## Loojt J

These values will be modified for eccentric loading conditions. The Perry-Robertson formula is the basis of BS 449 as shown in §2.7.

Struts with initial curvature

Maximum deflection <5max =

C0h where Co is the initial central deflection and h is the distance of the highest strained fibre from the neutral axis (N.A.).

Smith-Southwell formula for eccentrically loaded struts

With pinned ends the maximum stress reached in the strut is given by or

eh 1

where e is the eccentricity of loading, h is the distance of the highest strained fibre from the N.A., k is the minimum radius of gyration of the cross-section, and a is the applied load/cross-sectional area.

Since the required allowable stress a cannot be obtained directly from this equation a solution is obtained graphically or by trial and error.

With other end conditions the value L in the above formula should be replaced by the appropriate equivalent strut length (see §2.2).

Webb's approximation for the Smith-Southwell formula

eh fPe+0.26P

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