Displacement-based seismic design to AS5100.2: 2017 – simplified

The Australian code of practice AS5100 Bridge Design was revised in April 2017. Significant changes see the analysis methods for seismic design and also earthquake return-periods brought closer to those of major world codes. While retaining the response-spectrum and time-history analysis approaches of the former code as ‘normative’ (both representing dynamic ‘force-based’ methods) – the ‘informative’ Appendix B of the new code allows the optional use of ‘displacement-based’ earthquake design. This paper describes the empirical basis for displacement-based design, and seeks to clarify the differences and advantages of this method from the older force-based methods when applied to both new and existing bridges. Simplified approaches, and practitioner techniques are illustrated – with the view to encouraging the adoption of this modern and often beneficial approach to seismic design.