Behavior and Modeling of Semi Rigid Steel Beam to Column Connections.
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Date
2007-09
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Addis Ababa University
Abstract
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.
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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
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Keywords
Column;Connections