CHAPTER 4 - Rigid-Jointed Frames

Abstract

This chapter focuses on rigid-jointed frames. In a triangulated frame, any set of loads, provided all loads act at joints, could be supported in equilibrium by a system of internal forces acting as axial loads in the members without any bending action. Non-triangulated frames will support certain load systems also in this way, but only if the load systems are suitable. The behavior of frames so loaded is similar to that of triangulated frames statically determinate in their primary stresses, buckling modes being theoretically possible at a series of critical loads. The essential difference from triangulated structures is the incidence of sway modes involving the translation of one end of a member relative to the other. This chapter describes the calculation of critical loads of this type of frame. A frame that sustains the applied loads entirely in axial compression or tension is structurally the most efficient, but it is not possible so to support any arbitrary combination of joint loads acting on a rigid frame. The chapter also explores multistorey single-bay portals.