Behaviour of integral bridges under vertical and horizontal earthquake ground motion

Abstract

Integral bridges are monolithic and are known to possess good earthquake resistance when founded on a stable soil. One important consideration is the relative displacements which can occur at the support points on structures where there is significant spacing between, i.e. bridges. Factors such as soil, foundation types etc. can all influence the dynamic response, and the stiffness of the bridge can influence how relative displacements affect the internal force actions within the structure. In this study, the effect of earthquakes on integral bridges built on several different soil types is examined, through computer simulation of an integral abutment bridge. The study is made based on Eurocode 8 recommendations, which provides data for different types of soil to be used for earthquake analysis. A symmetrical medium length integral bridge obtained from an existing structure is used for the analysis. Artificial EC8 spectrum compatible time histories (with a 0.35 g peak ground acceleration) are applied to the structure for a range of soil stiffnesses. In conjunction with this, both static and dynamic relative displacement studies are carried out to develop insight as to the significance or dominance of either dynamic or relative displacement effects.The final aim of this study is to propose a simplified approach for design/appraisal which can allow predictions of dynamic response based on the results of static relative displacement studies coupled with simple computer models, without having to resort to full nonlinear integration time-history analysis. Synthetic time histories for 5 different types of soil were created using Mathcad. The synthetic acceleration time history was validated using Seismospect (by Seismosoft). The time histories were then used to carry our full integration time history analyses in ANSYS (engineering simulation software) to simulate the dynamic response of the bridge.The results show that relative displacements play an important role in overall structural response of the integral bridge, compared to the pure dynamic response. The results also confirm that lower stiffness soils suffer a more detrimental effect of the earthquake compared to a soil of higher stiffness.

Seismic Performance Evaluation of a Fully Integral Concrete Bridge with End‐Restraining Abutments

“…An integral bridge is known as a bridge type that integrates the superstructure and basic substructures. In general, integral bridges are considered as having more economic benefit than a regular bridge because an integral bridge can be constructed without expensive supplemental devices such as expansion joints and bridge bearings [1][2][3][4][5][6][7][8]. Integral abutment bridges (IABs) are commonly used in modern bridge construction, with well over 9,000 IABs in service across the US.…”