Experimental analysis of steel dissipative bracing systems for seismic upgrading

Abstract

Energy dissipating devices, such as metallic ductile dampers, could represent one reliable system for seismic performance upgrading of reinforced concrete (RC) structures. This paper illustrates the significant improvement to the seismic response of RC structures equipped with dissipative bracing systems, such as eccentric braces (EBs) and buckling restrained braces (BRBs). In fact, the results of experimental tests carried out on two similar two-storey one-bay RC structures, respectively equipped with EBs and BRBs, are described. Referring to EBs, 3 lateral loading tests have been performed. Each test is characterized by shear links with bolted end-plate connections. Different design criteria have been applied in the design of the connections. In the first test, capacity design criteria have not been considered. In the second test, a capacity design criterion has been applied, with a link shear over-strength factor equal to 1.5. In the third test, a design criterion similar to the one adopted for the second test has been implemented, but with a larger over-strength factor. In case of BRBs, two types of 'only-steel' braces have been tested: one type was made using two buckling-restraining rectangular tubes that are fully welded together with steel plates; the other type is detachable, being made again with two buckling-restraining rectangular tubes but joined together by means of bolted steel connections. In both cases, the internal yielding core was a rectangular steel plate. The experimental results of both bracing systems are encouraging about the possibility to use these devices for improving the seismic resistance of existing RC structures.