Mechanical Properties of Square Steel Tube Concrete Frame-Cross Stiffened Thin Steel Plate Shear Wall

Literature Overview

This study by Wang Xiantie, Bai Lianping, Wang Liangkun, Ma Yusuofu, and Liu Tianlong, published in Earthquake Engineering and Engineering Dynamics (2013, Vol. 33, No. 2, pp. 103–109), investigates the mechanical performance of square steel tube concrete (SRC) frame systems combined with cross-stiffened thin steel plate shear walls. The research was supported by the National Natural Science Foundation of China (Grants 51108369, 51208385), the Ministry of Education Doctoral Point New Teacher Fund (20116120120008), and the Shaanxi Provincial Department of Education Special Research Fund (11JKY0942).

Using ABAQUS 6.10 finite element software, the researchers conducted numerical analysis of both cross-stiffened and unstiffened thin steel plate shear wall systems, examining loading characteristics, stiffness, ultimate bearing capacity, shear force distribution, and column behavior.

Core Technical Findings

The study reveals several important behaviors of the hybrid SRC frame-thin steel plate shear wall system:

• When the rib stiffness ratio is 30, cross stiffeners effectively increase the elastic buckling load, ultimate bearing capacity, and initial stiffness of the steel plate shear wall.
• Cross stiffeners reduce the influence of column axial compression ratio on initial shear force distribution.
• During the initial loading stage (story drift angle less than 0.2%), the steel plate shear wall carries most of the shear force.
• As loading progresses, the steel plate shear wall's shear force share gradually decreases while the frame's share increases.
• When the story drift angle reaches 1%, the shear force distribution between the frame and steel plate shear wall stabilizes.
• The hysteresis loops of the SRC frame-thin steel plate shear wall system are full and stable, indicating good energy dissipation capacity.
• Due to the tension field action in the thin steel plate wall, separation between the steel tube column wall and concrete may occur, which should be addressed in design.

Steel Tube Column Behavior and Design Considerations

The separation phenomenon between the steel tube column wall and concrete is a critical finding that has direct implications for steel tube manufacturing and design:

• Tension field effect: The thin steel plate shear wall develops diagonal tension fields under lateral loading, which transfer forces to the column through the beam-column joints. These tension forces can pull the steel tube wall away from the concrete core.
• Column design implications: Engineers must ensure that the steel tube columns have adequate connection details to prevent separation. This may require additional mechanical interlocks, dowel bars, or bond enhancement measures at the steel tube-concrete interface.
• Steel tube fabrication: The steel tube columns must be manufactured with high dimensional accuracy to ensure proper fit with the concrete core. Any deviation in tube dimensions could lead to poor concrete fill and reduced bond strength.

Shear Force Distribution Analysis

The progressive change in shear force distribution between the steel plate shear wall and the frame is an important design consideration:

1. Initial stage (drift angle < 0.2%): The steel plate shear wall, being much stiffer than the frame, attracts the majority of the shear force. The design must ensure that the steel plate wall has adequate capacity at this stage.
2. Transition stage (0.2% < drift angle < 1%): As the steel plate wall begins to buckle and yield, its stiffness decreases, and the frame attracts an increasing share of the shear force. This transition must be smooth to avoid sudden load redistribution.
3. Stable stage (drift angle ≥ 1%): The shear force distribution stabilizes, with both the wall and frame contributing proportionally. The frame must have adequate capacity to carry its share of the shear force without excessive deformation.

Cross Stiffener Design Parameters

The rib stiffness ratio of 30 identified as optimal in this study is a key design parameter. The rib stiffness ratio is defined as the ratio of the bending stiffness of the stiffener rib to the bending stiffness of the steel plate. Engineers should consider:

• Rib dimensions: The cross-sectional dimensions of the stiffener ribs must be selected to achieve the target stiffness ratio. Typical rib depths range from 50 mm to 150 mm for thin steel plate walls.
• Rib spacing: The spacing between stiffener ribs must be optimized to prevent local buckling of the steel plate between ribs while avoiding excessive material usage.
• Welding of stiffeners: The stiffener ribs are typically welded to the steel plate. Weld quality is critical, as any weld defect could serve as a crack initiation site under cyclic loading.

Engineering Practice Recommendations

For engineers designing SRC frame-thin steel plate shear wall systems, the following recommendations emerge:

1. Stiffener design: Use cross stiffeners with a stiffness ratio of approximately 30 to achieve optimal performance in terms of buckling resistance, ultimate capacity, and stiffness.
2. Column separation prevention: Incorporate mechanical interlocks or bond enhancement measures at the steel tube column-concrete interface to prevent separation under tension field action.
3. Shear force distribution design: Design both the steel plate wall and the frame to carry their respective shares of shear force at all loading stages, with particular attention to the transition stage.
4. Steel tube quality control: Ensure that steel tube columns are manufactured with high dimensional accuracy, sound welds, and verified material properties. The columns must maintain their structural integrity throughout the seismic loading sequence.
5. Finite element modeling: When using finite element analysis for design, include realistic material models for both the steel tube and concrete, and account for the steel tube-concrete interface behavior.

Study Insights and Conclusions

This research provides valuable insights into the behavior of SRC frame systems with cross-stiffened thin steel plate shear walls, which is a promising structural system for seismic-resistant design. The finding that cross stiffeners with a stiffness ratio of 30 provide optimal performance is a practical design guideline. The progressive shear force distribution between the wall and frame is an important consideration that engineers must account for in their designs. The potential for steel tube column separation under tension field action is a critical design issue that requires attention through appropriate connection details and interface treatment. For steel pipe manufacturers, the study emphasizes the importance of producing high-quality steel tube columns with precise dimensions and sound welds, as these columns are critical structural components that must perform reliably under cyclic seismic loading. The research contributes to the advancement of steel plate shear wall technology and provides a foundation for future work on optimizing stiffener configurations and interface treatments.