6.3 Design of trapezoid-shaped footings The value of L must be known,and the area A will be based on the soil pressure and column loads(A=∑P/qa or∑Pu/qut). The minimum value of L is out-to-out of the column faces. When the end dimension a and b are found,the footing is treated similarly to the rectangular footing (as a beam)except that the "beam" pressure diagram will be linear-varying. The resulting shear diagram is a second-degree curve and the moment diagram is a third-degree curve. 6.3 Design of trapezoid-shaped footings ▪ The value of L must be known, and the area A will be based on the soil pressure and column loads ( A=∑P/qa or ∑Pu /qult). ▪ The minimum value of L is out-to-out of the column faces. ▪ When the end dimension a and b are found, the footing is treated similarly to the rectangular footing (as a beam) except that the “beam” pressure diagram will be linear-varying. ▪ The resulting shear diagram is a second-degree curve and the moment diagram is a third-degree curve