Mid-span hinge effects in the seismic performance assessment of an in-service curved prestressed concrete box girder bridge – preliminary analyses

Since a significant part of the Italian territory was not seismically classified until 2003, most of existing bridges were designed without taking into account earthquake induced excitations. Hence, load bearings devices and shear keys of in-service infrastructures may not be adequate to current codes, both in terms of resistance and displacement capacity. In this study, the seismic behavior of a case-study post-tensioned RC bridge built in 1985 was numerically analyzed. The structure is 440 m long and composed by nine spans, built with precast segments using the balance cantilever construction method. The deck is divided into two parts, connected by a hinged joint in the middle of the central span, obtained with three shear keys and originally designed to allow thermal expansion only. Most importantly, the mid-span hinge, the end joints and the bearing devices were designed without considering the effects of seismic action. In order to preliminarily investigate the performance of devices and joints, the case-study bridge was analyzed by means of non-linear dynamic time history simulations. Displacements over time were obtained for a set of seven accelerograms, and maximum values were compared to the capacity of the bridge devices. Results were then critically discussed.