Design for shear (pad and strip base:ACI 318)
Pad base shear design check
The nominal shear strength of the concrete in beam action, is given by1 |
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vn | = | 2*λ*MIN(√(f`c), 100psi)*d |
= | 0.17*λ*MIN(√(f`c) ,8.3MPa)*d | |
where |
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λ | = | modification factor related to the density of the concrete |
λ | = | 1.0 for normal weight concrete |
If | ||
vu | ≤ | Φshear*vn |
Then the foundation thickness is adequate for shear - Utilization ratio is then; |
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U-ratio | = | max [ vu / (Φshear*vn) ] |
Else the check has failed, the foundation thickness is inadequate. |
Note:
If the thickness is inadequate and the auto-design footing depth option is active then the foundation thickness gets increased.
Strip base shear design check
The principle of the strip base shear design check is similar to that for the pad base. Only the direction X is checked (around Y-axis) using segment widths.
Footnotes
1 ACI
318-08 Sections 11.1.2 and 11.2.1.1 Eqn (11-3)