Zhuojin Pipe Fitting Co., LtdExperimental and Finite Element Analysis of New Flange Connections for Prefabricated Concrete-Filled Steel Tube Core Columns
Literature Overview
This paper presents both experimental testing and finite element modeling of a novel flange connection system designed for prefabricated concrete-filled steel tube (CFST) core columns. The research is particularly significant in the context of modern construction practices that emphasize prefabrication and rapid assembly, as the connection design directly determines the seismic capacity and constructability of the entire structural system.
Experimental Program and Key Findings
The experimental investigation included the fabrication of full-scale specimens incorporating the proposed flange connection, followed by cyclic loading tests to evaluate the connection behavior under simulated seismic conditions. The test matrix covered different flange thicknesses, bolt arrangements, and concrete fill conditions.
Test Specimen Parameters
| Specimen ID | Steel Tube OD (mm) | Wall Thickness (mm) | Flange Thickness (mm) | Concrete Grade | Steel Grade |
|---|---|---|---|---|---|
| F-01 | 400 | 8 | 20 | C40 | Q345 |
| F-02 | 400 | 8 | 25 | C50 | Q345 |
| F-03 | 400 | 10 | 25 | C50 | Q345 |
| F-04 | 500 | 10 | 30 | C60 | Q420 |
The test results demonstrated that the proposed flange connection achieves ductile failure modes with adequate energy dissipation capacity. The failure typically initiates at the weld between the flange and the steel tube, progressing through plastic deformation of the flange before ultimate rupture.
Finite Element Analysis
The finite element model employed shell elements for the steel tube and flange, solid elements for the concrete core, and bolt elements with contact definitions for the bolted connections. The material models incorporated:
- Von Mises yield criterion with strain hardening for steel components
- M4 concrete damage plasticity model for the concrete core
- Frictional contact with penalty method for bolt-hole interfaces
- Tie constraints for weld connections between flange and tube
The simulation results correlated well with experimental observations, with maximum deviations in peak load not exceeding 8%. The FE analysis revealed stress concentrations at the bolt hole edges and at the weld toe between the flange and tube wall, which were not as clearly visible in the physical tests.
Welding and Fabrication Considerations
From a welding engineering perspective, the flange-to-tube connection represents a full-penetration T-joint that requires careful attention to:
- Preheating requirements for thick flange sections (typically above 20 mm) to prevent cold cracking
- Welding sequence to minimize distortion of the steel tube geometry
- Inspection requirements including phased array ultrasonic testing (PAUT) for full-penetration verification
- Post-weld stress relief if the combined thickness exceeds 30 mm
The prefabrication approach requires that all welding be completed in a controlled shop environment, which is advantageous for quality control but demands precise dimensional control during assembly.
Study Insights and Engineering Implications
The research validates that flange connections can provide adequate seismic performance for CFST core columns when properly detailed. However, I emphasize that the long-term durability of such connections in corrosive environments requires attention to drainage provisions, protective coatings, and bolt material selection to prevent galvanic corrosion between dissimilar materials. The combination of prefabrication with seismic design demands a holistic approach that considers not only structural capacity but also constructability, inspection accessibility, and maintenance requirements throughout the service life of the structure.