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İnternational Design Codes
TSC2018 : ilili yere link
ACI 318 : ilgili yere linkACI 318-19 : Flexural Strength
TSC 2018 : TSC Flexural Strength
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Notation
As = area of nonprestressed longitudinal tension reinforcement, in2
α = depth of equivalent rectangular stress block, in.
bw = web width or diameter of circular section, in.
c = distance from extreme compression fiber to neutral axis, in.
Cc = concretecompressive force, lb
Cs = reinforcement tension force, lb
d = distance from extreme compression fiber to centroid of longitudinal tension reinforcement, in.
fc'= specified compressive strength of concrete, psi
fy = specified yield strength for nonprestressed reinforcement, psi
Mn = nominal flexural strength at section, in.-lb
ϕ = strength reduction factor
εt = net tensile strain in extreme layer of longitudinal tension reinforcement at nominal strength, excluding strains due to effective prestress, creep, shrinkage, and temperature
β1 = factor relating depth of equivalent rectangular compressive stress block to depth of neutral axis
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Nominal flexural strength Mn is calculated based on the following Design Assumptions. Acconrding to ACI 22.1.3Codes, design strength of a section is ϕMn.calculated
Design assumptions
The flexural and axial strength of a member calculated by the strength design method, two basic conditions should be satisfied:
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Maximum strain at the extreme concrete compression fiber is assumed equal to 0.003.
Tensile strength of concrete is neglected.
The relationship between concrete compressive stress and strain is represented by equivalent rectangular concrete stress distribution method.
Concrete stress of 0.85fc' is assumed 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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The distance between the fiber of maximum compressive stress and the neutral axis, c, is perpendicular to the neutral axis.
The value of β1 is determined using ACI Table 22.2.2.4.3 Codes.
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Nominal flexural strength Mn is calculated as shown below.
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The total forces Cc and Cs resulting from the stresses of concrete and reinforcement are shown below.
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From the equation of equilibrium:
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Nominal flexural strength Mn:
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Acconrding to ACI 22.1.3, 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.
The difference between Design Strength ϕMn and Nominal Strength Mn is indicated in the figure below.
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