2025 年 25 巻 4 号 p. 4_86-4_96
This paper proposes a modal analysis method based on the energy-based overset finite element method (EbO-FEM) for rigid frame bridges. Rigid frame bridges and the foundations have complex geometries, which makes the mesh generation for finite element analysis expensive. The EbO-FEM has been developed to reduce the cost of mesh generation by allowing the use of nonconforming meshes without iterative computations. However, the EbO-FEM has only been applied to the static analysis and the applicability for the modal analysis has not been investigated. We applied the EbO-FEM for the finite element modal analysis, evaluated the accuracy of the method by comparing the solutions with existing FEM solutions, and utilized the EbO-FEM for the parameter identification with records of microtremors through the following procedure. First, a modal analysis of the virtual cantilever beam was performed to verify the accuracy, and the EbO-FEM solution agreed well with the conventional FEM solutions under different discretization scales, where overlapping regions is carefully localized. Second, the natural vibration modes and frequencies are estimated using the EbO-FEM for a frame bridge under construction. The EbO-FEM gives similar natural vibration modes to ones estimated by the frequency domain decomposition (FDD) method, and the elastic moduli of the surface soils were estimated so that the corresponding natural frequencies were consistent. The estimated elastic moduli were not significantly different from the data obtained from the preliminary survey. Above all, it was found that EbO-FEM can be as accurate as conventional FEM when the mesh overlapping is carefully minimized, in the modal analysis in spite of allowing non-conforming mesh.
