Experimental Study of an All-Steel Two-Segment Core Buckling Restrained Brace

Buckling Restrained Braces (BRBs) have been exceedingly used for resisting seismic forces in framed structures because of their advantages of non-buckling and large energy absorption capacities. A type of fully steel brace has been designed in the present study that provides ease of construction and replacement of the core. The term multi-zone indicates that the part of the core undergoing plastic deformation is divided into two or more segments in order to provide a more uniform distribution of the plastic deformation. In other words, the core consists of two or more segments that can become plastic. The end parts of the core and shield are so designed as to eliminate the problems that have existed in the previous designs. The aim here is to produce a robust type of brace that can be constructed without strict building requirements, and the test results show that this has been achieved. Three ½ scale specimens were constructed for testing. These specimens were tested under quasi-static loading up to a target displacement. The results for all three specimens tested show that minimum values of parameters specified by the AISC Steel code (maximum compressive stress factor, b= 1.3, and minimum energy absorption factor h =200 ) have been achieved and in all cases they exceeded the code requirements by a large margin (here: bmax= 1.21, hmin= 1102 ). In addition, each specimen was capable of carrying several additional cycles of loading (11 or more) at the end of the test. That is, they are more robust against fatigue than that specified by the said AISC code. Cyclic behavior of the specimens showed high energy absorption capabilities with strains of up to 4.6%. Based on the test results, it can be concluded that the multi-zone core BRB's with stiffened shield and restraining device tested here are suitable for use in new buildings as well as in retrofit of existing structures. The idea of using multi-zone cores not only allows for a better distribution of plastic region, but also enables us to stabilize the shield to the core at the middle zone, where no plastic deformation takes place. In this way, the stability of the shield is achieved by a simple mechanism without requiring elaborate details of a stopper.