Sistering joists - calculations

[Ant1]

Hi everyone,

I am planning on sistering a joist but I am confused about the required distance between each of the coach bolts.

The spacing is shown as S in the diagram available from https://www.labc.co.uk/news/how-get-it-right-bolting-timbers-together-correctly

The extracted table below are the calculations. My joist is 47mm x 145mm.

Which of the 3 sections (0.25, 0.50 or 1.25) is recommended to use if I do not know the permanent load? (ie. what is the worst case scenario? Or is there a way to measure that permanent load?

Also what is the loaded length? Is this the length of the cut piece from the original joist?

Thanks!

 

[Why Not Indeed]

The worse case covered by that table is "not more than 1.25".

 

[Dereekoo]

Permanent load (in the case of flooring ) would be the weight of the joists+weight of flooring (boards,tiles,etc) expressed in kn/m2 or tiles battens felt etc for roofs

 

[Ant1]

Thanks @Why Not Indeed and @Dereekoo , I have another question regarding that above table; is the loaded length the length of the joist between 2 supporting points?

In my case the joist between 2 supporting points is 3m long (47 x 145mm), I need to cut 50cm on one side (as it is rotten). Does this mean I need to use 3 coach bolts spaced at 52cm?

Tried to describe things (poorly) in the drawing below:

 

[Dereekoo]

Haven't come across this guidance before but my interpretation is that it refers to doubling up floor joists for the complete length and not for adding an extra bit on the end? Having said that if you are going to use it as shown in your diagram I would expect to start with a bolt a minimum of 7 times their diameter or 80mm from the joist end and then spaced at the required dims along as far as possible along the existing joist to finish 7 times their diameter or 80mm from the joist end adjusting the actual spacing to suit the length of wood. The table actually refers to bolts and not coach bolts that you infer you are going to be using. A view of the full code would be beneficial but is not available to see on the internet.