Final answer:
After calculating the stress on the soil caused by the load on the footings, it is determined to be 3686.28 psf, which exceeds the allowable soil-bearing pressure of 2500 psf. Therefore, the existing footings are not adequate to support the load.
Step-by-step explanation:
The question at hand involves determining if the existing footings are adequate to carry the load imposed on them by the columns of a building which are subject to a dead + live load of 45,000 pounds.
To evaluate the adequacy of the footings, we must calculate the stress on the soil and compare it to the allowable soil-bearing pressure provided by the soil report.
To calculate the stress, we divide the total load by the area of the footing: footing area = 3 ft 6 in. × 3 ft 6 in.
Converting these measurements to inches, so we have all units in pounds per square inch (psi), we get a footing area of 42 in × 42 in = 1764 in².
The resulting stress on the soil is the load divided by the footing area:
stress on the soil = 45,000 pounds / 1764 in² = 25.51 psi or 3686.28 psf (by converting pounds per square inch to pounds per square foot, where 1 psi = 144 psf).
The estimated allowable soil-bearing pressure is 2500 psf, which is less than the calculated stress of 3686.28 psf.
Therefore, the existing footings are not adequate to carry the load as they exceed the allowable soil-bearing pressure for sandy soil.