This paper presents a modified variational principle for the treatment
of thin plate bending on an elastic foundation. The foundation may be
of the Winkler or Pasternak type. A hybrid Trefftz (HT) finite-elemen
t (FE) model has been developed based on the principle and a new set o
f T-complete functions. The derivation of the new set of trial functio
ns is based mainly on the resolution approach of the differential oper
ator. Two numerical examples are considered to illustrate the correctn
ess and accuracy of the proposed formulation.