Column Required and Design Strength per ACI 318-19 with ideCAD

How does ideCAD calculate concrete column required, and design strength according to ACI 318-19?

Notation

D = dead load
E = earthquake load
L = live load
L_r = roof live load
M_n = nominal flexural strength at section, in.-lb
M_u = factored moment at section, in.-lb
P_n = nominal axial compressive strength of member, lb
P_u = factored axial force; to be taken as positive for compression and negative for tension, lb
R = rain load
S = snow load
T_n = nominal torsional moment strength, in.-lb
T_u = factored torsional moment at section, in.-lb
U = strength of a member or cross section required to resist factored loads or related internal moments and forces in such combinations as stipulated in ACI 318-19
V_n = nominal shear strength, lb
V_u = factored shear force at section, lb
W = wind load
ϕ = strength reduction factor

Required Strength

The required strength is calculated in accordance with the factored load combinations in Load Factors and Combinations per ACI 318-19 with ideCAD title. Combined Axial and Flexural Required strengths of a column P_u and M_u occur simultaneously for a column. Therefore, for each applicable factor load combination specified in ACI Table 5.3.1, the most unfavorable condition of P_u and M_u occurring simultaneously is considered.

Design Strength

Design strength in all sections should satisfy all conditions given below;

• ϕP_n ≥ P_u

• ϕM_n ≥ M_u

• ϕV_n ≥ V_u

• ϕT_n ≥ T_u

Strength reduction factors ϕ is determined according to using ACI Table 21.2.2. Interaction between load effects is considered.

P_n and M_n is calculated in accordance with Axial strength or Combined Flexural and Axial Strength per ACI 318-19 with ideCAD title. Combined Axial and Flexural strengths create a three-dimensional interaction failure surface. In addition to axial compression and biaxial bending, the formulation allows for axial tension and biaxial bending considerations. An interaction surface of a column is shown below.