“…al. did not make reference to variational considerations, rather, it took a "direct" approach, in which direct consideration was given to conditions of equilibrium and compatibility. Consequently, the paper stimulated numerous efforts to develop formulations for stiffness influence coefficients for a variety of different types of elements (Turner, 1959;Clough, 1960;Melosh, 1961;Melosh, 1963;Clough and Tocher, 1965 (Mallett and Marcal, 1968;Przemieniecki , 1968;Zienkiewicz, 1971;Desai and Abel, 1972). The method has been extended to deal with three-dimensional geometries using sub and superparametric elements, curvilinear elements, and account has been taken of inertia effects.…”