Replacing a timber lintel with a reinforced concrete lintel.

[veetail]

My barn has large timber 'A' frames supporting the roof. Most of the A frames rest on timber wall plates on top of solid stone walls. But one A frame rests on two timber lintels placed over the window openings. These timber lintels are 3 inches deep, 8 inches wide, and 66 inches long. The clear span is 36 inches. Both lintels are sagging under the weight of the A frame which is placed exactly in the middle of the clear span. I want to replace the timber lintels with reinforced concrete ones. Two standard 1.8 M, 100mm wide by 65mm depth concrete lintels would fit. But I have no idea if the concrete lintels will do the job, as they will simply be resting on top of the stone wall either side of the window opening, and will have to support a point load in their centres.
Anyone know if this will be ok?

 

[RonnyRaygun]

Is it a barn, or a barn conversion?

Anyway, I don't think a pair of 100x65 lintels would have the capacity if a pair of 8x3 timbers are failing.

I take it the lintels are alongside each other? If so, you will have room for more than two 100mm wide lintels.

I'm not sure, however, that you can put point loads onto 100x65 prestressed lintels. Naylor give no indication of point load capacities in their brochure for any of their lintels. You could give them a call for advice.

However, you will still need to work out the point load to the lintel from the A-Frames, depending on the spans, centres, and roof make-up.

 

[veetail]

Hello RR
It is a barn which I am insulating to make more useful, including additional Velux roof windows. I don't want to put more load on the suspect timber lintels, so want to replace them with stronger ones.
The A frames span 24 feet, to support a 35 degree pitch slate roof.
I have various bits of metal on site including sections of old railway line. Perhaps two 1.8 m lengths of rail might be stronger than two 65mm concrete lintels. Maybe stock steel lintels or small RSJs are available to do the job. I am an aircraft engineer not a builder.. hence my lack of knowledge on this basic stuff.

 

[RonnyRaygun]

Are you involving Building Control?

Truth is, either way you should get an SE to do a calc for you, or you should at least accurately work out the point load to the lintel. The A-frames span 24 feet, but what is the distance between the frames. Once you know all this you can work out the area of load to the lintel (Elementary stuff for an aircraft engineer surely? ).

I couldn't say whether using railway track would work as I have no idea of the profile of the track you have. I would imagine most standard railway track would be much stronger and stiffer than a couple of pieces of 8x3, but wouldn't want to say for sure. If you want to use that you should definitely get a calc done.

As I said before, probably the easiest solution would be to speak to Naylor - or another concrete lintel manufacturer - tell them the point load to the lintel, and ask what they recommend.
When you work out your roof loads, don't forget to allow 0.6kN/m^2 imposed load for snow.

 

[veetail]

Many thanks RR
Might get an expert to give it a look. No doubt he will share my opinion of the daft people who built the barn and put an A frame across the window openings. No building regs in 1820 I guess!