Tectum Decks at Diaphragms 1

[DHKpeWI]

I am working on a renovation to a building where a portion of the building is glulam arches, glulam rafters, and 3” tectum deck. The arches are approximately 16’-0” on center. The tectum deck has experienced water damage, and its ability to work as a diaphragm is suspect. One idea to stiffen the diaphragm is to add a metal roof deck above the tectum and rely on the metal deck alone to distribute lateral loads to the arches.
The question is whether the metal deck will be effective since it is supported by the soft tectum. The screws could potentially bend due to the 3 inches of soft tectum between the metal deck and the roof purlins. Roof deck attached to structural steel or steel joists provides a tremendous amount of diaphragm capacity, but usually there is no gap between the screws and roof framing members.
We want to avoid removing the tectum deck if at all possible. Any thoughts on how to get the diaphragm to work?

 

[ron9876]

Wouldn't count on steel deck screwed thru Tectum or on Tectum if you have much load.

 

[hokie66]

Tectum decks, as far as I know, never actually had verified diaphragm values.

You said glulam arches with glulam rafters. I assume this is a curved arch with glulam purlins going across the slope. What type curve and what are the overall building dimensions? Do the purlins frame into the side of the arches or sit on top? Spacing of purlins?

 

[MiketheEngineer]

Got a feeling that the Tectum needs to come off and be replaced with plywood or metal. How to insulate??

 

[DHKpeWI]

Thanks guys.

The portion of the building that has the tectum is approximately 14x 50', the purlins are spaced at 4'-0" o.c., and the frames at 16'-0" o.c. This portion of the building does not have much trib area subject to wind load. The purlins sit on the arched frames.

 

[hokie66]

In that case, you could provide cross bracing on the bottom of the purlins which would be continuous over the arches.

If the tectum is water damaged, it will not be safe to work on, so should be removed.

 

[TeraFirma]

Tectum Roof Decks have been tested in accordance with ASTM testing methods for diaphragm and wind shear.  The test report results are available by contacting the Tectum Inc. Technical Department.  A roof should never be attached directly to Tectum Roof Deck unless it is Tectum III or Tectum E.  In this case, please contact the roofing manufacturer for instructions on installing their roof over a Cementitious wood fiber deck.  The wet Tectum could be a problem, but not always.  You should look at the panels and look for deflection.  If there is more than a ? inch of deflection, that panel is bad and must be replaced before installing the roof.  For more info, contact Tectum Inc. directly at 888-977-9691