Abstract: The accurate grasp of structural stability of concrete encasement stage of arch bridge with stiff skeleton has become the key to ensure its construction safety. In order to study the stability of long-span CFTS arch bridge with stiff skeleton in the concrete encasement process, a 600 m main span arch bridge with stiff skeleton was taken as an example, and the nonlinear buckling behavior of the stiff skeleton arch during the concrete encasement process was analyzed. Besides, the influence of geometric nonlinearity and material nonlinearity on the stability of main arch was also explored. The components that may suffer from local instability problem were discovered, and the causes of component instability were determined on the basis of the stability mechanism; moreover, the stability strengthening measures were put forward. The research results show that with the pouring of outer concrete, the double nonlinear performance of main arch becomes more and more obvious. Before the overall instability of the structure, some members may have been locally unstable. Both material nonlinearity and geometric nonlinearity must be taken into account in stability analysis of stiff skeleton arch bridge. Otherwise, the ultimate bearing capacity will be overestimated. However, it may not be easy to find the weak structure of potential local instability of the structure only by double nonlinear analysis. In order to more clearly recognize the instability mechanism of main arch structure during the loading process, it is necessary to analyze the evolution process of the structural stress behavior under the condition of material nonlinearity. In the concrete encasement process of main arch, the cross brace web near the arch foot may be locally unstable. Strengthening the lateral support of the transverse bracing web members can effectively enhance the stability of the transverse web members.

Key words: bridge engineering; arch bridge with stiff skeleton; stability; construction stages; material nonlinear; local instabi

摘要： 劲性骨架拱桥混凝土外包阶段结构稳定性的准确把握是保障桥梁施工安全的关键。为了研究大跨径钢管混凝土劲性骨架拱桥混凝土外包过程稳定性，以某主跨为600 m的劲性骨架拱桥为研究对象，分析了混凝土外包施工过程中的劲性骨架拱的非线性屈曲行为，探究了几何非线性、材料非线性对主拱稳定性的影响；确定了可能发生局部失稳的构件，从稳定性机理出发确定构件失稳原因并提出稳定性加强措施。研究结果表明：随着外包混凝土的浇筑，主拱双重非线性表现地越来越明显，且结构的整体失稳之前部分构件可能已经出现了局部失稳；劲性骨架拱桥稳定性分析必须同时计入材料、几何非线性，否则会高估其稳定极限承载力，但只进行双重非线性分析可能不容易找到结构潜在的局部失稳的薄弱构造，为了更为清晰的认识主拱结构加载过程中的失稳机理，有必要仅分析材料非线性条件下结构受力行为的演化过程；主拱混凝土外包过程中靠近拱脚位置的横撑腹杆可能发生局部失稳的现象，增强横撑腹杆侧向支承能有效加强横撑腹杆稳定性。

关键词: 桥梁工程；劲性骨架拱；稳定；施工阶段；材料非线性；局部失稳