Zhuojin Pipe Fitting Co., LtdProgressive Collapse Mechanism of Large-Span Steel Tube Arch Bridges Under Ship Collision
Literature Overview
This paper by Ye Huawei, Qu Haobo, Wang Liwu, and Shi Zhanchong from Southwest Jiaotong University investigates the progressive collapse process of large-span steel tube arch bridges under ship collision loading. The study uses the catastrophic failure of Sweden's Almn Bridge as its engineering backdrop, applying AASHTO-based collision force calculations combined with three-dimensional nonlinear finite element analysis at both global and local levels. The work was published in World Bridges in 2016 (Volume 44, Issue 5, pages 26-32) and was supported by the National Natural Science Foundation of China (Grants 51208430 and 51408501). The research is significant because progressive collapse in arch bridges following localized damage remains one of the most challenging failure modes in long-span bridge engineering, and ship collision represents a credible threat for bridges spanning navigable waterways.
Core Technical Findings
The authors identify three critical vulnerability factors that contributed to the Almn Bridge collapse:
- Low span-to-width ratio: The overall structural geometry provided insufficient lateral stability, meaning the bridge had limited capacity to redistribute loads laterally after local damage.
- Lack of structural redundancy: The single-arch configuration offered no alternative load paths once the primary arch member failed, converting a localized failure into a global collapse.
- Inverse relationship between diameter-to-thickness ratio and critical buckling stress: Thinner-walled steel tubes exhibit higher critical buckling stress, but the localized deformation from impact drastically reduces the effective cross-sectional properties.
The progressive collapse sequence identified in the study follows a clear chain of events: ship impact causes cross-sectional deformation of the steel tube → deformation reduces the critical buckling stress of the tube section → local yielding at the impact zone increases axial compressive stress along the arch axis → when the axial stress reaches the reduced critical buckling stress, local buckling initiates → local instability propagates and triggers overall structural collapse.
Key Structural Parameters and Their Influence
| Parameter | Effect on Collapse Resistance | Engineering Implication |
|---|---|---|
| Diameter-to-thickness ratio (D/t) | Higher D/t reduces critical buckling stress | Thicker walls improve impact tolerance but increase weight |
| Span-to-width ratio | Lower ratio reduces lateral stability | Wider deck systems or lateral bracing needed for narrow decks |
| Structural redundancy | Absence of redundancy enables progressive collapse | Secondary load paths or energy-absorbing devices essential |
| Impact force magnitude | Higher force causes greater cross-sectional deformation | AASHTO force values must be used conservatively |
| Impact contact area | Larger area distributes load but may reduce peak stress | Impact geometry affects local buckling initiation |
Finite Element Modeling Approach
The study employs a dual-scale modeling strategy that is particularly instructive for engineers dealing with impact-induced collapse problems. The global model captures the overall structural response, including the arch's axial force distribution, lateral displacement, and the progressive nature of collapse. The local model focuses on the impact zone, capturing cross-sectional deformation, material yielding, and the onset of local buckling. This approach is consistent with the hierarchical modeling methodology recommended in progressive collapse research literature.
The AASHTO-based collision force calculation provides a standardized input, but the authors note that the impact force value and contact area both significantly influence the critical buckling stress. This observation has direct implications for the design of ship collision barriers and impact-resistant bridge components, as the force distribution rather than just the peak force governs the structural response.
Engineering Practice Integration
From a steel tube manufacturing and structural engineering perspective, this study raises several important considerations:
- Wall thickness selection: For bridges vulnerable to ship impact, the D/t ratio must be carefully balanced between weight efficiency and impact resistance. The inverse relationship between D/t and critical buckling stress suggests that maintaining a lower D/t ratio (thicker walls) is beneficial, but this must be weighed against overall structural weight and cost.
- Material grade selection: Higher-strength steel grades may provide improved local resistance, but the study implies that geometric properties (D/t ratio) and structural configuration (redundancy, lateral stability) are equally critical.
- Impact protection systems: The findings support the installation of ship collision barriers that absorb or redistribute impact energy before it reaches the primary arch structure.
Key Questions and Reflections
A critical question that emerges from this study is whether the progressive collapse sequence can be arrested at any intermediate stage. The study describes a deterministic chain of events, but in practice, energy-absorbing devices, sacrificial elements, or secondary structural systems could interrupt the progression. The lack of structural redundancy identified as a key vulnerability factor suggests that future bridge designs should incorporate redundant load paths, even if this means additional material usage.
Another important consideration is the validation of AASHTO collision force values for the specific geometry and material conditions of steel tube arch bridges. The study notes that both impact force magnitude and contact area significantly affect the critical buckling stress, implying that the force distribution model used in design may need refinement for tubular steel members.
Study Insights and Implications
This research provides a clear mechanistic understanding of how a localized impact event can trigger global structural failure in large-span steel tube arch bridges. The progressive collapse chain—cross-sectional deformation leading to reduced buckling resistance, followed by local yielding, local buckling, and finally global collapse—offers a valuable framework for assessing impact vulnerability in similar structures. The emphasis on structural redundancy and lateral stability as critical design parameters has direct implications for the specification of steel tubes used in bridge arch ribs, where wall thickness and geometric properties must be optimized not only for gravity loading but also for credible impact scenarios.