Displacement focussed seismic design

Abstract

This thesis is an analytical investigation of displacement focussed 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 single 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 prenominated 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.