Any structural engineers here?

Rebel74

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I am planning to build a 30x20or24 building that will be used as an exercise gym. One thing I need to find out, and for which I have searched the retardnets to no avail, is the answer to the following question:

With an open span of 20 feet plus I guess an 2 additional feet on each end for the supports, what size wood beam do I need to be able to support 3 120 pound heavy bags attached at evenly spaced intervals along the beam? So imagine two parallel walls, 20 foot of floor space between them, and a beam setting on top of the two walls spanning the open space between the walls. 3 heavy bags hanging from the beam with about 5 feet or so of space between them. I understand the pendulum load should be approx 2x the dead weight, so if each bag weighs 120 pounds, the pendulum weight should be about 240 pounds. So the total dead load would be about 360 plus the weight of the beam itself, and the "live load" (dynamic, pendulum load) would be about 720 assuming all three bags are swinging simultaneously. Adding a fudge factor of 1.5, this comes to about 1050 pounds live and 540 pounds dead (not including the weight of the beam). So how big a beam do I need? .

Obviously it needs to be mounted securely to the wall at each end, especially accounting for the "back and forth" forces and not just the "side to side" forces.

Any help would be appreciated. I have searched and searched and cannot find anything remotely approaching a knowledgeable answer on the glorious modern internet. 75% of the web results appear to be blog articles written by ESL speakers who are just regurgitating whatever they could scrape off the net from other ESL bloggers to create click bait no-real-answer webpages. The other 25% are people arguing about minor details without actually pointing anybody in the right direction or "span tables" that seem to assume the beam is going to be either a floor joist or roof rafter.
 

YY1

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I can't answer your specific question, but I have a Carolina Carport metal building with 30 foot open spans front and back made with 2.5" square tube trusses.

I have a full floor pan and a front bench seat along with several 1x6 and 2x4 long lumber stored up there, and a few battery chargers and hose and cord reels attached.
 

Hey-O

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You should check with your local building codes. That's who you'll answer to if it's wrong.
 

5.7 hemi

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I’d think 2x12, maybe.
 

eldubb440

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I slept in a Holiday Inn last night and still can't answer your question
 

Kern Dog

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You should check with your local building codes. That's who you'll answer to if it's wrong.
Those dipshits will likely say to contact an engineer. County officials have no balls. They want the liability on the engineering, not themselves.
They are like critics…. They only call out what they think is wrong but won’t stick their necks out to say what is right.
That is how it is here anyway…
 

1 Wild R/T

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Those dipshits will likely say to contact an engineer. County officials have no balls. They want the liability on the engineering, not themselves.
They are like critics…. They only call out what they think is wrong but won’t stick their necks out to say what is right.
That is how it is here anyway…
Didn't use to be that way but lawyers have changed the game...
 

Fran Blacker

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Buy an I-beam or at least check into it. Contact a company that sells I-beams. Do a cost comparison, wood and labor. Did my 28' X 28' darage used a 25 lb per foot beam. I did a flat roof only time I was nervous was when there was 30" of snow on it.
 

Hey-O

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Those dipshits will likely say to contact an engineer. County officials have no balls. They want the liability on the engineering, not themselves.
They are like critics…. They only call out what they think is wrong but won’t stick their necks out to say what is right.
That is how it is here anyway…
Where I live there is a building code standard and It's pretty easy to follow. To many variables to guess what's needed to support a given situation. Snow, rain , wind and what's going on inside.
 

Rebel74

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Where I live there is a building code standard and It's pretty easy to follow. To many variables to guess what's needed to support a given situation. Snow, rain , wind and what's going on inside.
Building codes? Snow, rain, wind, what's going on outside? This is a simple support structure meant to hold up punching bags. It isn't meant to be holding up a wall or anything. Building codes outline how to "properly" install a punching bag hanger in an outbuilding?

Anyway, I have discovered there are certain online calculators that can help calculate the strength of various timbers. I think though I will probably go with 3 posts stabbed into the ground and coming up through the floor, one for each bag.
 

Rebel74

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Buy an I-beam or at least check into it. Contact a company that sells I-beams. Do a cost comparison, wood and labor. Did my 28' X 28' darage used a 25 lb per foot beam. I did a flat roof only time I was nervous was when there was 30" of snow on it.
So did you decide that I-beams were better and more economical than trusses for the roof? I was thinking about a flat roof but I figured the cost would be greater than just getting four steel trusses and doing a simple gable roof?
 

Fran Blacker

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When I built (1988) my garage 28' 12" 25 lbs per ft. I beam cost $1000. Trusses couldn't be used would make roof to tall, added to the back of my house. A 28' free span with wood is it safe? I had 30" of snow the beam sagged about 1". Since then I do put a temporary column in the winter. I don't want a crushed convertible. Don't move cars in winter so it doesn't matter.
I'm not sure but beam guy think he said 25 lbs per ft. Think I told him give me a 30 lbs per ft. $125 more.
 

tak419

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Am I reading this correct, you're using the beam to support bags, not supporting any structural portion of the building such as the ceiling or roof ? Part of figuring the load you need to know where on the beam the bags will be placed. Even tho the bags aren't super heavy, the fact you're spanning 20' is a long ways to put something that is going to be bouncing around. You won't find a 2x12' that is 20' unless you special order it. You need to go engineered lumber (LVL). I would use 4-11.25" bolted together.
 

xs-ivv

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Those dipshits will likely say to contact an engineer. County officials have no balls. They want the liability on the engineering, not themselves.
They are like critics…. They only call out what they think is wrong but won’t stick their necks out to say what is right.
That is how it is here anyway…
You nailed it. These people must be the same everywhere. They wont approve anything that doesn't have an engineers stamp on it. Trying to get a simple answer out of them is like pulling teeth!
 

tak419

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You nailed it. These people must be the same everywhere. They wont approve anything that doesn't have an engineers stamp on it. Trying to get a simple answer out of them is like pulling teeth!
I'm only speaking on what I read and not arguing but it's not an inspectors job to engineer your project. Most are just hired hands with no degree of engineering. Their job is to read a chart or rules and let you know if you complied. It's mostly a money grab, but some is for lets say code, as in Fl so your roof doesn't come off as easy in a hurricane. If you put the liability on the county or city, every time something failed, such as your roof blew off in the hurricane, you'd have every ambulance chasing lawyer suing the county/city, and the tax payers would be footing the settlement.
 

xs-ivv

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I'm only speaking on what I read and not arguing but it's not an inspectors job to engineer your project. Most are just hired hands with no degree of engineering. Their job is to read a chart or rules and let you know if you complied. It's mostly a money grab, but some is for lets say code, as in Fl so your roof doesn't come off as easy in a hurricane. If you put the liability on the county or city, every time something failed, such as your roof blew off in the hurricane, you'd have every ambulance chasing lawyer suing the county/city, and the tax payers would be footing the settlement.
I dont expect them to engineer my project (and i certainly wouldnt want them to) but i do expect an explanation when plans are rejected, permits aren't issued etc. The amount of hoops to jump through and red tape is appalling.
 

mrhemi

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I dont expect them to engineer my project (and i certainly wouldnt want them to) but i do expect an explanation when plans are rejected, permits aren't issued etc. The amount of hoops to jump through and red tape is appalling.
I see you are in Ontario, some of the strictest (residential) building codes in North America.
 

Rebel74

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Am I reading this correct, you're using the beam to support bags, not supporting any structural portion of the building such as the ceiling or roof ? Part of figuring the load you need to know where on the beam the bags will be placed. Even tho the bags aren't super heavy, the fact you're spanning 20' is a long ways to put something that is going to be bouncing around. You won't find a 2x12' that is 20' unless you special order it. You need to go engineered lumber (LVL). I would use 4-11.25" bolted together.
I was just thinking. If I'm going to have steel trusses, spaced 10ft apart, that means I'd have four total. So I'm wondering if I could just run beams across those 10 ft spans, mounted to the trusses, and hang the bags from those? That would mean the support for the heavy bags was supported at 10 ft intervals, 5 ft open span on each side of each bag. I bet that would work. Either that or I'm just going to have to mount three posts into the flooring and mount the bags to a cross member on each post, or a metal mounting bracket on each post, whichever is easier...
 

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Hey-O

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Building codes? Snow, rain, wind, what's going on outside? This is a simple support structure meant to hold up punching bags. It isn't meant to be holding up a wall or anything. Building codes outline how to "properly" install a punching bag hanger in an outbuilding?

Anyway, I have discovered there are certain online calculators that can help calculate the strength of various timbers. I think though I will probably go with 3 posts stabbed into the ground and coming up through the floor, one for each bag.
I misunderstood the question, not needing it to help support the building. Any beam placed across the a 20 span that isn't tied to the ceiling with three bags is going to shake your building apart or at least come down on you. A doubled up 2 x12 will span 20 foot, but not with three bags being beat on. It will need to be tied off to the ceiling, "side to side" forces should be shared by using a 2x4x8 to tie several trusses together to absorb the force and one post in the center.
 
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