Evaluating Support Representation and Modeling Strategy for Skewed Steel I-Girder Integral Abutment Bridges during Deck Placement

Steel I-girder integral abutment bridges (IABs) have become popular in recent years due to their cost-effective construction and maintenance, even for skewed bridges in several states, despite their complex support restraints. During deck placement before casting of integral abutments, IABs often have fixed bearings (with anchor bolts) that provide restraints over girder bottom flanges, which induce complicated constraints and responses, such as large girder flange lateral bending stress. The realistic restraints are often overlooked during bridge design and analysis that uses models with simplified supports [usually defined at web–flange conjunctions (at single nodes)], which can inaccurately represent the complex lateral responses. This study evaluated standard simplified support representations in various levels of analysis for skewed steel I-girder IABs with fixed bearings during deck placement and proposed modeling improvements by comparing numerical simulation results with those from field-validated three-dimensional (3D) models. Six single-span IABs from the state transportation agency database (0°–45° skew) and their parametric variations of the cross-frame design were modeled for deck placement in 3D using ABAQUS (version 2023) and in partial 3D and two dimensions (2D) using CSI-Bridge (version 2025). All models with simplified supports underestimated lateral response near girder ends when deep cross-frames were used for IABs with staggered cross-frames. Defining proper restraints over girder bottom flange width to represent realistic fixed bearing conditions was found to be critical for lateral response evaluation of skewed IABs deck placement analysis for bridges with moderate skew (e.g., 30° and 45°) and with cross-frame-to-girder depth ratios meeting AASHTO requirements.