Response of Framed Structure Incorporating Buckling Restrained Braces

Abstract

In recent years, the seismic design of buildings has undergone significant changes due to the increased demand for optimization of the structural capabilities of buildings in order to minimize the level of damage, economic loss, and structural repair costs after an earthquake. A buckling restrained brace (BRB) is a structural brace in a building, designed to allow the building to withstand cyclical lateral loadings, typically earthquake induced. Buckling restrained bracing elements offer designers a way to add even more seismic energy dissipation capacity to braced frame systems. A typical BRB consists of a yielding steel core that provides axial resistance confined by a concrete/mortar filled steel casing that provides flexural and buckling resistance. For some commonly used BRB, the core is divided into three zones: the yielding zone, transition zones and connection zones. BRB uses the ductility of steel more effectively than conventional braced frames. Buckling restrained braces have been used extensively in Japan as hysteric dampers incorporating in moment resisting frames. Analysis and Design of G+4 storeyed building with various configuration and location of BRB is carried out using ETABS software. This study presents the optimal location and configuration for BRB in five storeyed framed structure. Analysis and Design of the Structures is carried out as per specifications of IS 1893(Part I)-2002, IS 875-1987 and IS 456:2000. Design data for BRB is taken from manufacturer M/S Core Brace. In this study a comparison of five storeyed building without and with BRB is carried out by extracting various parameters like storey shear, maximum storey displacement, storey drift etc. using static and dynamic analysis method. Effects on design of slabs, beams, columns and footings after placing BRB is also studied. Parametric study is carried out considering building with 5, 10, 15 and 20 storeys to understand the effect of height on behaviour of framed structure with BRB. Various seismic parameters and modal time period are compared. From the modal time period, storey displacement & storey drift it is found that cross diagonal configuration of BRB imparts higher stiffness to building under lateral loading. BRB are effective when building is subjected to lateral load due to earth- quake. Under gravity loading it is not much effective. A case study of existing B+G+7 storeyed building is considered to explore the use of BRB for increasing the number of floors. The building is analyzed using ETABS software as per the guidelines of Indian Standards. A study is made on the use of BRB for increasing the number of storeys in the same building. Various permutations and combinations were done to finalize the location and configuration of BRB placed to increase the strength of the building on addition of more number of storeys. The study concludes that BRB can be used as a retrofitting technique in order to increase the certain number of storeys by restoring the strength of beams and columns. BRBs have a capacity to take large lateral seismic forces thereby reducing displacements and drifts. In the end an experimental study is carried out on BRB.