Zhuojin Pipe Fitting Co., LtdProgressive Collapse Resistance Analysis of Circular Steel Tube Concrete Column-H Steel Beam Annular Plate Joints with Different Configurations
Literature Overview
This paper by Shi Yanli, Li Tianhao, and Wang Wenda from Lanzhou University of Technology, published in Journal of Natural Disasters (2017, Vol. 26, Issue 3, pp. 28-38), investigates the progressive collapse resistance of circular steel tube concrete (CFTC) column-H steel beam annular plate joints under middle column failure scenarios. The study is supported by the National Natural Science Foundation of China (Grant No. 51268038) and the Lanzhou University of Technology "Hongliu Outstanding Talent Training Program" (JQ201305). Finite element analysis using ABAQUS is employed to simulate the entire progressive collapse process, with particular attention to the influence of joint configuration variations on collapse resistance.
Progressive Collapse Background and Methodology
Progressive collapse, also known as disproportionate collapse, refers to the progressive failure of structural elements that extends far beyond the initially damaged area. This type of failure can be triggered by localized damage such as blast loading, impact, or fire, and it poses a significant threat to structural safety and human lives. The design against progressive collapse is now required by many building codes, including ASCE 37-16 and FEMA P-58 in the United States, and GB/T 51238-2016 in China.
The annular plate joint is a commonly used connection type for CFTC column-steel beam connections. The annular plate is welded to the outside of the circular steel tube column, and the steel beam is connected to the annular plate through bolted or welded connections. The configuration of the joint, including the dimensions of the annular plate, the details of the steel beam connection, and the treatment of the joint core region, significantly influences the joint's ability to redistribute loads after column failure.
The finite element model in this study captures the entire progressive collapse process, including the initial column failure, the load redistribution phase, and the formation of catenary action in the beams. The constitutive models for the steel tube, concrete core, and steel beam are calibrated based on material test data, and the contact interactions between the various components are modeled using appropriate contact algorithms.
Key Findings on Joint Configuration Effects
The study identifies three critical configuration parameters that influence progressive collapse resistance:
| Configuration Parameter | Influence on Progressive Collapse | Design Recommendation |
|---|---|---|
| Annular plate extension dimension | Affects plastic hinge formation location; limited improvement in collapse resistance | Select based on structural, fabrication, and economic considerations |
| Steel beam configuration | Influences catenary action development | Flared end preferred; web opening acceptable when clearance is limited; flange weakening not recommended |
| Joint core region configuration | Affects weld brittle fracture risk | Gusset plate reinforcement recommended |
The finding that the annular plate extension dimension has limited influence on progressive collapse resistance is practically significant. It suggests that designers do not need to excessively enlarge the annular plate to achieve adequate collapse resistance, and can instead optimize the plate dimensions based on fabrication convenience and cost considerations.
The steel beam configuration findings are particularly important for practical design. The flared end configuration promotes the development of catenary action by providing adequate rotation capacity at the beam end. The flange weakening configuration, while commonly used to reduce material usage, compromises the catenary action development and should be avoided in progressive collapse design. The web opening configuration offers a compromise solution when architectural clearance constraints limit the beam depth.
Welding and Fabrication Considerations
The joint core region configuration directly relates to welding practice. The study recommends gusset plate reinforcement to mitigate the risk of brittle fracture at the beam-column welds. This is consistent with welding engineering principles, as the joint core region experiences complex multiaxial stress states that can promote crack initiation and propagation.
From a welding quality control perspective, the following measures should be implemented:
- Preheat the base material to prevent hydrogen-induced cracking, particularly when welding high-strength steel or thick sections.
- Use low-hydrogen welding consumables and maintain strict control of welding environment humidity.
- Apply interpass temperature control to limit thermal cycling and residual stress accumulation.
- Perform post-weld heat treatment if required by the applicable code to relieve residual stresses.
- Conduct non-destructive testing (NDT) of all welds, including ultrasonic testing for volumetric defects and magnetic particle testing for surface-breaking defects.
For existing structures requiring progressive collapse reinforcement, the study recommends welding horizontal stiffeners or open brackets to the column. This retrofit approach can significantly improve the collapse resistance of existing structures without requiring major structural modifications.
Study Insights
This research provides valuable guidance for the progressive collapse design of CFTC column-steel beam joints. The finite element analysis methodology can be extended to other joint types and structural configurations, and the configuration recommendations can be directly applied to practical design. The emphasis on catenary action development highlights the importance of connection flexibility in progressive collapse resistance, a concept that is sometimes overlooked in conventional connection design focused on gravity and lateral load resistance.