Section 1905 addresses the design of footings, which are the foundation elements transferring building loads to the soil. Footing width is determined by dividing the total load by the allowable soil bearing pressure. A building with 100,000 pounds load on a footing with 2,000 pounds per square foot bearing pressure requires minimum 50 square feet of footing area. Square footings are more efficient than rectangular, so a 7 by 7 foot footing is selected. Footing depth must be below the frost line to prevent heave from frozen soil. Most frost lines range from 2-5 feet depending on climate. Footings must be cast on undisturbed soil or properly compacted fill material verified by the engineer. Reinforcement in footings provides tensile strength and is typically 1 layer of bars running both directions. Footing thickness is determined by shear and punching shear calculations. Concrete strength is typically 3,000 pounds per square inch for most residential and commercial buildings.