摘 要

无背索斜拉桥结构新颖，外观优美。随着社会的不断发展，人们对桥梁的跨径要求不断提高，因此有必要对无背索斜拉桥的跨径限制因素及合理结构参数做出研究，在合理结构参数的范围内探索无背索斜拉桥的极限跨径，拓宽该类桥型的适用范围。本文以甘肃省境内某桥梁为工程背景，对无背索斜拉桥跨径因素及合理结构参数开展了相关研究。

关键词：无背索斜拉桥；极限跨径；加权残值法；索膜假定；平衡荷载理论

abstract

The cable-stayed bridge without back cable has novel structure and beautiful appearance.With the continuous development of the society,people's requirements on the span of Bridges are constantly improving. Therefore, it is necessary to study the limit factors and reasonable structural parameters of the span of cable-stayed Bridges without backcables,and to explore the limit span of cable-stayed Bridges withoutbackcables within the range of reasonable structural parameters, so as to broaden the application range of this type of bridge. In this paper, the span factors and reasonable structural parameters of cable-stayed bridgewithout back cables are studied with a bridge in Gansu Province as the engineering background. The specific work is as follows.

Based on the theory of load balance and the assumption of cable film,a method for calculating the axial force of arbitrary section of main girder under different cable plane layout is established,and the differences of the axial force near the tower calculated by the method presented in this paper and the method in the literature are compared. The results show that the modified expression of main girder axial force and equivalent cable method are more accurate than Gimsing method. Compared with average cable method,the two methods can not only calculate the axial force near the tower of main girder, but also can calculate the axial force of the whole girder

In order to explore the influencing factors of the ultimate span of cable-stayed bridgewithout back cables, four main influencing factors are selected in this paper: axial force of main girder, cable strength, cable sag effect and buckling stability of main girder. Based on the load balance theory,the expression of main girder axial force, cable strength and ultimate span is derived. It is found that the span can be further increased by increasing the height to span ratio of tower girder and reducing the self-weight of main girder. However, cable strength has little effect on the span compared with other factors, so it is not the main factor affecting the ultimate span. Based on the static analysis theory of single cable,the deformation coordination equation of cable element was derived, the deflection equation of cable wasobtained by using the weighted residual value method, and the equivalent stiffness function of cable support considering sag effect was established. The influence of sag effect on ultimate span was analyzed from the deflection of main girder.Stability theory based on the theory of beam on elastic foundation and compressive bar,respectively girder surface inside and outside surface buckling stability formula is derived, on the basis of exploring the limit span and instability,the relationship between the girder and derived considering girder of the Leaning Tower of Pisa tilt Angle of a quarter of the equivalent coefficient of soil, the result shows that with the increase of span, the stability coefficient and decreases, the in-plane buckling instability type into outside surface instability, can take beam increase with the decrease of dead load set degrees or higher measures to improve the stability of the structure.