Green Tractor Talk banner

1 - 20 of 42 Posts

·
Registered
Joined
·
2,965 Posts
Discussion Starter #1
I need to clear span 40' for a second story floor and want to do this with metal trusses.

Wooden floor trusses max out at 36', and require 12" OC spacing at that length. Not only is that too short, but it's a bunch of material to ship/handle.

My intent is to make (4) trusses that each support (18) 2x10's, with the outside wall holding the loose ends via a ledger of some kind.

My current design idea uses a 2x4x.125" top cord, (2) 2x2x.125" angle bottom cords, welded to 1.75x1.75x.125" square tubing diagonal webs, with 3x3x.125" vertical webs @ 24" spacing.

I'd then laminate the top cord with a 2x4 to provide a nailing flange for the subfloor.

Two questions: Would this be sufficient @ 18" web depth? If not, would it be @ 24"?

If not, what would I need to change?
 

·
Registered
Joined
·
4,947 Posts
Oh, my aching head

I need to clear span 40' for a second story floor and want to do this with metal trusses.

Wooden floor trusses max out at 36', and require 12" OC spacing at that length. Not only is that too short, but it's a bunch of material to ship/handle.

My intent is to make (4) trusses that each support (18) 2x10's, with the outside wall holding the loose ends via a ledger of some kind.

My current design idea uses a 2x4x.125" top cord, (2) 2x2x.125" angle bottom cords, welded to 1.75x1.75x.125" square tubing diagonal webs, with 3x3x.125" vertical webs @ 24" spacing.

I'd then laminate the top cord with a 2x4 to provide a nailing flange for the subfloor.

Two questions: Would this be sufficient @ 18" web depth? If not, would it be @ 24"?

If not, what would I need to change?
That calculation is why I decided that I didn't want to be an engineer. . . At one point, I could do it but just didn't want to. . .

Based off nothing except seeing similar beams in commercial buildings, I'd guess the 18" depth would be enough but I'll wait for the experts.

Treefarmer
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #3
:lol: I've seen online calculators for it, and am not sure what numbers to plug in to make it spit out something meaningful.

It's raining pretty good here, so I'm holding out for a break to go grab my notebook with prints.
 

·
Registered
Joined
·
814 Posts
your issue will be deflection no matter your construction.....you need to seriously consider your deflection criteria as it will control your design

at 40' i think your seriously undersized unless you want the floor to act like a trampoline

i think you really need to have a direct consultation with a PE to discuss your complete construction picture and the materials you would like to use as this is far beyond internet engineering there are a LOT of pieces to the proverbial puzzle
 

·
Registered
Joined
·
920 Posts
your issue will be deflection no matter your construction.....you need to seriously consider your deflection criteria as it will control your design

at 40' i think your seriously undersized unless you want the floor to act like a trampoline

i think you really need to have a direct consultation with a PE to discuss your complete construction picture and the materials you would like to use as this is far beyond internet engineering there are a LOT of pieces to the proverbial puzzle
I'm new here. I was fascinated to see if any of the membership was actually going to give major league engineering advice on this rather esoteric construction problem.
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #7
your issue will be deflection no matter your construction.....you need to seriously consider your deflection criteria as it will control your design

at 40' i think your seriously undersized unless you want the floor to act like a trampoline

i think you really need to have a direct consultation with a PE to discuss your complete construction picture and the materials you would like to use as this is far beyond internet engineering there are a LOT of pieces to the proverbial puzzle
I've been looking at flat roof trusses in all kinds of buildings around here (MN), and they have very similar construction short of the tubular top chord.

42psf live load is our snow load here.

Top and bottom chords will be attached at either end to a pair of cargo containers. No issues with buckling the attachment points.
 

·
Registered
Joined
·
814 Posts
no advisement being given just discussion...


jim your first post said "floor" ........floor loads are significantly higher than roof loads and are applied differently...again deflection is a issue

pulled out one of my old Steel Bar Joist books ...thought i would post a design chart from it ...since these are highly optimized designs they provide some implied information can be gleaned from it

#1 the joist type designation the first two numbers are the height of the joists in inches
#2 the allowable live load # in blue is based on L/360 defection
#3 the joist weight in # per/ft....if your assembly is not similar of heavier your not in the ball park

hope this helps slightly

ie i cant imagine your "blue" number to be under 200# and probably significantly higher....so looking at the chart ...that implys a 28" member that weighs 13# a running foot...how does that compare to your proposed construction is a question you need to ask yourself....this is a "optimal" chart and i picked the 41' length because it had the header at the top.....obviously i have a full BOOK of every size couldnt post it all just a rule of thumb starting point
 

Attachments

·
Registered
Joined
·
62 Posts
Are you going to add plywood to strengthen the... just kidding 🙂

How long are the 2x10s?

I think you need to reduce the span. What’s the width the other way? Maybe use a big glulam to reduce the span to 20’ for the trusses (probably won’t need trusses at that length). How much headroom do you have in the floor below?

I agree with what others have said. If you are not a PE, then get one. I would be surprised if they charged more than $500. This will also go a huge way to squash your building officials!

With a 40’ span you will be fighting deflections (as was stated earlier). You will feel vibrations. Cracking of drywall will be a big problem if deflections are not managed. If you have any rooms with tile then you have more dead weight and tighter deflection limits.
I am assuming this a floor as you originally stated, if it is a flat roof you also need to limit deflections to limit the amount of rain that can pond.
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #11
It's 40x40'. I've got as much headroom below as needed, as I'll be elevating the upper containers to achieve my desired 10' ceiling height.
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #12
Ok, so looking into steel joists I got an idea to hybridize things a bit.

Say I took the traditional double angle chord and split it over a couple 2x6's and bolted the works together into a sandwich of sorts?

The web would still be present, but divided by the gap created via the wood. Geometrically speaking, it should be much stiffer in Y-Y, as well as X-X.

3x3x3/16 angle with 24" chord depth. Added bonus, I don't need to scab or drill for sheathing.

20190728_202114-1.jpg
 

·
Registered
Joined
·
62 Posts
I think you are putting the cart in front of the horse here. You are trying to detail a truss before we have any idea of the size of the truss.

Also don’t discount WT shapes (I-beam cut in half through the web) for the top and bottom chords. You can easily attach double angle members to the cut webs. There are plenty of commercially available hangers available to connect wood joists to the steel truss chords.

I don’t have a good truss computer software at home, otherwise I would have this designed already. If you understand basic trigonometry doing a hand truss analysis is quite simple, but it is time consuming.

If you get me a truss geometry with dimensions shown I can maybe analyze it tomorrow. The size of the individual members are irrelevant for a true truss analysis.
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #14
40'x24" The span has always been known, I just wasn't sure on the web depth.

Have you priced W-beams lately??

3x3x3/16" is $63 a 20' stick.
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #15
Horizontal Blue (ruled) lines are 2x10's, vertical pen lines are trusses.

Vertical web connectors @ 24" to bolt 2x10's to. Angled web connectors between them for compression loading.

20190728_212105-1.jpg
 

·
Registered
Joined
·
814 Posts
Jim.....allways keep in mind that in any truss/joist building that the goal of the trussing is to put the bottom cord in tension and top cord in compression......as this is the goal the connection points between the cords and webing become extremely important and cannot be compromised on....obviously this is a design component but it is many times overlooked in homebuilt situations


i do like your thought process in the-5 large trusses / with wood joists on top as a better concept and i think overall it would be a more cost effecient process since you have plenty of vertical space to work with.....really need to have a hr or two with a PE..

things to be able to discuss with a PE to optimize your time (in our area it would probably cost under $250 if your prepared)

things to think about and have answers for prior to meeting with a PE would be (conceptual sketches are great)

#1...have a general discussion of the ground up construction including footings etc
#2...have a understanding of the loading capabilities of the containers your working with and where the load bearing points are
#3 ...a full understanding of the ussage so design loads can be determined
#4 ...a framing concept with minimal options as each option requires work
#5.....a general idea of materials....steel and wood you would like to use such as you have already done IE angles are cheaper per # than beams or tube steel........a understanding of what wood types you have availible in your area and cost profiles......IE southern yellow pine is a commonly used product in wood design but can be prohibitively expensive to buy so a design with SYP lumber would not help or interchange with Douglas Fir etc..

i have built many structures on my farm from steel i have found and bought via craigslist etc but i am capable of changing designs to fit the materials.....in our area 40' barjoists are a relatively common demolition item from warehouse demo and regularly available as a used product if available in your area it would be worth checking and a consideration even if they were sized for the roof and needed to be placed closer together...might be worth your time to call a few commercial demo contractors and make some inquiries

so ...materials can sometimes drive the design vs the design driving the materials.....

i hate to ask...but what form of "floor" decking are you considering that will span 24" effectively
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #17
It's only 4 trusses. The outside wall will support the 5th loading point via ledger of some sort and may attach the joists to the studs as well.

I also plan on either double sheathing the interior wall above the open span, or sheath it in plywood to then cover the opposite side in steel paneling up to the ceiling. Need to see how the budget is doing at that point in the project. :)

I can also sheath the walls in the upstairs, if needed. I just think getting the floor right is a better use of resources. We'll have several protrusions, so designing the interior walls as structural members of the floor could be less than successful.

I don't have hard figures on the floorplan yet. I just know we'll have 3+ bedrooms, a minimalist kitchen of some form, and a couple larger central rooms.

My intention is to place the bathrooms within the containers, but the Mrs. does have a home gym that will wind up on this level (hopefully near the container walls :D ).
 

·
Registered
Joined
·
2,965 Posts
Discussion Starter #18
Floor decking will be T&G of some form. I'll use construction adhesive and either ringshank nails or deck screws with blocking at any unsupported joints.
 

·
Premium Member
Joined
·
7,298 Posts
your issue will be deflection no matter your construction.....you need to seriously consider your deflection criteria as it will control your design

at 40' i think your seriously undersized unless you want the floor to act like a trampoline

i think you really need to have a direct consultation with a PE to discuss your complete construction picture and the materials you would like to use as this is far beyond internet engineering there are a LOT of pieces to the proverbial puzzle
What he said. This is no area to try and save a buck or two on.
 
1 - 20 of 42 Posts
Top