1.7 Equations for p

What is p?

The abbreviation, $P$ , is used to describe the axial load on a member.

Basic requirements

The basic requirements for compression members are covered in Chapter E of the AISC Specification (page 16.1-27). Therelationship between loads and strength takes the form:

• $P_u$ = sum of factored loads
• $P_n$ = nominal compressive strength $A_g{F}_{cr}$
• $F_{cr}$ = critical buckling stress
• ${\phi }_c$ = resistance factor for compression members = 0.85

Design strength equation

The design strength equation,

• For ${\lambda }_c\le 1.5$
  $F_{cr}=\mathrm{0.658}^{{\lambda }_c^2}{F}_y$
• For ${\lambda }_c> 1.5$
  $F_{cr}=\frac{0.877}{{\lambda }_c^2}{F}_y$

Slenderness parameter

The slenderness parameter incorporates the material properties. If it is less than 1.5, the compression memberis said to be elastic. Then, if the value is over 1.5, $F_{cr}$ must be reduced to account for the effects of initial crookedness.

Put in figure p96.