in the event the CFRP system is damaged. The designer shall perform an analysis and design of the strengthened member to ensure that the member will fail in a flexure mode rather than a shear mode under overload conditions.
As a guideline, the designer should consider beam replacement when 25 percent of the strands in a beam no longer contribute to its capacity, or if excessive flexure cracks are present, which indicate substantial loss of prestress (FHWA, 2009b).
External Post-tensioning. Design using high-strength steel rods or strands. Refer to relevant sections of NCHRP Report 280: Guidelines for Evaluation and Repair of Prestressed Concrete Bridge Members (1985) and FHWA/TX-97/1370-3F: Evaluation and Repair of Impact-Damaged Prestressed Concrete Bridge Members (1996). These repair methods are discussed in more detail in Section 109.11 – Foundation and Substructure.
Strand Splicing. Induce a tension in the strand equal to that of adjacent undamaged strands. Only commercially available splicers such as “Grabb-It” cable splices are acceptable. The designer shall determine the required shortening for each splice based on the desired prestress force, stiffness of the splicer, exposed length of strand, and strand transfer length into the concrete (FHWA, 2009b). Specify “turn-of-nut” tightening method. Provide sufficient concrete cover following the repair, which may include the use of blisters on the surface of the concrete.
109.9.3 Steel Beams and Girders
For any major rehabilitation, the structure must be left in a redundant state unless approved by the Bridge Design Engineer. Refer to Section 188.8.131.52 – Redundancy Requirements regarding definitions and requirements.
184.108.40.206 Design Considerations
The designer must determine the extent of section loss of each steel member due to corrosion. Corrosion-induced section loss must be measured and included in an analysis. Both the location and extent of section loss must be defined and included in any calculations. Methods for field inspection and evaluation may be found in NCHRP Report 333: Guidelines for Evaluating Corrosion Effects in Existing Steel Bridges (1990).
Net section properties for riveted or bolted members are to be calculated following the relevant provisions of the AASHTO Manual for Bridge Evaluation (2013).
When evaluating existing beams or designing new beams as part of a widening project, the designer shall follow the requirements described in Section 106.8.8 – Steel-Plate Girder and Rolled Beam Bridges for steel-plate girder and rolled-beam bridges.
Barrier loads shall be distributed 75 percent to the exterior and 25 percent to the first interior girder unless a refined method of analysis is used. A structurally continuous barrier on a composite deck may be considered a participating structural element for service and fatigue if it is adequately connected to the deck to transmit the horizontal shear, but not for strength or extreme event-limit states.
When strengthening is required (RFOPR < 1.0), beams shall be strengthened or replaced based on a cost comparison. Exterior beam with less capacity than interior beams that do not need strengthening may remain as-is, provided that the difference in stiffness between interior and exterior beams is less than 15 percent, based on steel only.
For design of slip-resistant bolted connections, Class A surface conditions between the existing steel faying surfaces are to be assumed for analysis (representative of unpainted clean mill scale) unless disassembling, cleaning, and painting are performed as part of the rehabilitation.
Deck replacements are to be designed and detailed to be composite with beams. For widening projects or partial deck replacements in which existing noncomposite bridge decks are to remain, the new concrete deck shall be designed and detailed to be composite. Consideration is to be given when designing shear connections for unintended contribution from the noncomposite deck sections.
Existing bridges with beams having stiffness that differ more than 15 percent (steel only), and bridges with skews or curved members (as defined in other sections of this Manual for new design), will require refined methods of analysis for determining load distribution.
For bridge widening, new diaphragms will match type and spacing of existing diaphragms.
For bridge widening, new beams must be sized to include the possibility of dead loads from SIP forms and future wearing surface. Existing beams should be analyzed for these dead loads, but loads may be omitted if strengthening is required. Refer to Section 220.127.116.11 – Widening and Partial-Width Re-decking regarding the calculation and presentation of dead-load deflections.
Existing members, or components of built-up members, that do not meet current LRFD limiting slenderness ratios (e.g., b/t, D/tw) shall be reexamined using more refined methods, provided the method is fully documented.
18.104.22.168 Repair and Strengthening
The preferred method of repair and strengthening is with shop welding and field bolting, except as noted for shear studs. Field welding must be approved by the Bridge Design Engineer. For all field welding, including stud welding, the weldability of the existing steel is to be confirmed. Table 109‑4 provides information on steel specifications and periods of use.
|Table 109-4. Structural Steels Used in Bridge Construction|
|Dates in Effect||Specification Title|
|A7||1900 – 1967||Steel for Bridges and Buildings|
|A8||1912 – 1962||Structural Nickel Steel|
|A94||1925 – 1965||High-Strength Structural Steel (silicon steel)|
|A140||1932 – 1933||Steel for Bridges and Buildings (tentative revision to A7)|
|A242||1941 – present||High-Strength Low-Alloy Structural Steel|
|A373||1954 – 1965||Structural Steel for Welding|
|A36||1960 – present||Structural Steel|
|A440||1959 – 1979||High-Strength Structural Steel (for riveted construction only)|
|A441||1954 – 1989||High-Strength Low-Alloy Structural Manganese Vanadium Steel|
|A514||1964 – present||High-Yield-Strength, Q&T Alloy Steel Plate, Suitable for Welding|
|A517||1964 – present||Pressure-Vessel Plates, Alloy Steel, High-Strength, Q&T|
|A572||1966 – present||High-Strength Low-Alloy Columbium-Vanadium Structural Steel|
|A588||1968 – present||High-Strength Low-Alloy Structural Steel 50 ksi Minimum YP to 4” Thick|
|A690||1974 – present||High-Strength Low-Alloy Steel H-Piles and Sheet Piling|
|A709||1996 – present||High-Performance Steel|
|A141||1932 – 1966||Structural Rivet Steel|
|A195||1936 – 1966||High-Strength Structural Rivet Steel|
|A502||1964 – present||Steel Structural Rivets (Grades 1 & 2)|
|Ref: FHWA’s NHI 12-049 Bridge Inspector’s Reference Manual, December 2012|
The preferred method for making existing members composite is with automatic stud welding. Weldability of existing steel is to be confirmed as part of the investigation and design by identifying carbon content and CE. This can be determined using existing mill certificates or by chemical analysis of the existing steel. If heat input and/or preheat requirements following AWS D 1.5 prove prohibitive, mechanically fastened shear studs shall be used.
Removal of existing rivets is to be performed by mechanical methods only. Burning, arc-gouging, or oxygen lancing is not allowed.
Repairs to corroded sections in primary load-carrying members must result in a minimum steel thickness of 3/16 inch remaining. Knife-edged steel is to be removed by cutting or grinding, and the edges examined by nondestructive testing such as Magnetic Particle.
Bridge rehabilitation is to include maintaining acceptable clamping action from existing rivets. The designer is to consider head deterioration and looseness in identifying rivets to be removed and replaced with high-strength bolts. A procedure for sequencing of the rivet/bolt removal and replacement is to be included in the repair details, as required to maintain structural integrity.
Reduction in vertical bridge clearance due to repair details involving additional coverplates and bolts is to be considered and documented on the contract plans.
22.214.171.124 Fatigue Evaluation and Repair
Factors to be considered during rehabilitation design regarding fatigue evaluation include bridge skew, cover plates, attachment plates, web gaps, web penetrations, out-of-plane distortion, and traffic data. All category D though E′ details shall be checked for infinite life. If infinite life is not indicated, then a more refined site-specific fatigue analysis shall be performed.
For riveted bridges, stresses in base metal shall be calculated using the net section at the rivets, with the fatigue threshold to be taken as 7 kips per square inch for infinite life checks. For riveted members that have tensile stresses resisted by three or more elements, fatigue strength (finite life) shall be checked against category C. For simple riveted shear-type connections (e.g., coverplate ends, gusset plates, truss hangers), fatigue strength shall be checked against category D, unless the rivets exhibit good clamping force and bearing ratios are less than 1.5, in which case category C shall be used. The bearing ratio is defined as the bearing stress of the rivet on the plate, divided by the tensile stress in plate. Stresses in category D shear-type connections may be checked against category C if the rivets are removed, and holes reamed and replaced with fully tightened high-strength bolts.
Tack welds found on bridges that are uncracked are not to be evaluated for fatigue unless evidence of cracking exists, or as otherwise noted below. Cracks determined by nondestructive testing to have merely severed the throats of tack welds but have not propagated into the base metal, or have separated from the base metal, shall be left in place. Partial depth cracks in the throats of tack welds shall be removed by grinding. Uncracked tack welds found in tensile zones of primary load-carrying members oriented in the direction of primary stress and subjected to maximum calculated stress ranges above 10 kips per square inch should also be removed by grinding.
For existing structures where details such as connection plates and stiffeners do not satisfy current practices for control of distortion-induced fatigue, the preferred approach is as follows:
- No current problems: do not fix.
- Isolated problems (e.g., distortion-induced web cracks, broken fasteners): analyze and fix problems only.
- Widespread/systemic problems: fix relevant details structure-wide.
Crack repairs must include accurate identification of crack tip location through nondestructive testing, and confirmation by nondestructive testing that crack tips have been removed. For crack repairs involving modifications to connections, analysis shall verify changes in stress fields to confirm satisfactory performance of the repair.
In addition to other repair methods such as end-bolted coverplates, Ultrasonic Impact Treatment (UIT) may be used at weld toes of coverplate and stiffener details where the fatigue resistance needs to be improved. Effectiveness is limited to removal of shallow micro-discontinuities (e.g., slag intrusions) up to 0.025 inch in depth at uncracked weld toes, and where cracking from larger discontinuities at weld roots is unlikely.
126.96.36.199 Fire Damage
Exposed portions of steel bridges subjected to temperatures above 1,100°F (evidenced by damage to the zinc or lead primer) will decrease yield strength by more than 50 percent, and modulus of elasticity by more than 40 percent, compared to the undamaged condition. As a result, steels may suffer plastic deformations by exceeding the yield strength, or buckling caused by member stresses exceeding the limit of elastic stability. The degree of damage will depend on the maximum temperature to which the steel was exposed, the duration of the exposure, and the member loading during the event. Steel embrittlement can also occur from prolonged exposure at high temperature, followed by rapid cooling from fire-extinguishing foams or water. In cases where the steel has been exposed to high temperatures and/or significant deformation or embrittlement, the member(s) shall be replaced.
Rehabilitation of fire-damaged structures is to follow a project-specific inspection, design, and repair protocol to be developed as part of the preliminary engineering, and to be approved by the Bridge Design Engineer.
188.8.131.52 Surface Preparation and Painting
The extent of remediation of the coating on structural steel will depend on the condition of the existing coating. The designer has the following options:
- Minor cleaning and spot painting
- Partial cleaning and zone painting
- Full cleaning and full repainting
The first step is a visual inspection to evaluate the condition of the existing coating. Guidance for visual inspection should be performed in accordance with ASTM D610/SSPC-VIS-2: Standard Test Method of Evaluating Degree of Rusting on Painted Steel Surfaces (2001).
If overcoating is being considered, the designer should conduct the following tests:
- Adhesion tests
- Coating thickness for each existing layer
- Determination of existing paint type (alkalyd, organic, etc.)
- Determination of hazardous materials (e.g., lead content)
Multiple adhesion tests should be performed initially in accordance with ASTM D3359: Standard Test Methods for Measuring Adhesion by Tape Test for preliminary evaluation of existing coatings. Selected areas may then be examined in more detail in accordance with ASTM D4541: Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers. The designer shall propose a structure-specific paint-testing program to the Bridge Design Engineer for approval.
The designer must evaluate the test results in determining the best surface preparation and painting options. Existing coatings must have adhesion test results above 200 pounds per square inch to be suitable for overcoating. If the existing paint thickness is not greater than 20 mils and the adhesion test results are satisfactory, the bridge may be overcoated. If the paint thickness is greater than 20 mils, the paint must be removed before the steel is repainted.
Surface preparation and paint systems must be compatible with the existing paint system. If partial or zone painting is required, fascia beams should be completely recoated for a consistent appearance.
The designer shall identify the presence of any hazardous materials expected to be encountered in the execution of the painting work.
For truss and arch-type bridges, the designer shall perform additional structural analyses to determine the maximum allowable limits of a paint containment system (e.g., platforms and tarpaulins). The applied loadings shall consist of, but are not limited to, a vertical platform dead load of 35 pounds per square foot, and a horizontal wind load of 27 pounds per square foot (open truss) or 18 pounds per square foot (enclosed truss), based on a maximum wind velocity of 60 mile per hour.
The designer shall make allowances for the timing and sequencing necessary for the surface preparation and painting activities when preparing his/her construction schedule.
Surface Preparation. The method and extent of cleaning depends on the condition of the existing coating, the extent of repainting required, and the coating to be applied. Typically, the Department requires cleaning to bare metal (SSPC SP10 or SSPC SP11) for repainting of the existing steel. If overcoating is specified, a high-pressure water blast is recommended for the surface preparation, at a minimum.
Painting. The Department maintains a list of protective coating systems suitable for both new and 100 percent bare existing steel, or for overcoating based on the NEPCOAT Qualified Products List. Because of changing technology, the designer is encouraged to seek out the latest Department standards for paint application.
Factors considered when selecting a coating system include:
- Compatibility of the proposed coating with the existing coating;
- The presence of airborne chemical fumes or volatile organic compounds;
- The presence of water spray or misty conditions caused by nearby water;
- The height of the members above flood or tidal levels;
- Unusual roadway conditions (including open steel-grid decks) that allow drainage to pass over the structural steel or to pond water on the deck; and
- Accumulation of snow, ice, or debris against steel surfaces.
Usually, the Department employs different painting requirements on rehabilitation projects when full repainting or overcoating is necessary, compared to new bridges. Refer to Section 106.8.7 – Protective Coatings for additional paint system and painting requirements.
184.108.40.206 Cathodic Protection
Imposed current cathodic protection for steel members may be used only with the approval of the Bridge Design Engineer.
220.127.116.11 Heat Straightening
Heat straightening may be an effective means of repair to existing steel and should be considered for rehabilitations. Work is to follow FHWA IF-99-004: Heat Straightening Repair of Damaged Steel Bridges (1998). Heat straightening is not to be used for fire-damaged members.
Bridges shall be upgraded to meet Seismic Zone 1 requirements in accordance with Section A18.104.22.168 – Seismic Zone and Section A22.214.171.124 – Minimum Support Length Requirements when rehabilitated or widened. For existing bridges that do not meet the minimum support length requirements at expansion bearings, longitudinal restrainers shall be installed in accordance with Section A126.96.36.199 – Longitudinal Restrainers. Shock Transmission Units (STUs) and dampers shall not be used. Lateral restraint, if necessary, shall include the addition of shear blocks.
When rehabilitation work involves jacking (refer to bridge jacking requirements in Section 109.11.2 – Design Considerations) for any reason, out-of-position bearings should be reset to proper position. Resetting bearings may introduce eccentricity of load and modifications should be made or analysis performed to ensure that the new load path is acceptable.
Bearings should be the same type with the same components in both the widened and existing bridges.
Bearings are normally replaced as part of a bridge rehabilitation project, or when bearings or bearing areas become so severely deteriorated as to jeopardize structural integrity. When all bearings along a substructure unit (e.g., single pier or abutment) are replaced, the replacement bearings should be upgraded to meet current Department standard bearings, rather than the same bearing type being used for replacement. The designer shall assess the longitudinal and transverse effects (i.e., reactions and movements) at all bearing locations resulting from the change in bearing stiffness/restraint for all applicable design load combinations. Individual bearing replacements are to be replaced in-kind.
The designer shall be attentive to the condition of “frozen” bearings that become released during bearing repair or replacement work. Locked-in stresses in the bearings shall be estimated and provisions incorporated in the design drawings for safe removal. Contract documents are to require lubrication of all expansion bearings other than elastomeric bearings.
109.11 Foundation and Substructure
For substructures considered for reuse, where there is no evidence of structural distress and for which rehabilitation work will not result in greater than 10 percent increase in the sum of the factored loads, the substructure element may be deemed acceptable without detailed analysis. This load comparison and need for evaluation is to be element-by- element (e.g., backwall, stem wall, piles).
Where substructures are considered for reuse and there is a significant increase in load, the designer will develop a foundation report based on a review and understanding of all available information relevant to the foundations, verified by a program of field testing such as ground-penetrating radar, cores, borings, and test pits. The foundation report is to be based on known substructure information and local geologic data.
Effects of foundation construction on existing structures are to be considered in the design and mitigated or avoided accordingly. Initial and long-term settlements for existing and proposed construction are to be understood and differential foundation settlements must be considered in design and detailing.
Use consistent foundation types where new and existing substructure elements are connected.
Design substructure rehabilitations to meet vehicle collision force requirements for new and reused substructures.
Where substructures are being considered for reuse, seismic requirements, for bearings, beam seat dimensions, and column ductility are to be evaluated. Design substructure rehabilitations to meet load and seismic requirements for bearings (see Section 109.10 – Bearings) and beam seats. Upgrades necessary to satisfy criteria for column ductility shall be determined by the Bridge Design Engineer on a case-by-case basis.
The Department will determine the need and extent of scour evaluation and scour mitigation measures in bridge rehabilitation projects on a case-by-case basis. This determination is to occur once the scope of structural rehabilitation work is established, and will be based upon scour risk, project size, complexity, cost, and the anticipated service life of the rehabilitated structure. Perform scour evaluations and the design of scour mitigation measures in accordance with Section 104 – Hydrology and Hydraulics.
Upon completion of repairs, coat substructure surfaces as outlined in Section 188.8.131.52.5 – Protective Sealing of Surfaces.
109.11.2 Design Considerations
All widenings, rehabilitations, and conceptual temporary support designs shall be in accordance with AASHTO LRFD.
Refer to Section 107 – Final Design Considerations - Substructure for design of new substructure elements.
The designer shall consider the feasibility of converting conventional abutments into semi‐integral abutments to eliminate deck joints above the beam ends while retaining most of the existing abutment.
When encasing existing substructure elements, the minimum concrete thickness shall be 6 inches for conventional concrete and 4 inches for pneumatically applied concrete. The encasement is to be designed and detailed to be integral with the existing substructure element. Design conventional concrete encasements for temperature and shrinkage-reinforcing based on the encasement alone.
Where jacking and/or temporary support of bridge structure is required, the designer shall perform work as outlined below, and include in the contract drawings:
- Develop and show on contract documents conceptual design(s) for temporary supports, demonstrating complete load path from structure to foundation for all proposed locations of jacking and/or temporary support. Include material type, overall member dimension(s), and a bracing schematic.
- Verify the foundation is adequate for concept design, including accommodation of utilities and structures that may interfere with the concept support. Indicate the basis of foundation design and identify at a concept level where confinement or soil retention will be required.
- Provide both factored and unfactored jacking loads linked with traffic staging. Specify that jack capacity must provide a safety factor not less than 1.65 (= 1.5*1.10 for “sticky force”) based on the calculated unfactored design jacking loads. Factored loads may be used for contractor design of temporary structural supports (e.g., Maybe towers). Table 109‑5, and Table 109‑6 provide Sample jacking load tables.
- Prohibit lifting the bridge via hydraulic pressure under live load unless approved by the Bridge Design Engineer.
- Identify lateral and longitudinal load requirements for temporary supports and conceptual bracing. Seismic requirements may be waived. Fatigue requirements may also be waived, except for details, which are to remain permanent.
- Show where temporary member-stiffening is required, and show conceptual stiffener details. The designer is responsible for the analysis, design, and detailing of permanent jacking stiffeners.
- Specify prohibited means of work (e.g., field welding) and identify restoration requirements for existing members to remain upon completion of work.
- Provide jacking scheme-suggested work sequence linking jacking with all work to be performed. Evaluate and account for deck continuity and restraining elements, and specify the maximum allowable displacement and/or differential displacements (where applicable). Establish performance criteria for when and what monitoring is to be performed.
- Contract documents must specify that loads be secured before any existing material is removed. Jacked loads are secured by either temporary blocking (short columns or cribbing), or the use of locknut jacks. Hydraulic pressure is not to be used to support loads, even if the hydraulic pressure is maintained. During jacking, blocking or other means of support is to be maintained within 1 inch below the lifted structure.
|Table 109-5. Unfactored Loads for Jacking|
|Location||Girder||Stage I||Stage II||Stage III|
|DL + 15%||DL + LL + Imp||DL + 15%||DL + LL + Imp||DL + 15%||DL + LL + Imp|
|Table 109-6. Factored Loads for Jacking|
|Location||Girder||Stage I||Stage II||Stage III|
|DL + 15%||DL + LL + Imp||DL + 15%||DL + LL + Imp||DL + 15%||DL + LL + Imp|
Where PBES are a necessary component for constructing work shown in staged construction and traffic control plans, the designer is to develop and show a conceptual construction sequence consistent with the traffic plans. Task-specific time estimates are to be quantified and employed in the development of conceptual sequences. For more complete information on the use of PBES, refer to the FHWA website, https://www.fhwa.dot.gov/bridge/prefab/.
109.11.3 Repair Methods
General repair for foundations and abutments is similar to repair of concrete decks and slab bridges. Refer to Section 184.108.40.206 – Patching and Section 220.127.116.11 – Repair and Strengthening for repair methods. For typical repair details, refer to Section 301.03 – Concrete Repair Details. More specific repairs for certain foundation elements that require additional attention are described in the following subsections.
18.104.22.168 Bearing Seat Repairs
The designer shall investigate the cause of spalls and cracks in all raised pedestals or bearing seats, and determine their effect on the support for the masonry plate. Superficial spalls and cracks considered minor (nonstructural) may be repaired using concrete patching or epoxy injection. Spalls and cracks that result in significant loss of support for the masonry plate will require removal of the bearing load and complete rebuilding of the pedestal or bearing seat.
Pedestals that lack confinement reinforcement shall be evaluated, assuming a non-uniform bearing stress is applied. Refer to Section A5.7.5 – Bearings.
For repair or replacement of anchor bolts, the designer shall determine the location of reinforcing steel prior to developing details. Proposed details shall consider limitations due to anchor bolt access, risk of damage to existing beams, and size of construction tools anticipated.
If access and remaining material are sufficient and weldable, repair details consisting of threaded studs welded to the unthreaded portion of existing anchor bolts may be permitted, when in accordance with AWS D1.4: Structural Welding Code – Reinforcing Steel (2005). Weld-joint detail shall be a two-sided, full-penetration butt weld followed by 100 percent visual inspection.
The designer must evaluate all strength limit states (anchor steel, concrete breakout, and pryout) in accordance with Appendix D of ACI 318: Building Code Requirements for Structural Concrete (2014). Supplemental confinement reinforcement may be necessary when edge distance is limited. Frictional resistance beneath masonry plates will not be recognized unless approved by the Bridge Design Engineer.
22.214.171.124 Post-Tensioning Repairs
This subsection is relevant to repairs and rehabilitations employing post-tensioned high-strength steel bars and strands. Refer to Section 106.9 – Prestressed Concrete Bridge Superstructures regarding design and loads.
Post-tensioning design and detailing is to be developed considering redundancy so that it can be shown that failure of one bar or strand will not result in catastrophic failure. Design properties of existing concrete are to be verified by field testing.
Post-tensioning elements for permanent use are to be within grouted ducts unless impractical, and detailed in all cases for a minimum of three levels of corrosion protection for full length, including anchorages. Anchorages for permanent post-tensioning are to be within pour backs, and not blisters. Post-tensioning ducts are to be encased in concrete full length, or located in the interior of box beams.
The designer is to develop and include in contract documents a suggested work sequence, including verification of final loads, grouting, and inspection. Contract documents are to include requirements for mock-up testing of grout material and procedures.
126.96.36.199 Underwater and Splash-Zone Repairs
The splash zone is defined as the portion of the structure where alternating wetting and drying occurs from daily tidal cycles, wave action and wind action.
Where work is to be performed under water or in splash zones, the designer shall perform work as outlined below.
- Develop conceptual repairs and present in the contract documents.
- Identify specific repair type (e.g., spall repair, crack injection) and necessary preparatory work (e.g., sealing crack surfaces).
- Identify limits of work, including maximum working depth, if concept involves divers.
- Indicate permitting restrictions.
The designer shall review the Standard Specifications, and amend, if necessary, to provide additional information or direction to the contractor regarding work sequencing or dewatering concepts for unusual site conditions.
188.8.131.52 Pile Repairs
Analyses should be performed to evaluate pile capacity for the existing conditions, and during each phase of repair. The designer will identify any needed restrictions on live loads or contractor operations during construction. If the existing pile does not have adequate capacity to support load during repairs, supplemental support must be identified on the contract drawings.
To extend the life of timber piles by field preservative treatment, the designer shall specify the use of solid "anti-fungal" cartridges, and to seal drilled holes with hardwood preservative treated plugs.
The designer may refer to the U.S. Department of Defense Maintenance and Operation: Maintenance of Waterfront Facilities, UFC 4-150-07, June 2007 for other repair techniques used for timber bearing piles.
184.108.40.206 Scour and Undermining Repairs
Scoured areas can be successfully repaired only if cause is first identified and understood. The impact of any countermeasures must also be evaluated. Scour countermeasures must be properly designed. Refer to Section 104 – Hydrology and Hydraulics and FHWA-NHI-09-111 Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance – Third Edition, (HEC 23), 2009.
Riprap shall consist of stone meeting an R-5 gradation (see Standard Specifications. Desirable riprap slope is 2H:1V, but a maximum of 1H:1V is acceptable. The designer shall determine the limits of work, materials used, and method of construction for the riprap installation.
For undermined foundations accessible in the dry, the designer shall:
- Develop conceptual repairs and present them in the contract documents.
- Provide a suggested work sequence.
- Provide an estimated volume of void.
- Indicate where venting measures are needed.
For undermined foundations below water, the designer shall:
- Develop conceptual repairs and identify whether dewatering is anticipated. Present concept in the contract documents.
- Provide suggested work sequence.
- Provide estimated volume of void.
- Identify permitting restrictions.
- Identify nature of undermining repair (e.g., hand-placed grout bags, grout tubes, tremie grout, sheeting and filling) and preparations (e.g., pressure wash).
- Identify limits of work, including maximum working depth, if the concept involves divers.
Where undermining repairs can bond to existing piles, a structural analysis must be performed by the designer to evaluate the effect of the increased load.
Where scour and undermining exposes timber piling or cribbing, the designer will investigate the condition of the exposed timber, and incorporate into the scour repairs remedial measures to halt timber deterioration.
109.11.4 Stabilization and Underpinning
Stabilization and underpinning pertains to support for the existing superstructure, while permanent construction restores the bridge to full traffic. Stabilization or underpinning is normally a temporary repair. For measures intended for service up to 6 months, design for 2-year storm event. For anticipated service longer than 6 months, perform hydraulic and hydrologic evaluation as for permanent work. Drawings shall state the design-year storm event considered for the work.
For structural supports in temporary service, design in accordance with AASHTO LRFD. Do not include future wearing surface. Identify the basis of loads and design methodology on the plans. Live-load deflection criteria need not be considered.
109.12 Retaining Walls
This section pertains to the repair, rehabilitation, and the extension or modification of existing earth-retaining structures. Included are bridge wing walls, earth-filled arch spandrel walls, cantilever walls, gravity walls, gabion walls, mechanically stabilized earth walls, and cut or embankment retaining walls of various types for permanent installations. Refer to and work in conjunction with Section 109.11 – Foundation and Substructure, and Section 109.13 – Culverts, for breast walls and head walls for abutments and culverts respectively, and for guidance on the temporary support of excavation.
Refer to FHWA-CFL/TD-10-003: Retaining Wall Inventory and Assessment Program (WIP), National Park Service Procedures Manual (2010) for guidance on assessing the condition of existing retaining walls.
For earth-retaining structures considered for reuse, where there is no evidence of distress related to sliding, overturning, and global stability, and for which rehabilitation work will not result in greater than 10 percent increase in the sum of the factored loads, the earth-retaining structure may be deemed acceptable without detailed analysis.
Where earth-retaining structures are considered for reuse and there is a significant increase in load and/or evidence of distress, the designer will develop a foundation report for the proposed work addressing the existing structure and embankment affected by the proposed work. The report is to be based upon a review and understanding of all available information relevant to the structure, verified by a program of field testing such as ground-penetrating radar, cores, borings, and test pits. The foundation report is to be based on known structure information and local geologic data.
For work involving all proprietary wall systems, designer responsibilities and information to be provided is to be as identified for MSE walls in Section 220.127.116.11 – Designer Responsibility. The designer is responsible for designing and detailing transitions from existing to proposed walls.
Unless structurally isolated, new walls are to be of a type similar to the existing retaining wall structure and foundation support for partial replacement or extension of existing walls. The designer is to consider and account for differences in earth pressures and movements resulting from stages of construction.
109.12.2 Design Considerations
Design and detailing of extensions for existing retaining walls for bridge rehabilitations is to follow Section 107 – Final Design Considerations – Substructure. For extensions to stone masonry walls, incorporate form liners, staining, modular masonry units, or other measures for consistency in appearance, unless historic considerations intervene.
When temporary support of excavation is necessary for constructing work shown on staged construction and traffic control plans, the designer is to develop and show a conceptual construction sequence consistent with the traffic plans.
Reuse of existing earth-retaining structures is the preferred strategy for rehabilitations, including raising or lengthening existing facilities. Technologies to offset increased loads through control of unit weights and/or lateral pressures such as geofoams, expanded shales, urethane foams, geotextiles, or compressible inclusions are to be explored by the designer (Horvath, 1991 and 1999; Karpurapu and Bathurst, 1992). Cast-in-place facings, using technologies such as self-consolidating concrete (SCC), are preferable to shotcrete.
The designer shall evaluate drainage and groundwater conditions for rehabilitation of existing retaining structures, and incorporate modifications or remedial measures as needed. Drainage measures are to be incorporated where facing or stone-pointing work interferes with current draining patterns.
109.12.3 Repair Methods
For repair of retaining-wall concrete, refer to Section 109.11.3 – Repair Methods. For repair of modular or proprietary walls, refer to published proprietary information and manufacturer representatives.
Rehabilitation of stone masonry is to include routing and pressure-pointing. The designer is to investigate and provide information on anticipated depth of routing and pointing, and whether stabilization of stonework by shims or spacers is needed. For guidance on stone masonry repairs, refer to the Pennsylvania Department of Transportation’s Stone Arch Bridge Maintenance Manual (2007).
This section applies to structural elements (bridges, culverts, pipes), or a series of such elements, having a total opening of 20 square feet or greater, for which the primary function is to convey surface water across or from the roadway. These elements are classified as culverts by the Department, and are the responsibility of the Bridge Design Section. Culverts meeting the NBIS structure length definition (> 20 feet) are part of the Highway Bridge Program.
Culvert rehabilitation work typically involves the repair of known deficiencies, increasing hydraulic capacity, or extensions due to roadway widenings. Deficiencies may consist of structural deterioration, cracking, leaking, corrosion, and differential settlement, streambed misalignment, scour, and erosion. Refer to the FHWA-IP-86-2: Culvert Inspection Manual (1986) for further information.
Use of metal culverts for rehabilitation work is prohibited unless approved by the Bridge Design Engineer. Existing metal culverts requiring rehabilitation are to be replaced with either concrete or high-density poly ethylene (HDPE) material. Replacement of metal culverts is not considered rehabilitation work. Refer to Section 107.7.4 – Pipe Culverts.
109.13.2 Design Considerations
Design rehabilitation work, including extensions and new cross sections added to existing culverts, in accordance with Section 107.7 – Culvert Design.
Design culverts extensions using foundations matching that of the existing culvert.
Culvert extension cross section may be different, but may not constrict or infringe on the existing culvert cross section at the discharge end. Extensions on the inlet end must match the existing cross section.
Design and detail culvert extensions for shear transfer to the existing culvert using shear keys, dowels, or other positive means. Key or dowel grouting shall be sequenced so that differential settlements have taken place prior to establishing shear transfer.
Culvert rehabilitation will result in structures that meet or exceed project-specific hydraulic capacities as determined by a hydraulic analysis, in accordance with Section 104.3.1 – Culverts. Culvert rehabilitation will result in adequate structural capacity for all legal statutory loads; refer to Section 108.9.2 – Rehabilitated Bridges.
The designer is responsible for considering construction impacts to existing culverts during rehabilitation work, and is to incorporate provisions for protective measures and construction sequencing in the schedule, cost estimate, and contract documents.
Existing culverts may be abandoned in place but must be filled using flowable fill or lean concrete.
For modifications to headwalls and wingwalls, refer to Section 109.12 – Retaining Walls.
109.13.3 Repair Methods
Refer to Chapter 14, “Culvert Inspection, Material Selection, and Rehabilitation Guideline” of the AASHTO Highway Drainage Guidelines (2007), and FHWA Culvert Repair Practices Manual, Volumes I, FHWA-RD-94-096 (1994), and II, RD-95-089 (1995), for repair methods.
Any utilities on an existing bridge must be protected during rehabilitation. The designer is to incorporate in the contract documents planking or other protection measures to prevent damage from dropped items. The designer is to coordinate with the utility for requirements such as utility support rehabilitation, temporary support or relocation, and modifications necessary to accommodate jacking.
The designer should be aware of any utilities near the structure that may affect the contractor's operation during rehabilitation, and account for such conditions in the design, scheduling, and estimate. For example, high-powered electrical lines pose a hazard for crane operation.
109.15 Moveable Bridges
The Department has eight movable bridges in its bridge inventory, and has developed an Operations Manual (Volume 1), Maintenance Manual (Volume 2), and As-Built Drawings (Volume 3) for each bridge.
The Operations Manual consists of procedures for bridge operations and bridge operational troubleshooting. The Maintenance Manual consists of mechanical and electrical maintenance procedures for each component on the bridge. The As-Built Drawings consist of updated or revised as-built drawings for the mechanical and electrical systems.
These manuals require updating whenever mechanical and electrical work is completed on each bridge.
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