Proping a purlin of a crossbeam

[Bcg74]

Hi all

Can I just say , its my first post , so be kind ,lol.

Usually I can find everything I need to know on here , but not 100% on this one.just hope I have the right section as well.

Basically , we have got to sit a new purlin (2 x 275x75 , bolted together,sat against an existing inclined purlin ) . now because of the 8.5 metre span , its gonna be in 2 pieces .we have been told to sit it on a 100mm x 100mm prop,which is sat on 2 x 250x75 cross beams (bolted together) , I get that.

So would our cross beam be sort of sat in the middle ? Then the purlin from one end sat on a prop , then the purlin from the other end , sat on the same prop ,also how is the prop fixed to the purlin ? And how is the prop fixed to the 2 bolted crossbeams

Thanks in advance

 

[^woody^]

The prop just goes in between the two so that the purlin sits on the prop, and the prop sits on the beam, and you nail it all together, nothing fancy.

You should be forming a suitable scarf or lap joint where the purlins meet. But it is not clear if you are using 2x timbers to form a purlin, or bolting 2x timbers side by side over the 8.5m length? In which case they would be better bonded with no single central joint

 

[Bcg74]

The prop just goes in between the two so that the purlin sits on the prop, and the prop sits on the beam, and you nail it all together, nothing fancy.

You should be forming a suitable scarf or lap joint where the purlins meet. But it is not clear if you are using 2x timbers to form a purlin, or bolting 2x timbers side by side over the 8.5m length? In which case they would be better bonded with no single central joint

Hi woody.yes we've been told to use 2 lengths of 75x225 c16s , bolted together ,which fit on the underside of the rafters , so obviously one would be slightly higher than the other one before we bolt it.ill try and upload a pic , thanks

 

[Bcg74]

View media item 95653
Hopefully this pic would of loaded.as you can see , 2 timbers bolted together , sat against the existing purlin , which is sat on a 100x100 prop , which is sat on a crossbeam made up of 2 timbers bolted together.so I'm guessing the purlin coming from the party/next doors to the prop , will just sit on the prop ? And the same for the purlin coming from the gable end , will sit on the same prop ? Without the scarf joints ? Or are we forming one 8.5 meter purlin , bolted together with no scarf joints ? which is then sat on a prop halfway

Hope that's not to confusing

Thanks again

 

[^woody^]

I can't see any images

 

[Bcg74]

I can't see any images

can you see that ? I'll get there in the end

 

[Bcg74]

Hi woody ,can you see this image now ? Your advice would be appreciated ,thanks

 

[^woody^]

That's a bit of an odd arrangement. I would refer back to whoever designed it to ask how they propose it should be put together. I wonder if it has been calculated, or just thought up. The way it is drawn makes me wonder if it really needs to be two timbers of that size, and whether they are in fact acting as one beam?

It seems like there would be some rotation of that upper purlin as the roof pushes the upper one back. So I wonder if that post should be on the upper (rear) purlin. But then, there probably should be two posts - one for both the front and rear beam

Two purlins can be but jointed onto a post and a steel splice plate or length of ply nailed across the join to hold them together. This might be better than trying to carve a proper joint into the ends. But getting to the rear of that one purlin would be difficult. There is also a lot of load on a single post so, as well as a post front and back, I wonder if there needs to be two posts side by side instead of both beams bearing on a single post?

This should all have been specified on the drawing, not left to the builders imagination

But back to the original question, you could cut the post to fit between the purlin and whatever it is resting on below, and use some angle iron under the purlin, or a vertical splice plate up the top end of the post and up the side of the purlin.

 

[Bcg74]

Thanks for that.I was thinking along the same lines , for the sake of a bit of 100x100 prop , we are thinking of , propping it on 4 props , 2 for the front purlins and 2 for the higher purlins.like you say , surely that's going to sort of spread the load a little. These have been drawn by consulting engineers , although the customer hasnt said wheather he's had calcs of them or not.

 

[^woody^]

Here's some principles