Steel in the News
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Posted by Kim Miller on May 5, 2009 at 10:21 AM.
The following papers appear in the second quarter 2009 issue of AISC’s Engineering Journal. EJ is available online (free to AISC Members) at www.aisc.org/epubs.
Design of Unstiffened Extended Single-Plate Shear Connections
Larry S. Muir and Christopher M. Hewitt
Extended single-plate shear connections offer many advantages that simplify the construction process. Because the connection to the supported member is moved clear of the support, coping of the supported member is not required, and the only fabrication process required for the supported member is drilling or punching.
Also, because bolted connections are only used in the connection to the supported member, there is no safety concern over the use of shared bolts through the web of the support. Additionally, in some instances, extended single-plate connections are the only practical solution to a framing problem, such as the case of a member framing into the weak axis of a column with continuity plates.
The rigidity of single-plate connections at the support has always been a gray area. Designers have often been concerned about a considerable, unanticipated moment that could be developed in the connection, which could then result in either a moment delivered to the column that the column has not been designed to resist, or a sudden rupture of either the weld or the bolts. Section B3.6a of the AISC Specification for Structural Steel Buildings requires that simple shear connections have sufficient rotational capacity to accommodate the required beam end rotation.
This paper will address each of these concerns, and will present a general design procedure for extended single-plate shear connections.
Topics: Connections–Simple Shear
Experimental Evaluation of the Influence of Connection Typology on the Behavior of Steel Structures Under Fire
Aldina Santiago, Luis Simoes da Silva, Paulo Vila Real, Gilberto Vaz, and Antonio Gameiro Lopes
The behavior of steel joints under fire loading is a subject that has only recently received special attention by the research community. In fact, as recently as 1995, the European pre-standard on the fire response of steel structures deemed it unnecessary to assess the behavior of steel joints under fire conditions.
This approach was supported by the argument that there is increased thermal mass at the joint area. However, observations from real fires show that, on several occasions, steel joints fail, particularly their tensile components (such as bolts or end plates), because of the high cooling strains induced by the distortional deformation of the connected members.
The main objective of this paper is to describe an experimental test program carried out by the Department of Civil Engineering at the University of Coimbra on a steel sub-frame in order to evaluate the behavior of various types of steel joints under a natural fire and transient temperature conditions along the length of the beam.
The tests were carried out on a purposely developed experimental installation that could reproduce the transient temperature conditions measured in the seventh Cardington test. The results of these tests provide invaluable evidence on how to design joints that are able to survive a fire.
Topics: Fire And Temperature Effects; Connections–Moment; Connections–Simple Shear
Shear Behavior of A325 and A490 High-Strength Bolts in Fire and Post-Fire
Liang Yu and Karl H. Frank
High-strength ASTM A325 and A490 bolts were tested in shear at temperatures up to 800 C (1,472 F). The shear strength showed a gradual reduction in both types of bolts as the temperature was increased above 300 C (572 F). Strength reduction factors for both types of bolts at elevated temperatures were obtained to provide a means of estimating the bolt shear strength during fire.
The residual strength of A325 and A490 bolts after exposure to elevated temperatures was also investigated by both direct shear tests and hardness tests. Significant strength loss occurs on both types of bolts after exposure to temperature higher than the tempering temperature employed in the manufacturing process. The hardness value at 1/2R location on the bolt cross section was found to provide a good estimate of the bolts’ residual strength. The hardness test provides a simple and practical method to assess the post-fire strength of a bolt.
Topics: Bolts; Fire and Temperature Effects