Seismic design procedures for concentrically braced frames

This paper deals with the main behavioural issues involved in the seismic design of typical forms of concentrically braced frames. The response of bracing members under monotonic and cyclic axial loading is first considered, and the key parameters affecting the performance are highlighted. This is followed by an assessment of the different design approaches employed for the treatment of brace buckling, and the influence of the underlying assumptions on various aspects of frame response. The provisions of international codes of practice are examined within the discussions, with emphasis on the recommendations of Eurocode 8. Selected results from static and dynamic non-linear analysis on idealised frame configurations are presented in order to illustrate salient response criteria, particularly those related to ductility demand and inelastic distribution. The primary sources of inconsistency existing in code provisions are demonstrated, and their implications on the seismic performance of concentrically braced frames are addressed. It is shown that several code modifications are required in order to alleviate causes of undesirable performance and to facilitate a rational implementation of capacity design concepts.