Seismic design and performance evaluation of steel frames with knee-element connections

Abstract

In this paper, application of a structural steel frame system called Knee-element Connections Frame (KCF) is investigated as a seismic-force-resisting system. In this structural system, all beam-to-column and knee-element to beam and column connections are simple. This configuration creates a zonular rigid connection instead of concentrated rigid one in moment-resisting frame (MRF). It provides more flexibility in architectural design compared with laterally braced frames and reduces the costs and problems associated with the construction of rigid connections with complete-joint-penetration groove weld in MRFs. Moreover, KCF systems can be retrofitted with low cost, because the knee-elements can be easily repaired or replaced. In this study, two types of yield mechanisms (A and B) are introduced for the seismic design of the KCF system based on the capacity design concept. Then, its detailed seismic design procedure is developed based on mechanism A. For performance evaluation of the system according to FEMA P695 methodology, four sample KCF and special moment-resisting frames (SMRF) are designed and compared in terms of failure mechanism, collapse probability and seismic design parameters (Ω0, R and Cd). The results indicate that although the failure mechanism of KCF and SMRF is similar, collapse probability of KCF is less than SMRF. Moreover, the required ductility for both structural systems is provided properly. Consequently, KCF structural system can be classified in the category of MRFs, also seismic design parameters of SMRF can be used for KCF.