Experimental and Analytical Investigation of Live-Load Distribution Factors for Double Tee Bridges

In this study, the Icy Springs Bridge, located in Coalville, Utah, was load-tested to quantify the effects of significant deterioration on its live-load behavior. Visual inspection and load testing of this double tee structure indicated a severely deteriorated deck, undamaged girder stems, and partially effective transverse connections at the longitudinal joints. At the time of testing, the bridge was load-posted at 35.6 kN (total gross vehicle weight) with a maximum speed of $8\mathrm{km}/\mathrm{h}$ due to conservative rating assumptions. After a detailed analysis, a truck that was 7.5 times the posted weight was used for a load test. A shell-based finite-element model was created that used variable spring elements to model the deteriorated flange-to-flange connections, which accurately replicated the behavior of the bridge from the load test and validated the modeling technique. The model was used to perform a parametric study, using idealized flange-to-flange connections, to compare the calculated girder distribution factors to the finite-element model–estimated girder distribution factors, and poor agreement was found ($R^2=0.449$ and 0.237 for moment and shear, respectively). A multivariable linear regression analysis was used to develop moment and shear girder distribution factor equations for double tee bridges similar to the one investigated in this study, with a much better correlation of $R^2=0.86$ and 0.83 for moment and shear, respectively.