When a moment frame does not exceed 12 stories in height and the story height is at least \(10 \mathrm{ft}\), the ASCE standard provides a simpler expression to compute the approximate fundamental period:

T=0.1 N

where \(N=\) number of stories. Recompute \(T\) with the above expression and compare it with that obtained from Problem P2.16. Which method produces a larger seismic base shear?

Problem P2.16

Consider the five-story building shown in Figure P2.10. The average weights of the floor and roof are 90 lb/ft2 and 70 lb/ft² , respectively. The values of SDS and SD1 are equal to 0.9g and 0.4g, respectively. Since steel moment frames are used in the north-south direction to resist the seismic forces, the value of R equals 8. Compute the seismic base shear V. Then distribute the base shear along the height of the building.

Figure P2.10

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(B) T 5 @ 12'=60- 4 @ 25' 100' Plan (a) Building Section (b) 3 @ 30' 90' 3 @ 20=60- -N (c) 20 15 13 wind pressures in lb/ft