Civil Engineering Association

IMPROVING THE BEHAVIOR OF SPECIAL CONCENTRICALLY BRACE FRAMES WITH CAST STEEL INSERTS

A Cast Modular Ductile Bracing System (CMDB) has been developed as an alter-
native 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, stiness, and deformation capacity. A cruciform cross-section
has been chosen for the cast component geometry, which is specially detailed to en-
hance energy dissipation and increase low cycle fatigue life thereby reducing the
likelihood of fracture. In this dissertaion, capacity design parameters are estab-
lished that describe the axial strength and
exural strength of the cast components
relative to the main hollow structural section member. These parameters are varied
in 2D nite 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 combi-
nation 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 nite element anaylses and conclusions are drawn.