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Roof truss connectors

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It must be remembered that the roof diaphragm provides support for the 
building's walls with the pressure on one half the height on the windward 
side and the suction on one half the height on the leeward side being carried 
(supported) by the roof diaphragm.

For a sloped roof where the suction on the windward slope is equal to the 
suction on the leeward slope, both of which act normal to the roof surface, 
the horizontal components *do* cancel out, but the reactions from the 
walls are additive.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Imran Khan wrote:

. > 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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