Steel plate to timber lintel

[tony1851]

Looking at the figures on the second sheet: the floor live- and dead loads are about right, but the roof live- and dead loads look way over the top.

They have assumed that half the total roof load (ie the width of the roof from the ridge down to the eaves over the bay) is supported on the beam. This, in turn, is based on the assumption that your roof has no purlins. Most houses have one or two purlins on each of the front- and back slopes.

Your house is of average depth front-to-back, so I would guess you have one purlin on each slope, roughly half-way between eaves and ridge? If this is the case, only about one-quarter of the front slope will actually be supported by the beam over the bay - the rest of the front slope up to the ridge will be supported entirely by the purlin.

And as mentioned before, the floor closest to the eaves can be counted as 'loft storage' (0.25kN/m² rather than 1.5), thus further reducing the live loads.

This is why I believe their figures may be over-estimating the load on the beam by a considerable margin. That being the case, I would see little point in adding a steel plate. The beam does need strengthening, but a piece of timber (say 9x2) would be sufficient.

 

[messimagician]

Thanks Tony, yes there are 3 purlins. There is one on each plane about half way up the roof.

I'm not sure putting 9x2 onto the existing 9x3 would work, wouldn't the ends need to be supported on the 9x2? it's already near flush with the brickwork as it is.


I'm going to email the SE back and see what he says with regards to fixing plasterboard to these plates.

Thanks again for your help

 

[tony1851]

I'm not sure putting 9x2 onto the existing 9x3 would work, wouldn't the ends need to be supported on the 9x2? it's already near flush with the brickwork as it is.

No, a new piece would not need to be supported at the ends at all - it can be stopped a few inches short if needs be. The bending stress in the timber is greatest near the middle of the span - look at the second diagram down on the second sheet of your calcs. showing how the stress diminishes towards the ends - so near the middle is really where you need the extra thickness of timber. (Look at your SEs diagram showing the end of the steel plate - that's not supported off the brickwork either because it doesn't need to be). As long as it is well-screwed in, it would be fine. In fact, the steel plate itself need not be as long as the timber - around a 2m - 2.5m length would do because for the last 12"-18" of the beam, the original timber on its own would be good enough to take the bending stress.

PS - if you are still staying with the steel plate, don't use 10mm bolts, use 10mm coach screws instead. Despite how it may seem, the bolts are not as strong as the coach screws in shear, and shear strength is what you need in that situation. Surprisingly, many building inspectors and even SEs don't seem to realize this!- but it's all there in the BS 5268 code for timber design.

 

[messimagician]

Ok thanks, I'll bring up the coach screws v bolts with the SE

What length of coach screw would I require if the combine steel timber is 85mm?

I take it you don't need any washer at all with these?

Something I'm not sure of is the bolt spacings ect

When it says 40mm from the edge, is that referring to both the timber and the steel together? Or is it referring to just the steel giving a total 65mm from the timber edge?

I did do mechanical engineering years ago but these don't show the measurements on the actual drawings

 

[tony1851]

Ok thanks, I'll bring up the coach screws v bolts with the SE

What length of coach screw would I require if the combine steel timber is 85mm?

I take it you don't need any washer at all with these?

Something I'm not sure of is the bolt spacings ect

When it says 40mm from the edge, is that referring to both the timber and the steel together? Or is it referring to just the steel giving a total 65mm from the timber edge?

I did do mechanical engineering years ago but these don't show the measurements on the actual drawings

75mm length would be OK; drill pilot holes of course.
It's always adviseable to include washers.

For screws in timber, the spacing rules are slightly different than for bolts; for 10mm screws, it's min. 100 from the end of the timber; min 50 from the top and bottom edges; min 100 between adjacent screws in a line, and min 30 perpendicular distance between lines.
Obviously the spacings will be wider than the diagram in the calcs and will bring the screws in slightly from the end of the bearing but that doesn't matter.

 

[messimagician]

I have just had an email back from the SE and like you said, he recommends coach screws as they will be easier to fit than bolts

Reading what he said he says it won't matter if you use bolts or coach screws using the existing measurements? As long as it's 800 N/mm2 that's all that matters. That's just jargon to me haha

The drawing shows 5 bolts at the support end at approx 50mm into the wall. What your saying is that using coach screws they need to be 100mm from the end so essentially screwing these coach screws tight next to the wall?

So do I use the coach screws in the same layout as in the drawing except the screws will start at each wall instead of inside the cavity?

And if I've got this correct

So going from the bottom edge up to the top at the support ends you would have 50mm+10mm+47mm+10mm+47mm+10mm+50mm = 224mm

The second screw at the bottom of the support end, would the distance between the two coach screws be 40mm or 30mm? The same for the top two?

Then it would be a case of then working out equal distances for the 10 screws across the centre line? Each screw staggered 50mm above and below the centre line?

 

[tony1851]

This is for the timber beam (the screws can be nearer to the end of the steel plate).

 

[messimagician]

Thanks again for the help Tony, yep that makes sense the screws being nearer the edge on the steel

So the way my SE has drawn the bolt layout as 3 bolts in a straight line unlike your drawing, this would not be possible?


Also are the measurements you said based on the center of screw or edge of screw? It looks like you've drawn it to centers

 

[messimagician]

What I forgot to ask is where it has the minimum spacings like Sedge, Send ect. Does the S refer to steel.? So it would require screws to be 40mm from the edge and end of the steel

 

[tony1851]

Thanks again for the help Tony, yep that makes sense the screws being nearer the edge on the steel

So the way my SE has drawn the bolt layout as 3 bolts in a straight line unlike your drawing, this would not be possible?


Also are the measurements you said based on the center of screw or edge of screw? It looks like you've drawn it to centers

Yes, you can have them in a vertical line if you wish, the point being that there must be at least 30mm between them perpendicular to the grain, which you will easily achieve.
Measurements are always taken from the centreline of the fixing.

 

[tony1851]

What I forgot to ask is where it has the minimum spacings like Sedge, Send ect. Does the S refer to steel.? So it would require screws to be 40mm from the edge and end of the steel

"s" is usually shorthand for 'distance'.

The fixings can be a lot nearer the edge of the plate because the steel is much stronger than timber - 25mm from the end/edge to the centre of the fixing would be perfectly OK.

(I should be charging you time-and-a-half for this!)

 

[messimagician]

Haha thanks, it's good that you can help

So my SE sent this over, it's a trada coach screw designer. It will make more sense to you than me but one thing i'm unsure of is the different minimum measurements between my SE and what you've put unless I've misunderstood.

[url=https://ibb.co/cWFj9k] [/URL]


I have done a drawing myself with slightly more detail in measurements. With what you've helped wuth and guidance hopefully It shows I understand what you've said.


[url=https://ibb.co/bvZ0h5][/URL]