City Research Online

Abstract

The appropriate selection of end joint gaps in bridges with seat-type abutments has hardly received proper attention in the literature. The size of these gaps, which exist between the deck and the abutment of a bridge in its longitudinal and transverse directions, affects the boundary conditions of the bridge system and hence, its dynamic behaviour. In view of this, the effect of end joint gap sizes on the seismic performance of bridges is investigated here, and novel methods that allow for the optimisation of the dynamic response of bridges through control of joint gap size are developed.

The effect of joint gap sizes on the seismic performance of bridges is caused by the interaction between the deck and the abutment-backfill system as the gap closes. In this context, existing methods of modelling the resistance of abutment-backfill systems, including the shear keys, are extended, ending up with the development of a detailed (‘complex’) and a simplified (‘simple’) model of the abutment-backfill nonlinear behaviour. Filling a gap in the available modelling tools of abutment-backfill systems, a new hysteresis law that considers the softening region of the response of the backfill is proposed. Additionally, a sensitivity analysis is performed to examine the dependence of the abutment-backfill resistance on the backfill depth.

The newly proposed modelling methods are employed to parametrically investigate the effect of the deck-abutment-backfill interaction on the seismic response of bridges. To this end, the nonlinear model of an existing, seismically designed bridge is subjected to analyses with various joint gap sizes in the longitudinal and transverse directions.

Based on the conclusions drawn from the results of the parametric analyses, two methods of joint gap size optimisation are developed. Both methods can be used to either select the size of a conventional, fixed-width joint gap or to design a ‘Dynamic Intelligent Bridge’, i.e., a bridge with variable-width joints, whose size is optimised either continuously or with a one-off adjustment in the case of a seismic event. The first method is safety-factor-based, i.e., the optimisation of the joint gap size is based on the maximisation of a safety factor of the entire bridge against a selected limit state. The second one is a life-cycle-cost-based method, where the optimum gap size minimises the expected life-cycle cost of the bridge considering the seismic hazard. The feasibility of both methodologies is examined through pilot applications to a bridge efficiently designed according to modern seismic design guidelines.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TG Bridge engineering
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses School of Science & Technology > Engineering

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