Stability Analysis of Large-Span Steel Tube Concrete Truss Arch Bridges

Literature Overview

Published in 2010 in the Journal of Railways and Road Engineering by Wang Yan and Chen Huai from Zhengzhou University, this paper addresses the spatial stability analysis of the Xiao Sanxia Bridge main span, which is a through-type steel tube concrete (STC) truss arch bridge. The study employed the Midas/Civil finite element program to establish a three-dimensional FE model and evaluate the bridge's spatial stability characteristics. Funded by the Henan Provincial Outstanding Talent Program, the research provides practical recommendations for enhancing lateral stiffness of arch ribs and the deck system.

Core Technical Content

The analysis focused on two critical stability aspects: the lateral stability of arch ribs and the out-of-plane stiffness of the deck system. The computational results revealed that the arch rib lateral stiffness was insufficient, posing a risk of lateral-torsional buckling under asymmetric loading conditions. The deck system also exhibited marginally adequate out-of-plane stiffness, requiring reinforcement of connections between precast small T-beams and transverse beams, as well as enlargement of edge longitudinal beam cross-sections.

Technical Analysis of Stability Mechanisms

The spatial stability of large-span STC truss arch bridges is governed by the interaction between arch rib lateral restraint and deck system out-of-plane resistance. In a truss arch configuration, the arch ribs act as primary load-bearing elements, and their lateral stability depends on the effectiveness of transverse bracing members. When lateral stiffness is inadequate, even moderate eccentric or asymmetric loading can trigger lateral-torsional buckling, which is a sudden and catastrophic failure mode.

The steel tube concrete composite action provides significant compressive strength through the confinement effect of the steel tube on the concrete core. However, this composite action primarily enhances in-plane performance. The lateral stability is largely determined by the geometric properties of the steel tube section itself and the bracing system connecting the two arch ribs. For large-span structures, the slenderness ratio of the arch ribs increases, making lateral buckling increasingly critical relative to in-plane compression failure.

The deck system serves as both a load distribution element and a lateral restraint mechanism for the arch ribs. The precast small T-beams connected to transverse beams form the primary deck grid, and their out-of-plane stiffness directly influences the overall torsional resistance of the bridge. When the deck grid is not sufficiently rigid, the bridge becomes susceptible to torsional oscillation under wind loading and uneven traffic loads.

Engineering Practice Integration

For engineers designing or assessing large-span STC truss arch bridges, several key design principles emerge:

1. Lateral bracing optimization — Transverse bracing members should be designed not merely as structural components but as active lateral restraint elements. The bracing configuration should be optimized to provide uniform lateral support along the arch rib length, particularly near the arch crown where lateral displacement tendency is greatest.
2. Deck system rigidity — The deck grid system should be designed as an integral torsional resistance component. Rigid connections between edge longitudinal beams and transverse beams, achieved through welded or bolted moment connections rather than simple shear connections, are critical for forming a continuous beam-grid system.
3. Parametric sensitivity — Engineers should conduct parametric studies varying bracing stiffness, deck connection rigidity, and arch rib section properties to identify the most critical parameters governing overall stability.
4. Construction-phase stability — The stability requirements during construction, when the structure is incomplete and may have reduced lateral restraint, should be verified separately from the as-built condition.

Study Insights and Implications

This paper demonstrates the importance of spatial stability assessment in STC truss arch bridge design, which is often overlooked when attention focuses primarily on in-plane compression capacity. The practical recommendations regarding section optimization and connection enhancement are directly implementable in design practice. The use of commercial FE software (Midas/Civil) with appropriate boundary conditions and material models provides a reliable computational framework for stability evaluation. Engineers should recognize that for large-span arch bridges, the lateral stability design is not a secondary consideration but a primary design driver that can govern overall structural dimensions and connection detailing. The systematic approach of identifying weak components through FE analysis and then proposing targeted strengthening measures represents sound engineering practice that balances structural safety with economic efficiency.