# Forum Home Renovation Roofing  Carport Bracing Required?

## Danos

Hey guys 
I have designed a freestanding carport and council have shown knee bracing on the design.  I want to avoid post bracing by using suitable sized footings.  The posts are 2mm steel.   
From what I read in this reference manual this can be done by going to 500x500x800 footings.  http://www.kingston.vic.gov.au/files...004-Colour.pdf   
However I cannot find any reference to this in AS1684.  Does anyone know where I can verify the use of larger footings to avoid knee bracing? 
Thanks
Dane

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## ringtail

For starters the posts should be 89x89x5 (or 75x75x4 as a minimum)and embedded 1200mm to get some decent bracing via the footings. Also, there is no cross bracing on the roof itself. Add strap bracing with tensioners, up the post and footing size and I think you could do away with the knee bracing all together. Consulting an engineer is the best way to trump council.

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## Danos

Ok thanks.  Yep the posts were going to be 89x89x2 but I will find out if I can source 5mm.  Cross brace strapping isn't shown on that drawing but is part of the design.  Are the tensioners required for strapping?

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## intertd6

> Hey guys 
> I have designed a freestanding carport and council have shown knee bracing on the design.  I want to avoid post bracing by using suitable sized footings.  The posts are 2mm steel.   
> From what I read in this reference manual this can be done by going to 500x500x800 footings.  http://www.kingston.vic.gov.au/files...004-Colour.pdf   
> However I cannot find any reference to this in AS1684.  Does anyone know where I can verify the use of larger footings to avoid knee bracing? 
> Thanks
> Dane

  the council really can't specify additional items to a certified structural design, AS1684 is for timber design, this is a steel cantilevered post design below beam level, there is no reference to the minimum post size or maximum projection above the footing.
Regards inter

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## Danos

Hmm ok, it would make sense.   
When people say an "engineer" is required to signoff on a design what does this actually mean?  If I can get a structural or mechanical eng to review the design and provide supporting calculations would that suffice? or are they required to be chartered engineers?

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## ringtail

They have to be a registered engineer. Plenty of retired guys still keep their registration and do little jobs like yours. An engineer would have to fill out and sign a form 15 for design. 
oh, your previous question of tensioners and strap bracing-: no, not mandatory but for $5 each, the tensioners actually make the bracing work rather than just laying strap or speed brace across the rafters as decoration  :Tongue:

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## Danos

Ok, so i have built the carport and it has a bit more wobble in it than I would like.  Mostly in the left-right direction (when driving in).  I havent added any bracing to posts and I am working out which design to go for. 
I ended up with 89x89x2 gal posts.  The top beam is set at 2.8m from footing.  The bottom beam 2.33m. 
The tricky part is bracing the left-right orientation, the forward-backward bracing (as shown in red on drawing above) wont be a problem.  I need some help with the design of the brace.  As I see it there are a few options in preferred order. 
1. Timber brace off the posts secured to a "trimmer" in between the rafters.  The rafters dont align with the beams to make direct connection. 
2. Install a horizontal rafter running left right which sits on the lower beam and runs across to the left hand post.  One rafter installed on the front posts and one on the back posts. 
3. Threaded rod diagonally across the rear two posts (approx 6m each) secured to each post. 
I had considered welding t bar stiffeners to one side of each post but I dont think that will prevent the movement. 
Any other ideas or comments? 
Thanks
Dane 
Note photo taken before battens and strapping installed.

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## Danos

> For starters the posts should be 89x89x5 (or 75x75x4 as a minimum)and embedded 1200mm to get some decent bracing via the footings. Also, there is no cross bracing on the roof itself. Add strap bracing with tensioners, up the post and footing size and I think you could do away with the knee bracing all together. Consulting an engineer is the best way to trump council

   

> ... there is no reference to the minimum post size or maximum projection above the footing.
> Regards inter

  Having tested a few out option 1 looks horrible and both 1 and 2 dont seem to help the flex in the posts.  I may have to look at stiffening the posts.

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## cyclic

For side movement use 25x25 Gal RHS.
 Come down the posts about 600 and along the Rafter about the same and fix to post and Rafter on 45 degree angle with 2 screws each.
Put a small bend in the RHS approx 100 from each end to allow for the slight offset between post and Rafter
For front to rear movement use threaded rod crossing each other if you wish, attached to 50x50 angle brackets attached to posts top and bottom.
What you currently have is probably considered ok by most Engineers.

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## Danos

I've had a chat with a local fabricator mate and decided to upgrade to the 5mm posts originally suggested by ringtail.  I didn't understand how much flex you can get with 2mm posts at the time...doh! 
With an acro prop and doing it post by post I should be able to get it done easy enough.  I will have to get the 5mm posts galvanised as I can't find a galvanised supplier in WA.

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## phild01

> With an acro prop and doing it post by post I should be able to get it done easy enough.  I will have to get the 5mm posts galvanised as I can't find a galvanised supplier in WA.

  Surely you can get Duragal over there!  Southern Steel (WA) 66 Armstrong Rd Hope Valley WA 6165 https://www.google.com.au/url?sa=t&r...PKeJ5dRzy5Ks1g   *Malow Metals*_All Steel Supplies, Fabrication, Cutting & Bending. All Areas_Unit 1 
WA 6168 Rockingham 
Tel: (08) 9529 1555

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## justonething

> I've had a chat with a local fabricator mate and decided to upgrade to the 5mm posts originally suggested by ringtail.  I didn't understand how much flex you can get with 2mm posts at the time...doh! 
> With an acro prop and doing it post by post I should be able to get it done easy enough.  I will have to get the 5mm posts galvanised as I can't find a galvanised supplier in WA.

  I'd suggest you go to 100 square RHS x 4mm rather than staying with  89 square. There is a bigger difference in going to a larger size than just increasing the thickness.

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## phild01

Is that structure just sitting there un-braced or are the posts embedded in concrete already!

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## Danos

Haha no way, posts concreted in the ground 600mm.

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## phild01

> Haha no way, posts concreted in the ground 600mm.

  So now you are going to break that up and re-do with new posts!  Maybe wait and exhaust alternatives.

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## justonething

> So now you are going to break that up and re-do with new posts!  Maybe wait and exhaust alternatives.

  He's probably got a big demotion breaker waiting to be used  :Smilie:

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## phild01

I can see Metrix coming with that tool :Biggrin:

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## ringtail

2 mm wall thickness posts is way too small however, there are plenty of the stratco type around and they use nothing better. I would work on additional bracing rather than pulling the posts out. That will be nasty. What bracing do you have at the moment ?

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## r3nov8or

Have you got tensioned strap cross bracing on the roof yet? It should reduce the wobble down to more of a vibration. (It did for me). Don't skimp on the tensioners. Get ones with a hex bolt or phillips screw rather than butterfly nuts, and you'll be able to tighten them right up, doing it gradually, alternating each strap. Then fix off at each rafter. Just make sure your outside rafters can't be pulled inwards! If you already have battens on, thread the strap underneath them and/or loosen off where required. 
PS i would definitely try this prior to replacing posts !! Bunnings sells 6 x Pryda "bolt-through” tensioners for $12

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## Danos

> Have you got tensioned strap cross bracing on the roof yet? It should reduce the wobble down to more of a vibration. (It did for me). Don't skimp on the tensioners. Get ones with a hex bolt or phillips screw rather than butterfly nuts, and you'll be able to tighten them right up, doing it gradually, alternating each strap. Then fix off at each rafter. Just make sure your outside rafters can't be pulled inwards! If you already have battens on, thread the strap underneath them and/or loosen off where required. 
> PS i would definitely try this prior to replacing posts !! Bunnings sells 6 x Pryda "bolt-through” tensioners for $12

  Yep I used the tensioners to pull the strapping tight and nailed off at each rafter but without much luck.  A mate suggested I fill the posts with concrete.  Does sound like it would work a treat.

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## ringtail

Sounds like a plan. Can't hurt anyway. 
with your two beams, are they just bolted through the column ? If so, you should change it. You wont be able to get a decent connection between post and beam unless there are crush tubes within the column. The easy solution is to weld a long angle bracket onto the column and bolt through the beam that way.

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## phild01

> You wont be able to get a decent connection between post and beam unless there are crush tubes within the column.

  It is possible by boring out holes on one side of the post large enough to allow a socket through, something I have done in the past.

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## r3nov8or

I guess you still also have the council and its expectation of knee braces to deal with. Have you confirmed they will accept any of these alternatives? (I'm not saying their 'request' is appropriate, but...)

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## justonething

> A mate suggested I fill the posts with concrete.  Does sound like it would work a treat.

  That's a novel idea. It might even work if you could put a couple of reinforcing bars inside the hollow in the plane where flexing occurs before you fill with concrete. Reinforcing is necessary because the bonding between the RHS and the concrete inside will not be very strong, while initially may be sufficient to stiffen your posts, but with strong wind/storm/earthquake, the posts will attempt to flex while the concrete columns inside won't, causing the bonding to break off. And since concrete hardly has any tensile strength, the columns inside will crack, effectively adding more weight at the top to create a worse flexing problem and the posts might even shear off. With effectively reinforcing the concrete, the tensile strength will be available to stop the swinging. Now how you're going to insert these bars would be quite a challenge though and replacing the posts might turn out to be faster and easier.

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## ringtail

> It is possible by boring out holes on one side of the post large enough to allow a socket through, something I have done in the past.

  
True but with such a thin column I'd go the bracket.

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## phild01

Yeah, not keen the way the weight of the roof is held let alone the lack of bracing.

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## Moondog55

Aren't crush tubes the stronger way to do it?
I have built something similar as a BBQ shelter a while ago using 90*90 TP posts and the knee bracing is the simplest and easiest way to counter sway
To stiffen the structure in the opposite direction tho I ran a horizontal beam from the rear post to the front post; effectively triangulating the structure in that direction

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## ringtail

> Aren't crush tubes the stronger way to do it?

  
If welded in which would be impossible to do in situ with the beam there.

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## Moondog55

I was thinking of the last time I put a tow bar into a car, with the right sized tubes you can get a lot of torque on a bolt, I thought it was all to do with the wall thickness of the tube. There are of course the good old Barrel nuts but I haven't seen anything other than 9/16ths in ages Do they still make structural barrel nuts?

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