Parallel chord vaulted truss to span 80ft, freespan 1

[fastline12]

We are going to start work on a shop building for our own needs. Due to local taxes and modular ability, we decided to build an all wood building. We need a parallel chord vaulted truss and plan to design the structures, then have another PE bless and stamp. Trusses is not our line of work.

This looks to be a very common I beam type load with tension compression and the thought came to mind if doubling up a pair of trusses could better protect us on buckling? Anyone with experience with these trusses care to give me some thoughts on a direction to go with this? We are trying to avoid adding steel to the trusses but that is not totally out of the question. We will require design snow down load of 21 psf.

 

[dik]

Talk to a local wood truss fabricator... you will likely get the trusses for about the same price that you can pick up the lumber for, or slightly greater, and they may be able to provide you with sealed drawings.

Dik

 

[fastline12]

Thanks, we have quoted a couple designs locally and looks like the price will be roughly double or approx a 15K savings. We have built trusses before and have a plate press. That being said, plating might not be enough for a truss like this.

 

[TXStructural]

While this is within the capability of a plate connected wood truss, you should employ a proper designer, since very few independent engineers know the complications with these trusses, which use very slender members.

If you really want to design it yourself, get a copy of TPI's publications and get up to speed on the NDS. You will have to determine the stresses in the plates and select plates based on these forces. How the plates are positioned and the grade of the wood also controls the capacity.

Having spent a year redesigning and overseeing repairs on a improperly designed, plate connected wood truss building, I can assure you that having a PE truss designer on the project is the only way to go. Ironically, what took us a year to fix would have been avoided if the owner had hired the engineer who wanted $15k to do an initial design.

 

[hokie66]

Why do some people, even engineers, think structural design is so simple?

fastline12,
You are listed as an aerospace engineer. There is a lot of structural engineering involved in the design of aircraft, but those of us who design buildings and bridges would never think of designing something that flies. So why do you want to do this?