×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Lintel Arching effect interupted?
2

Lintel Arching effect interupted?

Lintel Arching effect interupted?

(OP)
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 ?

RE: Lintel Arching effect interupted?

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

RE: Lintel Arching effect interupted?

(OP)
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

RE: Lintel Arching effect interupted?

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.

RE: Lintel Arching effect interupted?

triangle for the brick, line load for the slab.

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

RE: Lintel Arching effect interupted?

Sita: Love the comment...

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

RE: Lintel Arching effect interupted?

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.

RE: Lintel Arching effect interupted?

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?

RE: Lintel Arching effect interupted?

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.

RE: Lintel Arching effect interupted?

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

RE: Lintel Arching effect interupted?

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.

RE: Lintel Arching effect interupted?

(OP)
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.

RE: Lintel Arching effect interupted?

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

RE: Lintel Arching effect interupted?

@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?

RE: Lintel Arching effect interupted?

(OP)
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!

RE: Lintel Arching effect interupted?

@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?

RE: Lintel Arching effect interupted?

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.

RE: Lintel Arching effect interupted?

(OP)
Tony,
please look at the pictures attached.
Isometric view
You basicly have a beam wich is suporting an wall above it.
In picture "view" you can see the view and a section thru it.
We usualy converted the whole wall to the line load acting on a beam.
Should the wall above beam also be converted to a triangle or not?

RE: Lintel Arching effect interupted?

If that was my job, I would take the whole load of the wall above as a udl on the beam. Is it a concrete frame?

RE: Lintel Arching effect interupted?

Mar2805:
In your last two attachments the entire brick wall load is on the spandrel beam below that particular wall, and the spandrels at each level should be designed accordingly. Keep in mind than concrete shrinks and clay masonry tends to expand with age, so you must leave a joint at the top of the brick, at each story, to tolerate this expansion/contraction activity.

Take a look at a few good masonry design texts, masonry construction handbooks or masonry association tech notes for some better understanding of the loading of lintels and the arching action of various types and ages of masonry. The 45̊ triangle is a practical representation of the masonry below an arch, which might/would fall out without support, or is loading the lintel. The exact angle is subject to a bunch of variables about the make-up of the wall, otherwise the arch is in compression and starts to support the brick. The 60̊ angle is a reasonable representation of a line where the masonry is being held up by a normal corbeling action of the wall system above and around it. And, you might think of the space btwn. the two angles almost as a real arch that has its two arcs separated by a height about twice the thickness of the wall. Both of these actions require some monolith of masonry wall beyond the extent (width) of the opening below. That is, the arch needs some structure beyond the opening to take the horiz. thrust induced by the arching action. If you cut these angled lines (the arch) by an opening above your lintel, then the arching action can’t really take place, and all bets are off. Thus, Tony’s first attachment 27FEB14, 16:16, is really only correct for a large expanse of wall with no openings or concentrated loadings in the region of the triangles. His attachment from is code book gives a pretty good general explanation of the way the loads are figured, note the “common sense...” admonition. But, in your earlier attachments I would apply the full slab above and the couple feet of masonry to the lintel, and quit the screwin around with the load, unless I needed to finesse the shear, reaction or bearing a bit at a jamb. In your sketch showing symmetrical windows above, you’ve cut into the loading triangles, so it is doubtful that arching action can take place. I would apply all the wall load btwn. the windows directly to the slab. I would allow that the inner window jamb load corbel out (45̊) down to the slab, and then apply that to the lintel. The outer window jambs pretty much get carried straight down and added to the jamb load at your large, lower opening. On your sketch with the door opening on the left, there is just no arching action possible because of the door opening. Again, if I needed to finesse things I would allow the 60̊ corbeling thinking on the right side, but all of this load must still be taken down to the lower, large opening jambs.

The thing that you have to be careful about, for all this chasing the loads around, is that you don’t lose or forget any loads in the process. That is to say... even if the lintel doesn’t carry all the loading from above it in bending, due to the arching action; the opening jambs and wall section immediately adjacent to the jambs must carry all the loading (total actual load) from above the opening, and concentrated loads above may concentrate these total loads more on one jamb than the other.

RE: Lintel Arching effect interupted?

(OP)
@tony
"Is it a concrete frame"
Yes the wall is sourronunede by EC columns and beams (beam slab action)

@dhenger
So for the situation with 2 Windows above the garage door the load should be something like this (attach)
I included the load from the slaba bove since it sits inside the 60deg triangle. The load from the walls is included inside the red polygon.
As tony mentioned reaction from the lintels above should be also included, right? Should they be coverted to unifrom load also or....? How?

RE: Lintel Arching effect interupted?

@dhengr,
You've explained it better than I could, and clarified a point for me also.
Thanks.

RE: Lintel Arching effect interupted?

Keep in mind that all the wall load needs to go somewhere. It doesn't disappear just because you drew a triangle on the elevation sketch.

When there is a door or window offeset from the opening below it serves to concentrate the loads at the opening jamb. This might include a great deal of tributary area from floors and walls above. When openings are offset at the lower level of a multi-story assembly it can be a real killer for the lintels below.

Your included load needs to go to the centerline of the windows above, not just the lintel's edge as shown in mar2805's sketch. And if it's a multi-story building ALL the load from above needs a path to the ground. It does not magically disappear when it encounters window or door lintel.

If you think in terms of stiffness and load path you can work these out for yourself (this is what an engineer is, and does). If you think in terms of rules of thumb and shortcuts you won't have a feel for what's happening and you might end up with a grossly unconservative design.

RE: Lintel Arching effect interupted?

Mar2805:
I’ll say it again..., Tony’s first sketch and the first diag. on his code copy really only applies in a solid (continuous) masonry wall. You can’t get the arching or corbeling action the 45̊ or 60̊ triangles contemplate when you cut the imaginary arch rib by an opening like your door (on the left) or your two windows. That 3rd fl. (roof) slab is carried by the window lintels to their jambs and by the red polygon (width btwn. the windows) directly down to the large, lower lintel. I would not count on any arching effect btwn. the windows. The loads on the outer window jambs can start to distribute (corbel) out into the wall beyond, but mostly they go right down into the large, lower jambs as a concentrated loading. At least that’s they way I’d design those lower jambs and a few feet adjacent to them. Some vert. rebar right at the jamb and maybe some extra cells grouted immediately adjacent. And, some of that vert. rebar might be carried right up to the 3rd fl. bond beam if the window openings permitted it. Your red polygon is mostly the masonry DL, plus the slab loading btwn. the windows, but within that polygon you also have the inner window jambs, and they would distribute out below the window sills at 45̊ like the ‘point load from partition’ as is shown on the second page of Tony’s code copy. I think you should remove the 60̊ triangle from your last sketch. You could grout and reinforce the masonry from the large lintel to the 2nd fl. slab and you would have a good deep lintel, tied into the bond beam under the 2nd fl.

RE: Lintel Arching effect interupted?

(OP)
Guys Im sorry but any chance that you might skecth what you said?
Its much easier to understand it.
YOu got me confusing...

@JLNJ
Can you see the attachement. Two situation:
1) Windows aligned vertical
2.) Windows not aligned verticaly

YOu say that the 2 situation is very dangeruous if you floolow "by the book" 45 and 60 deg load paths.
Can you please explain and post a sketech of your comment.
Thanx.

RE: Lintel Arching effect interupted?

(OP)
Ok.
Plase just simple yes or no.
Sketch attached.
Load on the lintel is coming from walls Dead weight (indicated in red polygon) + line load from the slab (indicated in yellow)
Correct?

If yes one can determine the lintels support reaction, bending moment....

Can someone please now sketch the load thats transfered ONLY from this window lintel to the large garage lintel.

RE: Lintel Arching effect interupted?

(OP)
errrr....guys you wrote half a page on "How to"...so can you please just answer my question from my last post "5 Mar 14 7:53 "
Thanx

RE: Lintel Arching effect interupted?

(OP)
Hi!
I found an article here that explains how to deal with concetrated loads.
It seems that you disperse the load to a width of 4x the wall thickness and then divide this lenght with the concetrated load in order to get a liner load acting on the lintel below.
See link on page 2.
http://www.ce.udel.edu/courses/CIEG407/Class_11/TE...
If I use this on my previous post were I got a support lintel reaction of 20 kN and use this force as the attacking force on the lintel below I get an value of 33.33kN/m. See sketch attached.
Is this correct?
Come on guys I need some advice sad

RE: Lintel Arching effect interupted?

Considering onlyyour 20KN reaction from the lintel,I would have thought that it would have dispersed downward at 45 deg, as the red lines, as far as the lower slab. What happens to that load below the slab would depend on its stiffness. Conservatively, you could assume it continues down at 45 deg until it reaches the lintel.

RE: Lintel Arching effect interupted?

Are these CMU walls supporting the slab/concrete beam or does the concrete beam/slab support the block or is this like a brick veneer?
Is this new design or analysis of existing?
The southeast brick institute has a publication on brick lintels which you could add some continuous longitudinal joint reinforcement to the courses just above the lintel.
Are we talking about behaviour or design? The brick or block especially if placed in a stack bond will not only arch but act as a deep beam. This is behaviour but you need to be careful when using this information for design as you do not want excessive deflection.

I would think that the 60deg would be more appropriate considering there is masonry only on one side of the point load (reaction), but this is only a guess. Tony may know better. But before we get too carried away, I suppose no matter how you slice it these are approximations.

EIT
www.HowToEngineer.com

RE: Lintel Arching effect interupted?

Yes, the attachment you've posted 5 Mar 14 7:53 shows the correct solution for the top left window. I don't know if I'd bother taking it to this level, as it would be easier to simply carry everything down to the lower lintel which is actually above the top left window. That said, you are absolutely able to have arching above the slab where the opening and insufficiently deep masonry occurs below.

Note that beyond all the academic discussion, brick needs to be in at least fair to good condition, properly maintained (ie: 1/3 depth repointed with matching mortar), in order to arch. Where in doubt, carry loads straight down without 45 or 60 degree triangles. You will then be conservative and avoid a common source of failure.

RE: Lintel Arching effect interupted?

Mar2805:
You haven’t bothered to show us details of the wall construction, or told us what type of mat’l. the wall or lintel is made of. You haven’t bothered to put any dimensions on your sketches or the loads. These are all important bits of info. if you are wanting a meaningful discussion, they do influence the discussion and a proper design. And, an experienced engineer will draw conclusions and first impressions from that more complete info. fairly quickly, and without it he is almost blind, just guessing what you are really doing. Without it, your question and sketches seem kinda hypothetical and textbookish, so it is tough to give anything other than general answers. You have gotten some good info. from a number of the posters here, and you should read it a couple times for its full meaning. It seems that you did finally do a little literature digging on your own, I think someone suggested that too, and that is a really important thing to do if you want to become a good engineer and retain what you’re learning. Your latest sketch looks about right. And, if you look back, I said about the same thing in talking about the jambs and an adjacent couple of feet of wall taking all the loads from above. There’s that 60̊ again, and give or take a few degrees it doesn’t make much difference in the final analysis. Don’t undersize the lintel and don’t forget, for all the screwin around with the loads, the two jambs plus a couple feet of adjacent wall must carry all the loads from above; don’t chase the loads around and lose them, and then not account for them, that’s dangerous. Learn to think like the loads, how will they act, and take the most direct path to the foundation; look at the structure and follow this path all the way to the ftg.. Remember compatibility (re: strain and various element movement), if an element starts to be overloaded (a lintel, a jamb) can, or will, above elements (w.r.t. the lintel), or adjacent elements (the jambs) pick up some of that load, without any serious repercussions. If you do cut that load path (your windows or door vs. arching) or you can’t draw a clean load path, then you better think damn hard about how to provide a proper load path around the void. I don’t think I’ve ever seen a properly designed structure fail because it was overloaded by 5-10%, but I’ve seen plenty of failures because a proper load path wasn’t provided or because of poor detailing. The load didn’t know you shot a bull, it tried to go where it knew it should, and you didn’t provide a path or detail which would take that loading.

RE: Lintel Arching effect interupted?

(OP)
Thanx for advices.
I attached an .pdf drawing of the problem.
You have some dimensions in there as well as mine "load chategorisation" on the garage door lintel.
Wall self weight, slab support reactions, lintel reactions.
I wonder if the 2nd floor lintel raction have any influence on the garage door lintel.
I think that their influence is lost due to fact that the wall self weight, at some point going down from the small window lintel, becomes bigger then the window lintels disperesed reaction force.
Something like Boussinesq formula for stresess in soild due to surface loads...
I now it suonds funny but its kinnda similiar situation...
What do you think

RE: Lintel Arching effect interupted?

That looks correct - BUT why would you ever want to be so very precise? There is no justification for spreading the load in the brick "just because you can".

Apply arching ABOVE a lintel.
Apply loads straight down from reactions.
Ensure you continue all loads down to foundation.

These are safe, time tested methodologies that won't fail you.

RE: Lintel Arching effect interupted?

Mar2805:
For about the eighth time, you are chasing the friggin loads around and losing half of them along the way. You have an arching type triangular load right over the window lintels for lintel design and lintel reactions, but you don’t indicate any way that the rest of the loads over that window (above the arching triangle and added to the lintel reactions) get concentrated at the window jambs due to the arching action. That extra (lost) load includes masonry and slab loads above the triangle area on both sides of the window center line. And, you have the masonry weight btwn. the windows to add to the red slab loads. Don’t worry real much about finessing Boussinesq’s work until you have a better grasp of basic loads and load paths. CELinOttawa and I are saying essentially the same thing.

RE: Lintel Arching effect interupted?

I STRONGLY urge you to listen to dhengr. The more you over-complicate this, the more opportunity you ggive yourself to screw up. Relax, a firm and deep understanding of load paths and all the finess in the world will come with time. Slow down, and account for all loads as *simply* and *reliably* as you can.

The Cross method works not because it tells you some magically "correct" state of stress in a structure, but because it ensures that there is a possible state of stress at which the structure will be strong enough.

Worry about these three basics:

- Strength
- Stiffness
- Stability

Forget the rest; You'll pick it up along the way whether you want to or not. Right now you're just cruzing for a brusing.

RE: Lintel Arching effect interupted?

(OP)
@dhenger
Are you talking aboth loads on window lintels that I didnt draw in previous sketch couse you got me realy scared now?!
Have I missed something?
I didnt say in my previous post anything aboth this, but I just draw the load coming from window lintels.
This is now (hopefully) THE COMPLETE LOAD SCENARIO....
and guys, please do post your sketches couse its much easier sometimes to solve problems.

RE: Lintel Arching effect interupted?

It looks to me that you just have 350 cm tributary length from the walls, floor, and roof, and you apply it as a uniform load to your lintel at the lower level.

Then you go talk to the architect because you need a very deep lintel. You might even need to beg for a pier on each end because the bearing stress will be very high.

You might have shear problems with the design of the lintel and you will comtemplate a higher f'm or maybe shear reinforcement. Or a steel lintel (if permitted by fire code).

Then you look up the mechanical guys and tell them they are not permitted to run duct or piping through this important lintel. Murphy's law says that this is where the HVAC header needs to go.

Then you get with the electrical group and inform them that, no, it's not OK to cut a slot through this lintel for cable tray.

Lastly you will need to make sure the control joints are as far as you can get them from the lintel jambs to maximize your bearing length.

RE: Lintel Arching effect interupted?

@mar,

FWIW, assuming the brickwork is sound or new, and putting aside the books for the moment, I would have just taken the whole loading within the red line on the attached sketch - walls, slabs and roof - job done. It wouldn't be that far out - I might have missed some (small) loads, but have probably added some in as well.

Look at it from a practical viewpoint; if the beam sheared off completely at both bearings, gut feeling says it's highly unlikely the whole facade would drop down by the span of the beam.

RE: Lintel Arching effect interupted?

(OP)
Thank you all for the assistance.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources