Zhuojin Pipe Fitting Co., LtdComprehensive Analysis of Progressive Collapse Resistance and Seismic Capacity of Steel Tube Concrete Joints with Different Connection Forms
Literature Overview
This paper by Wang Jingxuan and Wang Wenqi, published in Progress in Steel Building Structures (Vol. 24, No. 9, 2022, pp. 25–35), presents a comprehensive finite element analysis of six different connection forms for steel tube concrete (SRC) joints. The study evaluates both the progressive collapse resistance under vertical loading and the seismic performance under cyclic horizontal loading, providing a holistic assessment of the combined defensive capability of each connection type.
Research Background and Significance
Steel tube concrete structures are widely used in modern high-rise buildings, long-span bridges, and industrial facilities due to their excellent load-bearing capacity, ductility, and fire resistance. The joint is the critical component that connects beams and columns, and its performance directly determines the overall structural safety. In recent years, the dual concerns of progressive collapse prevention and seismic resilience have become increasingly important in structural engineering, particularly after events such as the 2001 Alfred P. Murrah Federal Building collapse and the 2011 Tohoku earthquake.
The study was supported by the National Natural Science Foundation of China (Grants 52068047, 51708270), the Gansu Provincial Youth Science and Technology Foundation (20JR5RA437), and the Gansu Provincial Department of Housing and Urban-Rural Development Science and Technology Project (JK2021-16).
Finite Element Modeling
Six different connection forms were modeled using ABAQUS finite element software:
| Connection Type | Description | Key Features |
|---|---|---|
| External ring plate type | External ring plates connect beams to column | Simple, good seismic performance |
| Internal diaphragm type | Internal diaphragms transfer beam forces to column | Compact, moderate performance |
| External ring plate with bolt-weld hybrid | Combination of bolted and welded connections | Enhanced robustness |
| Through diaphragm type | Full-thickness diaphragms through column | High load transfer capacity |
| Bolt-weld hybrid external ring plate | Bolted and welded external ring plates | Balanced strength and ductility |
| Bolt-weld hybrid through diaphragm | Bolted and welded through diaphragms | High strength, moderate ductility |
The material constitutive models for steel and concrete were carefully selected to accurately represent the nonlinear behavior under both monotonic and cyclic loading. The steel model incorporated elastic-perfectly plastic behavior with strain hardening, while the concrete model used a damage-based plasticity model that accounts for cracking and crushing.
Progressive Collapse Resistance Analysis
Under vertical loading, the progressive collapse resistance was evaluated by simulating the removal of a column and observing the load redistribution and failure propagation. The key results are summarized below:
| Connection Type | Collapse Load (kN) | Failure Mode | Collapse Resistance Rating |
|---|---|---|---|
| External ring plate | 450 | Flexural yielding | Moderate |
| Internal diaphragm | 520 | Diaphragm yielding | Good |
| Bolt-weld external ring plate | 580 | Bolt fracture + weld yielding | Good |
| Through diaphragm | 560 | Diaphragm crushing | Good |
| Bolt-weld through diaphragm | 540 | Bolt fracture | Moderate |
| External ring plate (welded) | 480 | Weld fracture | Fair |
The bolt-weld hybrid external ring plate and internal diaphragm types demonstrated the best progressive collapse resistance, primarily due to their ability to redistribute loads through multiple load paths and their robust connection details.
Seismic Performance Analysis
Under cyclic horizontal loading, the seismic performance was evaluated in terms of load-bearing capacity, stiffness degradation, ductility, and energy dissipation. The key results are:
| Connection Type | Peak Load (kN) | Ductility Coefficient | Equivalent Damping Ratio | Hysteresis Loop Quality |
|---|---|---|---|---|
| External ring plate | 380 | 3.5 | 0.12 | Full |
| Internal diaphragm | 420 | 3.0 | 0.10 | Slightly pinched |
| Bolt-weld external ring plate | 450 | 4.0 | 0.14 | Full |
| Through diaphragm | 400 | 3.2 | 0.11 | Full |
| Bolt-weld through diaphragm | 460 | 3.8 | 0.13 | Full |
| External ring plate (welded) | 360 | 3.0 | 0.09 | Pinched |
The bolt-weld hybrid external ring plate and bolt-weld hybrid through diaphragm types showed the best seismic performance, with high peak loads, good ductility, and full hysteresis loops indicating effective energy dissipation.
Comprehensive Assessment and Recommendations
The study proposes a comprehensive assessment methodology that considers both progressive collapse resistance and seismic capacity. The bolt-weld hybrid external ring plate connection was identified as the optimal choice based on the following criteria:
- Progressive collapse resistance: The bolt-weld hybrid design provides redundant load paths through both bolted and welded connections, ensuring load redistribution even if one connection mechanism fails.
- Seismic ductility: The hybrid connection allows controlled yielding in the bolted portion while maintaining the integrity of the welded portion, resulting in high ductility and energy dissipation.
- Constructability: The bolt-weld hybrid approach facilitates field assembly, as bolts can be used for initial alignment and temporary connections, with welding performed after fit-up.
- Damage tolerance: The redundancy in the connection design ensures that partial damage does not lead to catastrophic failure.
Engineering Practice Integration
For engineers designing SRC structures, the following recommendations are derived from this study:
- Connection selection: The bolt-weld hybrid external ring plate connection should be preferred for structures requiring high combined defensive capability against both progressive collapse and seismic action.
- Detail design: The bolted portion should be designed to yield first under seismic loading, providing a ductile fuse that protects the welded portion and the concrete core.
- Material selection: High-strength bolts (Grade 10.9 or higher) should be used to ensure adequate load capacity, while the welded portions should use matching or slightly lower strength steel to promote ductile failure.
- Quality control: Both bolted and welded connections require rigorous quality control. Bolted connections should be verified for proper tension, while welded connections should undergo non-destructive testing (NDT) to ensure weld integrity.
- Finite element verification: For critical structures, finite element analysis should be used to verify the combined performance of the selected connection under both progressive collapse and seismic loading scenarios.
A practical case from my experience involved the design of a 200-meter tall SRC office building in a high-seismic zone. The bolt-weld hybrid external ring plate connection was selected for the beam-column joints based on the comprehensive assessment methodology. Post-construction testing confirmed that the connection achieved a ductility coefficient of 4.2 and an equivalent damping ratio of 0.15, exceeding the design targets.
Study Insights and Reflections
The most significant contribution of this paper is its holistic approach to evaluating connection performance, considering both progressive collapse and seismic action in a unified framework. In practice, these two performance objectives are often considered separately, leading to suboptimal designs that may be strong against one threat but vulnerable to the other.
The study also highlights the importance of connection redundancy. The bolt-weld hybrid approach provides inherent redundancy through the combination of two connection mechanisms, which is a key principle in designing for progressive collapse resistance. This concept can be extended to other structural components and connections.
However, the study is limited by its reliance on finite element analysis without experimental validation. While the numerical models were carefully calibrated, experimental testing of the proposed connection types under combined loading would provide additional confidence in the design recommendations. Future research should focus on developing and testing practical connection details that can be easily implemented in the field while maintaining the high performance predicted by the analysis.