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re: variable pitch connectors[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: re: variable pitch connectors
- From: "Andrew Kester, P.E." <akester(--nospam--at)cfl.rr.com>
- Date: Wed, 5 Dec 2007 08:24:22 -0500
If you need uplift connectors already, and you have something that takes care of the sloped rafter issue and of the uplift reaction and shear load, then it would seem you would be killing two birds with one stone. Otherwise you may need a mitred top plate and an uplift strap.
If you are trying to transfer shear from the roof deck diaph. into the shear wall you still need full depth blocking or cross bracing in the plane of the wall in between the TJIs. Even if the connector has a rated lateral or shear load, this is from my understanding always rated at the base of the connection at the top plate, not as if the load was applied to the top of the truss or rafter. For this to be the case it would have to be capable of resisting the effects of overturning of the member as well as a shear load applied to the top of the rafter/truss. Also, uplift and shear loads have to be checked in tandem as applicable.
This would include two possible cases depending on your structural system layout and MWFRS:
1) wind direction/pressure lateral to the walls causing a lateral out-of-plane force going from the wall into the connector into the roof AND uplift
2) wind direction/pressure parallel to the walls causing shear force IN-plane of the wall going from the roof diaphgram into the blocking or into the connector AND uplift
I usually use the blocking and nail it off to the top plate so that transfers the shear if possible, this keeps the shear load out of the connector so I can max the uplift capacity of the connector. It also totally depends on the connector and connecting member, as they all have very different allowable uplift and lateral loads.
Andrew Kester, PE
ADK Structural Engineering, PLLC
1510 E. Colonial Drive, Suite 301
Orlando, FL 32803
That is a very good question. It seems the variable pitch connectors
have allowable lateral loads, which, depending on the magnitude of the
diaphragm shear to be transferred, might eliminate the need for a
positive connection between diaphragm sheathing, blocking and the shear
wall. Nevertheless, there are various ways of providing shear blocking
between the TJI's, some easier than others. That would also hold true
for blocking over a beveled top plate and the type of eave shown by the
Doug Mayer, SE
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