Help with Size of RSJ

[The Shadow]

We are removing 2no single doors on a detached garage and replacing with a double door.

The garage is brick single skin with 225mm pillars each side at the front with 225mm central pillar which needs to be removed. The roof is marley tile as per the picture.

The garage opening width is 4.572 plus 225mm each side pillar for the new RSJ to sit on is 5022mm

Due to the design of the roof and internal trusses there is not a lot of dead weight in the centre as the weight appears to be distributed to the outer walls.

I have been told that a 178mm x 102mm RSJ 5000m long will be OK, would any body be kind enough to confirm that the size will be adequate.

I am new to DIYnot, I hope to be able to contribute to the forum as a fully qualified plumbing and drainage engineer.

Many thanks in advance

 

[tony1851]

A 178 x 102 would probably be too slender over that span, unless it was to be firmly fixed to the underside of the wall plate, eg by coach screws.
A 152 x 152 x 23 would probably be better.

 

[The Shadow]

A 178 x 102 would probably be too slender over that span, unless it was to be firmly fixed to the underside of the wall plate, eg by coach screws.
A 152 x 152 x 23 would probably be better.

Hi Tony many thanks for your comment, As i see it the new RSJ would simply sit on top of the existing outer brick pillars on each side of the garage. There is no wall plate for the RSJ to sit on.

 

[^woody^]

A lot will depend on the direction of the trusses which could reduce the load on any beam if the trusses span sideways. But there are vertical and lateral loads in that arrangement, so you need it properly calculated - unless the person who told you that a 178 beam will be OK is prepared to warranty it.

 

[tony1851]

Hi Tony many thanks for your comment, As i see it the new RSJ would simply sit on top of the existing outer brick pillars on each side of the garage. There is no wall plate for the RSJ to sit on.

The steel beam would not sit "on" any wall plate - it would be underneath it. But you say there is no wall plate, so what supports the rafters forming the front slope?

 

[The Shadow]

A 178 x 102 would probably be too slender over that span, unless it was to be firmly fixed to the underside of the wall plate, eg by coach screws.
A 152 x 152 x 23 would probably be better.[/QUOTE

A lot will depend on the direction of the trusses which could reduce the load on any beam if the trusses span sideways. But there are vertical and lateral loads in that arrangement, so you need it properly calculated - unless the person who told you that a 178 beam will be OK is prepared to warranty it.

Thanks Woody comments noted, 2 main roof trusses splay out following the line of the ridge tiles at the front of the garage these 2 roof trusses take a lot of the live load and sit on the outer garage side pillars. there are another 7 roof trusses which would sit on the new RSJ.

There are 2no existing 9 x 3 inch wooden lintels in place which currently span the front of the garage, one each side and rest on the central pillar. I was thinking of leaving the wooden lintels in place and placing the new RSJ along side them and bolting through to join them together with long coach screws or threaded rod.
The existing roof trusess would still sit on top of the new RSJ providing it was strong enough.

 

[tony1851]

If you are leaving the 9x3s in postion, then you would best be using a steel channel-section rather than an I-beam because with the latter, you won't get a proper connection between the steel and timber.

 

[The Shadow]

If you are leaving the 9x3s in postion, then you would best be using a steel channel-section rather than an I-beam because with the latter, you won't get a proper connection between the steel and timber.

Thanks point taken, would it be feasible to pack out the RSJ at connection points to marry up with the existing 9 x 3 s

I have the the 178 x 102 RSJ, just need to know for peace of mind if its man enough, i have uploaded a picture of the inside of the garage showing the arrangement of the roof trusses on to the outer walls and existing 9 x3 s

 

[The Shadow]

The steel beam would not sit "on" any wall plate - it would be underneath it. But you say there is no wall plate, so what supports the rafters forming the front slope?

Many thanks for the comment, i have uploaded a picture of the inside of the garage showing the arrangement of roof trusses

 

[^woody^]

You will need it calculated. No one here can give the answer unless they have done something exactly the same, and you should not accept anyone's "that will do".

There is relatively little loading frrom the infill mono-trusses, but those loads and the live wind and snow loads still need to be considered, and that's a bit of a wide span for a 178 beam

 

[The Shadow]

You will need it calculated. No one here can give the answer unless they have done something exactly the same, and you should not accept anyone's "that will do".

There is relatively little loading frrom the infill mono-trusses, but those loads and the live wind and snow loads still need to be considered, and that's a bit of a wide span for a 178 beam

Many thanks, comment noted

 

[tony1851]

If it's a case of bolting existing 9x3s to a 7x4 steel, you will of course need to fix something like a 6x2 to the web and bolt firmly through, best with lengths of threaded bar.
Unlike Woods, I think it would be OK, as long as the steel and timber were very securely bolted together. If the existing roof structure is fixed to the 9x3s, and the 9x3s securely fixed in turn to the steel, that would effectively reduce the slendernesss of the steel beam and reduce the sideways buckling tendency.
But deflection might still be an issue and would need to be calculated. That is not straightforward with 2 materials in parallel and one effectively split in the middle - it's all back to making sure that there are sufficient bolts to make them work together.

 

[The Shadow]

If it's a case of bolting existing 9x3s to a 7x4 steel, you will of course need to fix something like a 6x2 to the web and bolt firmly through, best with lengths of threaded bar.
Unlike Woods, I think it would be OK, as long as the steel and timber were very securely bolted together. If the existing roof structure is fixed to the 9x3s, and the 9x3s securely fixed in turn to the steel, that would effectively reduce the slendernesss of the steel beam and reduce the sideways buckling tendency.
But deflection might still be an issue and would need to be calculated. That is not straightforward with 2 materials in parallel and one effectively split in the middle - it's all back to making sure that there are sufficient bolts to make them work together.

Thanks Tony for the comment, it makes sense to leave the 9 x 3 s in place and bolt through as you suggest.
This way i dont need acrow props to hold the roof up while i remove the existing 9 x 3s. This way i can offer up the RSJ into position and bolt through the RSJ, spacer wood and existing 9 x 3s.

I did also think about fixing long lengths of steels to plate to the existing 9 x 3s. to make a continuous length and also give additional strength. I am sure this is also doable but i would need to take advice on length and width of steel plates or is this OTT