Historic Wood Truss

[Greatone76]

I have an existing building built in the early 1900's (I believe) that has what appear to be wood roof trusses. They are spaced 13' o.c. and span around 48'. The typical truss is around 6' deep and the top and bottom chords are (6) 2x11's. Between them are webs that make an X at 45 degrees which are (8) 1x8's. The web members and chord members appear to alternate and be connected that way. When I first saw them I didn't want to consider them a truss due to the unconventional web configuration and tried to get the bottom chord carrying an attic load and top chord carrying the roof load to work, but they were no where close to working, so it would appear that they would have to work as a truss to work at all. So after doing a little searching I'm seeing picture of old timber truss bridges with this non conventional X web configuration. Has anyone ever encountered this type situation in a building. I'm still hesitant to look at it as a truss, but looking for input from anyone on my situation.

 

[jayrod12]

Pictures would help. The key would be the connections at the joints I would think.

 

[KootK]

I'm sure that it was intended as a truss and you'll probably need to treat it as such to make a go of it. I've run into a similar configuration in a building steel truss before. Connection evaluation probably won't be much fun.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Greatone76]

Attached is a pic. I have other pics and from the outside I'm seeing like 5 nails connecting the webs to the top chord. Again I don't know if that is the consistent or how to look at the different layers. That is one of my concerns even if I figure out how to analyze it and get members to work what do I do with the connection points.

 

[Greatone76]

Attached is a graphic detail of the typ truss.

 

[JAE]

I vote its a truss.

What is the focus of your effort on this? Are the trusses failing or something?

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[Greatone76]

My basic thought right now is that I don't have enough information to perform a full analysis. I don't feel comfortable with the connections and web configuration to go forward with a truss type check.

 

[KootK]

I'm not put off by the web configuration. That can be analyzed easily enough. For the connections, perhaps you could approach it by telling the owner that, no matter what your analysis results, you'd need to remediate the connections in order to give it your blessing. With that knowledge in hand, the owner can decide if they want to proceed. If all you can see is some nails through the outer ply, about the best you could do would be to assume (somewhat riskily) that each ply is nailed that way.

For joint remediation, perhaps you could install drift pins etc through the joints. Octuple fastener shear should work wonders.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SlideRuleEra]

A simplified form of Ithiel Town's (patented c. 1820) Lattice Truss, used in covered bridges:

Edit: For general guidance on how to analyze a Town Truss see pages 12 thru 21 at this link: Structural Analyses of Two Historic Covered Wooden Bridges

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[JAE]

What is the focus of your effort on this? Are the trusses failing or something?

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