STIFFNESS-STRENGTH-DUCTILITY-DESIGN FOR CRESCENT SHAPED BRACES

摘要

As recently also recalled by Priestley in a keynote lecture given at the 1st ECEES, Geneve 2006, the emphasis on Performance-Based Seismic Design has forced a re-examination of the methodology employed in the seismic design of structures. Skipping all details, direct Displacement-Based Design of structures has opened up new possibilities for the structural engineer in terms of conceiving and dimensioning a structural system which offers optimized seismic performances. Focusing directly on the non-linear behavior of the lateral-resisting elements of a given building structure, the secant stiffness approach allows "logical choices regarding the force distribution" between different lateral-resisting elements.This paper aims at investigating how these logical choices concerning strength, stiffness and ductility of lateral-resisting elements can be made.In general, the lateral-resisting system of a given building structure can be seen as composed of a series of single lateral-resisting elements working together. The mechanical characterization of each component necessarily requires to capture both its elastic and inelastic behavior and can be assumed to be an elastic-perfectly plastic one, univocally identified by three independent parameters: stiffness (secant at yield point), strength and ductility. The mechanical characterization of the whole lateral-resisting system, as composed of the n lateral-resisting components working in parallel, can be directly obtained from the mechanical characterization of each single component and is therefore controlled by 3n parameters.Consequently, depending upon the type of lateral-resisting used, the structural designer is allowed to control up to 3n parameters upon which he can "act" to reach the desired seismic performance objectives.