Cam-Type Compression Free Device for Energy Dissipative Brace System

Abstract eng:
A newly developed hysteretic-type energy dissipative brace for suppression of structural responses under earthquake ground motions, namely Compression-Free Braces (CFBs), is introduced herein. Resembling to Buckling Restrained Braces (BRBs), CFBs transform kinetic energy in buildings under earthquake into plastic strain energy in a mild steel core. However, in contrast with BRBs, the energy dissipation in a steel core in CFBs occurs only under tension whereas zerostiffness and zero-resistance behavior occurs under compression as a result of compression-free mechanism. Two rotary cams, pinned to the body of CFBs, are used to grip a mild steel core by friction force only under tension and disengage a core readily at the mobilization of compression. The resulting near-zero compression force in a steel core in CFBs benefits majorly in very minimal requirement in steel core restraint, unlike the BRB system that depends upon a weighty casing (steel tube filled with mortar) to maintain a steel core’s compressive force. As a result of an extermination of restraining casing in CFBs, the light weight CFB system promotes ease of installation and replacement of a plastically-deformed steel core after the earthquake. Furthermore, retrofit and strengthening for earthquake of existing buildings is much easier than the counterpart system. In this research, the pseudo-static experiments were performed in steel frame sub-assemblage, equipped with CFD, under different level of story drifts. We obtained stable and predictable hysteretic loops which appear only in tension force side from a number of tests under different loading protocols. In the experiments, steel core replacements were carried out conveniently.

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