Environment-Induced Behavior of Transverse Tie Bars in Adjacent Prestressed Box-Girder Bridges with Partial Depth Shear Keys

Adjacent box-girder bridges are commonly built in United States because of their fast, easy, and economical construction. They have shown good performance and service life except for frequent longitudinal cracking in the shear keys. Past research attributed the development of longitudinal cracks in shear keys primarily to temperature fluctuations. However, it is not obvious how temperature fluctuations cause the shear keys to crack. An adjacent box-girder bridge with partial depth shear keys and transverse tie bars was instrumented at the time of construction and subsequently monitored to study temperature effects. A finite-element model of the bridge was used to study the behavior of the bridge generally and failure modes that partial depth shear keys experience under daily and seasonal temperature fluctuations. The bridge girders move considerably in the transverse direction, and each girder expands or contract individually in response to temperature changes. The failure in the shear keys appeared to be caused by these environmental loads, which can be exacerbated by truck loads. Tie bars did little to stop this type of failure. (C) 2017 American Society of Civil Engineers.