Energy dissipation of compression members in concentrically braced frames: Review of experimental data

Design and detailing requirements of seismic provisions for concentrically braced frames (CBF) were specified based on the premise that bracing members with low KL/r and b/t will have superior seismic performance. However, relatively few tests investigate the cyclic behavior of CBF. It is legitimate to question whether the compression member of CBF plays as significant a role as what has been typically assumed explicitly by the design provisions. In this paper, the existing experimental data are reviewed to quantify the extent of hysteretic energy achieved by bracing members in compression in past tests, and the extent of degradation of the compression force upon repeated cycling loading. Although it is recognized that many parameters have an influence on the behavior of braced frames, the focus of this paper is mostly on quantifying energy dissipation in compression and its effectiveness on seismic performance. Based on the experimental data review from previous tests, it is found that the normalized energy dissipation of braces having moderate KL/r (80-120) do not have significantly more normalized energy dissipation in compression than those having a slenderness in excess of 120. The normalized degradation of the compression force envelope depends on KL/r and is particularly severe for W-shaped braces.