Practical Approach for Estimating Distribution Factor for Load Rating: Demonstration on Reinforced Concrete T-Beam Bridges

This paper presents a new, practical methodology with simple analysis methods coupled with rapid experimental tests to identify distribution factors (DFs) for existing highway bridges. This approach is demonstrated on a reinforced concrete T-beam bridge population. It is shown that the moment DFs of single-span T-beam bridges can be determined by using skew angle, modal frequency, and the flexibility coefficient, where the frequency and the flexibility coefficient can be identified by means of rapid impact testing that can be conducted using an impactor, such as a falling weight deflectometer (FWD). This approach is first demonstrated using finite-element model (FEM) simulations. Moment approximation to FEM results with the new approach is 6%, whereas this approximation is on the order of 30% compared with the conventional beamline analysis given in the AASHTO code. This new approach is then demonstrated by using experimental data from four real-life bridges for the computation of moment values as well as the load ratings. It is shown that this new approach can conservatively approximate live load increases for the four existing bridges.