Thunderbolt spacing.

[roryfirth]

Can anyone offer some advice on Thunderbolt spacing and selection please?

I am looking to use them to secure a 45mm batten to the wall to then hang floor joists over a distance of 2.5m

The walls are 5m and 2.5m long.

I was looking at the 12x130mm bolts for the job.

 

[jeds]

A floor is approx. 2.3kN/m² - dead and live. Work out how many square meters will bear on the bolts and multiply by 2.3 for the total load. Then find the bearing capacity of the bolts and divide the total by that amount. The result is the number of bolts required. Just space them evenly.

 

[roryfirth]

Hi jeds.

Thanks for the reply, the room is 12.5sqm.

So looking at the chart, using 12mm bolts it would be 12.5 x 2.3 / 0.78 = 36 bolts? View media item 91063

 

[jeds]

No. A 12mm Thunderbolt with 60mm embedment has a safe working load of 6.5kN and a safe shear of 13.5kN. Taking the lower figure divided by 5 bolts = 28.5kN/5 = 5.75kN on each bolt. So I'd use 5 bolts.

 

[RonnyRaygun]

Thunderbolt do not give any technical guidance for use in masonry.

The table you have attached is for C20/25 concrete and it's safe to assume (based on other fixing manufacturers' data) that the capacity in masonry is far lower than in concrete.

I'd use Thunderbolts with caution in this situation, safer to use fixings with specified capacities in masonry such as Rawl or Hilti fixings.

 

[jeds]

www.unifix.co.uk/sites/default/files/Thunderbolt Technical Information.pdf

 

[RonnyRaygun]

www.unifix.co.uk/sites/default/files/Thunderbolt%20Technical%20Information.pdf

Where's their data for masonry?

 

[jeds]

That's fair enough but Hilti, Fischer and Thunderbolt all quote approximately the same values for concrete so for small loads like this I'd be happy to take them as equivalent. And experience tells us that M12 bolts at 600 centres will do the job in masonry as long as it's reasonably decent and not crumbling to bits.

 

[RonnyRaygun]

My up to date Rawlplug Brochure gives a capacity of around 1/3 in tension and shear for their Rawlok mechanical anchors in masonry when compared with concrete (the only mechanical anchor in their brochure that is even suitable).

Haven't checked Hilti's brochure but I bet it is similar - they don't recommend any of their screw anchors for structural work.

You may be correct that Thunderbolts would be OK, but for the sake of a few £, why not use a suitable anchor, one that has supporting data? I know I would.

 

[roryfirth]

My up to date Rawlplug Brochure gives a capacity of around 1/3 in tension and shear for their Rawlok mechanical anchors in masonry when compared with concrete (the only mechanical anchor in their brochure that is even suitable).

Haven't checked Hilti's brochure but I bet it is similar - they don't recommend any of their screw anchors for structural work.

You may be correct that Thunderbolts would be OK, but for the sake of a few £, why not use a suitable anchor, one that has supporting data? I know I would.

Thanks for the advice guys, I believe Thunderbolts are designed to be used int his case but Ronny, which suitable anchor would you recommend?

 

[RonnyRaygun]

I believe Thunderbolts are designed to be used int his case but Ronny, which suitable anchor would you recommend?

They can be used in masonry, but there is no available capacity data for structural use in masonry. I know this because I spoke to them about the very subject quite recently.
This is why their technical data sheet only shows them being used to hold up handrails and satellite dishes in masonry.

As said, I would use something like a Rawlok by Rawlplug, or resin anchors, but you might find the spacings are a bit closer together if you want to comply with their data.

I'll take a look at the capacities at lunch time if you like.

 

[RonnyRaygun]

OK, had a look and you won't get the Rawlok to work without putting them in at ridiculously tight centres, so I took a look in a slightly earlier Rawlplug brochure and I think you will need something like the below:

RAWLBOLT® SHIELD ANCHOR LOOSE BOLT M12 at 300mm crs.

This is based on a joist span of 5.0m (based on 12.5sq m / 2.5m). Let me know if this is wrong?