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Truss Load Capacity

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Forum topic by kramttocs posted 05-26-2014 04:20 PM 2771 views 0 times favorited 22 replies Add to Favorites Watch
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kramttocs

6 posts in 923 days


05-26-2014 04:20 PM

I’ve been looking around online for similar topics and found this one: http://lumberjocks.com/topics/43029 where everyone seemed to know what they were talking about :)
Had a situation where I needed to lift a piece of equipment to load on a trailer and thought having an overhead winch would be useful.
Was wondering if spanning a pipe over several of the rafters would be able to handle any significant load (like 500-600lbs)?
My barn is 40×60 with the rafters on 24” centers. If it is possible, I would put the pipe about 5 feet from the wall.
I’ve attached some images but will gladly provide any additional information that might help. Based on what I have been reading, I suspect the answer will be that it would be a bad idea.


22 replies so far

View CudaDude's profile

CudaDude

176 posts in 1770 days


#1 posted 05-26-2014 04:38 PM

Well I’m certainly no engineer, but I don’t think it matters how many rafters you span the pipe across. The rafters on each side of the load are going to bear all the weight. I think it’s a bad idea. Try checking with your local auto parts house. Ones around here used to rent out engine hoists for just a deposit and then you get that back when the tool is turned back in.

-- Gary

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kramttocs

6 posts in 923 days


#2 posted 05-26-2014 04:43 PM

Thanks Gary! The two rafters bearing it all makes sense and one nay is enough for me to not risk my roof.

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firefighterontheside

13458 posts in 1318 days


#3 posted 05-26-2014 04:56 PM

I guess you’ve already decided not to do it, but I think you could do it and be fine. I’ve seen some pretty big carpenters during construction standing on one bottom cord and not causing the thing to fall. You could use something like a 6×6 and actually distribute the load to several trusses. I’m no engineer and you will probably not find something to tell you how much weight the bottom cord will support, because it was not designed for that. Do what you feel comfortable with though.

-- Bill M. "People change, walnut doesn't" by Gene.

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REO

889 posts in 1536 days


#4 posted 05-26-2014 09:22 PM

if the roof is high enough put a spanner between two on one end and two on the other end in the crotch where the members meet. then hang the pipe between the two from the center of the spanners. make sure you pick up the load between the centers of the middle two this will exactly distribute the load between four trusses. that would be less than 150 pounds per truss. as has been said most contractors weigh more than that. the problem with throwing the beam or pipe between the top and bottom chord is that under load the beam flexes and does not deliver a distributed load across the span.

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kramttocs

6 posts in 923 days


#5 posted 05-26-2014 10:04 PM

Thanks guys. After the votes of confidence, I am back to entertaining the idea of doing this. The spanner approach makes sense and getting it down to 150 per truss isn’t worriesom.
With the same idea (the roof is 11’ high to bottom of truss) since I am not wanting to life anything that high, would another layer cut it down more? So to use REO’s example:

(Assume everything is equally spaced)

Is it correct that this would be down to 100/truss given 600lbs?

View kyscroller's profile

kyscroller

44 posts in 1355 days


#6 posted 05-26-2014 10:18 PM

Most trusses that support metal roofs are designed for a 20lb live load and at most 10lb ceiling load per sq ft. I design trusses everyday. I wouldn’t do what you’re thing of doing. The trusses are not designed for the exter load even if you distribute it over a few of them. May want to think about making a tripod setup or making a setup like a swing set but supporting the legs so they won’t spread when the load is lifted. Bolt everything together and don’t use screws. They are too brittle.

View thetinman's profile

thetinman

294 posts in 1000 days


#7 posted 05-26-2014 10:26 PM

It appears from your pics that you have scissors trusses on the wall and out some distance where they transform into center span trusses. If this is the case I don’t see any reason the scissors can’t carry a total load of 500 lbs spread out across 3-4 trusses as others have described. I personally think even more weight could be lifted. The scissors are at an angle. That’s important because it means that the wall itself is carrying part of the load. I’m not going to get all nerdy here so to keep it simple – if the angle was 45 (I know it’s not) ½ the weight would be on the truss members and the other half directed to the wall. Your angle is steeper so more weight is angled to the wall and less “sag” weight is on the truss.

I’ve lifted the back end (engine end) of a 2400 lb golf course greens mower by spanning only 2 horizontal trusses and let it hang for 1 ½-weeks waiting for parts. Call that a 1200 lb lift. Frankly I was nervous about it but had no other options. Worked fine. I wouldn’t hesitate to do what you are talking about – simply lifting loads from time to time. That’s just me and I offer it for what it’s worth.

Heck, you’r get more weight than that if you drywalled the ceiling.

-- Life is what happens to you while you are planning better things -Mark Twain

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REO

889 posts in 1536 days


#8 posted 05-26-2014 10:45 PM

HEY! how did you get that to work? I tried the same EXACT approach to a diagram and it came out all scrambled!
The truss loads are per square foot. take the span times 30 (sum of live and ceiling load) and you get the load that the truss is designed to carry bearing on one end since the trusses are 24” OC. point loads are not so neat and tidy but you have plenty of cushion In my opinion.

View kramttocs's profile

kramttocs

6 posts in 923 days


#9 posted 05-26-2014 11:03 PM

You get all the credit for that diagram for sure :)
Yours came through the email and I assumed you edited it out of the post but wasn’t sure why….until I tried to do it myself and quickly understood.
So I took a screenshot, threw it in ms paint, and inserted the image.

I really appreciate everyone’s input on this question. While I lean towards it being able to handle it without issue, there’s always that ‘what if’ factor. My dad’s a good welder so building a sturdy and portable swing set setup seems to safest route.

View Jimbo4's profile

Jimbo4

1432 posts in 2224 days


#10 posted 05-27-2014 01:09 AM

Firefighterontheside has the right answer. There are several different truss designs – some distribute loads to the outside walls, some designed to hold weight, i.e., attics. The ones you have pictured are outside load bearing trusses, not for hanging items from them.

-- BOVILEXIA: The urge to moo at cows from a moving vehicle.

View AlaskaGuy's profile

AlaskaGuy

2406 posts in 1771 days


#11 posted 05-27-2014 02:06 AM

I did a Google search. I found this said several times. “Trusses are typically designed for about 10PSF on the bottom chord. That’s to allow for drywall, insulation, and misc. loads”.

Is it worth the chance?

-- Alaskan's for Global warming!

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kramttocs

6 posts in 923 days


#12 posted 05-27-2014 03:10 AM

Nope :)
After looking at gantry cranes they fit the bill perfectly and offer a lot more flexibility.

I’ve learned a lot from this thread. Thanks all!

View woodchuckerNJ's profile

woodchuckerNJ

1153 posts in 1095 days


#13 posted 05-27-2014 03:19 AM

You don’t state where you live.
If you live in a northern climate, you already have experienced snow loads.
More than 500lbs.

Just some info.

-- Jeff NJ

View bigblockyeti's profile

bigblockyeti

3668 posts in 1182 days


#14 posted 05-27-2014 03:24 AM

You should be fine depending on where in the country your pole barn is. If it’s where snow is possibility and whom ever designed it to meet code, the trusses by default have to support a much greater load than they are normally loaded to with nothing on the roof. Whatever you place against the bottom of the trusses, it would be a good idea to attach it by means of all thread or something similar running to close to the very top of the truss, effectively loading the top instead of just pulling on the bottom. I have seen this done many times with a lightweight tall section I-beam supporting a beam trolley to move heavy things along a single plane in a building. One other consideration is having the pipe or beam substantial enough to distribute the single point load to all of the trusses and not with the vast majority being placed on the truss closest to that load.

View Paul's profile

Paul

721 posts in 1027 days


#15 posted 05-27-2014 04:51 AM

Kiss!
Keep it simple stupid!

Not directed at anyone, have you considered a 1 ton shop crane? HF sells one cheap.sounds like it should fit the bill at under $200.

Paul

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