薄壁箱梁剪力滞效应分析的初参数法

INITIAL PARAMETER METHOD FOR ANALYZING SHEAR LAG EFFECT OF THIN-WALLED BOX GIRDERS

选取剪力滞效应引起的附加挠度作为广义位移,在定义新的剪力滞广义力矩及广义翘曲位移函数基础上,将薄壁箱梁的剪力滞变形状态从初等梁挠曲变形状态中分离出来作为一种独立的基本变形状态进行分析。对广义翘曲位移函数引入两个修正系数以充分考虑剪力滞翘曲应力的自平衡条件。提出了剪力滞翘曲应力的简便计算公式,它与初等梁弯曲应力公式具有相同的形式。用能量变分法建立了剪力滞控制微分方程,以广义力矩、广义剪力、附加挠度及其变化率作为四个初参数,给出了微分方程的初参数解。对两跨连续箱梁模型的应力计算表明:本文计算值与实测值及其它文献给出的计算值均吻合良好,从而验证了该文分析方法的正确性。挠度计算表明:剪力滞效应使该箱梁在集中荷载和均布荷载作用下的跨中挠度分别增大17%和16%。

The additional deflection induced by shear lag effect is adopted as the generalized displacement of a thin-walled box girder. Based on the new generalized moment and warping displacement function defined, the shear lag deformation state is separated from the flexural deformation state of an elementary beam and analyzed as a fundamental deformation state. Two modification factors are introduced in the generalized warping displacement function to consider fully the self-equilibrium of shear lag warping stresses. A simple and convenient formula for shear lag warping stress is proposed, which has the same form as that of the bending stress of an elementary beam. The governing differential equation for shear lag is established by using energy calculus and its initial parameter solution is given, in which the generalized moment, generalized shear force, additional deflection and its variation rate are chosen as the initial parameters. A two-span continuous box girder model is analyzed and the calculated results are in a good agreement with test results and those provided in other reference literatures. The shear lag effect increases the mid-span deflection of a box girder under concentrated and uniformly distributed loads by 17% and 16%, respectively.