Plastic design for knee braced steel frame using performance and mechanism control

Abstract

The knee braced steel frame (KBSF) has seen widespread application in practical engineering due to its minimal spatial requirements and ease of assembly. However, the absence of key research findings regarding the synergistic between knee braces and joints has hindered the accurate calculation of the stress state in structural components. This limitation makes a challenge for the better seismic performance of structures designed using current methodologies. This paper proposed a new design method, referred to as the Plastic Design using Performance and Mechanism Control (PDPMC), for knee braced steel frames, which could control the yield sequence of structural components, ultimately enhancing the seismic performance of the structure. Additionally, a keen braced steel frame was designed using the proposed methodology and subsequently compared with the conventional method known as Performance-Based Plastic Design (PBPD) and Theory of Plastic Mechanism Control (TPMC) to assess its accuracy. The results shows that the designed structure using the PDPMC method will utilize 20.9 % and 21.6 % less steel compared to the PBPD and TPMC methods, respectively. Moreover, the structure designed using the proposed methods exhibits excellent seismic performance. Specifically, the maximum inter-story drift ratios at top-floor drift ratios of 2 % and 4 % are comparable to those designed using PBPD and are 17 % lower than those designed using TPMC. The results of the nonlinear dynamic time-history analysis conducted on structures designed using three different methodologies indicate that all design methods satisfied with the safety requirements under various seismic ground motions. It should be noted that the structures designed using the proposed method demonstrate superior control over maximum displacement and inter-story drift angles compared to those designed with the TPMC, while exhibiting performance comparable to that of structures designed using the PBPD.