Bending Bearing Capacity Calculation Method for Steel Tube Concrete Column-Beam Through RECC Ring Beam Joints

Literature Overview and Research Context

This study addresses the calculation methodology for the bending bearing capacity of joints in steel tube concrete (SRC) columns connected to reinforced recycled concrete (RECC) ring beams. The through-type joint configuration, where the beam passes through or is integrally connected with the column, is a critical structural component in moment-resisting frames designed for seismic resistance. The use of recycled concrete in the ring beam introduces material variability that must be accounted for in the bearing capacity calculation. The research aims to develop a rational analytical method that captures the complex stress distributions and failure mechanisms at this joint region.

Core Technical Content and Key Findings

The joint region in SRC columns with RECC ring beams is characterized by complex interactions among multiple materials and structural elements. The steel tube provides confinement to the concrete core, while the ring beam transfers bending moments and shear forces between the column and the connected beams. The through-type configuration ensures continuity of the beam reinforcement through the column, enhancing the moment transfer capacity.

The bending bearing capacity calculation method likely incorporates the following components:

Interpretation of Technical Points

The analytical method for joint bending capacity must address several key mechanical phenomena. First, the stress concentration at the column-beam interface due to the abrupt change in cross-sectional geometry creates complex three-dimensional stress states that cannot be accurately captured by one-dimensional beam theory. Second, the confinement effect of the steel tube on the concrete core is modified by the presence of the ring beam, which may alter the lateral expansion pattern of the concrete. Third, the recycled concrete in the ring beam exhibits lower elastic modulus and potentially different Poisson's ratio compared to natural aggregate concrete, affecting the strain compatibility between the beam and column.

The calculation method should follow a systematic approach:

1. Determine the equilibrium conditions at the joint, including moment balance and shear flow continuity.
2. Establish the constitutive relationships for each material component (steel, natural concrete, recycled concrete).
3. Apply compatibility conditions at the interfaces between different materials.
4. Solve the resulting equations to obtain the ultimate bending moment capacity.
5. Verify the results against experimental data or finite element analysis.

The FMEA approach can be applied to identify potential failure modes at the joint, including steel tube local buckling, concrete crushing in the column core, reinforcement yielding in the ring beam, and interface debonding. Each failure mode should be evaluated for its likelihood and consequence to determine the governing failure mechanism.

Integration with Engineering Practice

In practical design, the joint region requires careful detailing to ensure adequate ductility and moment transfer capacity. The reinforcement layout in the RECC ring beam must provide sufficient anchorage length to develop the required yield strength. The connection between the steel tube and the ring beam—whether through welded plates, bolted connections, or mechanical anchors—must be designed to prevent premature failure.

Quality control measures for this joint type include:

• Pre-welding inspection of steel tube surfaces and connection plates.
• Verification of reinforcement placement and concrete cover thickness.
• Post-welding non-destructive testing (magnetic particle or ultrasonic) of critical welds.
• Concrete strength verification through cube testing and in-situ methods.

The construction sequence is also critical, as the relative timing of steel tube installation, concrete placement, and ring beam construction affects the final structural behavior. Proper coordination between structural steel fabrication and concrete pouring schedules is essential to avoid delays and quality issues.

Key Questions and Reflections

A significant challenge in the analysis of these joints is the accurate representation of the recycled concrete properties in the calculation model. The variability of recycled aggregate properties—depending on the source demolition waste, crushing method, and cleaning process—introduces uncertainty into the predicted bearing capacity. Engineers must establish appropriate safety factors or partial factors to account for this variability in design.

Another important consideration is the seismic performance of the joint under cyclic loading. The calculation method for static bending capacity must be complemented by considerations of energy dissipation, stiffness degradation, and progressive damage accumulation under repeated seismic events. The ductility of the joint is particularly important for ensuring that the structure can survive near-collapse level earthquakes without sudden failure.

Study Insights and Implications

This research contributes to the advancement of recycled concrete applications in structural engineering by providing a systematic calculation method for a critical joint configuration. The development of reliable analytical tools is essential for the widespread adoption of recycled materials in moment-resisting frames, as engineers require confidence in the predicted performance to incorporate these materials into design codes and standards. The integration of recycled concrete with steel tube confinement represents a promising pathway for sustainable structural systems that combine environmental benefits with adequate structural performance.