Seismic Design of GRS Integral Bridge

摘要

The current version of the seismic design of a new bridge type, called Geosynthetic-Reinforced Soil (GRS) integral bridge, used in practice is described. This new type of bridge comprises a girder integrated to a pair of abutments (i.e., full-height rigid facings) without using bearings and a pair of approach blocks of compacted cement-mixed gravelly soil reinforced with geogrid layers connected to the facings. A seismic design method based on the pseudo-static push-over analysis of a lumped-mass frame model representing the RC members (i.e., the integrated girder and facings) is described. The most critical failure mode defined based on results from a series of model shaking table tests is the rotation of the facing, which is triggered by the passive failure in the upper part of the approach block on the passive side and the tensile rupture of the geogrid at the connection with the back face of the upper part of the facing on the active side, both caused by the lateral inertia of the girder and facings. The sub-grade reactions of the approach blocks at the back face of the facings and the subsoil at the bottom face of the footings of the facings are modeled by springs having bi-linear or tri-linear force - displacement properties upper-bounded by the passive earth pressure and bearing capacity, respectively. A working example illustrating this seismic design procedure is presented. It is shown that the GRS integral bridges that are stable when subjected to very high seismic loads equivalent to the one experienced during the 1995 Great Kobe Earthquake (so called Level 2 seismic load) can be designed.