The implementation of general-purpose programs for the numerical analysis of plate and shell structures calls for the adoption of finite element stiffness expressions which take account of both lateral distortion and membrane action. It is particularly desirable that design-oriented programs of the above kind be perfectly general. In particular the element behaviour must be independent of the choice of base axes, and not prone either to singularities or to doubts over convergence with successive mesh refinement. Ideally the program should allow the assembly of relatively simple elements, oriented in any conceivable way and of any freely chosen shape. The present paper documents a procedure for obtaining stiffnesses for a three node element which satisfies the above requirements. Lateral distortion of such an element calls for curvature changes across its surface.
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