Pb

where a is approximately equal to 11 \Jm/s, B is the building width in the direction of vibration, and H is the building height. This empirical formula suggests that a shear beam model with f inversely proportional to H is more appropriate than flexural beam for predicting natural frequencies of buildings.

2.13.8 Portal Frames

A portal frame consists of a cap beam rigidly connected to two vertical columns. The natural frequencies of portal frames vibrating in the fundamental symmetric and asymmetric modes are shown in Table 2.8

TABLE 2.8 Fundamental Frequencies of Portal Frames in Asymmetrical Mode of Vibration

First asymmetric in-plane mode

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