Seismic assessment and rehabilitation of existing steel braced frames designed in accordance with the 1980 Canadian code provisions
Bibliographic record
Abstract
Seismic loading provisions were introduced in the National Building Code of Canada (NBCC) in 1941, and seismic design and detailing provisions in CSA S16 were only implemented in 1989. The potential seismic deficiencies of steel braced frames built before the 1990’s were investigated for a 10-storey fictitious commercial steel building located in Vancouver, British Columbia. The structure was designed with two seismic load resisting systems commonly used in that era: tension-only X-bracing and tension-compression chevron bracing built with back-to-back double angle braces. The steel concentrically braced frames were designed according to the provisions of the 1980 NBCC and CSA-S16.1-M78 standard. The paper presents the seismic assessment of the tension-only X-braced frames that was performed using nonlinear time history analysis. The ASCE 41-06 standard was used to evaluate the structure. A numerical model was developed using the OpeenSees platform and nonlinear beam-column elements with fiber discretization of the cross-section were used to model the back-to-back double angle brace members. It was found that excessive inelastic deformation demand was imposed on the braces located at the 8th and 9th storeys of the frame. All brace connections had insufficient capacity. The resistance of the columns was exceeded in all but the 10th storey. All of the beams were found to have sufficient strength. To further assess the braced frame response, the nonlinear column behaviour, including section yielding and flexural buckling was represented in the model. Column buckling was observed in the lower levels, before yielding of bracing members in the upper storeys. These results clearly show that the evaluation of seismic demand is highly sensitive to the assumptions made in modelling process which in turn can significantly impact the structural assessment.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".