Improving the behavior of special concentrically brace frames with cast steel inserts

A Cast Modular Ductile Bracing System (CMDB) has been developed as an alternative to special concentrically braced frames. The CMDB system introduces cast components at the ends and center of the brace in an attempt to produce a system with reliable strength, stiffness, and deformation capacity. A cruciform cross-section has been chosen for the cast component geometry, which is specially detailed to enhance energy dissipation and increase low cycle fatigue life thereby reducing the likelihood of fracture. In this dissertation, capacity design parameters are established that describe the axial strength and flexural strength of the cast components relative to the main hollow structural section member. These parameters are varied in 2D finite element models to understand the nature of the system and identify the best performing designs. The cruciform shape of the casting is varied to produce better performance and self-centering enhancements are introduced. 3D FE models of the CMDB system and a typical special concentrically braced frame, in combination with fracture indices, are used to compare the expected low cycle fatigue life of the two systems. The dynamic performance of the system is assessed through nonlinear finite element anaylses and conclusions are drawn. The performance of the system is proved experimentally.