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Plastic analysis of prismatic compression members in buildings is permitted if (Fy)½(l/r) does not exceed 800 and Fuless than equal to 65 ksi (448 MPa). For axially loaded members with b/t less than equal to (lambda)r , the maximum load P u , ksi (MPa= 6.894 X ksi), may be computed from
Pu = 0.85AgFcr
Where Ag=gross cross-sectional area of the member
F cr =0.658 lambda Fy for lambda <= 2.25
=0.877 Fy/lambda for lambda > 2.25
lambda =(Kl/r)2(Fy/286,220)
The AISC specification for LRFD presents formulas for designing members with slender elements.
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