Load Bearing Clay Brick Wall

[asixth]

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.

 

[apsix]

BA
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.

 

[BAretired]

apsix,

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

 

[hokie66]

asixth,

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.

 

[asixth]

hokie,

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.

 

[BAretired]

asixth,

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

 

[hokie66]

asixth,

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.

 

[BAretired]

hokie,

Does that mean I don't get any Wallaby stew on my next visit?

BA

 

[hokie66]

No, no. Just give me a bit of notice so I can get a good one. Actually, some steaks off one of the animals parading around in that arena of asixth's would be a better introduction to Australia. Along with some Barossa Shiraz.