Methods for Evaluation of the Remaining Shear Capacity in Steel Bridge Beams With Section Losses Attributable to Corrosion Damage

About the report:

Steel bridges commonly have corrosion at beam ends because of leaking joints, which provide a pathway for de-icing salts to fall onto the beams from the roadway above.  Once beam ends have corrosion damage, it becomes more difficult to determine their remaining shear capacity to be used for load rating.  This is because classical design equations are based on intact sections and do not account for corrosion damage.  This study was conducted to understand better the structural behavior of unstiffened steel bridge beams that have section loss near the bearings and to determine a simple, effective method for determining the remaining shear capacity of corroded beams during load rating.

Seventeen beams from four decommissioned structures throughout Virginia were experimentally tested in a laboratory to induce web shear failure near the bearing locations and were measured for load, vertical displacement, and web strain behavior.  Strain was measured using a digital image correlation system to create a digital strain field at discrete load and beam displacement intervals during testing. The large-scale test results were compared to shear capacity calculations conducted in accordance with the AASHTO LRFD Bridge Design Specifications; AISC (American Institute of Steel Construction) 360-16; the Massachusetts Department of Transportation LRFD Bridge Manual; and other methods found in the literature for calculating the shear capacity of the damaged steel beam ends.  The study found that using the shear capacity calculations presented by Tzortzinis et al. (2019a) in Development of Load Rating Procedures for Deteriorated Steel Beam Ends resulted in reliable shear capacity predictions. 

The study also concluded that AASHTOWare Bridge Rating (BrR) can be used for determining the capacity of steel beams with corrosion using the percent web thickness loss input in the program.  When doing so for a corroded steel beam without holes, the accuracy of BrR can be improved by calculating the percent thickness loss input in the BrR deterioration profile using a portion of the web with a height equal to the bottom or top 3 in of the web, depending on the location of severe corrosion, and a length equal to the lesser of the bearing length plus the beam height or the extent of the corrosion damage near the bearing.  When doing so for a corroded steel beam end with holes, the accuracy of BrR can be improved by using the same portion of the web and by modifying the remaining average web thickness using the guidelines provided in the Massachusetts Department of Transportation LRFD Bridge Manual before inputting the percent thickness loss into the BrR deterioration profile.

Based on these conclusions, the study recommends that the Virginia Department of Transportation provide guidance (1) in a job aid to bridge inspectors for enhanced web thickness measurements and measurements of holes to be used when inspecting unstiffened corroded steel beam ends in Condition State 4 on bridges without diaphragms or a concrete deck, and (2) in its upcoming new load rating user manual to define the portion of the web and web thickness modification to account for holes when the same corroded steel beam ends are load rated.

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