DO TALL BUILDINGS SWAY?

Evening Star, Issue 18052, 21 August 1922, Page 6

DO TALL BUILDINGS SWAY?

There is a popular impression that tall office buildings sway considerably in a gale of wind. That there is some movement is unquestionable, but it is very slight. It would be more oonrect to say that they bend rather than sway. All natural growths, from the blade of grass to the giant fir tree, bend under the pressure of the wind, for they arc flexible or elastic, and under any side pressure duo to the wind they give way proportionately. Tho tall office building is also flexible, being built of stool that has high elasticity, and in a heavy wind, where the total side pressure may amount up to hundreds of tone, tho steel framework will be,nd over before it. If the wind v/ilodty never varied, if there were no gusts, and the pressure for a given period of time never changed, tho building would bend to leeward to a certain extent, and remain stationary in that position as long ns the wind pressure remained constant. Wind pressure is not constant, but comes in gusts,, and tho building will b<? bent over in proportion to the ,strength of these gusts, moving to and fro, in accordance therewith. Occasionally this swaying is perceptible to the senses; but as a rule in the most modern buildings the movement is so very slight as to bo imperceptible, except by instrumental, measurement. Formerly it was customary to allow for a uniform pressure per square foot over the whole surface from street level to cornice —solb per square foot being the usual unit. To-day it is recognised that the unit pressure increase with the height, and calculations are made accordingly.—‘ Scientific American.’