Load Bearing Clay Brick Wall
Load Bearing Clay Brick Wall
(OP)
Hi guys,
I need to provide a concrete stair that is adjacent to a historic building to provide new access. The building itself is classified a "historic landmark" so it cannot be touched.
The architect has the idea of using 110mm (4.5") wide loadbearing clay brick to support this stair so it has the same appearance as the landmark building which was built before 1900.
I do not know much about masonry design in general but I have done some numbers which show the clay brick wall has capacity for 93kN (9.3 tonnes / 20kipf) and the ultimate load from my analysis is 110kN (11 tonnes / 25kipf).
The wall dimensions are 2000 (7') wide and 3010 (10') high.
My questions are as follows:
1. What should I be looking at when designing loadbearing clay brick walls? I think a slenderness ratio has to be satisfied.
2. How can I strengthed this wall so it can support the load required? Can I provide reinforcement of any nature.
Just by looking at the section my natural instict is that the wall doesn't look right. I would rather provide a concrete masonry unit wall with a non-loadbearing clay brick vaneer.
All comments will be appreciated.
I need to provide a concrete stair that is adjacent to a historic building to provide new access. The building itself is classified a "historic landmark" so it cannot be touched.
The architect has the idea of using 110mm (4.5") wide loadbearing clay brick to support this stair so it has the same appearance as the landmark building which was built before 1900.
I do not know much about masonry design in general but I have done some numbers which show the clay brick wall has capacity for 93kN (9.3 tonnes / 20kipf) and the ultimate load from my analysis is 110kN (11 tonnes / 25kipf).
The wall dimensions are 2000 (7') wide and 3010 (10') high.
My questions are as follows:
1. What should I be looking at when designing loadbearing clay brick walls? I think a slenderness ratio has to be satisfied.
2. How can I strengthed this wall so it can support the load required? Can I provide reinforcement of any nature.
Just by looking at the section my natural instict is that the wall doesn't look right. I would rather provide a concrete masonry unit wall with a non-loadbearing clay brick vaneer.
All comments will be appreciated.






RE: Load Bearing Clay Brick Wall
Go with your instinct. You can build the wall in brick, but not single skin. Check the robustness requirements of AS3700.
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
You really can't connect the 110 single skin of brick to the slab, as there is no place to put reinforcing. My advice would be either to use a double brick wall, 230 thick; or otherwise use a 350 x 350 square pier at each end. In the piers, you can build in a vertical bar.
Tell the architect that it is not structurally honest to use a single skin bearing wall in a historic building, as they would never have used just a single skin in those days.
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
I remember making a crude model, mainly so I could estimate the deflection and moments for the stairs. I know I didn't make an accurate assumption of the brickwork stiffness and my model was getting 12mm deflection (0.5") at the top of wall. I have not modelled any moment transfer into the wall so it esentially acts as a roller support.
hokie,
It is attaching to the side of the old grandstand at the exhibition grounds. The inside skin will not be visible from any direction and I have to completely isolate it from the existing stand, I just want to make it appear as one structure.
RE: Load Bearing Clay Brick Wall
It will possibly be English or Colonial bond (see http://w
Unless stability is a particular problem an unreinforced 230mm thick wall should be fine. As per above, 110mm thick is too slender.
RE: Load Bearing Clay Brick Wall
My question is:
Is this an appropriate solution for the architectural requirements I was briefed?
That being, a clay brick masonry appearance that cannot tie in with the existing structure.
I have heard stories of engineers providing a 100mm (4") cavity between brick leafs, providing steel reinforcing and then core-filling to get more capacity out of the brick walls.
RE: Load Bearing Clay Brick Wall
The cheek wall (the one beside the flight) can be non load bearing, but it has to be braced at the flight. As well, the balustrade itself cannot be unreinforced brickwork. Unreinforced brick cantilevers should be avoided. What happens to the balustrade on the landing?
It is no story, you can reinforce a brick masonry wall in the manner you described. You need some ties across the cavity.
RE: Load Bearing Clay Brick Wall
When you mention 230 brickwall, that is two skins of 4.5" brick (110 brick), this only leaves room for a 10mm cavity, I would image that the cavity would need to be reinforced with a minimum of N12-400 each way if core-filled.
Do you know of any clay brick institute websites on the web that have some good reference material. I found the clay brick paver institute of Australia to be lacking detail?
Is it possible to make the inside wall loadbearing and constructable at the same time. I image you can downturn the stair slab onto the wall to match the stretcher bond however, the wall that would then sit onto the stairs would need to be cut to suit the stairs.
RE: Load Bearing Clay Brick Wall
I will try to find some reference material for you.
RE: Load Bearing Clay Brick Wall
Or you could build three walls under the stair such that the concrete is cantilevered, say 600 mm on three sides. This would permit a reduction of about 3" in slab thickness. The steel railings would then be fastened to the concrete.
BA
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
BA
RE: Load Bearing Clay Brick Wall
A point to watch if supporting the stair on mixed block/brick. Concrete shrinkage and brick growth could result in the brick carrying all the load, it's best if there is asoft joint at the top of the brick.
RE: Load Bearing Clay Brick Wall
Here is another idea (see attached).
BA
RE: Load Bearing Clay Brick Wall
Not bad idea. I would adopt it, or at least a serious consideration among all solutions, if a cantilever beam extended to the end of the landing.
RE: Load Bearing Clay Brick Wall
I thought a 200 mm slab was adequate without a beam, but we don't have any fixed dimensions, so it's hard to say. The wall could be extended out a bit more if desired. I don't think the architect would like a beam.
BA
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
BA
RE: Load Bearing Clay Brick Wall
Then take out 2' beam stem, with shoes on, his hair could be rub against the bottom of the beam, and looked like a perfect post for the landing :)
Just kid around a little in the lazy sunday afternoon. Enjoy the hangout, before go back to work.
RE: Load Bearing Clay Brick Wall
I think Yao Ming is the tallest in the NBA and he is around 7'-6". I don't know who is the tallest player in Europe.
BA,
The architect was really keen on a brick balustrade so it can adapt with the existing grandstand.
RE: Load Bearing Clay Brick Wall
How about 8" block wall with 4" brick extended above stairs (8" wall hiden below stairs). I think it wouldn't be too difficult to detail out. Maybe someone has suggested it already, just to repeat it again as a "thank you" notes for your tips (on Yao's height :).
RE: Load Bearing Clay Brick Wall
If you mean the single skin brick will serve as a balustrade, it won't. He has to have a wall thick enough so that he can reinforce in the middle. Did you ever get your head around how central reinforcing can work? I remember in another thread you doubted it. Anyway, that is the way you reinforce masonry walls for bending.
RE: Load Bearing Clay Brick Wall
How thick are the existing balustrades at the EKKA? What kind of brick? Has the architect determined that he can obtain an acceptable match with the existing brick?
RE: Load Bearing Clay Brick Wall
As long as the 4" face brick can cover the exposed side and extends above the stairs, then I don't see much problem they can make it work. Don't make it more harder than irt deserves.
RE: Load Bearing Clay Brick Wall
This is a substantial lateral load, equivalent to 205 plf. I don't know what the requirement is in the UK, but I don't think brick veneer is going to be capable of doing the job by itself.
You might use a concrete wall or a steel framework and apply the brick as a veneer on one or both sides but that makes the balustrade pretty thick.
Correct me if I'm wrong, asixth, but I thought you said in an earlier post that the masonry on the landing was to be replaced by a steel balustrade. Why wouldn't the architect do the same on the side of the stair?
BA
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
I thought the building was in the UK. I think you suggested that the situation must have arisen in the existing building, so how was it handled there? Maybe they can simply duplicate what was done before.
BA
RE: Load Bearing Clay Brick Wall
Yes, asixth will need to beef up the 4" brick above the stairs to meet both strength and architectural requirements.
How about provide dowels from the concrete stairs, then add another 4" voided brick wall as inner face. The dowels will be extended through the voids, and grouted. A cap layer can then placed over, and cover the combined 8" reinforced wall (balustrade). Of course, the selection of suitable brick is very important.
Only a suggestion, no intention to step on other's idea.
RE: Load Bearing Clay Brick Wall
The architect has done away with the load-bearing wall which supports the landing (rightmost wall as shown on elevation) so they can get some additional storage space under the stair. So we are now using two load-bearing 140 (5.5") CMU walls running parallel to the stairs. The slab section can be reduced to 6" (150mm) spanning in the short direction and downturned so it can suit the coarsing of the block.
Likewise, they did not like the idea of cutting blocks so the wall can sit on top of the stairs and have suggested a r/c wall with a nice smooth formwork finish.
I am relying on the block wall to cantilever out-of-plane in order to brace the stair against any notional horizontal forces. I have kept the detailing of the stair similar to previous design, but have bulked up the reinforcement spanning transverse across the stairs to the two load bearing walls as this is now the direction of span.
Thanks to everyone for their positive contribution to this thread.
RE: Load Bearing Clay Brick Wall
RE: Load Bearing Clay Brick Wall
I would prefer to see 8" concrete walls below the stair too.
BA
RE: Load Bearing Clay Brick Wall
I also realized that after I sketched it up, I will make sure the cad-techs get it right.
RE: Load Bearing Clay Brick Wall
It's a rigid box structure with 1 wall missing, I can't see stability being a problem.
RE: Load Bearing Clay Brick Wall
I think the plan dimensions are approximately 8' x 20'. The missing wall is the 8' wall at the 10' high end. It has some rigidity to be sure, but it is not a rigid box and, in my opinion it should be braced at the right end on the sketch.
asixth said:
I don't think he should rely on those walls in that way.
BA
RE: Load Bearing Clay Brick Wall
I agree that relying on the walls cantilevering is optimistic. The block to slab connection has moment capacity which will help.
My reasoning is:
For lateral movement to occur the stair flight has to rotate about the lower end.
This rotation is resisted by in-plane shear in the 2 reinforced block walls.
RE: Load Bearing Clay Brick Wall
I agree with you, but I think it is essential for the designer to recognize the behavior of the structure. Moreover, I do not like three shearwalls when the aspect ratio is 2.5 with one short wall omitted.
BA
RE: Load Bearing Clay Brick Wall
BA's point about lateral robustness should not be overlooked. You could incorporate returns on the walls at that end, or if that encumbers the storage space too much, tying the landing to the existing structure may be the best way to go. It would only require a few tie bars, but I don't know what you have to tie to. I know you won't have "crazed soccer fans" in this grandstand, but the crowd may be anxious to get out after watching the grand parade or a concert.
RE: Load Bearing Clay Brick Wall
I think the only thing the stand is used for these days are watching cattle parades and the occasional speedway, not sure if they still have racing at the ground.
BA,
I had one of the senior guys in the office say the same thing to me today, that I need something to brace the stair, I'll put it to the architect whether we can have returns at the 10' high end. Looking over preliminary architecturals, I think we should have some room for this.
From a constuctability view, how difficult is it to downturn the stair to suit the coarsing of the block. Both myself and the architect don't have alot of site exposure behind us. Would it be simplier to only make the stair load-bearing at the 10' high landing where the soffit is constant?
If I do this then I will need to thicken the stair section again.
RE: Load Bearing Clay Brick Wall
I have never been a fan of 6" concrete block to support a concrete structure even though I know it will work if properly built. It seems to me that this structure warrants 8" concrete walls under the stair. Brick veneer can be applied later. Architecturally, it makes little difference.
If the space below the stair is to be used for storage, I would think you would want lockable doors. The end wall would then have a nice 3' chunk of wall over the door which, combined with a 12" column at each corner would give you a pretty stiff frame which should suffice in resisting lateral loads.
Changing the slab back to the original concept would be the wrong move, in my opinion.
BA
RE: Load Bearing Clay Brick Wall
It is not difficult to turn down the stair slab onto the blocks. Just a bit of extra formwork, done all the time. I see nothing wrong with your latest concept, as long as you provide some lateral resistance on the high end. Yes, watching the Charolais parade and the sheep dogs perform are the main activities. But they do sometimes have music performances at night during the EKKA week.
BA,
We usually agree, but in this case, I think the 140 block solution works, provided cleanouts are provided and the wall is fully core filled, as is normal practice here. We rarely use partially grouted walls. I prefer 190 blocks in most cases, but this is a minor structure, and 140 block will do the job. I wouldn't use a concrete wall, as I think it is overkill.
RE: Load Bearing Clay Brick Wall
Does that mean I don't get any Wallaby stew on my next visit?
BA
RE: Load Bearing Clay Brick Wall