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RE: Shear Tabs (was RE: seaint Digest for 27 Jul 2004)

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Mark,
 
The checker's concerns could probably be addressed by using a more ductile connection like the double clip angles as someone has already suggested. Shear tabs connected to rigid supports (column flange or heavy girder web) will build up considerably more end moment than most other simple shear connections.
 
Alternatively, if you are sure you want shear tabs, then the moment transferred to the girder by the shear tab can be reduced by using a double row of bolts and/or short slots. Also be sure not to exceed the maximum allowed tab thickness to ensure tab yielding and rotational ductility. The tab should be as light as possible.
 
Understand that shear tabs, like all simple shear connections, are designed to yield and rotate under initial loading so that they behave the way they are modeled (as frictionless pins). This is accomplished by yielding of tab, short slots, and bolt shear deformation, resulting in an initial permanent deformation of the connection and strain hardening of the yielded steel.
 
The torsion transferred by a properly designed simple shear connection should be negligible after initial loading and yielding. That's why they are called simple shear connections.
 
To be fair to the checker, a shear tab connected to one side of a girder web is usually considered a flexible support condition. This means that initial deformation of the shear tab may not occur as intended. Instead, torsion will be transferred into the supporting girder. In your case, the girder could probably be considered restrained by the concrete deck allowing the shear tab to perform properly and resulting in negligible moment transfer.
 
Christopher A. Banbury, PE
Vice President
Nicholson Engineering Associates, Inc.
7468 Horse Lake RD Brooksville, FL 34601
(352) 799-0170 (o)  (352) 754-9167 (f)
www.nicholson-engineering.com
 
 
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From: Mark Gilligan <
MarkKGilligan(--nospam--at)compuserve.com>
Subject: seaint Digest for 27 Jul 2004
To: "INTERNET:seaint(--nospam--at)seaint.org" <
seaint(--nospam--at)seaint.org>

I have a steel structure with a simply supported wide flange girder
adjacent to a stair opening.  The loads from the beams come primarily fro=
m
one side and are transfered using a standard AISC shear tab connection. =

There is metal deck with concrete fill on top of this girder.  =


The plan checker is asking me to address the torsion on this beam.  My
practice has been to not explicitly address torsion in these cases since
whatever torsion there may be will be self limiting.  While the beam may
initially apply a torsion to the girder, if the girder attempts to contin=
ue
to rotate, the beam to girder connection and the beam stiffness will act =
to
resist any torsion.  ACI specifically addresses this situation in ACI 318=

but I do not believe that AISC does.

I am trying to figure out a polite answer other than "NO", that will not
take too much time.  Probably the best answer would be to reference a
position by AISC.   Input would be appreciated.


Mark Gilligan