Displacement focussed seismic design

Abstract

This report is an analytical investigation of displacement focused seismic design methods. These are design methods that have the ultimate structural displacement as a primary focus in the design process followed by strengths. The design methods that were investigated were the direct displacement based design method and capacity spectrum method. Both methods are based on the equivalent viscous damping theory. The third method reviewed was a modified version of the force based design method.

The theory of equivalent damping is considered in detail and the challenges facing its implementation in design methods are outlined. A different damping concept, substitute damping, was proposed as being an effective representation of the hysteretic behaviour in yielding structure and its suitability for use in design methods was verified.

The inelastic response of singe degree of freedom structures behaving in a variety of hysteretic forms when subjected to different ground motions was reviewed. Relationships were developed to express the required strength levels of these structures to attain pre-nominated ductility levels.

The challenges facing the conventional force based design method were also reviewed in detail. A new design approach, displacement focussed force based design, which is based on force based design but with an enhanced focus on displacements is proposed. Its effectiveness in designing single degree of freedom structures was confirmed in time history analyses.

P-delta effects were not considered in this work.

Published papers:

Judi, HJ; Davidson, BJ; Fenwick, RC, 2001 - Displacement forcussed force based seismic design, ASEC 2001 Conference

Judi, HJ; Davidson, BJ; Fenwick, RC, 2001 - Direct displacement based design- a definition of damping, NZSEE 2001 Conference

Judi, HJ; Davidson, BJ; Fenwick, RC, 2001 - Damping for the nonlinear static procedure in ATC-40, 7th National Conference on Earthquake Engineering

Judi, HJ; Davidson, BJ; Fenwick, RC, 2002 - Influence of hysteretic form on seismic behaviour of structures, NZSEE 2002 Conference

Davidson, BJ; Judi, HJ; Fenwick, RC, 2002- Force based seismic design: A displacement focussed approach, 12th European Conference on Earthquake Engineering, Paper Reference 552

Judi, HJ; Davidson, BJ; Fenwick, RC, 2003 - Displacement focused seismic design methods - A comparative study, 2003 Pacific Conference on Earthquake Engineering, Page No 108