Attach awning brackets to a Steel Hollow Section

[Z-ster]

I'm attempting to attach retractable awning brackets to a Steel Hollow Section Column, which is proving challenging.

The awning comes with 4 brackets each with 4 x 12mm holes. They also provide 16 SS Dynabolts for installations into concrete and brick but nothing for timber or steel which is what I need. The Awnings weight is around 80kgs.
So far I have discovered one product that would do the job but it seems new and not widely available… A blind bolt (The Blind Bolt Company (http://www.blindboltaustralia.com.au/)) The site has video demontrations on the home page.

The other possible way is to use a tap (tap and die) to create a thread on the outer wall of Steel Hollow Section. The wall of the Hollow section is about 5mm thick so I do have some concern whether this is thick enough.
Can anyone offer alternative suggestions or which approach would be best? Would a short dynabolt work in this situation despite not designed for this application?

Oh, there is one other approach. Create a hole, using a hole saw, big enough to pass the bolts into the hollow section and then thread them through the 12mm holes. But that could be a little tricky.

[SurfinNev]

Not enough wall thickness for a thread in my opinion. I assume you are using M12 bolts with a pitch of 1.75mm. There are Nutserts, but grip length of a 12mm may be to short at around 4mm for the 5mm wall thickness. If access from the back is possible I would just bore a hole the size of a socket to fit the bolt or nut and a 12mm hole through the front then plug holes later with a cap of some sort.

Nev

[pipeclay]

The HD bolt would appear to be the best option if this is what you end up using.
The british site has a lot of usefull data.

[Stustoys]

How big and what else is the Steel Hollow Section Column doing?

Hi Nev,
While I agree that 3 turns of thread isnt much, I wonder if it would be stronger the the super clever bolt?

Stuart

[Z-ster]

Hi Guys, thanks for the quick responses.

The Hollow beam is actually running vertically on either side of a 6 bi-fold door set. There is also what appears to be an I beam (Could be a C beam) that runs horizontally across the top of the bi-folds between the two vertical hollow beams. The hollow beam and I beam are welded together. Also two of the brackets need to attach to the I beam, I've not worked out how yet.

Edit: access from the back is not possible, even drilling from the side won't be possible without special equipment/adapters as there is not enough room for a drill

[pipeclay]

How big and what else is the Steel Hollow Section Column doing?

Hi Nev,
While I agree that 3 turns of thread isnt much, I wonder if it would be stronger the the super clever bolt?

Stuart
I doubt it.

[shedhappens]

The technical data for the 12mm HD bolt indicates that it requires a minimum of 10mm fixing thickness.
Technical Data for the Heavy Duty HD Bolt (http://www.blindboltaustralia.com.au/tech-data-for-the-hd-bolt/)

john

[shedhappens]

zster why don't you drill and tap the holes to suit 12mm with a 1mm pitch ?
just nip them up with a drop of locktite, an awning would never pull them out.

[Z-ster]

The technical data for the 12mm HD bolt indicates that it requires a minimum of 10mm fixing thickness.
Technical Data for the Heavy Duty HD Bolt (http://www.blindboltaustralia.com.au/tech-data-for-the-hd-bolt/)

john

I suspect that is the total thickness being referred to, in other words including the thickness of the item you intent to attach, in this case the bracket.
The bracket is also 5mm thick, maybe a little thicker.
The PDF (technical data) actually explains it better.

[Z-ster]

zster why don't you drill and tap the holes to suit 12mm with a 1mm pitch ?
just nip them up with a drop of locktite, an awning would never pull them out.

I think this would be the easiest approach, is this a common thread (12mm/1mm pitch)? I'm trying to establish if it's something that woudl be readily available at most haradware stores, and for that matter the bolts too.

[shedhappens]

zster you will need to find your local industrial supplies outlet, even 12mm x 1.25 would do.

put one into something and try to rip it out:U

[Stustoys]

While I agree that 3 turns of thread isnt much, I wonder if it would be stronger the the super clever bolt?
Not an easy question to answer it seems, though my searches seem to say it will be a close thing.
The numbers I came up with are these, they may or maybe not be correct but it there was some interesting ready.
If the bolt and the nut thread are the same material, the thread stripping strength will equal the bolt strength when the nut is .47*diameter.
So if the column was made of the same material as the bolt the thread would be a little weaker than the bolt.
A grade 4.6 M12 bolt has a tensile strength of about 45kN.
The HD bolt has a tensile strength of 30kN.

How the steel in the column compares with the steel in a grade 4.6 bolt I'm not so sure.

Stuart

[NCArcher]

Can you weld the brackets on, or pay someone to weld them if you don't have the appropriate welder?

[shedhappens]

I'm a mathematical moron but this might solve the problem, can someone here work it out for a 12mm bolt ?

The screw should fail before the thread strips. For this, it is necessary the shear area of the threaded feature be at least 2 times the tensile area. (Assuming the threaded feature is of the identical material).
http://www.engineersedge.com/thread_strength/image/Le.gif Where:
Le = Minimum Thread Engagement Length
At = Tensile Stress Area
D = Major Diameter of fastener (screw)
p = 1 / Number of threads per inch (n)



Minimum Thread Engagement Formula and Calculation ISO - Engineers Edge (http://www.engineersedge.com/thread_strength/thread_minimum_length_engagement.htm)

[DJ’s Timber]

One option is to weld a pad onto the column where the bracket needs to go.

For example, a plate that matches your bracket then drill and tap both pad and column.

[Stustoys]

For example, a plate that matches your bracket then drill and tap both pad and column.
Now this idea I like.


shedhappens The stuff I was reading said formulas dont work very well for this sort of thing as the first turn of thread holds over 1/3 of the load, each thread after that holding less and less.
http://www.elexp.com/tips/AllAboutScrews.pdf page 16.

Stuart

[Karl Robbers]

The awning weighs only 80KG so it is by no means heavy, (in structural terms). To be quite honest I have no idea why 12mm bolts are being used, 8mm bolts would easily hold the weight.
I would have no concerns at all tapping holes in 5mm steel to take M8, M10 or M12 bolts, just ensure that you have a good hole, undersized rather than oversized and use a good cutting lubricant so as to cut a good quality thread. In the case of M12, metric fine would possess some advantages over course, but I wouldn't get too bent out of shape worrying about it. For that matter heavy gauge TEK screws would have adequate strength.

[Bryan]

The awning weighs only 80KG so it is by no means heavy, (in structural terms). To be quite honest I have no idea why 12mm bolts are being used, 8mm bolts would easily hold the weight.

Wind loads perhaps?

Edit: Wind can generate a lot of force. I've seen a shade sail pull down a besser brick garage wall. It wasn't a big sail and I don't recall it being excessively windy either.

[SurfinNev]

Maybe attach awning to thickish plates that can have the nut countersunk, or tap the plates themselves for the M12 bolts, then attach plates and awning to posts with a series of smaller bolts, such as M8?

Nev

[Z-ster]

I just wanted to provide you all with an update on my decision/approach.

Firstly I think the best approach offered, and probably the more professional one, is welding a plate on the the existing steel section. But I don't have a welder or any spare metal.

The thread approach, as suggested by many tapping a tread in the steel section may have also be adequate, but I was reluctant as I would need to purchase a tap and die set. This solution also didn't offer me the piece of mind I would need to sleep better at night.

In the end I decided to just drill a 25mm hole, with a hole saw, in the middle and pass the bolts into the steel section and out through the holes. Could have done it with a 22mm but they didn't have one in stock. BTW, the steel section is around 150mm wide.
It was a lot easier than I expected. The hole saw cut through the steel much easier than the 12mm bit I used for the bolt hole.

Threading the bolts though the holes was quite easy too. I used braided fishing line and some spring wire. Spring wire to hold the bold horizontal while inside the steel section, and braided fishing line to pull it through the hole.

Also, I was able to better measure the thickness of the steel section with vernier calipers once I removed the piece out of the hole saw. It was 6mm thick.

Thanks

John