analyzing old parallel chord roof truss with 1x6 webs and 2x4 chords

[charliealphabravo]

I am looking at a set of parallel chord roof trusses on a commercial building (perhaps 50's or 60's era) in west central Alberta. The trusses are 50" deep and span 30 ft at 24 inches on center. The connections are nailed with what looks like 8d or 10d nails without gusset plates.

This is my first time encountering trusses with 1x6 webs so I'm mainly just wondering if anyone has seen these before and can tell me anything about the history of their use. Someone (a contractor) has taken it upon themselves to add roof-over construction and there is a concern that the roof may be overloaded now. To make matters worse the new joists now bear at the center of the old trusses which once carried the roof load uniformly.

I guess I am wondering if a computational analysis of the trusses would add any information to the problem. In view of the age and light framing members used and the unknowns related to the connections, perhaps any increase in load should be discouraged and presumed deficient.

TIA

 

[msquared48]

1X6 web members means using them as tension only members. I strongly suggest that uplift was not considered, nor any uneven snow loading, to include drifting.

I think a formal, updated analysis is fully warranted here.

Mike McCann, PE, SE (WA)

 

[woodman88]

They are from before my time, but I would not increase any loads on fifty year old wood frames. Or even state that they are still structurally safe.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[manstrom]

Sounds like a new roof may be in order.

I wouldn't trust it. I doubt you could make the connections work. I would bet that it was field framed with no engineering involved.

 

[XR250]

I agree with Manstrom. Put it in a 2d frame program to see how bad it is - prolly not even close.
Is is possible to add some interior girders? The webs would likely have to be reinforced due to the stress reversals, however.