Experimental Study of Rectangular Steel Tube Concrete Column-H Steel Beam Through-Type Diaphragm Joint

Literature Overview

Published in 2011 in the Journal of Hebei University of Technology by Yang Xinlei, Wang Hailiang, Dong Peng, and Ren Quanchang from Tianjin Chengjian University, this paper presents experimental results from two through-type diaphragm joints connecting rectangular steel tube concrete columns with H-steel beams. The tests were conducted under low-cycle reversed loading to evaluate the seismic performance of the joints. The research was supported by the Ministry of Housing and Urban-Rural Development Research and Development Project (2011-K2-18) and the Tianjin Higher Education Science and Technology Development Fund (20100904).

Core Technical Content and Test Configuration

Two joints with different configurations were tested under low-cycle reversed loading. The primary focus was on hysteresis curves, failure modes, and displacement ductility.

Key Findings and Hysteresis Behavior

The experimental results reveal the following important observations:

1. Both joints exhibited the same failure mode: plastic hinges formed at the beam ends. This is the desired failure mode for seismic-resistant structures, as it localizes damage in replaceable beam components rather than in the more critical column elements.
2. The design objectives of "strong column, weak beam" and "strong joint, weak component" were successfully achieved. This indicates that the through-type diaphragm joint design provides adequate strength and stiffness to transfer loads from the beam to the column without premature joint failure.
3. The hysteresis curves of both joints were spindle-shaped (梭形), indicating good energy dissipation performance. The spindle shape suggests that the joints can undergo large deformations with stable load-carrying capacity.
4. The joint configuration has a significant effect on displacement ductility. Different diaphragm configurations result in different ductility levels, which is a critical consideration for seismic design.

Interpretation from a Steel Pipe and Welding Perspective

The through-type diaphragm joint involves a steel plate (diaphragm) that passes through the rectangular steel tube concrete column and connects to the H-steel beam. This joint type requires careful welding of the diaphragm to the column tube walls and to the beam flanges. The welding quality is critical because the joint must transfer large shear and moment forces during seismic loading.

The rectangular steel tube concrete column itself presents specific challenges. The corners of the rectangular tube are more susceptible to local buckling under cyclic loading than the flat faces. The concrete infill provides confinement to the tube walls, but the corners may still experience local buckling if the steel tube is too thin or if the concrete filling is incomplete.

Engineering Practice Implications

For engineers designing through-type diaphragm joints for rectangular steel tube concrete columns, the following considerations are important:

1. The diaphragm thickness and material grade should be selected to ensure that the joint strength exceeds the beam plastic moment capacity. This ensures that plastic hinges form in the beam rather than at the joint.
2. The welding sequence should be carefully planned to minimize residual stresses and distortions. Sequential welding of the diaphragm to the column walls, followed by welding to the beam, is recommended.
3. The concrete filling of the column must be complete and uniform. Any voids near the joint region will reduce the confinement effect and may lead to premature local buckling of the steel tube.
4. The displacement ductility of the joint should be verified through testing or validated analytical methods. The joint configuration must be designed to achieve the required ductility for the seismic design category of the structure.

Key Questions and Reflections

One important question is how the through-type diaphragm joint performs under out-of-plane loading. The tests described in this paper focus on in-plane loading, which is the primary seismic loading direction. However, in multi-story frames, the joint may also be subjected to out-of-plane forces from perpendicular beams. The through-type diaphragm design should be evaluated for out-of-plane stability and strength.

Another consideration is the effect of concrete degradation on joint performance. Over time, the concrete in the column may degrade due to carbonation, chloride ingress, or freeze-thaw cycles. This degradation reduces the confinement effect on the steel tube and may affect the joint's ability to transfer loads. Engineers should consider the long-term durability of the joint in addition to its initial seismic performance.

Study Insights and Implications

This paper provides valuable experimental data on the seismic performance of through-type diaphragm joints for rectangular steel tube concrete columns. The successful achievement of the "strong column, weak beam" and "strong joint, weak component" design objectives demonstrates that this joint type is suitable for seismic-resistant structures. The spindle-shaped hysteresis curves indicate good energy dissipation, which is essential for reducing seismic forces transmitted to the structure.

From a steel pipe manufacturing and welding perspective, the study reinforces the importance of high-quality fabrication and welding of the joint components. The diaphragm plate must be cut and machined to precise dimensions to ensure proper fit-up and weld quality. The welding consumables must be compatible with the steel grades used in the column tube, diaphragm, and beam. The welding procedure must be qualified according to relevant standards such as GB/T 19866 or AWS D1.1, and the welders must be certified for the specific welding processes and positions used.

The finding that joint configuration significantly affects displacement ductility provides a clear design lever for engineers. By varying the diaphragm thickness, width, and connection details, the ductility of the joint can be tailored to meet specific seismic design requirements. This flexibility makes the through-type diaphragm joint an attractive option for a wide range of seismic design applications, from low-seismicity regions to high-seismicity zones.