4.1.7.2. Classification of Buildings

(See Note A-4.1.7.2.)

(1)

Except as provided in Sentences (2) and (3), a building is permitted to be classified as not dynamically sensitive.

(2)

A building shall be classified as dynamically sensitive if

(a)

its lowest natural frequency is less than 1 Hz and greater than 0.25 Hz,

(b)

its height is greater than 60 m, or

(c)

its height is greater than 4 times its minimum effective width considering all wind directions, where the effective width, w, of a building shall be taken as,

where the summations are over the height of the *[[a-1.4.1.2.#building|building]]* for a given wind direction, h_i is the height above *[[a-1.4.1.2.#grade|grade]]* to level i, and w_i is the width normal to the wind direction at height h_i ; the minimum effective width is the lowest value of the effective width considering all wind directions.

(3)

A building shall be classified as very dynamically sensitive if

(a)

its lowest natural frequency is less than or equal to 0.25 Hz, or

(b)

it contains a human occupancy, and its height is more than 6 times its minimum effective width as defined in Clause (2)(c).