Evaluation of live-load distribution factors for high-performance prestressed concrete girder bridges

Advancement in bridge design/construction technologies altered typical bridge parameters utilized in the development of AASHTO LRFD live-load distribution factors developed more than two decades ago. A girder bridge constructed using high-performance, high-strength concrete has been instrumented and tested under controlled-load condition. AASHTO LRFD distribution factors were compared to the factors computed from girders measured strains. AASHTO LRFD distribution factors were on average 21% higher than computed factors. A detailed finite element model (FEM) was developed and calibrated to match the controlled load test results. Several variations of the FEM were created to account for the presence of end & intermediate diaphragms, girders continuity, and bridge skewness. The addition of end diaphragms decreases distribution factors on average by 6% while addition of intermediate diaphragms redistributes the moments between interior and exterior girders. Effect of diaphragms was more evident for bridge with large skew angles and less significant for skew angles less than 20.. Bridges with skewness have decreased distribution factors which was evident for skew angle in excess of 20 degrees; AASHTO LRFD has good estimates of skewness effect on distribution factors. Considering the continuity effect in the calibrated FEM revealed that AASHTO LRFD distribution factors are overestimated on average by 17%.