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RE: Roof truss connectors

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What seismic zone are you in?  If you are in a high risk zone, have you
considered the tributary area of the masonry wall connected to the roof
diaphragm? If I recall, the minimum connection the diaphragm must make
to the wall (forces normal to the wall) is 285-plf or approximately 30%
of the lateral weight of the wall tributary to the roof truss (1/2 the
story height plus the parapet depth times the truss spacing). I would
think that if seismic was an issue, it would not unreasonable to develop
1500 pounds of shear in each truss - but then I have not run the
numbers. The load normal to the masonry wall is generally high enough
that the spacing of anchors lies between each truss and the diaphragm
then connects to the truss connection at the ledger or point of bearing.

Just a few thoughts.

Dennis S. Wish, PE
California Professional Engineer
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-----Original Message-----
From: Imran Khan [mailto:ikhan40(--nospam--at)hotmail.com] 
Sent: Wednesday, December 12, 2001 11:31 AM
To: seaint(--nospam--at)seaint.org
Subject: Roof truss connectors

I am designing a masonry building with a gable roof made up of cold form

roof trusses. The roof pitch is 5/12 and roof deck acts as a diaphragm
to 
distribute the loads to the end walls. The code is ASCE7-95.

I am concerned about the connectors between the truss and the wall. The 
truss mfr has submitted a load summary sheet from his in-house program
which 
shows lateral loads as high as 1500lb from roof trusses. The trusses are

classified as component and cladding.

I believe there should be no lateral loads if the truss is treated as a 
component. To obtain lateral load I claculated the pressures using MWRS.

When wind is perpendicular there is suction on both sides (no net
lateral 
pressure) and only 400lb lateral when wind is parallel.

I expalined this to the truss mfr but he claims that nobody has raised
this 
issue before.

Also when I claculate the the net lateral from the roof and the walls do
I 
evenly distribute that load to the connector at each end of truss.





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