Special concentrically braced frames (SCBFs) are economical and provide substantial lateral resistance and stiffness. They are frequently used in seismic design, since recent issues with steel moment resisting frames have increased the cost and raised doubts about the performance of the moment frame system. Unfortunately SCBFs are not as well understood as many other structural system, because they rely on inelastic post-buckling of the brace during extreme seismic events. As a result, several research studies have been undertaken to better understand and improve SCBF seismic behavior. This paper will present two recent developments in this direction. First, a research study has been in progress at the U. of Washington (UW) to improve the seismic performance of SCBF gusset plate connections. To date 21 large scale SCBF frames with gusset plate connections have been tested, and extensive analysis has been performed. This work is summarized, and the broad general conclusions from the work are noted and demonstrated. The results lead to recommended changes in the current design methods. In particular, a modified method for assuring end rotational capacity for brace buckling is proposed. This method provides lighter more compact gusset plates, which develop greater inelastic deformation capacity from the frame and less secondary damage to framing members. The importance of connection stiffness and gusset plate welding and the relative performance of bolted vs. welded and tapered vs. rectangular gusset plates are shown. Initial recommendations are provided. Second, the continuing interest and concerns related to SCBF construction has lead to recent funding of a group research project on steel braced frames by NSF. The project involves researchers from UC Berkeley, U. of Minnesota, and UW as well as Japan and Taiwan. This is broad based effort to improve the seismic performance and design methods of SCBFs. This project is briefly described.
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