Hypercircle Bounds for Trefftz Elements. The Swansea Plate Triangle with Its Dual and Its Plane Stress Analog as an Example

Abstract . Bounding by the hypercircle method in FEM is costly in its original form, as it requires two independent approximate solutions, one with kinematically conforming and another one with statically conforming elements . It is proposed to supplement , say, a statically non-conforming element by a suitable shape function to static conformity and to seek tolerable bounds by a crude approximation to the supplement instead of a complete solution with the statically conforming element . The Swansea element , non-conforming in both respects , and its supplements to conformity are taken as an example.