Seismic Response Analysis of Steel Frames Braced with Buckling-Restrained,Ordinary and Special Concentrically Braces

Based on the facts of overstrength of the postyield chevron buckling-restrained brace (BRB) due to the strain-hardening effect and almost without vertical support for the braced beam by this brace,a method for design of the frame with buckling-restrained braces (BRBF) is proposed in this paper. Furthermore,a seismic response analysis has been carried out on the special concentrically braced frame (SCBF) and the ordinary concentrically braced frame (OCBF) to compare the aseismic performance of the BRBF. The analysis reveals that,although the story drift of the BRBF and SCBF are slightly larger than those of the OCBF,the first story shear forces of the former are greatly smaller than those of the latter. Under severe earthquakes,columns in three kinds of the structures remain elastic. For most OCBs and SCBs,the out-of-plane flexural buckling occurs. Whereas,the buckling-restrained braces can yield in both tension and compression,exhibiting better energy dissipation capacity. The maximum vertical deflection of the beam connected by the braces occurs in the segments of beam between the column and braced points before the braces yielding or buckling,whereas at the braced points after the braces yielding or buckling. Compared with the larger vertical shear forces from the braces to the braced beams in the OCBF or SCBF after the braces buckling,smaller such shear forces occur in the BRBF after the braces yielding.