Evaluation and rating of older non-composite steel girder bridges using field live load testing and nonlinear finite element analysis

Abstract

 This research addresses the evaluation of five, non-composite, simple-span steel girder bridges using field load testing and finite element (FE) analysis. During field loading, maximum moments of between 74% and 87% of the moment caused by AASHTO HL-93 loading with impact were applied to the structures. Strain readings indicated partial to full unintended composite action and significant restraint at the girder ends for all structures. HL-93 operating load ratings were modified using the strain measurements recorded during diagnostic load tests, leading to an average increase in moment rating factor of 52%. A novel approach of calibrating 3D FE models was developed that captures the observed full and partial composite action observed during testing, as well as restraint of the girder ends, giving good agreement between model-predicted and measured strains. The FE models were used to directly predict bridge capacities and rating factors while explicitly capturing girder yielding and load redistribution. The effects of unintended composite action, end restraint and concrete deck stiffness on capacity were examined using these models. The most conservative FE-estimated rating factors that ignored unintended composite action and end restraint – which are likely unreliable at large loads – were 54% higher than the conventional, code-based rating factors.