Current Trends in the Seismic Design and Analysis of Bridges

Synopsis

Over the last two decades, researchers and practising engineers have gradually shifted towards the performance-based seismic design concept, wherein a structure is designed to meet multiple performance objectives under different levels of seismic actions, the objectives being (preferably) defined in terms of displacements (drifts) and/or deformations. This can be done with the aid of either elastic or inelastic analysis. If elastic analysis is used, the expected inelastic response of the building is accounted for by techniques like the secant stiffness approach and the use of ‘over-damped’ elastic spectra. If inelastic analysis is used (using a fully or partially inelastic model), the procedure becomes more involved but also more reliable, since the safety verification involves comparing the inelastic demands against the deformation capacities to verify the performance of the structure with respect to a given performance objective (e.g. allowable member rotation for ensuring life safety under a ground motion having an appropriately selected probability of occurrence). In many of the available design methods, regardless of whether elastic or inelastic analysis is used, the procedure involves a number of iterations.

The lecture will focus on two procedures for performance-based seismic design of bridges, each following one of the previously described approaches. In the first one, the ‘direct displacement based design approach’, pioneered by Priestley and Kowalsky and involving elastic analysis and over-damped elastic spectra, is extended with a view to making it applicable to a broad spectrum of bridge systems, including those affected by higher modes, and also introducing additional design criteria not previously used in this method. The second method involves more advanced analysis tools, i.e. response-history analysis (for different levels of ground motion intensity) of bridge models wherein any regions that are expected to yield under the selected seismic actions are modelled as inelastic, whereas the rest of the bridge is modelled as elastic; the initial analysis (relevant to service conditions) is an elastic one. A critical aspect of this (currently under development) procedure is the a-priori definition of the inelastic behaviour of dissipating zones, by exploiting the deformation limits for the specific performance level, which are related to the damage level of the structural members.

About the speaker

Andreas Kappos is Professor of Civil Engineering at City University London since 2013. Prior to joining City he was a Professor at the Department of Civil Engineering of the Aristotle University of Thessaloniki. From 1995 to 1999 he worked at Imperial College London, first as a lecturer and later as a Reader. He works in the field of Structural Engineering, in particular analysis and testing procedures for structures subjected to earthquake loading. He has published extensively in the field (over 280 papers in refereed journals and conference proceedings), and his work is recognised internationally (over 2000 citations). He has been involved in several consultancies on topics like the seismic design of bridges and buildings, assessment and retrofit of damaged structures, and various aspects of use of concrete in bridges, tunnels, etc. He is the Secretary of the European Association of Earthquake Engineering and Coordinator of its Working Group on Bridges. He also served as a member of a number of committees dealing with seismic design (incl. the Eurocode 8 Project Team) and assessment (various fib and EAEE task groups).

Further information

This evening meeting is organised by SECED and chaired by Prof. Ahmed Elghazouli (Imperial College London). Non-members of the society are welcome to attend. Attendance at this meeting is free. Seats are allocated on a first come, first served basis. For further information, please contact Greg James (tel. 020 7665 2229).