Experimental Study on Rectangular Steel Tube Concrete Column-H Steel Beam Joints with Hollowing

Literature Overview

This paper by Liu Dianzhong, Li Hongxian, and Chen Yang, published in the Journal of Jilin Jianzhu University (2020, Vol. 37, No. 1, pp. 1-6), presents experimental research on the seismic performance of rectangular steel tube concrete (STC) column-H steel beam joints with internal hollowing (air voids). The study is supported by the National Natural Science Foundation of China (Grant No. 51378238) and addresses a practical quality concern in STC construction: the occurrence of voids or hollowing within the concrete core due to inadequate compaction.

Core Technical Content

The research focuses on the internal diaphragm joint type, which is one of the most widely used connection details for STC columns in multi-story and high-rise buildings. Three specimens representing edge-span joints (JD-1, JD-2, and JD-3) from a multi-story frame structure were tested under low-cycle reversed loading to evaluate their bearing capacity and seismic performance under varying degrees of hollowing.

Specimen Configuration

The three test specimens represent different hollowing ratios, allowing the researchers to establish a quantitative relationship between the extent of hollowing and the structural response:

Low-Cycle Reversed Loading Test

The low-cycle reversed loading test simulates the cyclic deformation demands imposed on structural joints during seismic events. The test protocol typically involves displacement-controlled cycles at increasing amplitudes, allowing the evaluation of:

• Peak load capacity
• Energy dissipation capacity
• Ductility ratio
• Stiffness degradation
• Damage evolution

Influence of Hollowing Ratio

The study investigates how the hollowing ratio affects:

1. Bearing capacity: The load-carrying capacity of the joint under monotonic and cyclic loading.
2. Seismic performance: The energy dissipation, ductility, and deformation capacity of the joint.

The internal diaphragm in the joint serves as a critical load-transfer element, distributing beam forces into the STC column. When hollowing occurs, the concrete-steel composite action is reduced, potentially leading to premature failure of the joint.

Engineering Practice Integration

Hollowing Formation Mechanisms

From my experience in steel pipe fabrication and construction quality control, hollowing in STC structures can arise from several sources:

1. Concrete placement issues:

• Insufficient concrete workability for placement in confined spaces
• Inadequate vibration during pouring
• Segregation of concrete due to improper mix design
• Placement from too great a height causing compaction loss

1. Steel tube quality factors:

• Internal surface roughness or mill scale preventing good bond
• Insufficient internal cleanliness before concrete placement
• Geometric deviations (ovality, out-of-straightness) creating local gaps

1. Construction sequence errors:

• Delay between steel tube erection and concrete placement
• Inadequate expansion joints or construction joints in the concrete fill

Quality Control Measures

Welding Considerations for Joint Details

The internal diaphragm joint involves critical welds connecting the beam flanges and web to the diaphragm plate and column. These welds must be designed and fabricated to withstand the cyclic loading demands:

The welding procedure specification (WPS) for these connections should include:

• Preheat temperature requirements based on carbon equivalent (CEV)
• Interpass temperature control to limit HAZ hardness
• Post-weld heat treatment (PWHT) for high-strength connections
• Non-destructive testing (NDT) coverage per seismic detailing requirements

Standards and Design Considerations

Study Insights and Reflections

This research addresses a practical concern that is often overlooked in the design and construction of STC structures. While the theoretical design of STC joints assumes full concrete confinement, actual construction practices may result in varying degrees of hollowing. The experimental data from this study provides essential information for:

1. Design verification: Engineers can use the test data to verify whether joints with limited hollowing still meet seismic performance objectives.
2. Quality acceptance: The results help establish acceptable limits for hollowing in STC construction, informing inspection and acceptance criteria.
3. Repair strategies: Understanding the impact of hollowing enables the development of effective repair methods for existing structures.

The study also highlights the importance of the internal diaphragm as a force-transfer mechanism. In joints with significant hollowing, the diaphragm may become the critical element, and its design should be verified for the reduced composite action.

From a steel pipe manufacturing perspective, the quality of the steel tubes used in STC columns directly affects the potential for hollowing. Tubes with precise geometry, clean internal surfaces, and adequate straightness facilitate better concrete placement and compaction. Manufacturers should consider offering STC-specific pipe grades with controlled internal surface quality.

In conclusion, this experimental study provides valuable data on the seismic performance of STC joints with hollowing, contributing to the development of more robust design guidelines and quality control procedures for concrete-filled steel tube structures in seismic regions.