• Looking for a smarter way to manage your heating this winter? We’ve been testing the new Aqara Radiator Thermostat W600 to see how quiet, accurate and easy it is to use around the home. Click here read our review.

Calculating number of props / strongboys needed

Joined
3 Aug 2023
Messages
77
Reaction score
4
Country
United Kingdom
I am trying to figure out the number of Acrow props / Strongboy heads needed to support the floors / walls while I install an RSJ, but the numbers aren't making much sense.

Plan is to prop / scaffold board under the floor joists to take most of the load off the wall, and use strongboys to take the remaining load of the wall itself.

So, using the SE's load table, the floor dead, & floor live loads come out to 24.38kN (unfactored total, both sides)
Using a kN to kgf calculator, this results in 2486kgf. The size of Acrow prop I need has a working load of 1500kg, so that's only 2 props!

Then I take the wall & loft dead load which is 25.48kN = 2598kgf (unfactored) = 8 strongboys (max load 340kg)!!!

This doesn't seem realistic to me because the RSJ is only a 2.1m span, so it would mean a strongboy every 250mm! And this is with the floor load already taken out!
Is there a fault in my calculations or are strongboys really that weak?
 
The calculations are OK, the logic is not

You want 3 props either side of the wall and 2 to push the beam up
 
The norm is around 3foot centres. The important thing is to make sure the acrows are vertical and sitting on a good timber to spread the load and reduce the chance of slippage. The theoretical capacity plummets when they go out of vertical.

No bad thing to have a spare ready just in case 1 decides to play up
 
The calculations are OK, the logic is not

You want 3 props either side of the wall and 2 to push the beam up
Was planning on lift into place with a beam lifter and dry packing above, so that would mean 4 each side? I don't even know if that would fit in a 2.1m span. It certainly would give no room to work.
The norm is around 3foot centres. The important thing is to make sure the acrows are vertical and sitting on a good timber to spread the load and reduce the chance of slippage. The theoretical capacity plummets when they go out of vertical.

No bad thing to have a spare ready just in case 1 decides to play up
Yes the max span is 900mm / 3ft but the max weight is only 340kg to would only go near that span if using lightweight blocks I suppose
 
Do you really need a beam lifter for an RSJ that short. Or have you thought of using a catnic lintel instead they are much lighter and easier to work with.
 
I am trying to figure out the number of Acrow props / Strongboy heads needed to support the floors / walls while I install an RSJ, but the numbers aren't making much sense.

Plan is to prop / scaffold board under the floor joists to take most of the load off the wall, and use strongboys to take the remaining load of the wall itself.

So, using the SE's load table, the floor dead, & floor live loads come out to 24.38kN (unfactored total, both sides)
Using a kN to kgf calculator, this results in 2486kgf. The size of Acrow prop I need has a working load of 1500kg, so that's only 2 props!

Then I take the wall & loft dead load which is 25.48kN = 2598kgf (unfactored) = 8 strongboys (max load 340kg)!!!

This doesn't seem realistic to me because the RSJ is only a 2.1m span, so it would mean a strongboy every 250mm! And this is with the floor load already taken out!
Is there a fault in my calculations or are strongboys really that weak?
A 2.1m span will give you a beam of around 2.4m long. I could lift that on me ****.

As per Woody, 3 props plus two for the beam. Get six and you should be comfortable, just in case you need to do a bit of swapping about.








 
Last edited:
Any pictures of the finshed opening Noseall?

Andy
I dont really catalogue the finished article so much as I don't have much use for the images, i.e. i take stuff in case people like building control want a squint at anything relevant like Fire-line boards or end bearings etc. I have some piccies of his mate going in on the outer leaf, the other internal beam connected to it, the drawing I did for the steel company
and some of the padstones and fire boards etc...














 

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Back
Top