CYCLIC BEHAVIOR OF DEEP SLENDER WIDE-FLANGE STEEL BEAM-COLUMNS UNDER COMBINED LATERAL DRIFT AND AXIAL LOAD
Bibliographic record
Abstract
During a seismic event, first-story end columns in steel Special Moment Frames (SMFs) experience lateral drift demands combined with high levels of axial load due to gravity loading and dynamic overturning moment effects. Deep slender wide-flange sections are typically assigned for the seismic design of perimeter SMFs in North America. The flange and web of these sections have high slenderness ratios, just below the compactness limits specified by AISC 360-10. This makes these sections vulnerable to local and lateral torsional buckling failure modes. In this paper, the cyclic behavior of deep slender wide-flange steel beam-columns, under combined lateral drift and axial load, is investigated through detailed finite element analysis (FEA). The main design variables that are considered as part of the FEA investigation are (a) the section slenderness; (b) the lateral loading protocol; and (c) the axial load level. Emphasis is placed on the effect of these variables on (a) the cyclic deterioration in flexural strength; (b) the column axial shortening; and (c) the lateral torsional buckling of the steel beam-columns. To this end, a range of deep slender wide-flange sections, commonly found in low to mid-rise SMFs, is selected. Two lateral loading protocols are used: 1) a symmetric protocol and 2) a near fault protocol. The axial load is applied in two forms: 1) constant compressive load; and 2) cyclic axial load varying from compression to tension. The latter represents the variation in the axial load experienced by an end column due to the dynamic overturning moments during an earthquake. Using a validated FEA modeling approach, typical first-story end columns of prototype steel SMFs are modeled and analyzed under the aforementioned-coupled lateral and axial loading protocols. The boundary conditions at the base of the columns are fixed. At the top of the columns the flexibility associated with the corresponding exterior beam-to-column connection is considered. Lateral braces are also provided to the column, as per the design code requirements. The FEA simulations demonstrated that higher rates of cyclic deterioration in flexural strength are associated with sections with larger web slenderness, due to severe web local buckling. Sections with large web and flange slenderness ratios also suffer from higher axial shortening levels at lower story drifts compared to more compact sections. It is also concluded that deep slender wide-flange sections with lower resistance to out-of-plane and torsional force demands, experience higher twisting and are likely to be subjected to lateral torsional buckling. The study also shows that axial force demands on the column’s lateral braces exceed their code design capacity at relatively low story drift ratios. Furthermore, the location of the column inflection point and the associated column moment gradient is monitored during the finite element analysis in order to assess the potential of plastic hinge formation at the top of the column once plastification and cyclic deterioration in flexural strength of the column occurs at its base. This is a critical issue since it could potentially lead to weak-story collapse mechanisms.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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) | 0.001 | 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 teacher head, 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".