FLEXIBLE BEAM-COLUMN JOINTS

ABSTRACT Engineering students learn to analyze beams with fixed or pinned ends. A fixed end transmits moment but does not allow rotation of the end. A pinned end allows rotation but does not transmit any moment. Neither end condition is fully achievable in practice. In 1986 the American Institute of Steel Construction (AISC) specifications defined two types of construction; Type FR (Fully Restrained) and Type PR (Partially Restrained). When Type PR construction is used, the effects of joint flexibility must be considered in the design and analysis of beam to column connections for example. Kishi and Chen [1] presented analytical procedures and data for several types of beam-column joints. Their results included both the initial stiffness and the ultimate moment-rotation characteristics. Abolmaali and Razavi [2] addressed these same beam-column joints by developing web-based FEM meshes for use in the analysis and design of these structures. In this paper a simple analytical approach is taken to show how the flexibility of the beam's ends effect the maximum bending moment, maximum deflection, and the fundamental bending natural frequency. The beam's ends are considered restrained by linear rotational springs. Results are presented for several beam-column connections using the initial stiffness data from Kishi and Chen [1]. INTRODUCTION In any engineering course on "Strength of Materials" basic beam analysis employs several idealizations. Two of these have to do with end supports. A pinned end support is idealized as frictionless and thus cannot support an end moment. A clamped or fixed support is idealized as infinitely rigid supporting a moment but not allowing any rotation. Neither of these idealizations is fully realized in practice. The purpose of this paper is to analyze the effects of variable rotational constraints on the moments, deflections, and natural frequencies of single span, uniform beams