Square Steel Tube Bearing Capacity

[Manassas]

I'm putting up what will essentially be a carport with a steel truss and roof of steel sheeting. I want to use steel uprights rather than concrete. They are widely available at all the home stores in various sizes 4x4, 5x5, 6x6 usually with around a 2.5mm thickness. The trouble is nobody can tell me the load bearing capacity of the various sizes of steel tubing. Not just the weight but standing up to high wind conditions. Of course, the salesmen and friends and relatives all have an opinion of what is "enough," but nobody can tell me why. 

 

Can any of the engineers or builders out there point me to a chart that tells me the capacity of the various sizes? There's a significant price difference so I'd rather avoid buying the biggest just to be sure. I looked all over the internet for what I thought would be a standard table of specs but can't find anything.

[Crossy]

I doubt you will find an easy to use table unless you are a structural engineer (in which case you won't need the table).

 

This is our carport.

 

 

I pinched the original design off the net but my step-son modified it somewhat as he didn't think it was strong enough to support the planned solar panels (not installed yet), I can hang on the beams and they don't move, I am not a jockey!

 

It's seen a good few blows over the last three years and hasn't gone anywhere.

 

EDIT By the way, go to your local steel supplier, they will be far cheaper than the "home" places and will deliver, usually free.

 

[Artisi]

One point to consider is that not all steel is up to standard spec. - you need to purchase from a reputable supplier. 

If what you are offered something cheap - be wary. 

[weegee]

I used 4x4 post beams 4 mm thickness, on 3 mtr centres...for a workshop. "C" (75x50x 2.5 mm) channel makes up the rest including the roof rafters...shed size is 12x6x3mtrs

I lift engines and machines with a endless chain hanging from the roof rafters no problems.

 

Hopes this gives you an idea of about whats required for strength...in case you cant get the table you are looking for.

[Manassas]

11 hours ago, weegee said:

I used 4x4 post beams 4 mm thickness, on 3 mtr centres...for a workshop. "C" (75x50x 2.5 mm) channel makes up the rest including the roof rafters...shed size is 12x6x3mtrs

I lift engines and machines with a endless chain hanging from the roof rafters no problems.

 

Hopes this gives you an idea of about whats required for strength...in case you cant get the table you are looking for.

 

Thanks. In looking around a[[ I've found is 2.7mm thickness which looks and seems a little light. I'm just guessing that the thickness is more important than the dimensions, but both play a big role in capacity no doubt I'll keep looking at more shops.

[Manassas]

13 hours ago, Crossy said:

I doubt you will find an easy to use table unless you are a structural engineer (in which case you won't need the table).

 

This is our carport.

 

 

I pinched the original design off the net but my step-son modified it somewhat as he didn't think it was strong enough to support the planned solar panels (not installed yet), I can hang on the beams and they don't move, I am not a jockey!

 

It's seen a good few blows over the last three years and hasn't gone anywhere.

 

EDIT By the way, go to your local steel supplier, they will be far cheaper than the "home" places and will deliver, usually free.

 

That's just about what I'm planning although a bit bigger. Your uprights look like 4x4. What is the thickness?

[Crossy]

Yes, posts are 4" x 2.7mm wall thickness, the regular stuff from the local metal outlet.

 

These closed tubes (as opposed to C section) are very strong and rigid, the C can twist if it's not doubled up back to back to form an I. The whole structure is closed tube and moves very little if I swing on it.

 

We have a number of roofs and structures using similar construction all have withstood anything that the weather can throw at them (famous last words of course).

 

EDIT The only thing we've done slightly differently on the later structures is to weld a steel plate to the bottom of the "legs" and anchor-bolt that to the concrete pad rather than burying the steel in the concrete. The reasoning being it's easy to undo the bolts and remove the steel if we decide to move the structure. Pre-drilled plates came from the metal shop too.

 

[Manassas]

1 hour ago, Crossy said:

Yes, posts are 4" x 2.7mm wall thickness, the regular stuff from the local metal outlet.

 

These closed tubes (as opposed to C section) are very strong and rigid, the C can twist if it's not doubled up back to back to form an I. The whole structure is closed tube and moves very little if I swing on it.

 

We have a number of roofs and structures using similar construction all have withstood anything that the weather can throw at them (famous last words of course).

 

EDIT The only thing we've done slightly differently on the later structures is to weld a steel plate to the bottom of the "legs" and anchor-bolt that to the concrete pad rather than burying the steel in the concrete. The reasoning being it's easy to undo the bolts and remove the steel if we decide to move the structure. Pre-drilled plates came from the metal shop too.

 

 

Thanks. Just by looking and with no knowledge of specs it seemed to me like the 4" 2.7mm would be strong enough to support a sheet roof. Also a more favorable price! The roof will be light but on top of a slope so it will take some wind in storms.

 

The salesman was going on about the C shape is better, but that just didn't make any sense. 

[oxymoron]

5 hours ago, Manassas said:

 

Thanks. Just by looking and with no knowledge of specs it seemed to me like the 4" 2.7mm would be strong enough to support a sheet roof. Also a more favorable price! The roof will be light but on top of a slope so it will take some wind in storms.

 

The salesman was going on about the C shape is better, but that just didn't make any sense. 

The problem in Thailand is steel is sold not only by size but by weight as well. I am a Chartered Ozzie engineer and I nearly got caught when designing the trusses for my house.

 

If you want 100 x 50 x  3  "C channel" you need to specify the weight as well:

ie you can get 6000 x 100 x 50 x 3mm as 18,20,22 Kg from memory. Quality TIT.

 

I am talking black rolled steel, not the Bluescope rolled products.

[Fruit Trader]

To be sure of continued good night sleep, maybe best to employ a structural engineer for this car port project. Try the local Tessabahn. 

[Kwasaki]

Global house supplied steel will adequate for a carport, just make sure posts/columns are secured in a good concrete foundation.

The following steel construction of rafters, purlins & roof cover is just straight forward.

If your worried about exposure to wind and your carport will have to be situated in a exposed area, just put more steel bracing & more roof fixings.      

[mogandave]

Yes, posts are 4" x 2.7mm wall thickness, the regular stuff from the local metal outlet.
 
These closed tubes (as opposed to C section) are very strong and rigid, the C can twist if it's not doubled up back to back to form an I. The whole structure is closed tube and moves very little if I swing on it.
 
We have a number of roofs and structures using similar construction all have withstood anything that the weather can throw at them (famous last words of course).
 
EDIT The only thing we've done slightly differently on the later structures is to weld a steel plate to the bottom of the "legs" and anchor-bolt that to the concrete pad rather than burying the steel in the concrete. The reasoning being it's easy to undo the bolts and remove the steel if we decide to move the structure. Pre-drilled plates came from the metal shop too.
 

This should help with corrosion also, as water can drain out between the tubing and the plate.

One advantage of c-channel over tubing is that you can prime/paint it.

Ideally, you could have your steel hot-dipped prior to delivery. It’s pricy, but it lasts forever and you never have to paint...

[Manassas]

16 hours ago, mogandave said:

 

This should help with corrosion also, as water can drain out between the tubing and the plate.

One advantage of c-channel over tubing is that you can prime/paint it.

Ideally, you could have your steel hot-dipped prior to delivery. It’s pricy, but it lasts forever and you never have to paint...

 

One of the salesman's points was the ability to paint the c-channel. Makes sense as far as it goes, but would worry about the c-channel uprights twisting. Though fine for the truss.  I'm guessing the closed square uprights will last as long as I do...

[mogandave]

One of the salesman's points was the ability to paint the c-channel. Makes sense as far as it goes, but would worry about the c-channel uprights twisting. Though fine for the truss.  I'm guessing the closed square uprights will last as long as I do...

Do not make the mistake of discounting corrosion issues with hot-rolled steel, particularly tubing.

It is amazing how fast stuff corrodes here. There is a reason you see so much GA & SS...

[sometimewoodworker]

On 02/05/2018 at 6:26 AM, Manassas said:

 

Thanks. In looking around a[[ I've found is 2.7mm thickness which looks and seems a little light. I'm just guessing that the thickness is more important than the dimensions, but both play a big role in capacity no doubt I'll keep looking at more shops.

I doubt that is too thin.

this is built using 2.5mm steel, 5 years ago.