Seismic Performance Evaluation of Steel Buckling-Restrained Braces Subjected to Subduction Interface Earthquake Demands
Bibliographic record
Abstract
Steel Buckling-Restrained Braced Frames (BRBFs) are commonly used as lateral-force resisting systems in multi-storey buildings located in high seismic regions of North America. The reliable seismic performance of BRBFs is attributed to their Buckling-Restrained Braces (BRBs), which provide high ductility and energy dissipation capabilities. BRBs were first developed in Japan in 1988, later adopted into the AISC Seismic Provisions (AISC 341) in 2005, and subsequently incorporated into the Canadian steel design standard (CSA S16) in 2009. Canadian standards have since referenced the BRB prequalification provisions from AISC 341, which require two tests: (1) a uniaxial test to evaluate the performance of the device, and (2) a subassemblage test to assess stability under additional rotational demands introduced by the connections. Both tests must be conducted under a standardized symmetrically increasing loading protocol, which was primarily developed from analytical studies of near-field and far-field seismicity in Los Angeles, California. The loading protocol development may not account for the demands due to more severe, long-duration subduction interface earthquakes of the Cascadia Subduction Zone. The adequacy of the prequalification loading protocol to capture the demands imposed by subduction interface earthquakes is therefore uncertain. In addition, studies specifically examining BRB demands under such events remain scarce. This gap in understanding emphasizes the importance of further investigation on the seismic response of BRBs under subduction interface earthquake demands. This M.Sc. research project aims to examine the seismic demands imposed on BRBs in low- to mid-rise steel buildings equipped with BRBFs subjected to seismicity expected in the west coast of Canada, develop a subduction interface-consistent loading protocol, and experimentally evaluate the seismic performance of steel BRBs subjected to subduction interface earthquake demands. Five different prototype BRBF buildings are first designed under Canadian standards. A fibre-based numerical model is developed for one of the BRBFs in each building and subjected to Nonlinear Response History Analyses (NLRHA) using three suites of 11 historical records each: shallow crustal, in-slab, and subduction interface events. The results show that the largest demands imposed on BRBs pertaining to peak strain demands, force overstrength, cumulative inelastic ductility, and fatigue life, are consistently largest under subduction interface events. The results of one of the prototype buildings are then statistically analyzed to develop a symmetrically increasing, subduction-consistent loading protocol. Following the analytical evaluation, an experimental program consisting of five full-scale BRB specimens is developed. Two of the BRB specimens have been previously tested and strain-aged for two years and eight months, while the remaining three are new. Both strain-aged specimens and one new specimen are subjected to direct brace deformation histories representing two historical subduction earthquake events. The other two new specimens are tested under symmetric loading protocols: the AISC 341 loading protocol and the subduction loading protocol developed in this study. The results of the experimental tests show that BRBs subjected to symmetric loading protocols exhibit post-yield envelope behaviour that is in good agreement with each other, irrespective of protocol. BRBs subjected to direct brace deformations confirm significant strain capacity and fatigue life available in BRBs. Furthermore, BRB force overstrength can generally be reproduced by post-yield slopes of symmetric loading protocols studied here. The strain-aged BRB shows a noticeable increase in peak forces, however, additional test data is required to verify this effect, particularly since the large tensile strain generated by the monotonic push in the strain-aged BRB was not imposed in the replica new BRB.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".