Seismic Performance of Square Steel Tube Concrete Frames with Diagonally Stiffened Thin Steel Plate Shear Walls

Literature Overview

This paper, published in the Journal of Xi'an University of Architecture and Technology (Natural Science Edition) (2015, Vol. 47, No. 4, pp. 503-510) by Wang Xiantie, Liu Lida, Gao Yajing, Ma Yusufu, and Zhou Qinghan from Xi'an University of Architecture and Technology, presents low-cycle reversed loading tests on two single-bay, two-story 1:3 scale specimens of square steel tube concrete frames integrated with thin steel plate shear walls. One specimen featured diagonally cross-stiffened steel plate shear walls, while the other served as a comparison with unstiffened steel plate shear walls. The research was supported by the National Natural Science Foundation of China (grant 51108369), the Shaanxi Provincial Youth Science and Technology Star Project (2013KJXX-54), and the Ministry of Housing and Urban-Rural Development Science and Technology Project (2014-K2-007).

Core Technical Points

Structural System Configuration

The tested structural system combines square steel tube concrete (CFST) columns and beams with thin steel plate shear walls, creating a hybrid lateral force-resisting system. The key design features include:

• Square CFST columns: Providing high axial load capacity and ductility for gravity and lateral load resistance
• Thin steel plate shear walls: Serving as the primary lateral force-resisting element with efficient use of material
• Diagonal cross stiffeners (X-shaped): Installed on the steel plate to enhance strength, stiffness, and out-of-plane stability
• CFST vertical edge members: Ensuring proper force transfer between the steel plate wall and the frame system

Test Results and Hysteretic Behavior

The low-cycle reversed loading tests produced comprehensive performance data including:

The load-displacement hysteretic curves and skeleton curves obtained from the tests demonstrate that the square CFST frame with stiffened thin steel plate shear walls exhibits high lateral stiffness and load-bearing capacity, good ductility, and satisfactory energy dissipation performance.

Role of Diagonal Cross Stiffeners

The diagonally arranged cross stiffeners (X-shaped configuration) serve multiple structural functions:

1. Strength enhancement: The stiffeners provide additional load-carrying capacity to the thin steel plate, delaying the onset of local buckling and allowing the plate to develop its full membrane tension field strength.
2. Stiffness improvement: By dividing the steel plate into smaller panels, the stiffeners increase the effective bending stiffness of the wall, resulting in higher initial lateral stiffness.
3. Out-of-plane deformation control: The primary function of the stiffeners is to restrain the buckling mode of the thin steel plate, preventing excessive out-of-plane deflections that could compromise the wall's load-carrying capacity and structural integrity.
4. Force distribution modification: The X-shaped stiffener pattern creates a triangulated load path that distributes shear forces more uniformly across the steel plate surface.

Welding and Fabrication Quality Considerations

The seismic performance of this structural system is heavily dependent on the quality of welded connections:

• Steel plate to edge member welds: The perimeter welds connecting the thin steel plate to the CFST vertical edge members are critical for force transfer. These welds must be designed for full strength and subjected to rigorous quality inspection, including ultrasonic testing (UT) and magnetic particle testing (MT).
• Stiffener to steel plate welds: The attachment welds for the diagonal stiffeners must accommodate the relative deformation between the stiffeners and the steel plate during cyclic loading. Weld design should consider fatigue resistance and crack initiation resistance.
• CFST column fabrication: The square steel tubes used for columns are typically fabricated from rolled steel plates using submerged arc welding (SAW). The quality of longitudinal and transverse welds directly affects the column's ductility and seismic performance.
• Beam-to-column connections: The moment-resisting connections between steel beams and CFST columns require careful design and fabrication to ensure adequate rotational capacity and energy dissipation.

Critical Reflection and Independent Analysis

While the test results demonstrate the effectiveness of the stiffened thin steel plate shear wall system, several engineering considerations deserve attention:

• Scale effect: The 1:3 scale model results may not fully represent full-scale behavior due to scale effects on buckling, weld performance, and material properties. Full-scale testing or validated numerical modeling is recommended for final design verification.
• Cyclic loading protocol: The low-cycle reversed loading test simulates earthquake loading but does not capture the complex multi-directional loading patterns that can occur in real seismic events. The system's performance under biaxial loading should be investigated.
• Steel plate buckling behavior: While the X-shaped stiffeners effectively control out-of-plane deformation, the post-buckling behavior of the steel plate panels between stiffeners is critical for energy dissipation. The membrane tension field mechanism should be carefully considered in design.
• Connection detailing: The interaction between the steel plate shear wall and the CFST frame is mediated through the vertical edge members and perimeter connections. These connections must be designed to accommodate the large inelastic deformations that can occur during severe seismic events without premature failure.
• Material compatibility: The thin steel plate, diagonal stiffeners, and CFST members may use different steel grades. Compatibility of deformation characteristics and fracture toughness between different steel grades should be verified to prevent brittle failure mechanisms.

Reference Value and Outlook

This research contributes valuable experimental data on the seismic performance of square CFST frame systems with diagonally stiffened thin steel plate shear walls. The findings support the adoption of this structural system for seismic-resistant construction, particularly in applications where high lateral stiffness and load-bearing capacity are required. The X-shaped stiffener configuration emerges as an effective solution for enhancing thin steel plate wall performance while maintaining ductility. Future research should focus on full-scale testing, parametric studies of stiffener geometry and spacing, and the development of simplified design methods for practical engineering application.