Rating of Prestressed Concrete Adjacent Beam Bridges without Plans

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Title: Rating of Prestressed Concrete Adjacent Beam Bridges without Plans

Author(s): Carlos V. Aguilar, David V. Jáuregui, Brad D. Weldon and Craig M. Newtson

Publication: Special Publication

Volume: 323

Issue:

Appears on pages(s): 5.1-5.20

Keywords: concrete cracking, diagnostic testing, load rating, Magnel diagram, prestressed concrete bridge, proof testing, rebar scanner, shear key, strain measurement

Date: 5/1/2018

Abstract:
Off-system concrete bridges with no design plans are currently a concern in New Mexico as many exist throughout the State. Load rating these bridges is problematic since the design documentation is limited or missing, thus creating uncertainties regarding the safe load limits. Two prestressed concrete bridges, a double T-beam and box beam bridge, were evaluated using advanced analyses and experimental methods (including load testing and rebar scanning). Both bridges have damaged and/or missing shear keys between the adjacent beams and thus, the load distribution path was uncertain. The bridges were evaluated based on the following procedures: estimating the material properties from past specifications and amount of prestressing steel via Magnel diagrams; verifying the steel estimate with a rebar scanner; load testing based on strain measurements; and rating the bridges using the load test results. Rating factors were determined for legal loads based on serviceability (i.e., concrete cracking) and strength (i.e., shear or flexural capacity). The serviceability ratings from load testing and strength ratings from analytical software were compared to determine the final load ratings and need for posting the bridges.