TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
9-4. General behavior. The behavior of columns and pilasters under axial loading is dependent upon. the
cross sectional capacity of the column materials and the lateral stability of the column. Figure 9-6 illustrates
this relationship between capacity and stability. In very short columns crushing failure occurs as the result
of the load exceeding the ultimate material strength and stability does not become a design consideration. For
most columns, inelastic deformation of the materials occurs on some portion of the column cross section
before general column buckling occurs. Nonetheless, the allowable compressive stresses used during for
design of the cross section are reduced to account for potential instability of the column. For long slender
columns, elastic buckling failure will occur before any material reaches the yield state.
a. Effective height. The assumed behavior of columns and pilasters is a function of the slenderness of the
member. The slenderness is expressed as the ratio of the effective height, h*, to the radius of gyration, r. h*
is the product of the clear height of the column, h, and the factor, K, which considers the effects of column
end restraint and whether or not lateral deflection (sidesway) occurs at the top of the column. Values of K
are provided in table 9-1. Since pilasters act as stiffening elements within a wall, they can be considered
laterally supported in the direction parallel to the plane of the wall. However, slenderness effects must be
considered in the direction perpendicular to the plane of the wall, and the design for that direction will be
based on the effective wall height.
9-4
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