passive resistance for mat slabs

Passive Resistance for Mat Slabs

RISAFoundation v11.0 now includes the added ability to enter a passive pressure for slabs. The passive pressure represents soil pressure along the perimeter of the slab and will contribute to the sliding resistance of the slab.

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RISAFoundation will multiply the passive pressure by the vertical area along the slab’s perimeter in both the slab’s local z and local x direction. This passive force will then be added to the sliding resistance due to friction in the Safety Factors spreadsheet.

In the below example we have a 10’ x 10’ x 1’-0” slab and we have set a passive pressure of 0.25 ksf.

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The sliding resistance due to passive pressure in one direction would therefore be equal to 0.25 ksf x 10’ width x 1’ depth = 2.5 kips. This would be added to the sliding resistance due to friction which is equal to 0.145 kcf x 10’ x 10’ x 1’ x 0.3 = 4.35 kips. Total resistance = 2.5 kips + 4.35 kips = 6.85 kips. We can confirm this within the Safety Factors spreadsheet.

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