I need some engineering advice.

maulcruiser

maulcruiser

Well-Known Member
Joined
Aug 13, 2005
Location
Bladenboro/Wilmington, NC
Simply put, I need to know what size steel beam to use for a lean to. Excuse my crude drawing. I need to know what size horizontal beam to use for the 36' span. 800 lb dead load evenly distributed. Need more info? Please ask. No one locally wants to just tell me that size, and I'm not exactly wanting to overkill it.

20230313_105823.jpg
 
There's not enough information in the sketch to determine the loads. Even if there were, anybody qualified to answer the question will have to sign/seal it. You might get an answer from somebody who has a steel construction manual laying around, but again... not enough information to solve the problem.

Mind you, a 36ft span is long. You're looking at a deep/heavy beam just to carry its own weight.
 
maulcruiser said:
No one locally wants to just tell me that size
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Not to be a dick but....




The Graybeard engineer retired and a few weeks later the Big Machine broke down, which was essential to the company’s revenue. The Manager couldn’t get the machine to work again so the company called in Graybeard as an independent consultant.
Graybeard agrees. He walks into the factory, takes a look at the Big Machine, grabs a sledge hammer, and whacks the machine once whereupon the machine starts right up. Graybeard leaves and the company is making money again.
The next day Manager receives a bill from Graybeard for $5,000. Manager is furious at the price and refuses to pay. Graybeard assures him that it’s a fair price. Manager retorts that if it’s a fair price Graybeard won’t mind itemizing the bill. Graybeard agrees that this is a fair request and complies.
The new, itemized bill reads….
Hammer: $5
Knowing where to hit the machine with hammer: $4995
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The folks that will know what size beam that SHOULD be, will also hold that information close. Liability alone would be enough to bankrupt them if they gave "advice" and something went sideways.
 
I'm no engineer, but I am thinking the size of steel beam you'd need would be massive, expensive, and would need a hellova foundation fr the supports. So if metal is the way your set on, an engineered beam is your best bet.
 
Tear the plywood off the other beam and measure that?

Probably be better off getting a metal truss than an ibeam there. Or get the same size beam as you already have and space your posts the same distance the existing posts are.
 
braxton357 said:
In Wilmington you're going to have to factor in wind load too. Adding a column in the middle will save you a lot of height and a couple thousand. If this is inspected you will need a stamp anyway.
Cold-Formed Steel Beam and Column Load / Span Tables - CFSEI https://cfsei.memberclicks.net/assets/docs/designguides/3_loadspan.pdf
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Need to know what the loads actually are first. The 800# number is suspect. If you assume a simple span, don't know the loads from the existing structure and look only at the lean-to, it works out to 3psf, which ... sounds unreasonable.

1679497616676.png
 
shawn said:
Need to know what the loads actually are first. The 800# number is suspect. If you assume a simple span, don't know the loads from the existing structure and look only at the lean-to, it works out to 3psf, which ... sounds unreasonable.

View attachment 394243
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You right, and I'm assuming in actuality he's going to put new posts in to support the side against the carport too doubt the current wall is sufficient to support it.
 
36’ span?

So the lean-to is ~14’ wide and 36’ deep. Are you looking to have the 14’ beam sized? Or are you only wanting to add 2 columns, 14’ from the building to support the entire length of the 36’ deep lean to?

Dead loads and live loads play a huge factor in sizing. If you placed a center beam (or two) in the 36’ depth of the lean too, you can drastically reduce the member size.

Remember, wind uplift forces cannot exceed 200lbs per connection. So depending on your wind zone and looks like you are less than 5:12 pitch, then rafter/purlin spacing and connection type must be considered as well as anchoring the structure to the ground. Otherwise your lean to will end up on your roof come the first decent hurricane.
 
If I remember correctly, the beam on the loft of my shop is 33'1" span, 12" flange width, 1/2" flange thickness, 12.5" web height, 5/16" web thickness, and would hold a point load of somewhere around 20k pounds at the center of the span with about 1/2" of deflection. Based on those numbers, and using farm math, a heavy 12" tall I beam, or a lighter 14-16" I beam will have no problem with what you are wanting to do.
 
CasterTroy said:
Not to be a dick but....







The folks that will know what size beam that SHOULD be, will also hold that information close. Liability alone would be enough to bankrupt them if they gave "advice" and something went sideways.
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You're absolutely right. I have offered to compensate the few I have contacted. I was told they're booked out until May before they could provide an answer.

awheelterd said:
Tear the plywood off the other beam and measure that?

Probably be better off getting a metal truss than an ibeam there. Or get the same size beam as you already have and space your posts the same distance the existing posts are.
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Yes, I could remove the plywood and find that out. I was hoping to not destroy it to do that, but likely will be what I have to do.

rockcity said:
36’ span?

Or are you only wanting to add 2 columns, 14’ from the building to support the entire length of the 36’ deep lean to?

Dead loads and live loads play a huge factor in sizing. If you placed a center beam (or two) in the 36’ depth of the lean too, you can drastically reduce the member size.

Remember, wind uplift forces cannot exceed 200lbs per connection. So depending on your wind zone and looks like you are less than 5:12 pitch, then rafter/purlin spacing and connection type must be considered as well as anchoring the structure to the ground. Otherwise your lean to will end up on your roof come the first decent hurricane.
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The depth is 14' and 36' wide. I would like to attach the rafters to the existing beam on the carport and have the other end supported by the beam.

shawn said:
Need to know what the loads actually are first. The 800# number is suspect. If you assume a simple span, don't know the loads from the existing structure and look only at the lean-to, it works out to 3psf, which ... sounds unreasonable.

View attachment 394243
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I came up with 800 lbs by taking the approximate weight of the 2x8's and the weight of the corrugated metal, then halving it due to one end being supported by the existing structure. I overestimated this number, but I'm probably wrong. Figuring these numbers by the air dried weight of a 2x8x16 treated board (50 lbs), plus the approximate weight of the roofing material. Came up with approximately 1600 lbs total roof weight.

Thank you all for your responses! I wasn't pulling permits for this.
 
If I were building it in Greenville, I’d probably use a W16x31 with some 4x4x1/4” HSS columns with a 10x10x1/2” baseplate with 4, 5/8” anchor bolts with Hilti re 500v3, minimum 6” deep anchored into 4,000 psi concrete footer, 24” square, 16” thick with 2 mats of #5 rebar spaced 6” OC, EW, with 1” of 5 star grout under the baseplate and the foundation. I like to dry pack but pouring it works too.


I’m no engineer and this isn’t engineered. I take no liability if you decide to do it like I would. :D
 
rockcity said:
If I were building it in Greenville, I’d probably use a W16x31 with some 4x4x1/4” HSS columns with a 10x10x1/2” baseplate with 4, 5/8” anchor bolts with Hilti re 500v3, minimum 6” deep anchored into 4,000 psi concrete footer, 24” square, 16” thick with 2 mats of #5 rebar spaced 6” OC, EW, with 1” of 5 star grout under the baseplate and the foundation. I like to dry pack but pouring it works too.


I’m no engineer and this isn’t engineered. I take no liability if you decide to do it like I would. :D
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My alro price on that beam in 40' is $1300, really not as bad as I was thinking. 1200lb not all that bad either.
Should be plenty stout
 
rockcity said:
If I were building it in Greenville, I’d probably use a W16x31 with some 4x4x1/4” HSS columns with a 10x10x1/2” baseplate with 4, 5/8” anchor bolts with Hilti re 500v3, minimum 6” deep anchored into 4,000 psi concrete footer, 24” square, 16” thick with 2 mats of #5 rebar spaced 6” OC, EW, with 1” of 5 star grout under the baseplate and the foundation. I like to dry pack but pouring it works too.


I’m no engineer and this isn’t engineered. I take no liability if you decide to do it like I would. :D
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No liabilities expressed or implied. I make these actions on my own free will and accept all risks. Now the CYA is documented. I appreciate everyone's opinion or advice.
 
If you added some 45* gussets from your post to the 36' header beam, would that shorten your span and possibly reduce the size of the beam? In my mind that essentially cuts your span down some.

I have seen what I call "trailer house ibeam" used for things similar to this. It's usually 12" tall and a 3" flange. I have also seen them stich welded together on longer lengths to support bigger loads.
 
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