Symbols and Terminology
This section presents a table of symbols and variables referenced by the ACI 318 design codes.
| Symbol | Description |
|---|---|
| Ac | Area of concrete in compression (inside the Whitney compression-block) |
| Ag | Gross area of section |
| As | Reinforcing steel area |
| Av | Shear Reinforcing steel area |
| a | Depth of equivalent rectangular stress block as defined in ACI 10.2.7.1 |
| b |
Total Section Width Length of critical section in compression |
| C | Column section maximum compression capacity |
| Cc | Compression force in concrete |
| Cs | Compression force in reinforcement bar |
| d | Distance from the top of compression surface to center of the flexure reinforcement perpendicular to that direction of the shear plane |
| db | Nominal diameter of reinforcement bar |
| Ec | Concrete modulus of elasticity |
| Es | Reinforcement steel bar modulus of elasticity |
| Fs | Individual reinforcement stress |
| f'c | Concrete max permissible stress |
| fct | Average splitting tensile strength of lightweight aggregate concrete (psi units) |
| fy | Reinforcement stress capacity (psi units) |
| h | Total section depth |
| k | Effective length factor of column |
| Lc | Distance from Neutral Axis (N.A.) to maximum concrete compression fiber |
| Ls | Distance from Neutral Axis (N.A.) to center of reinforcement bar being considered |
| lc | Length of compression member in a frame, measured from center to center of the joints in the frame |
| ld | Reinforcement bar development length |
| Ms | Moment capacity contribution of reinforcement bars to section capacity |
| Mc | Moment capacity contribution of concrete to section capacity |
| Mn | Nominal moment capacity of concrete section |
| Mu | Factored ultimate moment on section |
| Mθ | Moment about a given angle. Calculates as |
| P | Section compression capacity for given neutral axis and compression side |
| Pb | Balanced compression capacity |
| Pn | Nominal axial capacity of concrete section |
| Pu | Factored ultimate axial on section |
| Tc | Torsional capacity of concrete section |
| Ts | Tension force in reinforcement bar |
| Tu | Factored ultimate torsion on section |
| s | Reinforcement spacing |
| Vu | Factored ultimate shear force on section |
| Vs | Shear reinforcement capacity |
| Vc | Concrete section shear capacity |
| ϕc | Concrete compression capacity reduction factor
|
| ϕb | Flexure capacity reduction factor of concrete (0.90 for ACI 318-99) |
| ϕT | Torsional capacity reduction factor of concrete (0.85 for ACI 318-99, 0.75 for ACI 318-02) |
| ϕs | Shear capacity reduction factor of concrete (0.85 for ACI 318-99, 0.75 for ACI 318-02) |
| δc | Actual concrete density used |
| ρ | Reinforcement ratio of section |
| ρb | Balanced reinforcement ratio |
| εc | Concrete max permissible strain |
| Ψ | Ratio of ΣEI/lc of compression members to ΣEI/l of flexure members in a plane at one end of a compression member |