Plastic design of knee-element connection frames (KCFs) using mechanism control

Abstract

In the past two decades, extensive research has been conducted to evaluate the seismic performance of Knee-element Connection Frames (KCFs) and to determine the most efficient configurations. KCFs are of particular advantage over other load-resisting systems in terms of their ample access for maintenance and enhanced structural performance. This paper presents an enhanced energy-based plastic design for KCFs using mechanism control. The design methodology developed in this study constitutes the design criteria employed in Performance-based Plastic Design (PBPD) and Theory of Plastic Mechanism Control (TPMC) at the same time. In this design approach, the external forces are derived from the energy balance equation directly considering second-order effects, and design is carried out according to the PBPD method. Then, undesired collapse mechanisms are identified and prevented by the use of a Design-Capacity Ratio-based (DCR-based) approach as the controlling criteria. To evaluate the design performance, nonlinear static and dynamic analyses were performed. The results indicate an acceptable correlation between the expected general yield mechanism and structural response and an acceptable economy in terms of material usage compared to comparable moment resisting frames.