Design Example of Bridge Pier Cap Beam Considering Torsional Effect

摘要

A bridge pier cap beam supporting girders of two unequal spans was designed per AASTHTO LRFD Bridge Design Specifications (AASHTO LRFD BDS-17) and the ACI 318 Building Code Requirements for Structural Concrete (ACI 318-19) with consideration of torsional effect. Envelopes of bending moment, shear, and torsional moment are given in the problem statement as the result of a comprehensive structural analysis on the bridge. Flexural design is presented firstly based on the bending moment envelope to determine the required area of longitudinal reinforcement. Then shear and torsion design is presented to determine the required area of transverse reinforcement and additional longitudinal reinforcement. Based on the design calculations, the arrangement of reinforcement is illustrated in a cross-section view for the cap beam. Comparison between the two approaches is also included in terms of the equations used and areas of shear and torsion reinforcement determined.