term, R, reduced the stress to the point where buckling will not occur. R also accounts for the increase in

moment due to lateral deflection or the P-Delta effect.

For an uncracked section (fa $ fb);

Where:

M = The computed bending moment, inch-lbs.

For a cracked section (Fa < fb );

Where:

d = The effective depth of the flexural section measured from the extreme compression fiber to the

centroid of the tension reinforcement, inches.

k = The ratio of the depth of the compressive stress to the depth, d.

j = The ratio of the distance between the centroid of the flexural compressive forces and the centroid

of the tensile forces to the depth, d.

j = 1 - k/3.

and pilasters, Fb, is determined as follows:

Fb = 0.33f*m (psi)

(eq 9-5)

If f*m = 1,350 psi; Then Fb = 0.33(1,350) = 450 psi

determined as follows:

Where:

Ast = The cross sectional area of the reinforcing steel that is considered in tension only, psi.

strength of the reinforcement is equal to or greater than 60,000 psi is:

Fs =24,0000(psi)

(eq 9-7)

basic interaction equation as follows:

than the design determined using dead and live loads only. Load interaction methods based on accepted

principles of mechanics may be used in lieu of equation 9-8.

conditions at the top of the member; at (or near) mid-height of the member, where the maximum bending will

usually occur; and at the bottom of the member. Normally, masonry columns or pilasters will be given lateral

support at the top by roof or floor system members and will be connected to the foundation below with

reinforcing dowel bars. For this condition, the conservative assumption is made that the tops and bottoms

of the members are simple supports. When other support or fixity conditions exist, calculations will be based

on established principles of mechanics. At the top of a column or pilaster, a combination of the axial load,

P, the eccentric moment, Pe, and any other loads and moments present will be considered. When determining

Fa at the top of the member, the load reduction factor need not be considered. At (or near) the mid-height

of a column or pilaster, a combination of axial load, P, the eccentric moment, approximately Pe/2, the lateral

load moment, and any other loads and moments present will be considered. At mid-height, the P-Delta effect

is at its maximum, thus Fa will be reduced by the load reduction factor, R. Since some value of lateral loads

and lateral load moments will generally act in either direction on the member, the maximum combination of

axial load, eccentric moment at the mid-height, moments created by lateral loads acting in either direction

will be considered.

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