Abstract: At present, the research on the arching problem of steel truss bridges in engineering mainly focuses on the N-type truss sections, but there is no unified calculation method for the pre-camber setting of K-type steel truss bridge sections. In order to solve the problem of arching in K-type sections, the mathematical expression for the expansion and contraction of each member was derived, which was based on the mechanical equilibrium equation of a structure formed in stages and took the relative pre-camber of the sections as an input. Aiming at the characteristics of the pre-camber setting of the through type steel truss girder bridges, the formulas for the expansion and contraction of the members were further obtained for three cases: simultaneous expansion and contraction of the lower diagonal web members and vertical web members, simultaneous expansion and contraction of the lower diagonal web members and upper chord members, and simultaneous expansion and contraction of the upper chord members and upper and lower diagonal web members. With the help of real bridge data calculation and geometric trial calculation, the proposed method was verified. The research results show that the proposed method is practical and feasible, which fully verifies that the unstressed arching of K-type steel truss bridge sections is an absolutely geometrical arching, and the arching process will not generate additional internal forces or reaction forces from the arching support.

Key words: bridge engineering; steel truss girder bridge; K-type truss; pre-camber curve; unstressed arching method

摘要： 目前工程上对于钢桁梁桥起拱问题的研究主要针对N式桁架节间，但K式钢桁梁桥节间的预拱度设置尚未有统一的计算方法。为解决K式节间的起拱问题，基于分阶段成形结构力学平衡方程，将节间的相对预拱度作为输入，推导得出各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，进一步得出同时伸缩下斜腹杆与竖腹杆、同时伸缩下斜腹杆与上弦杆、同时伸缩上弦杆与上下斜腹杆共3种情况下的杆件伸缩公式，并借助实桥数据计算和几何试算进行验证。研究结果表明：该方法实用可行，充分验证了钢桁梁K式节间的无应力状态起拱为纯几何起拱，起拱过程不会产生附加内力和起拱支座反力。

关键词: 梁桥工程；钢桁梁桥；K式桁架；预拱度曲线；无应力状态起拱法