Abstract
Abstract Expanding the use of smart braced frames to govern the seismic response of structures by providing ductility and elasticity has been hampered and delayed by cost indexes. The braces in frames comprise two segments of expensive shape memory alloys (SMAs) and high-strength steel with high stiffness. These smart materials can reduce seismic damage by providing stiffness, yielding, and phase shifting. In this study, the length of the SMA segments in three- and six-story frames (applied either at all floors or as part of a dual system) was increased to determine the optimal length at a constant period. Performance levels and fragility curves were obtained to evaluate the seismic behavior of the optimized frame. The response modification factor determined based on the static pushover, incremental nonlinear dynamic analysis, and linear dynamic analysis suggests the ductility and over-strength of the optimized frame. The probability of being in or exceeding each damage state was determined with a Monte Carlo analysis and was acceptable and in accordance with previous deterministic analysis results.
Highlights
The aspiration of a design must always be balanced by safety and cost
Three- and six-story concentrically braced frames proposed by McCormick and derived from the investigation conducted by Sabelli on broadening the assessment of braced frames complementary to a FEMA/SAC project [32] in Los Angeles, USA were used in this assessment for consistency
Smart braced frames and dual-braced frames were optimized by considering the amount of shape memory alloys (SMAs) in the braces of each floor and were subjected to both deterministic and probabilistic analyses
Summary
The aspiration of a design must always be balanced by safety and cost. Increased observations, new inventions, and a progressive shift in design philosophy have tended to challenge the creativity and approach of engineers. Super-elasticity eliminates severe strain during cyclic loading In this regard, the material exposed to a load above the austenite finish temperature shifts from fullaustenite (A) to de-twinned martensite (B). Questions persist about what the optimized length should be, and how any change in that length may affect the structural behavior To this end, SMA segments in three- and six-story concentrically braced frames with a constant stiffness at the braces were varied and analyzed using the Open System for Earthquake Engineering System (OpenSEES) [31]. The fragility curve for each damage state of the optimized frame, along with the probability of being in or exceeding each damage state, were estimated with a Monte Carlo probabilistic analysis This time-wise method was found to be effective in reducing the seismic response and limiting the structural cost, as a large number of frames were generated and compared with the obtained optimum one. Optimum dual-braced frames in this regard were found to be suitable representatives of the lateral load system
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