Lintel load for patio doors

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My SE has specified a steel beam 152x152x30 with 10mm plate welded to top and bottom flange. This is support a clear span of 1.8m for a patio door. In their calculations, they said the load on each bearing is 33.8kN so total load is 67.6kN.

From what l have tried to understand about how to calculate load on lintels, this seems very high. There is a window direct above the opening on the 1st floor and dormer loft above that. It’s a normal cavity wall.

Reason I am doubting all their calculations is because they also specify a steel beam 178x102x19 for a 1st floor lintel to support an opening of 1.9m. Here the load given is only 10kN so don’t understand why a concrete lintel would not suffice.

Before I go back to them (as they are slow at answering), I just wanted to get a idea if my concerns are valid or not.
 
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That's a monster beam for such a short span over the patio. Why don't you just use a standard lintel? No need for calculations.

Likewise for the first floor beam which seems over-specified.

Were they proper engineers, or the inexperienced office trainee maybe?
 
Thanks for your reply Woody. It’s good to know that I am not completely stupid to be questioning it. My concern is dealing with building control if we don’t use what is specified in the drawings.
 
Typically, if you specify a standard lintel then as long as the lintel is suitable for the situation and the loads, the building inspector will accept it without needing proof or calculations.

So if your proposed concrete lintel can take the loads (from the manufacturers data), then it should be accepted.

BTW, those loads for the patio beam seem really high. If there is a window above, it does not seem like they have allowed for this and just used the load from the area of wall that would be there instead of the window and the dormer roof too, instead of allowing for the roof loads to be running down the side of the opening
 
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Unless the beam forms part of a railway bridge, it will not be carrying 67.6kN over a span of 1.8m. As Woods noted, a standard off-the-peg lintel would be fine.
The bottom welded plate is to support the outer skin, but why have they specified a plate welded on top as well?
 
Tony, I don’t understand anything that this SE does. Everything just feels wrong. For example they have specified a 40mm thick mild steel plate that is 900mm long to support a beam in the loft. I can’t seem to find a steel plate of this thickness easily.
 
I got the structural calculations for the lintel. Can anyone tell me if there is anything wrong with the figures used?
I don’t know why they used a calculation of 4.55x2.7 for the bricks.

I did ask the “engineer” to check but they insist it is the correct beam size for the clear span of 1.8m.
 

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The 4.55 x 2.7 = (load of wall in kN/m2 x height of wall in m) to give the load in kN per meter run (all the loads are worked out in kN/m run).

There will be some torsion on the beam due to the outer skin being supported off the bottom plate and offset from the centreline of the beam. This will add some additional bending moment to the beam.

They could have reduced the floor live loads by 10% to 1.35kN, which is an allowable reduction for two floors, but that would not make much difference to the final load. Also, they could have worked on the clear span of 1.8m, instead of what looks like a span of 2.1m.

But looking at the overall loads, I'd say the choice of section is not unreasonable. Maybe a 152 x 152 x 23 would have done, but cost-wise hardly much less.
 
They seem to calculate based on the length of the beam rather clear span. Also, why does the 45 degree triangle of load not apply here? Instead they have used the load of the full column of bricks.
 
We want to widen the old entrance by 30cm to 1.2m clear span. They have specify a beam of 203x203x46 with length of 2.2m. They said this is due to point load from a beam directly above in the loft floor and need the longer length to spread the load. I have attached the calculations for this beam which has an even high load on it (118kn).
Is it worth paying another engineer to calculate the beam for these openings?
 

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There would be no harm in getting a 2nd opinion, don't tell the other guy the calcs that's already been done.

That way if they come out the same then you know the first guy was right,
 
They seem to calculate based on the length of the beam rather clear span. Also, why does the 45 degree triangle of load not apply here? Instead they have used the load of the full column of bricks.
Yes, their maximum bending moment has been calculated for a span of 2.1m. Working on a 1.8m span, the bending moment comes down to just under 13kNm.
They will then also have over-calculated the deflection by around 40%, having regard to the reduced span and load.
If there is no window over the beam, you can allow for the arching effect of the brickwork, particularly on the outer skin, which will reduce the torsion on the beam.
Looking at this again, you might possibly get away with a 178 x 102 + welded plate, but at the end of the day, there might not be much cost difference between that and what they have specified - some of the cost will be taken up by the welding of the plate.
 
We want to widen the old entrance by 30cm to 1.2m clear span. They have specify a beam of 203x203x46 with length of 2.2m. They said this is due to point load from a beam directly above in the loft floor and need the longer length to spread the load. I have attached the calculations for this beam which has an even high load on it (118kn).
Is it worth paying another engineer to calculate the beam for these openings?

They allow a bearing length of 50cm. If the inner skin is celcon or similar, this then implies that they are assuming that all the load is going on just the inner skin, which can't be right?
And worse than that - as with the previous beam - they've worked on a clear span of 2.2m instead of 1.2m, which makes a huge difference to the bending moment and deflection. No wonder they computed such a high load (118kN) which would be difficut to achieve on a 1.2m span in a domestic setting, even allowing for an incoming point load.
Frankly, all this is just a rookie design.
 
There would be no harm in getting a 2nd opinion, don't tell the other guy the calcs that's already been done.

That way if they come out the same then you know the first guy was right,
No harm except for a small dent in my pocket.
 
Tony, in the loft there is a floor beam which sits a steel lintel over a doorway. This doorway is directly above the doorway we want to widen on the ground floor. Surprisingly, this lintel only need to bear 10cm at either end when there is a large support beam sitting on it. It’s frustrating!

Builder said it makes more sense to have to first floor doorway beam longer and the ground floor doorway shorter. Is he right?
 

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