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NEEDHAM AND GERARD METHODS FOR DETERMINING CRIPPLING

STRESSES

(I) NEEDHAMS METHOD:

More recent semi-empirical methods for the determination of cripplin stresses of col!mns "erede#eloped $% Needham and &erard' In the Needham method the str!ct!ral mem$er section isdi#ided into anle elements as sho"n in i' **'+,' The cripplin strenth of these elements can$e esta$lished $% theor% andor tests' The cripplin fail!re strenth of the mem$er section thencan $e determined $% s!mmin the cripplin strenths of each anle element that ma.es !p thetotal section' Thro!h e/tensi#e tests Needham arri#ed at the follo"in semi-empirical e0!ationfor the cripplin stress of anle sections:

The cripplin stress for the act!al mem$er section is o$tained $% !tili1in the follo"in e0!ation:

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(II) &E2A2DS METHOD:

&erards method for calc!latin cripplin stresses is a enerali1ation of Needhams method' Hise/tensi#e in#estiation led to the form!lation of three semi-empirical e0!ations for determininthe cripplin stresses in #ario!s shapes of str!ct!ral mem$ers'

or sections "ith straiht !nloaded edes s!ch as plates tee cr!ciform and H sections thefollo"in cripplin stress e0!ation applies: