Pole Barn Truss Raising

[bglass]

I am in the process of building a pole barn, and am considering different methods of raising the roof. I have seen a pole barn roof constructed on ground level, then winched into place.
I didn't actually see this done, but drove by on my way to work and the truss/purlins etc were all framed up around the poles on ground level. I saw a boat winch hanging from every gable pole. When I came home from work the whole thing was in the air.
This would seem to have some advantages. The option of raising trusses individually requires getting them back in plumb then tying them together with purlins while 20' in the air. I am thinking about getting some help and am worried about someone falling.
Problem: I havent been able to find anything about this method of construction - pitfalls etc. Any input?

 

[evelrod]

Well, I have been around a long time as has this method of erection. Talk about your "backwards engineering"!!! The last time I saw this done was in Baja, Mexico on Rosarita Beach. Not exactly a cost effective method in the U.S. where labor is a great deal more expensive. The good part is that it DOES work on smaller buildings but even then the final connections are really tough to make. It also requires a great deal of skill in the original layout---something, in my experience, lacking in many of the companies doing "pole barn" type of construction. I did a couple of "pole barns" when I was a kid in Texas but, we built them in "bents" and tilted them up individually then pulled the purlins up on hand lines (ropes) one at a time. Hard work but quite fast and NOT labor intensive. No need for fancy rigging or cranes. Just a fork lift or an "A" frame truck.
Also refer to R. Buckminster Fuller, Geodesic Domes, Temcor Inc., Spruce Goose Long Beach 1982, etc. for some different configurations of this "build down" technique.

http://www.northeastaquastore.com

re. geodesic dome construction.

Rod

PS---If your ever in the Los Angeles area you might stop in at the Powell Library on the UCLA campus and check out the huge collection of photos during the construction of the campus in the 1920's/1930's. A real eye opener!

 

[bglass]

Thanks for the reply...
I am wondering why you think this would be more time intensive.
I can see the added cost of building some sort of rigging for the post tops and the winches/chain hoists. This would be somewhat offset by the cost to rent a fork lift.
I once rigged up a fairly large superstructure with hydraulic cylinders and raised it the 6" necessary... sort of like set of camper jacks. It worked pretty well, this seemed like a similar problem.
Interesting link you sent, I may opt for the more conventional approach. Sometimes convention is driven by experience.

 

[Escher]

I know of a builder (here in Australia) who built all his roof frames on the concrete slab on ground. He installed all the concrete roof tiles except for a few and installed long-stroke hydraulic jacks (the jacks poked through the missing tiles) and raised the lot in one go. THEN he installed the walls below and dropped the roof onto it. The problems are ones of alignment (vertical & horizontal)and safety.

Some months ago a Contractor I am connected with did the same thing; but in reverse. Built a concrete basement slab over the harbour and lowered it into the water to provide a below water level carpark. Required many jacks and checks during lowering.

Also it has been standard practice here and New Zealand to build timber portal frames on the ground and lift the roof as a whole with cranes in one go (but generally not wth the roofing on).

Jim