A New Type Of Buckling-restrained Braces With Concrete-filled Tubes

The global stability problem of all-steel buckling-restrained braces (BRB) is one of the concerned issues in design especially for long braces, since most of the cross-sectional dimensions of the casings of all-steel BRBs are restricted by that of the steel core. However, special unbonding materials should be painted onto the steel core to eliminate the bonding force for BRBs with concrete filled steel tube as the casing, which will also increase the total production cost of BRBs. To this end, a novel type of BRB with concrete-filled steel tubes combined as the casing and a core plate as the steel core is developed by the authors.The design methods and the corresponding characteristics of the new BRB are studied first based on the research findings and analytical theory of conventional BRBs, including global stability, local stability, width-to-thickness ratio of core plate and gap selection, etc.Second, one reduced scale and one full scale specimen of the new BRB were designed for the rehabilitation of the Hebei provincial library, and component tests were conducted on these two specimens to investigate its cyclic behavior. The fabrication process of such new BRB showed that it has the advantages of easier assembly, less time consuming and easier control on member quality. The test results showed that such new BRB exhibited excellent cyclic performance, which can well satisfied the seismic demands of the actual engineering project.Finally, parametric studies were performed on such new BRB by using the finite element analysis software ABAQUS, in which the effect of gap between the core and the casing, frictional response, cross-sectional dimensions of the external tube and axial deformation were analyzed and compared with the test results. The finite element analysis shows that the cyclic behavior of the specimens can be well simulated by numerical analysis, which will help to further optimize the specimen parameters in future study.