Residential Building Inspector B1Footings and FoundationsMedium
A geotechnical report indicates that the soil at a building site has a presumptive load-bearing value of 3,000 psf. The proposed continuous footing is 20 inches wide and will support a design load of 4,500 pounds per linear foot (plf). What is the calculated actual bearing pressure exerted by this footing?
- A3,000 psf
- B1,500 psf
- C2,700 psf
- D4,500 psf
Show answer & explanationAnswer & explanation
Correct answer: C. 2,700 psf
To calculate the actual bearing pressure, divide the design load per linear foot by the footing width (converted to feet). 4,500 plf / (20 inches / 12 inches/foot) = 4,500 plf / 1.6667 feet = 2,700 psf. This value should be compared to the presumptive load-bearing value.
Why the other options are wrong
- A. This is the presumptive load-bearing value of the soil, not the actual pressure exerted.
- B. This is incorrect; it might result from an incorrect calculation or misinterpretation of the values.
- D. This is the design load per linear foot, not the pressure per square foot.
Actual Bearing Pressure
Actual bearing pressure is the force per unit area exerted by a footing on the soil, calculated by dividing the design load by the footing's contact area.
- Calculated as Load / Area.
- Footing width must be in feet for psf calculation.
- Must be less than or equal to the soil's allowable bearing capacity.
Memory trick: Load on the foot, pressure's the root.