Lintel Arching effect interupted? 2

[mar2805]

HI guys.
This is my First time caclulating a amasonry structure and Ive been reading a lot of topics on this matter but few things are not clear to me.
If you look at the picture attach:
Imaginary arching triangle is intrupted by a RC floorslab (green line).
Should I still provide the traingle load from wall Dead weight or should I take full rectangular block from the lintel top side to the top side of the slab + tringular shape from the top side of the slab ?

 

[wildehond]

i'd take the full triangular masonry load & add a "line" load for the slab only.

 

[mar2805]

Isnt that wrong?
Reading thru these forums I was under the impression that If arching cannot be established one should ignore the triangular shape above the lintel.
Basicly like looking if there wasnt any lintel above the opening, would bricks fall down or not?
Looking at my first picture (#1 post) I can clearly see that there cant be any arching wich would mean if I remove my lintel the whole row of bricks above the lintel would probably fall down.
Right?

So I was thinking maybe of something like this
1.) rectangular block of masonry
2.) Slab support reaction (line load)
3.) triangular block wall above the slab acting down on the slab and lintel

forgot also the lintels selfweight

 

[CELinOttawa]

mar2805 is correct... Where your arching is interrupted, you have to treat this as all imposed line loads; You could, at most, consider the slab as a lintel and use a triangular load distribution onto this from above the slab.

I would not encourage such an approach, however... Always best to be conservative when not entirely certain as to behaviour.

 

[SLTA]

triangle for the brick, line load for the slab.

and by the way - we're not all guys.

 

[CELinOttawa]

Sita: Love the comment...

But I think the triangle for the brick is inappropriate when interrupted. You need arching and cannot develop it.

 

[dhengr]

Mar2805:
The triangular loading over the lintel is some attempt to represent the arching action on the brick or conc. blk. which could fall away (if the lintel was removed) or it is loading the lintel. In some fashion any masonry above the triangular shape (exact angle in some dispute) is carried out to the opening jambs and the wall beyond, by the inherent arching action of the masonry wall. The arching action also requires sufficient masonry wall beyond the opening, on both sides, to provide the horiz. thrust at the spring line of the arch, that is at the top of the opening and on down to the found. Of course, reinforcing and grouting can easily start to turn the lintel into a deep beam up to the slab level. If you only have a few courses of masonry up the underside of the slab, I’d use a full rectangular shape for the masonry loading. But, if the slab is high enough so that .5, .67 or .75 of the triangular load shape height is below the slab bottom, I’d be comfortable using the triangular shaped masonry loading, plus a line load for the slab and all above it, which it is carrying. The length of this line load might be a little less than the full width of the opening below, with the realization that the arching action carries that last couple feet of load out to the jambs and wall beyond. Maybe akin to a strut and tie action above your triangular shape. You might run the jamb rebar up into a bond beam under the slab to tie it all together. Lintel deflection may be as important as bending. This whole loading thing is a bit subjective and may not offer much savings in rebar or grout. We are kinda nit-picking here, but the arching action tends to reduce the bending and shear loading on the lintel, but you must still provide for the total loading from above immediately around the two jambs. And, you must tie sufficient wall in on each side so the thrust from any arching action can take place.

 

[mar2805]

What aboth a more complex situation like this (attach picture)
Wide garage doors...
How to determine the load shape here?

 

[mar2805]

I attached an egsample and Im interested if the red area enclosed would be the right assumption of the loading on the garage door lintel.
Im not certain if the lintel reactions from Windows should be included also as a load or not?

 

[CELinOttawa]

If the left and right top dark grey areas are "cap stands", ie: similar to parapets with concrete caps, why are they not included in the loading?

Please label or otherwise clarify your sketch... Also, what are the green reactions?

 

[mar2805]

Please look at the updated picture.
Green arrows would be forces that lintel press down the wall (support)

 

[tony1851]

The BS code considers two triangles, a load triangle @45 deg, where all the load is on the lintel, and an interaction zone @60 deg. in which the masonry is not regarded as being supported by the lintel.
Any point or distributed load in the load triangle is dispersed at 45 deg. and carried by the lintel. Half of any such load in the interaction zone is regarded as being carried by the lintel. Where openings cut completely across the I.Z., no load above is added, but where it cuts into the zone, then yes it becomes more complex.

 

[mar2805]

And lets convert your word into work...my previous attached picture would you say that it is correct assumption?

 

[tony1851]

mar2805,

This is how I would interpret the situation on your lintel.
The small window lintels just about cross the 60 eg line, but it might be my line that's a little out, though I personally would take the reactions there into account.
In practice best to be more conservative than this, particularly in an old building.

 

[mar2805]

tony your from UK?

Im interested if you could do the same for my sketch in my post from "25 Feb 14 6:46".
Its more complicated.
Would like to hear you explenation.

 

[AELLC]

tony,
Why does 1/2x1/2xW2 bear on lintel? - I should think it is 1/2xW2

 

[tony1851]

@mar, your problem gives food for thought.
Our BS code for lintel design states that 1/2 any point or distributed loads within the interaction zone is carrieed by the lintel. But in your sketch, I would not be happy in halving the load to the right of the door between the two triangles and would assume all that load acts on the lintel (sorry if I haven't explained it too well).
The sketches on the r.h.side show how I would view the effect of all the loads on the lintel split into components - any different views anyone?

 

[mar2805]

Tony thanx.
But I dont understand that 60 deg. line?
Form where does it come from?
Isnt load dispersion line supposed to be 45 deg?
OnE more when you transfer the suppor reaction from lintels above to the lintel you are designing, how do you do it?
You devide the point load (kN) with the lintel lengt thats affected withn the 60 deg triangle in order to get a line load or...?
Same thing for the slab support reactions?
tHANX!

 

[tony1851]

@mar,
Frankly I'm not sure of the relevance of the 60 deg. line also.
Most of my work is alterations to older 2 and 3 storey brick buildings where we remove ground floor l/bearing walls and insert steel beams.
I don't trust a lot of old brickwork; as an example, for an opening say 4 or 5m wide, I just take vertical lines from the bearings and count everything within those lines (walls,floors,roof etc). Yes, it's very conservative and I can sleep at night.
Purists might say that's not engineering, but I've seen old Victorian brickwork cracked vertically top to bottom, and arching seems irrelevant then.
For new-build masonry yes, you could refine the loadings with more confidence.
FWIW the attached shows examples of the code we (sometimes) use - though they may not be relevant and your code will no doubt have something similar?

 

[CELinOttawa]

Tony: That is engineering, and it is entirely correct to be conservative when materials are at all in doubt. That's called honouring your obligation to protect the public.

I do the same thing on anything with brickwork 50 years and older. I recently had a job where I asked the contract to install a lintel two meters below another lintel and carried floor loads above as direct point loads, no arching action. The contractor was arguing black and blue that I'd oversized and that my warning to him to prop the wall was "overkill".

He apologised after the bricks fell out while they worked. The recent repointing job was to a depth less than 5mm.