How does ideCAD calculate flexural strength according to ACI 318-19?
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Nominal flexural strength Mn is calculated based on the following Design Assumptions. According to ACI 22.1.3, the design strength of a section is ϕMn.
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Equilibrium means balancing of forces acting on the element cross section at nominal strength. Stress-strain relationship for the concrete and the reinforcement at nominal strength is established within the design assumptions described followfollowing:
Equilibrium is satisfied at in each section.
It is assumed that strain in concrete and reinforcement is proportional to the distance from the neutral axis.
Design strength is calculated by using these assumptions together with design assumptions for concrete described followfollowing:
Maximum strain at the extreme concrete compression fiber is assumed equal to 0.003.
Tensile The tensile strength of concrete is neglected.
The relationship between concrete compressive stress and strain is represented by the equivalent rectangular concrete stress distribution method.
Concrete stress of 0.85fc' is assumed to be uniformly distributed over. Equivalent rectangular concrete stress zone bounded by edges of the cross-section and a line parallel to the neutral axis located a distance α from the fiber of maximum compressive strain, as calculated by:
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According to ACI 22.1.3, the design strength of a section is taken as the nominal strength multiplied by the applicable strength reduction factor ϕ. Therefore, the design force is ϕMn.
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