基于无应力状态控制法的钢桁梁桥起拱研究

Pre-camber setting of truss bridge based unstressed state control method

为探讨已知预拱度曲线的钢桁梁桥的预拱度设置方法,将节间相对预拱度作为输入变量,由分阶段成形结构力学平衡方程出发,推导得出各单元杆件伸缩量的数学表达式。针对下承式钢桁梁桥预拱度设置特点,进一步得出了只伸缩上弦杆,同时伸缩上弦杆和斜腹杆,同时伸缩上弦杆、竖杆和斜腹杆三种情况下的杆件伸缩公式,并通过实桥算例说明该方法的应用。分析结果表明:无应力状态起拱法为纯几何起拱法,起拱过程不会产生附加内力和起拱支座反力;计算结果与设计值和文献计算值吻合,说明该方法进行预拱度设置是可靠的。本文方法计算结果可靠,值得同类桥型借鉴。

This paper focuses on the method of setting pre-camber for steel truss girder bridges with a known pre-camber curve.The relative elevation between two adjacent joints is taken as the input variable to deduce the mathematical expressions of the length variation of each member based on the mechanical equilibrium equation of a structure formed in stages.Considering the pre-camber setting characteristics of through steel truss girder bridges,the length variation formula of each member is further developed in three cases:only the length of upper chord member bar is changed;the lengths of the upper chord and diagonal wed member bar are changed;and the lengths of the upper chords,diagonal wed,and vertical member bar are changed simultaneously.An example study was carried out to illustrate applications of the method.The analysis results show that the unstressed pre-camber setting method is an absolutely geometrical method,which will not generate stress in members and supports during the pre-camber setting.The numerical results are in accordance with the design values and the reference value,which illustrates that the pre-camber setting used in this study is reliable.The method is clear and reliable and deserves to be developed for applications in the other types of bridges.