MINIMAL ASSUMED MOMENTS AND OPTIMAL LOCAL COORDINATES FOR PLATE ELEMENTS BASED UPON THE COMPLEMENTARY ENERGY FUNCTIONAL

In most plate/shell elements founded on the complementary energy funct ional, the assumed moment spaces are not minimal. The reason of introd ucing additional moment modes is to build elements with sufficient sti ffness. A new method of using incompatible deflections to select the m inimal moment modes is attempted. A square 4-node and a square semiLoo f plate elements are derived. They are both stable and not overflexibl e. To generalize the elements for distorted geometry, three different local coordinates are employed. Unexpectedly, the skew coordinates for med by the convariant base vectors of the natural coordinates are leas t desirable.