Design for shear (pad and strip base:ACI 318)

Tekla Structural Designer
Modified: 2 Jun 2023
2024
Tekla Structural Designer

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

vn = 2*λ*MIN(√(f`c), 100psi)*d
= 0.17*λ*MIN(√(f`c) ,8.3MPa)*d

where

  
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;

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)
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