关键词: eigenfunction expansion method, two-dimensional (2D) elasticity problem, upper triangular operator matrix, general solution

Abstract: In this paper, we study the relationship between the number of redundant forces and the number of load conditions in a super-static truss without sick members in order to accomplish fully stressed design.This paper will not only improve the conclusion given by R. H. Gallagher et al., but also clarify the choice of load conditions (number, magnitude and form). Moreover,it will explain that some counter-examples in literatures are invalid.

Key words: eigenfunction expansion method, two-dimensional (2D) elasticity problem, upper triangular operator matrix, general solution