Tangent Stiffness in Plane Frames

With reference to planar framed structures, a tangent stiffness matrix is derived that does not require any approximation beyond those used in the conventional beam-column theory. The matrix is given in such a form as to clearly separate the contributions of large rigid body displacements from elastic and locally nonlinear effects, and its numerical evaluation appears to be routine. Possible approximations, analogous to those used by previous investigators, are also examined.