Beams again (again)

[adder1969]

Hi, usual kind of message - I already have a single doorway from my lounge through to the dining room, through a wall in the middle of the house, and I want to make this opening into a double one.

The wall is blockwork but there are no internal block or brick walls upstairs. I had a look & the current lintel is an inch deep, 4 inch wide piece of corrugated steel. The upstairs joists rest on this middle wall, therebeing one joist rear-to-middle, then another middle-to-front of the house.

I want to get an understanding of what is required so, of course, I downloaded superbeam 4 to have a bit of a play. The example in there is for a loadbearing wall with a brick wall upstairs so I changed that to loadings for a stud wall. Am I right that I can delete the roof load? The upstairs floor load is half of the length of each joist - i.e. half of the distance from front ot rear of the house multiplied by the loading factor?

For the current door this gives me "r1comp=4.66, r2comp=4.66, Max S.F=4.66" Are any of these the UDL? Going to the catnic website they ask for UDL. The max UDL of the catnic corrugated beam is 7kN. It would appear that just about any beam long enough would do for the double door opening. Is there any advantage of using a catnic over a UB?

In terms of bearing area, am I right in thinking that the bearing area of the beam (the part in the wall) needs to be enough so that the pressure is spread and within the limits of the block work i.e. the large the loading the more of the beam needs to go into the wall. The catnic website simply states "150mm".

Cheers!

[John Rumm]

I would expect so...

If the joist in uniformly loaded, then you will see half the reaction of the total down force at each end. Hence the load on your lintel will be the weight of the blocks/bricks above it, plus the sum of the downforces of all the beams resting on the lintel.

I presume UDL is Uniformly Distributed Load (as opposed to a point load)...

Don't know...

You don't want it concentrated on a tiny section, but once you have got to something like 150mm I would expect you will need a fairly serious load to raise the pressure at the contact point to something that would crush even fairly light blocks.

[Tony Bryer]

Yes: if the load is uniformly distributed it can generally be higher than if concentrated at one point. The R1comp and R2comp are the reaction R1 and R2 components of each load so if all the OP's loads are UDLs it would appear that his total UDL is 9.32kN, more than a Catnic corrugated lintel will take, according to his figures.

[adder1969]

Ok, so I took the measurements properly last night :-) ..and using a 7 metre length of house rather than guessing at 8 and using a span of

80cm for the *opening* (not the length of the lintel) I got 3.44kN on each end which I guess is more or less 7kN UDL so the corrugated lintel is within spec. I guess that the point loads of the joists above are more or less converted to uniform loads by the presence of the brick/blockwork inbetween them & the lintel. Opening up the span to 1.6m I get a total load of about 18kN.

Now to factor in the full size snooker table going in the room above.... :-)

[Tony Bryer]

Joists at 600mm centres or less are treated as a UDL. The alternative is too horrible to contemplate!