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在承受扭矩(例如由于桥面偏心荷载)M_z时,桥孔结构的作用可分为两部份:净扭作用M_k和弯扭作用M_(u.k)。净扭矩由桥孔结构整个截面(包括顶、底联结系)对扭转的抗力(剪力流)组成,并不在主梁弦杆成翼缘中引起应力。弯扭矩由各主梁(不包括顶、底面联结系)承受不同的弯矩而在各梁截面上发生相应的剪力组成,并对主梁弦杆(或翼缘)应力有直接影响。设置顶、底面联结系并适当地布置断面联结系是保证桥孔结构空间整体作用的必要条件。M_k 和M_(u.k) 的相对比值是桥孔结构空间整体作用发挥程度的指标。这个比值视断面联结系抗剪与主梁抗弯的相对刚度而定。本文利用结构力学的简单方法,导出了具有单片或数片断面联结系的双主梁或多主梁桥的实用计算公式。
In the torque (for example, due to the deck eccentric load) M_z, the role of the bridge structure can be divided into two parts: the net torsion M_k and bending torsion M_ (u.k). The net torque consists of torsional resistance (shear flow) through the entire cross-section of the bridge structure (including the top and bottom linkages) and does not cause stress in the flange of the main beam. The bending moment is subjected to different bending moments by the main girders (excluding the top and bottom joint systems) and the corresponding shear component occurs on each beam section and has a direct effect on the stress of the chord (or flange) of the main girder. Setting the top and bottom joint system and properly arranging the cross-section joint system are the necessary conditions to ensure the overall function of the bridge hole structure space. The relative ratio between M_k and M_ (u.k) is an index of the overall effect of the bridge structure space. This ratio depends on the relative stiffness of the cross-section shear and the main beam bending. In this paper, a simple method of structural mechanics is used to derive a practical calculation formula of double main girder or multi-girder bridge with single or several sections of cross-section connection system.