High-precision solution to the moving load problem using an improved spectral element method

摘要

In this paper,the spectral element method(SEM) is improved to solve the moving load problem. In this method, a structure with uniform geometry and material properties is considered as a spectral element,which means that the element number and the degree of freedom can be reduced significantly.Based on the variational method and the Laplace transform theory,the spectral stiffness matrix and the equivalent nodal force of the beam-column element are established.The static Green function is employed to deduce the improved function.The proposed method is applied to two typical engineering practices—the one-span bridge and the horizontal jib of the tower crane.The results have revealed the following. First, the new method can yield extremely high-precision results of the dynamic deflection,the bend-ing moment and the shear force in the moving load problem. In most cases,the relative errors are smaller than 1%.Sec-ond,by comparing with the finite element method,one can obtain the highly accurate results using the improved SEM with smaller element numbers. Moreover, the method can be widely used for statically determinate as well as stati-cally indeterminate structures.Third,the dynamic deflection of the twin-lift jib decreases with the increase in the moving load speed,whereas the curvature of the deflection increases. Finally,the dynamic deflection,the bending moment and the shear force of the jib will all increase as the magnitude of the moving load increases.