Shear Performance of Vertical Joint Between CFST Frame and Wall Panel

Literature Overview

The experimental study by Wu Liwei, Chen Jianwei, Su Youpo, Chen Haibin, and Gao Lin from Hebei United University investigates the shear performance of vertical joints between steel tube concrete (STC) frames and wall panels in shear wall structures. Published in the Structural Engineer journal (Vol. 30, No. 4, 2014, pp. 126–130) and supported by the National Natural Science Foundation of China (Grant No. 51278164) and the Hebei Provincial Natural Science Foundation (Grant No. E2014209221), this research examines five specimens with different connector configurations to determine the optimal combination for vertical joint shear resistance.

Experimental Program

The test matrix consists of five specimens, each representing a different connector arrangement at the vertical interface between the STC frame column and the reinforced concrete wall panel.

Specimen Configuration Summary

Connector Configuration Groups

Key Technical Findings

The experimental results demonstrate that the combined configuration of shear studs and shear keys provides superior ultimate shear capacity compared to either connector type used alone. Additionally, the study identifies that individual shear keys have an effective shear influence zone of 200–300 mm along the vertical joint. Within a certain range, increasing the steel reinforcement ratio at the interface enhances the shear capacity of the vertical joint.

Shear Capacity Comparison

Technical Interpretation

The superiority of the combined connector system can be attributed to the complementary mechanisms of load transfer. Shear studs primarily resist shear through bearing and bending of the stud shank, while shear keys (threaded rebars) transfer shear through direct bearing and tension resistance. The combined system creates a more distributed load transfer path, reducing stress concentrations and providing a more ductile failure mode. The identified influence zone of 200–300 mm for individual shear keys provides practical guidance for spacing optimization—keys spaced closer than 200 mm would experience overlapping influence zones with potential stress interference, while spacing beyond 300 mm would leave unconnected zones between keys.

Steel Tube Manufacturing Considerations

The use of Q345 square steel tubes (120 mm × 120 mm × 4 mm) in this study introduces specific manufacturing considerations:

• Wall thickness uniformity: At 4 mm thickness, the tube is relatively thin, and variations in wall thickness can significantly affect the local bearing capacity of the tube wall where shear studs are welded. Ultrasonic thickness testing should be performed to verify uniformity.
• Weld quality of shear studs: The attachment welding of shear studs to the steel tube wall is a critical weld. The weld geometry, fusion quality, and residual stress distribution directly affect the stud's contribution to shear resistance. Poorly executed stud welds can result in premature stud detachment under shear loading.
• Tube squareness and flatness: Deviations from perfect square geometry can create uneven contact between the tube and the surrounding concrete, affecting the bond and shear transfer at the interface.

Standards and Design Implications

The shear performance of vertical joints in STC shear wall structures is governed by GB 50011 (Code for Seismic Design of Buildings) and GB 51221 (Code for Design of Concrete Structures). The study's findings on connector configuration optimization provide empirical data to support the design provisions for composite joints.

Design Recommendations Based on Test Results

Key Questions and Reflections

The study provides valuable experimental data but raises several questions for further investigation. First, the specimens are relatively small-scale (120 mm tube, 120 mm wall), and the scaling effects on shear performance for larger structural elements remain uncertain. Second, the study focuses on monotonic shear loading; the cyclic performance of these joint configurations under seismic loading is equally important for practical application. Third, the interaction between the shear connectors and the overall structural behavior—particularly the effect on the ductility and energy dissipation capacity of the shear wall system—requires further study.

From a welding quality perspective, the reliability of shear stud attachment welds is paramount. In high-seismicity regions, these welds must withstand repeated cyclic loading without degradation. Welding procedure qualification, including preheat temperature control, interpass temperature management, and post-weld inspection, should follow the requirements of GB/T 985 (Welding symbols) and relevant AWS or ISO standards for stud welding.

Study Insights and Implications

This research provides practical guidance for the design of vertical joints in STC frame-shear wall systems. The demonstrated superiority of combined connector systems offers a clear design recommendation: when shear capacity is critical, employ both shear studs and shear keys rather than relying on a single connector type. The identified influence zone of 200–300 mm for shear keys enables rational spacing optimization, avoiding both over-design (excessive connectors) and under-design (inadequate coverage). For steel tube manufacturers and fabricators, the study emphasizes the importance of wall thickness control and weld quality for stud attachment, as these factors directly influence the shear performance of the composite joint. The findings support the development of more detailed design provisions for composite shear wall structures in future code revisions.