Live-Load Analysis of Posttensioned Box-Girder Bridges

This paper presents an evaluation of flexural live-load distribution factors for cast-in-place box-girder bridges. The response of a typical box-girder bridge was recorded during a static live-load test. This test involved driving two heavily loaded trucks across the instrumented bridge on selected load paths. The instruments used to record the response of the bridge were strain gauges, displacement transducers, and tilt sensors. The measured data were then used to calibrate a finite-element modeling scheme using solid elements. From this finite-element model, the theoretical live-load distribution factors and load ratings for the test bridge were determined and compared with the factors and ratings predicted in the AASHTO LRFD specifications. A parametric study of cast-in-place, box-girder bridges using the calibrated finite-element modeling scheme was then used to investigate how various parameters such as span length, girder spacing, parapets, skew, and deck thickness affect the flexural live-load distribution factors. Based on the results of the parametric study, a new equation, which more accurately predicts the exterior girder distribution factor, is proposed.