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Download ideCAD for Beam Design Limits according to ACI 318-19 |
Notation
Ag = gross area of concrete section, in2
bf = effective flange width, in.
bw = web width or diameter of circular section, in.
c1 = dimension of rectangular or equivalent rectangular column, capital, or bracket measured in the direction of the span for which moments are being determined, in.
c2 = dimension of rectangular or equivalent rectangular column, capital, or bracket measured in the direction perpendicular to c1, in.
Ec = modulus of elasticity of concrete, psi
Es = modulus of elasticity of reinforcement, psi
fc'= specified compressive strength of concrete, psi
fy = specified yield strength for nonprestressed reinforcement, psi
h = overall thickness, height, or depth of member, in.
l = span length of beam or one-way slab; clear projection of cantilever, in.
ln = length of clear span measured face-to-face of supports, in.
Pu= factored axial force; to be taken as positive for compression and negative for tension, lb
sw = clear distance between adjacent webs, in.
ϕ = strength reduction factor
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Minimum beam depth
For nonprestressed beams, the limits of overall beam depth h are given in ACI Table 9.3.1.1.
Supoort condition | Minimum depth, h |
|---|---|
Simply supported | l/16 |
One end continuous | l/18.5 |
Both ends continuous | l/21 |
Cantilever | l/8 |
The expressions in ACI Table 9.3.1.1 shall be multiplied by (0.4 + fy /100,000) if reinforcement yield strength fy is different than 60,000 psi.
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Deflection limits
If nonprestressed beams do not satisfy ACI 9.3.1, immediate and time-dependent deflections are calculated according to ACI 24.2 and checked not to exceed the maximum values in ACI Table 24.2.2.
Member | Condition | Deflection to be considered | Deflection limitation | |
|---|---|---|---|---|
Flat roofs | Not supporting or attached nonstructural elements likely to be damaged by large deflections Immediate deflection due to L | Immediate deflection due to maximum of Lr, S, and R | l/180 | |
Floors | l/360 | |||
Roof or Floors | Sıpporting or attached to nonstructural elements | Likely to be damaged by large deflections | That part of hte total deflection occurring after attachment of nonstructural elements, which is the sum of the time-dependent deflection due to all sustained loads and the immediate deflection due to any additional live load | l/480 |
Not likely to be damaged by large deflections | l/240 | |||
Reinforcement strain limit in beams
If Pu< 0.10fc’Ag for nonprestressed beams, the strength reduction factor ϕused for tension-controlled according to ACI Table 21.2.2.
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Beams of Earthquake-Resistant Structures
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Beams should have a minimum of two continuous bars at the top and bottom faces. Minimum reinforcement conditions are given in the Beam Reinforcement Limits per ACI 318-19 with ideCAD title.
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Download ideCAD for Beam Design Limits according to ACI 318-19 |