| Concrete-filled steel tubular (CFST) arch bridge are widely used in the construction of city and highway arch bridge in the world, because of their advantages such as long-span, high load-carrying ability, low engineering cost, little maintenance cost, convenience construction and the unique shape. To long-span CFST arch bridge, especially the narrow bridge, the lateral stability of the structure is a key question, and it is an important control factor in the design. Based on the summary of current researches of lateral stability of arc rib curves, this paper gives the study of the lateral stability of deck, half-through and through X-type double ribs fixed-end arch bridge. The main research work covers the following aspects:1. With the energy principle, taken the ribs center distance of deck as the width of bridge, considered the deck position of the half-through arch, a uniform lateral stability calculation formula including deck, half-through and through X-type double ribs is established, subjected to the orientedly conservative loadings and non-orientedly conservative loadings. Meanwhile the structure parameters influencing on lateral stability, such as the torsional stiffness and vertical flexural rigidity of arch rib, the flexural rigidity and numbers of crossbeams, the rise-to-span of arch, the inclination of rib, the position of deck and the lateral flexural rigidity of the deck, are discussed. And the corresponding numerical charts are given. The methods to improve stability of X-type double ribs arch are presented. The results of the studies indicate that the ratio of the flexural rigidity at a tangent of crossbeam to the lateral flexural rigidity of rib should be selected as 0.5-3.As to half- through arch bridge, f0/f(the position of the deck in elevation)can be selected as 0.7~0.9.2. With spatial FEM analysis, the deviation of result created by defect of displacement function hypothesis in analysis can be covered. The relationship between optimum arch ribs included angle and other parameters of deck, half-through and through X-type double ribs arch bridge are systematically analyzed. By the regression methods, optimum arch rib included angle approximate expression of deck, half-through and through X-type double ribs arch bridge are gained, which can be referenced by engineering practice. The results of the studies indicate that not all of the X-type double ribs arch bridge's lateral stability is better than that of the parallel arch bridge. It depends on some parameters whether theinclination of rib can improve the lateral stability of arch, such as the width-span ratio of arch, the flexural rigidity of crossbeams in arch rib tangential plane, and the number of crossbeams, the position of the deck in elevation, etc. With the reasonable included angle, the inclination of ribs can improve the lateral stability of arch efficiently. To half-through and through arch, reasonable included angle can bring economic benefit. But to deck arch bridge, the inclination of ribs must be chosen carefully.3. The common horizontal type lateral bracing is simply analyzed and equaled as straight brace, then conversion flexural rigidity is drawn. Approximate expression of K-shaped brace's conversion flexural rigidity is deduced by means of the response surface method. The layout and type of double ribs arch bridge's lateral bracing are optimizing analyzed by means of the FEM numerical analysis. The results of the studies indicate as the following: First, when the brace numbers are over 3, the vertical flexural rigidity of brace at arch crown can't influence the lateral stability of arch a lot. Second, when the lateral buckling mode of arch is half-wave symmetry, it will be helpful to position the plan type bracing symmetrically at 0.2 L~0.38 L. When the lateral buckling mode of arch is half-wave antisymmetry, the effective layouts of the plan type brace are at 0.08L-0.21 L and 0.42L -0.5L. To X-type double ribs arch, because the lateral buckling mode is usually half-wave antisymmetry , the layouts o...
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