Pasternak地基Timoshenko梁全相分析的超越有限元与剪力分配计算

TRANSCENDENTAL FINITE ELEMENT FOR ALL-PHASE ANALYSES OF TIMOSHENKO BEAM ON PASTERNAK FOUNDATION AND SHEAR DISTRIBUTING CALCULATION

  • 摘要: 将Pasternak地基Timoshenko梁微分方程求解分为3相,基于各相的微分方程挠度解,建立了任意截面的挠度、转角、剪力和弯矩用单元结点位移表达的解析式,取单元结点力,建立了超越有限元列式,其实质是用微分方程位移奇次解作为单元的位移模式。根据变分原理的自然边界条件要求,单元结点剪力应取总剪力;基于有限元列式,建立了Pasternak地基和Timoshenko梁各自承担剪力的计算方法。利用Timoshenko深梁单元的传统位移插值函数,建立了Pasternak地基Timoshenko梁单元的常规有限元列式。超越有限元收敛性好,计算精度不依赖于网格密度。算例表明,该文超越有限元、常规有限元结果与理论结果一致,超越有限元用1个单元就可得到精准结果。有关文献的有限元构造理论不正确、计算结果存在误差。刚性地基梁(Δ>0相)中,荷载只影响其直接作用的局部区域,对其他区域的影响可以忽略。

     

    Abstract: There are three phases in the solutions to the differential equation of Timoshenko beam on Pasternak foundation. Based on the displacement solutions to the differential equation of all phases, the displacement, rotation, shear force and moment at any cross-section can be expressed by the nodal displacements and rotations. When the shear forces and moments at nodes are evaluated, a transcendental finite element is formulated, in which the homogeneous solutions of displacement and rotation are used as the displacement model in essence. The essential boundary condition of the variational principle requires that the total shear should be implemented as the nodal shear. The theoretical formulae to calculate the distribution of shear force between the Pasternak foundation and Timoshenko beam is derived based on the finite element formulation. A conventional finite element formulation based on the displacement interpolation functions of the Timoshenko beam element is established. The transcendental finite element owns excellent convergence property, whose calculation accuracy does not depend on the mesh density. The results of examples demonstrate that the results of transcendental finite element and conventional finite element are consistent with the theoretical solutions. Even there is only one element meshed, it still achieves the exact results. There are some theoretical inaccuracies in the finite element formulation existed in other literatures, which lead to remarkable errors. For elastic beam on hard foundation (the phase is Δ>0), the actions of load only affect the local place subjected to the load directly, for other places, the actions of load can be neglected.

     

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