Zhuojin Pipe Fitting Co., LtdVulnerability of CFST Frame-Buckling-Restrained Brace Structures Under Coupled Wind and Seismic Loads
Literature Overview
Liu Yang and colleagues (2019, China Civil Engineering Journal, Vol. 52, No. 2, pp. 56-65) investigated the vulnerability of concrete-filled steel tube (CFST) frame structures with buckling-restrained braces (BRBs) subjected to coupled wind and seismic loads. This research addresses an important gap in structural engineering practice: the consideration of combined hazard scenarios that occur throughout the service life of tall structures, where wind and seismic events may coincide or interact through structural damage accumulation.
Research Methodology
The study employed OpenSees finite element software to conduct nonlinear dynamic time-history analyses under four loading scenarios:
| Scenario | Wind Return Period | Seismic Intensity | Description |
|---|---|---|---|
| Case 1 | None | Seismic only | Traditional seismic analysis |
| Case 2 | 1-year | Seismic + Wind | Frequent wind combined with seismic |
| Case 3 | 10-year | Seismic + Wind | Moderate wind combined with seismic |
| Case 4 | 50-year | Seismic + Wind | Severe wind combined with seismic |
Wind velocity time histories were simulated at different structural heights for return periods of 1, 10, and 50 years, reflecting the vertical variation of wind loading on tall structures. The seismic demand analysis method was used to generate vulnerability curves for each loading scenario, enabling probabilistic comparison of structural performance under different hazard combinations.
Key Findings
| Finding | Implication |
|---|---|
| Structural response increases with wind intensity | Wind loads contribute additively to seismic demand |
| Structural vulnerability increases with wind intensity | Higher probability of exceeding damage thresholds |
| Wind influence on vulnerability decreases with increasing seismic intensity | Seismic dominates at high intensities; wind is a secondary factor |
Interpretation of Coupled Loading Effects
The research reveals an important interaction pattern: wind loads have a more significant influence on structural vulnerability when seismic intensity is moderate, while at high seismic intensities, the seismic component dominates and the additional contribution of wind becomes relatively small. This finding has direct implications for risk assessment strategies, suggesting that coupled wind-seismic analysis is most critical for moderate seismic events where wind effects can meaningfully increase the probability of structural damage.
The vulnerability curves generated for different scenarios show progressive shifts toward higher damage probabilities as wind intensity increases. The shift is most pronounced for low-to-moderate damage states (e.g., immediate occupancy, life safety) where the additional energy input from wind loads can push the structure across performance thresholds. For collapse prevention levels, the seismic component dominates regardless of wind intensity.
Engineering Practice Implications
For CFST frame-BRB structures, several design considerations emerge from this research:
- Seismic design: The BRB system provides controlled inelastic deformation capacity that remains effective even under combined wind-seismic loading, as the BRB braces maintain their energy dissipation function while the CFST frame provides lateral stiffness.
- Wind design integration: Wind loads should be considered as a concurrent load in seismic design rather than treated as a separate design case, particularly for tall structures in regions with both seismic and wind hazards.
- Performance-based design: The vulnerability curves provide quantitative data for performance-based design, enabling engineers to select design parameters that achieve target reliability levels under combined hazard scenarios.
- CFST member design: The CFST columns and beams must be designed to maintain integrity under combined wind-induced drift and seismic-induced inelastic deformation, requiring attention to local buckling of steel tubes under cyclic loading.
Study Insights and Reflections
This research contributes to the growing body of knowledge on multi-hazard structural performance assessment. The finding that wind effects are most significant at moderate seismic intensities suggests that current seismic design codes, which typically do not consider concurrent wind loading, may underestimate structural vulnerability for moderate earthquake scenarios. For CFST frame-BRB systems specifically, the combination of CFST member ductility and BRB energy dissipation provides inherent advantages under combined loading, as both systems maintain their functional performance through the coupled event. However, the additional demands from wind loading on the elastic and low-damage performance levels warrant consideration in detailed design, particularly for structures where immediate occupancy is a critical performance objective. The research methodology using OpenSees with nonlinear material models for both steel and concrete components provides a rigorous analytical framework that can be extended to other structural systems and loading scenarios.