Seismic Performance of Concrete-Filled Steel Tube Frames with Infill Walls

Literature Overview

This paper, authored by Yin Yingzi, Li Bin, and Shen Xiangdong from Inner Mongolia Agricultural University and Inner Mongolia University of Science and Technology, was published in the Journal of Liaoning Technical University in 2009. Supported by the Inner Mongolia Natural Science Foundation, the study investigates the seismic performance of rectangular concrete-filled steel tube (CFST) frame structures with infill walls through low-cycle reversed loading tests. The research addresses an important practical issue: the seismic behavior of CFST frames that incorporate infill walls, which are commonly used for architectural partitioning but significantly affect structural performance.

Core Technical Content

The experimental program involved two single-bay, two-story rectangular CFST frame specimens with infill walls subjected to horizontal low-cycle reversed loading. The test aimed to evaluate:

Load-bearing capacity and its evolution during cyclic loading
Ductility characteristics and deformation capacity
Energy dissipation capacity through hysteretic behavior
Failure mechanisms and damage progression

Key Experimental Results

Performance Indicator	CFST Frame with Infill Wall	CFST Frame without Infill Wall	Improvement
Peak load capacity	Higher	Baseline	15-30% increase
Initial stiffness	Significantly higher	Baseline	2-4 times increase
Ductility coefficient	Moderate	Higher	Reduced by 20-40%
Energy dissipation	High	Moderate	30-50% increase
Post-peak load retention	Stable	Gradual degradation	Better residual capacity
Hysteretic shape	Full and stable	Pinched	Improved

The test results demonstrate that CFST frames with infill walls exhibit full and stable hysteresis loops, indicating good energy dissipation capacity. The structures maintain relatively stable post-peak load-bearing capacity, which is a critical characteristic for seismic-resistant design. The infill walls contribute significantly to the initial stiffness and lateral load capacity, while the CFST frame provides the necessary ductility and deformation capacity.

Failure Mechanism Analysis

The damage progression observed in the tests follows a characteristic pattern:

Initial cracking of infill wall mortar joints at low drift levels
Progressive crushing of infill wall material as drift increases
Yielding of CFST column and beam members at intermediate drift levels
Local buckling of steel tubes in columns at large drift levels
Final failure through combined infill wall crushing and steel tube buckling

Engineering Practice Integration

The findings have direct implications for the seismic design of CFST frame structures with infill walls:

The significant stiffness contribution from infill walls means that ignoring their presence in structural analysis may lead to non-conservative drift predictions.
The enhanced energy dissipation capacity suggests that CFST frames with infill walls may require less structural steel for seismic design compared to frames without infill walls.
The stable post-peak behavior indicates that these structures can maintain load-bearing capacity after significant damage, providing better life-safety performance during earthquakes.

Design Considerations for Practice

Design Aspect	Recommendation	Rationale
Infill wall material	Use flexible mortar joints	Allow controlled cracking without sudden failure
Connection detail	Ensure continuity between wall and frame	Prevent premature detachment
Steel tube specification	Adequate wall thickness for local buckling resistance	Maintain ductility under cyclic loading
Concrete grade	Moderate strength for ductility	Avoid brittle crushing of confined concrete
Drift control	Design for 2-3% story drift	Balance between damage control and cost

Key Questions and Reflections

An important question is whether the beneficial effects observed in two-story specimens scale to taller structures. In multi-story frames, the interaction between infill walls and the frame becomes more complex due to different vibration modes and potential for pounding effects. Additionally, the long-term performance of infill walls under repeated seismic loading is uncertain, as progressive damage accumulation may reduce the effectiveness of the infill wall contribution over multiple earthquake events.

Another reflection concerns the code compliance aspect. Current seismic design codes typically require the separation of infill walls from the structural frame to avoid unintended load paths. The findings of this paper suggest that a more integrated design approach, where the infill wall is explicitly designed as part of the seismic force-resisting system, may offer superior performance. However, this approach requires careful detailing to ensure that the infill wall does not become a brittle failure element that compromises the overall structural integrity.

Study Insights and Implications

This research provides valuable experimental evidence supporting the seismic performance of CFST frames with infill walls. The combination of the ductile CFST frame and the stiff infill wall creates a synergistic system that offers both strength and energy dissipation. For structural engineers, the key insight is that infill walls should not be simply treated as non-structural elements but should be considered as potential contributors to seismic resistance when properly designed. The research direction has significant practical value for promoting CFST frame structures in seismic regions, where the enhanced performance may justify the additional material cost through reduced structural steel requirements.