Zhuojin Pipe Fitting Co., LtdMechanical Performance of Bolted Connections Between Prefabricated Steel Tube Concrete Composite Columns and PEC Beams
Literature Overview
The paper by Wang Jingfeng, Wang Hanlan, Guo Lei, and Guo Xiang (2022), published in Journal of Progress in Steel Structure Construction, investigates the mechanical behavior of bolted connections between prefabricated steel tube concrete (STC) composite columns and prefabricated partially encased concrete (PEC) beams. The study employs finite element analysis using ABAQUS, validated against low-cycle reversed loading test data. This research addresses a critical practical need in modern prefabricated construction, where the connection detail determines the seismic performance of the entire structural system.
Finite Element Model Development
The numerical model accounts for several complex phenomena inherent to this connection type:
| Modeling Aspect | Approach | Importance |
|---|---|---|
| Material constitutive relationships | Bilinear/isotropic hardening for steel, Mander model for confined concrete | Captures nonlinear behavior |
| Contact conditions | Penalty method with friction coefficient | Simulates bolt preload and slip |
| Bolt modeling | Preload application through boundary conditions | Represents connection stiffness |
| Concrete-steel interface | Tied constraints with damage criteria | Models composite action |
| Geometric nonlinearity | Large displacement formulation | Accounts for P-Δ effects |
The model was validated against experimental results showing good agreement in both failure mode and skeleton curve characteristics, confirming the reliability of the numerical approach for parametric study.
Parametric Study Results
The parametric investigation examined the influence of geometric, material, and loading parameters on connection performance. The key findings are summarized below:
| Parameter | Effect on Flexural Bearing Capacity | Effect on Initial Stiffness |
|---|---|---|
| Column steel strength | Significant positive effect | Moderate effect |
| Column concrete strength | Significant positive effect | Significant effect |
| Axial compression ratio | Significant effect (complex) | Significant effect |
| Bolt diameter | Significant positive effect | Moderate effect |
| Column section steel ratio | Significant positive effect | Significant effect |
The bolt diameter emerges as a particularly important design parameter for flexural capacity. Increasing bolt diameter enhances the connection's ability to resist bending moments through the increased cross-sectional area available for shear transfer and the increased lever arm for moment resistance. However, larger bolts also introduce greater stress concentrations and potential fatigue concerns under cyclic loading.
Failure Mode Analysis
The study identifies the failure mode as governed by the interaction between bolt shear capacity, steel tube local buckling, and concrete crushing at the connection zone. The progressive failure sequence typically involves initial bolt slip, followed by plastic deformation of the bolt shank, local yielding of the steel tube wall near bolt holes, and finally concrete crushing in the confined zone. Understanding this failure sequence is essential for designing connections that achieve ductile failure rather than brittle fracture.
Welding and Fabrication Considerations
From a steel pipe fabrication standpoint, this research highlights several critical manufacturing requirements. The steel tube concrete composite columns require precise fabrication of connection zones where bolts penetrate the steel tube wall. The bolt holes in the steel tube must be drilled with tight tolerances to ensure proper bolt fit and avoid excessive clearance that would reduce connection stiffness. The welding joints connecting steel tube segments near the connection zone must be located at sufficient distance from bolt holes to avoid interaction between weld defects and bolt stress concentrations.
The prefabrication approach demands exceptional dimensional accuracy. The steel tube outer diameter, wall thickness, and the positioning of bolt holes must all be within tight tolerances to ensure proper assembly in the field. Any deviation can result in bolt installation difficulties, reduced connection performance, or even assembly failure.
Key Questions and Reflections
The study raises important questions about the long-term durability of bolted connections in composite structures. The presence of concrete within the steel tube creates a corrosive environment for the embedded steel components, including the bolts. The interaction between concrete carbonation, chloride ingress, and the bolt material requires careful attention in the design phase. Additionally, the thermal expansion mismatch between steel tubes, bolts, and concrete could lead to progressive loosening of bolt connections under thermal cycling, particularly in structures exposed to significant temperature variations.
Design Recommendations and Practice Integration
This research provides a scientific foundation for the design of bolted connections in prefabricated steel tube concrete composite structures. Engineers should prioritize the optimization of bolt diameter and column section steel ratio for flexural capacity, while paying close attention to concrete strength and steel ratio for stiffness requirements. The finite element methodology validated in this study can be directly applied to the design verification of similar connections, provided that appropriate material models and contact definitions are employed. For manufacturing quality control, the bolt hole positioning accuracy and steel tube dimensional tolerances should be specified with reference to the parametric sensitivity identified in this research.