Ductility, Overstrength and Residual Drift in Buckling-Restrained Braced Frames


Abstract eng:
Buckling-restrained braced frames (BRBF) have become a very popular lateral resisting system due to their balanced, full hysteresis and the ability to tailor both stiffness and strength to meet specific design requirements. This paper reports the results of an analytical investigation on the performance of buckling-restrained braces (BRB) and the global performance of BRBFs with a focus on the ductility and overstrength demands on the braces. Nonlinear analytical models of various three and six-story frames were subjected to a suite of earthquake records to determine the demands on the BRB elements and the overall frame response. The earthquake suites were amplitude scaled to the two seismic hazards and include both near-field and far-field ground motions. The structure variations include the building height, seismic hazard, seismic importance factor (I e ), brace configuration (chevron versus single diagonal), and BRB core yielding length. It was determined that many parameters impact the ductility and force demands on the braces as well as the global performance of the system. The results included story drift, residual drift, roof acceleration, normalized brace force (overstrength), brace strain and multiple ductility metrics. The three ductility metrics are the single cycle ductility demand (maximum inelastic single tension-tocompression or compression-to-tension cycle), reference ductility demand (maximum tension or compression ductility demand with reference to the undeformed configuration) and the cumulative ductility demand. The analysis results indicate that an importance factor of 1.5 reduces the system and brace demands. A shortened brace yielding length has a beneficial effect on both story drift and residual drift but experiences significant increases in acceleration, normalized brace forces, brace strain and all the ductility metrics. The results show that at the mean plus one standard deviation measure of the ratio of the single cycle ductility demand to the reference ductility demand in an actual earthquake is 1.36. Current testing protocol requires braces to undergo a single cycle ductility demand that is two times the reference ductility demand. This is indicative that the brace overstrength capacities which are based on symmetric cyclic testing may be overestimated. A more comprehensive analytical study is needed to identify the best way to relate the overstrength to the brace properties.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
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Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 2330.:
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