I-shaped steel plate girders with vertical stiffeners in the web are widely used for bridge construction. For economy, the web plate is very thin relative to the depth of the girder. Unlike typical rolled I-shape members, these girders rely on the development of tension-field action (TFA) after the web buckles to resist shear. Both the bridge design code (AASHTO Specifications) and building design code (AISC Specification) provide equations for calculating design shear that takes advantage of TFA in the past half century. But these equations are applicable for interior, but not end, panels. When performing evaluation of existing steel girder bridges in California, Caltrans engineer realized that end panels quite often do not have a sufficient shear strength in the end panels. Thus, Caltrans funded a research at UCSD to evaluate if end panels can also benefit from TFA such that expensive retrofit is unnecessary.
A total of eight large-size plate girders were tested in the Powell Laboratory. A TFA model was established based on the observed failure mode (see Figure 4), from which a shear strength equation that reflects the partial TFA was developed based on plastic analysis:
This shear strength is also being considered for adoption in the 2022 edition of AISC Specification for Structural Steel Building.
