non-uniform motion at the roof level. For the southern library, similar mode shapes are identified, and the frequencies of its first modes in horizontal directions are also summarized in Table 1.
The FEM model for the superstructure of the northern library was constructed as shown in Figure 5. It has 4,891 elements, 7,968 nodes, and 206 ton of total mass. Continuum-equivalent Young's modulus is evaluated by simulating base-fixed frequencies of the first horizontal modes summarized in Table 1. The Young's modulus is evaluated as 850 N/mm2 for both of NS and EW directions, which is about 1/15 of 13,000 N/mm2, a value obtained by the laboratory test.
Figure 6 shows first horizontal translation modes obtained by the finite element model for the northern library in NS and EW directions. The NS mode
has larger amplitude along the north and the south edges compared to the east and the west edges, which is in accordance with the variation of peaks in transfer functions shown in Figure 4.
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