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Pe = axial compression load based on gravity load and seismic (framing) action Pb = axial compression capacity at the maximum nominal (balanced) moment on the section = 0.425 bif'Ag bi = compression stress block factor < 0.85 Pto = axial tensile capacity of the column = —Astfsu Ast = area of longitudinal reinforcement fsu = ultimate tensile strength of the longitudinal reinforcement

D' = pitch circular diameter of the reinforcement in a circular section or the out-to-out dimension of the reinforcement in a rectangular section, this generally may be assumed as 0.8D

' 0.32 for circular sections

0.375 for square sections with 25% of the longitudinal Kshape = reinforcement placed in each face

0.25 for walls with strong axis bending

0.5 for walls with weak axis bending

k0 = a factor related to the centroid of compression stress block and should be taken as 0.6 and

0.5 for circular and rectangular sections, respectively. It should be pointed out that Equations 20.12 and 20.13 are rearranged in the simpler format given above.

For reinforced concrete column, a moment-curvature section analysis taking into account the expected strength, confined concrete properties, and strain hardening effects of longitudinal reinforcement.

For a steel column, nominal flexural resistance (Mn) shall be determined either in accordance with the AASHTO-LRFD [38] or

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