Seismic behavior of Chilean bridges with external sacrifice shear keys in high seismic hazard zones

Abstract

The damage observed in highway bridges after the earthquakes produced in the USA, Mexico, Chile, China, Haiti and Japan, from 1985 to the present, evidences the existence of problems in the design philosophies and considerations established in the standards. The seismic events observed in the 2010 Maule earthquake in Chile have shown that highway bridges are vulnerable to failure or collapse, in particular to damage caused by transverse displacement or excessive rotation of the superstructure; loss of vertical support; damages associated with the dynamic effects caused by the horizontal skew of the superstructure and damage on the bottom flange of prestressed beams induced by the impact of external shear keys designed with excessive overstrength.This research assesses whether the use of sacrificial external shear keys designed according to the Chilean seismic design standards constitutes an improvement in the seismic performance of highway bridges, or if the contrary, they favor the occurrence of not desired damages in other elements. Fragility curves were calculated using nonlinear models of bridges designed under different hazard and soil conditions. It can be concluded that, given the fact that the Chilean design provisions consider the seismic hazard zone as the only parameter to determine the required design strength of external shear keys, the seismic performance of bridges is not uniform through different soil types, where the fragility increases as soil quality decrease. Also, external shear keys are essential to reduce the probability of loss of continuity of operation in bridges located in areas of high seismicity.