Statically equivalent seismic loads based on two-mode-based approach for single layer reticulated shells

Abstract

The present study discusses a method to express statically equivalent seismic loads based on the two dominants modes with emphasis on single-layer reticulated shells encompassing spherical, cylindrical, and free-form shells. The shells investigated are shallow roofs of three-way member arrangement. For the earthquake response analysis, a set of twelve artificial earthquake motions are introduced compatibly with the design response spectrum specified in the building code of Japan. First, to analyze the response behavior and to find the relationship between the shell geometries and their vibrational properties, a vibration database is set up based on the response spectrum method using the results obtained from eigenvalue analysis. Second, an analysis of pseudo-seismic energy and mass ratios of free vibration modes is performed to discuss what have important roles in estimating the equivalent seismic loads. Third, from a viewpoint of the two-mode-based aaproach, the importance of the pseudo-seismic energy is discussed, then followed by a proposal of the equivalent seismic loads for the reticulated shell roofs. Finally, the validity of the proposed formation is confirmed under a certain restraint to its application.