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Title: Experimental Investigation and Refined Load Rating of a Concrete Pan Girder Bridge

Author(s): Nuzhat Kabir

Publication: Web Session



Appears on pages(s):



Date: 10/17/2021

In the load rating process, bridges that do not have sufficient capacity to carry the legal loads are load posted. Rating procedures can include conservative assumptions, which may result in load posting bridges that have sufficient load carrying capacity. Such load postings can lead to additional costs to the traveling public due to the time required to detour around a posted bridge. This paper aims to investigate the accuracy of load distribution factors and determine potential refinements to the load rating process for simple span concrete pan girder bridges. The AASHTO Manual for Bridge Evaluation (MBE) provides guidelines for load rating bridges in the United States using Load and Resistance Factor Rating (LRFR), Load Factor Rating (LFR), and Allowable Stress Rating (ASR). These procedures are intended to be conservative and can have varying degrees of accuracy as compared to the in-situ behavior of specific bridges. A typical load-posted simple-span concrete pan girder bridge, without as-built drawings, was selected as a representative case study to further investigate the distribution of live load between the girders and potential refinements for load rating. Ultrasonic pulse velocity testing and rebound number testing were used to determine the in-situ concrete compressive strength onsite. Information regarding the steel reinforcement, such as spacing and cover, was also determined on site using ground penetrating radar. The behavior of the bridge, including live load distribution, was studied through FEM modeling and field testing. The results obtained from the field tests were compared with recommendations from AASHTO specifications and guidelines and were used to calibrate the FEM model. The FEM model was found to accurately capture the distribution of loads across the bridge width. The AASHTO Standard Specifications live load distribution factors (LLDFs) for interior girders were slightly conservative, while those in the AASHTO LRFD Specifications were highly conservative, when compared to those obtained from field testing.