Progress of parallel computing enables us to conduct large-scale finite element (FE) structural analysis using high fidelity finite element mesh of a structure with complex geometry. In the present study, a high fidelity solid element mesh of a 31-story super-highrise steel building frame is generated, and a seismic response analysis is conducted. A series of researches have been conducted by the present authors since 2007. A parallel finite element structural analysis code, E-Simulator, which has been developed at the National Research Institute for Earth Science and Disaster Resilience (NIED), Japan, is used in the analysis.
The 31-story frame is a center-core-type office building whose total height is 129.7 m, and the size of the plan is 50.4 m × 36.0 m. The FE mesh has 15,598,662 elements, 24,220,688 nodes, and 72,662,064 DOFs. The number of multi-point constraints (MPCs) that are used to connect component meshes is 2,832,402. Plates such as the flanges and webs of beams are divided into at least two layers of solid elements in the thickness direction. The mesh is generated manually using the mesh generation module in a 3D solid modeler. A concept of mesh generator for steel frames using hexahedral solid elements is proposed in which a database of component solid element meshes for beams, columns, and connections is constructed and used. A mesh for a frame is made by assembling the component meshes.
A parallel FE structural analysis software package, ADVENTURECluster is used as a platform of E-Simulator. The algorithm of the analysis code is based on the domain decomposition method. The Coarse Grid Conjugate Gradient (CGCG) method has been developed originally for the ADVENTURECluster as a powerful linear solver. In the present study, E-Simulator is implemented on K computer, which was one of the fastest supercomputer in the world when it started operation in 2011.
The seismic response analysis of the super-highrise frame subjected to a simulated ground motion of great Nankai Trough earthquakes is conducted. The computation is performed on K computer using 256 computation nodes (2048 cores). The large strain elastic-plastic analysis is conducted. Time increment is taken to be 0.1 s for observing the response due to lower order eigenmodes excited by the long-period ground motion. Duration of the analysis is 125 s. The vibration due to coupled two lowest modes in the longitudinal and transverse directions and a torsional mode is continued many times. Distribution of equivalent plastic strain is visualized. Region in plastic state spreads gradually as the number of cycles of the oscillation increases. The equivalent plastic strain more than 30 % is observed. A downward vertical drift is observed in the time history of up-down displacement, which is due to plastic deformation of the whole structure. Discussions on computation performance on K computer are also described.
Concluding remarks are as follows. 1) Mesh generation of super-highrise frame using hexahedral solid elements takes very long time. However, a concept of mesh generator for steel building frames is proposed. Component meshes for beams, columns, and connections are re-used and assembled in the system. 2) Both local yielding in the members and global plastic deformation of the entire structure in the vertical direction are analyzed under the long-period ground motion that continues more than two minutes. 3) Efficient visualization can be performed on K computer using an offline rendering code. 4) Although computation performance on K computer is better than those on previous supercomputers, further improvement of computation performance is necessary for the analysis code. Use of too many MPCs has an unavoidable effect on the performance.
