钢桁梁桥面系第一体系纵向力分配情况

Distribution of longitudinal forces of the first system on bridge deck in steel-truss beam

为了考察钢桁梁桥面系第一体系纵向力的分配情况,为钢桁梁计算的简化提供可靠依据,任取钢桁梁的一个节间进行分析。将横梁的面外变形模型简化为一个含弹性支座的三跨连续梁(桥面系中含4片纵梁)或单跨梁(桥面系中含2片纵梁)。根据弦杆和桥面系纵梁、横梁的变形协调条件,假设钢桁梁弦杆各杆轴力之比与相应平面桁架弦杆各杆轴力之比相同,推出钢桁梁桥第一体系纵梁轴力与弦杆轴力之比值的公式,并通过一个算例说明了本文公式的可靠性。计算结果表明,纵梁上的轴力远较按刚度EA之比分配的值要小,下弦杆的轴力则远较上述比值要大;桥面系参与承担纵向力的程度,由端部节间向中部节间逐渐增大。

The distribution of longitudinal forces of the first system on bridge deck system in steel - truss beam was reviewed and the reliable dependencies were given to simplify calculation for this structure. Meanwhile, a panel on bridge deck system was analyzed. The out - plane deformation model of transverse beams was simplified to a three- spans continuous girder with elastic supportions （there are four longitudinal beams on bridge deck system） or a one- span girder with elastic supportions （there are two longitudinal beams on bridge deck system）. According to deformation conditions of chords and longitudinal beams, transverse bean,s on bridge deck system, the ratios of the axial force in chord members were supposed to be equal to those of the correspond plane tress. The formulae of the ratios for the axial forces in longitude beams to those in bottom chord members were obtained. An example validates the reliability of the proposed formulae. The results show that the axial forces in longitudinal beams are much less than the distributed values on the scale of stiffness EA, the axial forces in bottom chord members are much more than above values and the degree for bridge deck system to undertake longitudinal forces increases little by little from side panels to middle panels.