Experimental Evaluation of Aluminium Core Buckling Restrained Knee Braced Truss Moment Frame Under Cyclic Loads

Abstract eng:
Buckling Restrained Braces (BRBs) offer robust cyclic performance and significant cost savings, compared to conventional bracing systems. These braces are becoming increasingly popular alternative to conventional bracing system in high seismic regions due to their ability to yield both in tension and compression. Buckling Restrained Knee Braced-Truss Moment Frames (BRKB-TMFs) are relatively new structural systems which utilize the advantages of both BRBs and TMFs. Experimental study was performed on scaled subassembly of a four-story four-bay BRKB-TMF frame. BRKB-TMF frame was designed using Performance Based Plastic Design (PBPD) method with pre-selected target drift and yield mechanism as key performance indicators. PBPD method ensures controlled distribution of inelastic activity throughout the structure by predefining Designated Yielding Members (DYMs) during the initial design process. These DYMs are designed to dissipate seismic input energy and all other frame members are designed to remain elastic under earthquake excitations. The use of annealed aluminum as a suitable BRB core material was explored. Quasi static cyclic tests were performed on a 1:3 reduced scale model of the BRKB-TMF sub-assemblage according to the provisions of FEMA 461 (2007). The application of BRB with annealed aluminum core significantly enhanced the energy dissipation capacity of the TMF. The BRB performed very satisfactorily and acted like a fuse for the frame by bearing all inelastic deformations. The study frame could successfully meet the 3% target drift imposed by MCE hazard level. The test assembly could even sustain two cycles of 3.75% lateral drift without any considerable damage to primary truss members.

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