Browsing by Author "Wondimu, Temesgen"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Behavior and Modeling of Semi Rigid Steel Beam to Column Connections.
    (Addis Ababa University, 2007-09) Wondimu, Temesgen; Taye, Sjifferaw
    In most steel frame designs the beam to column connections are assumed to be rigid or pinned. Rigid joints, where no relative rotation occurs between the connected members, transfer not only substantial bending moments, but also shear and axial forces. On the other extreme, pinned joints are characterized by almost free rotation movement between the connected elements that prevent the transmission of bending moments. Despite these facts, the great majority of joints doesn’t exhibit such idealized behavior. A substantial effort has been made in recent years to characterize the behavior of semi rigid connections. Most design codes included methods and formulas to determine both their resistance and stiffness. EC3 and EC4, for instance, allow the use of springs attached to the end of the beams at both sides of the joints. In order to account for the panel shear deformation the code allows the use of interaction parameter, called the β factor. But since the definition of the β factor implies an approximation of internal forces at the joint, it requires an iterative process at the time of the global analysis of the structure. In order to avoid this iterative process various researchers proposed new elements accounting for various deformation modes of the connections. Although the new proposed element by Bayo et.al accurately characterizes the behavior of semi-rigid connections based on the EC component method it is not appropriate to use in commonly available software. In this thesis a new component-based two-node-connection element is proposed. By using the proposed two-node element the static and dynamic response behaviors of a semi-rigid frame as compared to a rigid frame of the same geometry and cross section are studied using a general purpose finite element package ANSYS. The study showed that connection flexibility tends to increase vibration periods and hence reduces the internal stresses due to a given earthquake action in the frame elements as compared to those in rigid frames. 12 CHAPTER ONE 1.1. INTRODUCTION Traditionally, steel frame design assumes that beam-to-column joints are rigid or pinned. Rigid joints, where no relative rotations occur between the connected members, transfer not only substantial bending moments, but also shear and axial forces. On the other extreme, pinned joints are characterized by almost free rotation movement between the connected elements that prevents the transmission of bending moments. Despite these facts, it is largely recognized that the great majority of joints doesn’t exhibit such idealized behavior. This is explained by the fact that in semi – rigid frames the internal force distributions, lateral displacement magnitudes, collapse modes are functions of joint flexibility. Extensive studies have been carried out over the past twenty five years to estimate the actual behavior of such joints. Innumerable studies have been produced on composite and steel semi-rigid connections, covering the state of the art [1], numerical studies and experimental tests [2 - 8]. The fundamental results of these investigations led to code specifications that provided structural engineers with adequate procedures to evaluate the moment rotation characteristics of semi rigid connections. A good example of this new design trend is available in Eurocode3 [17]. Despite the substantial increase in structural design knowledge, the semi-rigid connection design is still facing resistance from structural engineers. This is explained by: 1. Lack of detailed information on the advantages of semi-rigid design philosophy. Semi-rigid frame design has many advantages. These include: a. Economy