In the preceding examples, we have used the simplifications that single-wythe panel walls can be designed assuming that the entire load is resisted by vertically spanning strips, and that two-wythe panel walls can be designed assuming the entire load is resisted by vertically spanning strips of the inner wythe. It is now appropriate to consider the theoretical basis for this simplification. We first consider the simplification of wythes as crossing strips using the strip method, and then derive additional simplifications based on the relative stiffnesses of those strips. Consider the differential equation for the out-of-plane deflection of an elastic plate with a uniformly distributed, out-of-plane load:
