Contribution of Transverse Tie Bars to Load Transfer in Adjacent Prestressed Box-Girder Bridges with Partial Depth Shear Key

Abstract

Adjacent box-girder bridges have become a popular choice as they can be constructed quickly, easily, and economically. In spite of their good performance during many years of service, one major problem has been recurrent longitudinal cracking of the grout material in the shear key. A combination of shear keys and transverse posttensioning (TPT) ties in such kind of bridges is typically used to connect the bridge girders together so that they would behave as a single integrated unit. However, information regarding the contribution of the TPT tie bars on load transfer between adjacent box girders is limited. In this study, a single-span precast prestressed concrete adjacent box-girder bridge was instrumented and monitored to study the effect of TPT tie bars on load transfer mechanism and overall bridge behavior under static and dynamic truck loads. Two sets of instruments were installed in the girders and tie bars during and after the construction of the bridge. A good correlation was achieved between experimental measurements and results from a three-dimensional (3D) finite element (FE) model. An in-depth analysis of the data indicated that, under static loads, there was a contribution from the tie bars to the load-transfer mechanism between the girders. The maximum measured relative displacement at the joints was below the damage limits. Under dynamic loading, the dynamic load allowance (DLA) obtained was higher than that of the standard design procedure of bridges. Based on the FE analysis, the relative displacement of the joints and the load distribution between the girders are influenced by the initial TPT force applied during construction. The level of stresses generated in the concrete girders and shear keys under truck load was not high enough to cause damage.