Assessment of yielding core length in a tube-in-tube all steel buckling restrained brace

Several different parameters influence the amount of energy absorption, ductility, global and local buckling of buckling restrained braces. One of them is the length of the steel core in a BRB, which could have a significant influence on the overall behavior and energy dissipation of the system. Because of this property, BRBs could be utilized as a fuse in braced frames. In this study, the effects of yielding core length on story drifts, as well as, the base shear in frames using a specific type of all-steel buckling restrained brace called "buckling controlled brace”, is investigated. The gap between the core and the outer casing in this type of brace is such that provides two phases of behavior, no buckling happens in the first phase while controlled buckling deformations occur in the second phase. The results of incremental dynamic analysis in short and medium height buildings indicates that the amount of increase in the base shear due to the shortening of yielding core, becomes more significant with increasing the height of the frame. In other words, taller buildings are more sensitive to the rigidity of bracing. Also the story shear and base shear will increase by shortening of the yielding core, and the amount of this increase in lower floors tends to be more than upper floors. Additionally by increasing the length of the yielding core and reducing the rigidity of the structure,the drift of the stories will increase and the maximum drift in short-height structures occur in upper floors, While in medium-height structures the maximum drift occurs in middle floors.

Keywords:

Buckling-restrained brace , Incremental dynamic analysis , Story drift , Story shear