EFFECTS OF CONNECTION FLEXIBILITY AND PANEL ZONE DEFORMATION ON THE BEHAVIOR OF PLANE STEEL FRAMES (FRAME)

Conventional analysis and design of frames are usually carried out under the assumption that the rotational stiffnesses of the connections joining the beams to the columns are either infinite or non-existent. In particular, the AISC Specification designates three types of construction in its 1969 and 1978 editions: Type 1 (rigid-framing) construction assumes that the beam-to-column connections have sufficient rigidity such that as the frame deforms the original angles between intersecting members remain virtually unchanged. Type 2 (simple framing) construction assumes that the connections do not possess any moment resisting capacity in so far as gravity loading is concerned. Type 3 (semi-rigid framing) assumes that the connections possess a dependable and known moment resisting capacity intermediate in magnitude between that of Type 1 and Type 2 construction. In Type 2 construction, although the moment-resisting capacity of the connections are assumed non-existent when the frame is designed for gravity loads only, this assumption is obliterated when the same frame is designed for wind load. Recognizing the dilemma of having to assume pinned connection for gravity loads and rigid connections for lateral loads in Type 2 construction, the newly published Load and Resistance Factor Design (LRFD) Specification for Structural Steel Buildings designates only two types of constructions: Type FR (fully-restrained) construction and Type PR (partially-restrained) construction. Type FR and Type PR constructions are analogous to the aforementioned Type 1 and Type 3 constructions respectively. In this study, a large displacement second-order-elastic-plastic hinge plane frame analysis including the effect of nonlinear connection behavior and panel zone deformation is presented. An updated Lagrangian approach is utilized in the formulation. The nonlinear moment-rotation behavior of the connection is represented by an exponential function and the panel zone is represented by a finite element. The main objective of this study is to investigate the effect of the loading/unloading phenomenon of the connection on frame behavior and the moment transfer mechanism of flexibility-jointed frames. Further studies include the effect of connection flexibility and panel zone distortion on frame drift. Based on subassemblage analyses, design recommendations on flexibly-jointed frames will be presented