Zhuojin Pipe Fitting Co., LtdMechanical Behaviour of Square Steel Tube Concrete Frames with Two-Sided Connected Thin Steel Plate Shear Walls
Literature Overview
The paper by Wang Xiantie, Yang Hangdong, Wang Liankun, Liu Lida, Ma Yousufu, and Dang Tao (2014), published in the Journal of Xi'an University of Architecture and Technology (Vol. 46, No. 5, pp. 665–670), investigates the mechanical properties of square steel tube concrete (CFT) frames connected to thin steel plate shear walls (SPSW) with a two-sided connection configuration. The research was supported by the National Natural Science Foundation of China (Grants 51108369 and 51208385), the Shaanxi Provincial Science and Technology New Star Project (2013KJXX-54), and the Ministry of Housing and Urban-Rural Development Science and Technology Project (2014-K2-007).
The two-sided connection configuration separates the thin steel plate shear wall from the vertical edge members, creating a connection where the steel plate is only connected to the top and bottom beams (the mid-span beams) rather than to all four sides. This configuration offers improved architectural applicability and provides better protection for the frame columns during seismic events.
Structural Configuration and Loading Characteristics
The two-sided connected SPSW system consists of a thin steel plate that is bolted or welded to the top and bottom beams of the bay, while the left and right sides are left free or connected through flexible links. This configuration allows the steel plate to deform independently of the vertical edge members, which are typically the CFT columns.
Under lateral loading, the steel plate develops a tension field mechanism similar to that of a four-sided connected SPSW. However, the absence of vertical edge connections changes the load path and the boundary conditions, resulting in a different distribution of forces and deformations. The mid-span beams (the top and bottom beams) experience additional shear forces from the steel plate tension field, which must be accounted for in the beam design.
The authors used ABAQUS 6.10 to perform nonlinear finite element analysis of both the two-sided connected and four-sided connected SPSW systems. The analysis included the geometric and material nonlinearity, the bolt connection behaviour, and the concrete-steel interaction in the CFT columns.
| System Configuration | Lateral Load Capacity | Hysteresis Performance | Energy Dissipation | Ductility |
|---|---|---|---|---|
| Four-sided connected SPSW | Higher | Stable | High | Good |
| Two-sided connected SPSW | Lower (reduced) | Stable | Good | Good |
The comparison between the two configurations revealed that the two-sided connection significantly reduces the lateral load capacity of the frame-shear wall system. This reduction is attributed to the absence of vertical edge connections, which eliminates the contribution of the edge members to the lateral resistance. However, the two-sided connected system still exhibits stable hysteresis behaviour, good energy dissipation capacity, and satisfactory ductility.
Design Formulas and Seismic Design Philosophy
The authors proposed a calculation formula for the shear force at the end of the mid-span beam and a design recommendation formula for the web thickness of the mid-span beam at the opening location. These formulas are derived from the analysis of the force characteristics of the two-sided connected SPSW under lateral loading.
The shear force at the mid-span beam end is calculated based on the tension field mechanism of the steel plate. The tension field angle, which is typically 45 degrees for thin steel plates, determines the direction of the tensile force in the plate. The vertical component of this tensile force is transferred to the mid-span beam through the bolted or welded connections, resulting in a shear force at the beam end.
The web thickness recommendation formula ensures that the mid-span beam has adequate shear capacity to resist the forces from the steel plate. The formula considers the steel plate thickness, the bay dimensions, and the connection details.
The seismic design philosophy of "weak plate, strong frame, strong column, weak beam" is achieved through the proposed design formulas. This philosophy ensures that the steel plate yields first under seismic loading, dissipating energy through inelastic deformation, while the frame members remain in the elastic or near-elastic range. This dual seismic defence target provides a safety margin against collapse during strong earthquakes.
Engineering Practice and Steel Pipe Considerations
The two-sided connected SPSW system offers several advantages for practical construction:
- Improved architectural flexibility: The separation of the steel plate from the vertical edge members allows for more flexible architectural layouts and easier installation of mechanical and electrical services.
- Better column protection: The CFT columns are shielded from direct damage during seismic events because the steel plate absorbs the lateral energy.
- Simplified construction: The two-sided connection reduces the number of connection details and simplifies the fabrication and erection process.
From a steel pipe manufacturing perspective, the CFT columns in this system must be manufactured with precise dimensional tolerances to ensure proper fit-up with the beam connections. The square steel tubes should have uniform wall thickness and minimal ovality to maintain the concrete-steel interaction and the structural performance. The welding or bolted connections at the column-beam joints must be designed to accommodate the reduced lateral forces from the two-sided connected SPSW system.
The thin steel plate used in the SPSW system is typically made from low-yield-point steel (e.g., Q235 or Q345) with a thickness of 3 mm to 6 mm. The plate should be manufactured with a flatness tolerance of 1/500 of the plate width to ensure uniform tension field development. The bolted connections between the steel plate and the beams should use high-strength bolts (e.g., Grade 8.8 or 10.9) to ensure adequate load transfer.
Study Insights and Reflections
This study demonstrates the potential of the two-sided connected SPSW system as an alternative to the conventional four-sided connected system. The reduction in lateral load capacity is a trade-off for improved architectural flexibility and column protection, which are important considerations in modern building design.
The proposed design formulas provide a practical basis for the engineering application of the two-sided connected SPSW system. The formulas can be incorporated into design codes and standards to facilitate the widespread adoption of this system.
The integration of CFT columns with the two-sided connected SPSW system represents a hybrid structural system that combines the advantages of both systems. The CFT columns provide high axial load capacity and good seismic performance, while the SPSW provides lateral resistance and energy dissipation. This hybrid approach is consistent with the trend towards multi-functional structural systems in modern construction.
The study also highlights the importance of connection design in hybrid structural systems. The performance of the system depends not only on the properties of the individual components but also on the quality and behaviour of the connections. The proposed design formulas for the mid-span beam ensure that the connections are designed to accommodate the forces from the steel plate, which is essential for the overall system performance.