Assessment of Bridge Performance - Seismic Isolation versus Ductility

Abstract eng:
Severe earthquake events are still marked by the collapse of bridges due to an inductile structural performance. In order to reach a high level of seismic safety and an economical design these structures should be able to dissipate a significant amount of the input energy, so that seismic forces are reduced. Energy dissipation can either be achieved by a ductile structural performance via plastic hinges in the piers or by seismic isolation using specific high damping rubber bearings. To both problems, which are linked together in practice, enhanced material laws were formulated describing the non-linear material behavior of reinforced concrete and elastomer subjected to cyclic loading. The nonlinear behavior of reinforced concrete piers is modeled using the fibre beam theory. That theory was extended by a bond-slip approach, so that e.g. anchorages of reinforcement can more realistically be considered. In order to facilitate an objective simulation of large deformations with material softening a nonlocal damage approach from continuum mechanics was implemented. For the modeling of the high damping rubber bearings an enhanced finite visco-elastic material law with an isotropic damage function was developed. Due to the fact, that elastomer is almost incompressible, the constitutive law is based on the uncoupling of the stress response into a linear volumetric and into a non-linear deviatoric part. The latter is described mathematically by a relaxation function and a distortion-supported damage function. In this work the upgrading procedures and the effectiveness of both approaches will be discussed on the basis of realistic earthquake scenarios.

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