The bilinear quadrilateral element offers a bilinear displacement approximation where the displacement within the element is assumed to vary bilinearly (linear in two directions within the element). It is usually easier to discretize a domain by using triangular elements however, when the domain to be discretized has a regular shape, quadrilateral elements can be used to offer a more regular displacement discretization, which, in some cases, might offer a better approximation to the displacement shape. Quadrilateral Elements Quadrilateral Elements Linear Quadrilateral Elements Open Educational Resources Two Dimensional Solid Elements: