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.

 

[kslee1000]

BA:

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.

 

[BAretired]

kslee,

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

 

[kslee1000]

Or it (the cantilever) maybe rejected by a 7' tall ball player

 

[BAretired]

He'd have to jump 3' to hit it. The slab is 10' clear.


BA

 

[kslee1000]

Well, 7' is a round number, he could be 7'-10, 7'-11. By the way, who is the tallest ball player in the world?

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.

 

[asixth]

kslee1000,

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.

 

[kslee1000]

Surprised to know Yao hasn't been surpassed. Seems MBA grows a few inches every couple of years.

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 .

 

[hokie66]

kslee,

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.

 

[hokie66]

asixth,

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?

 

[kslee1000]

Hokie:

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.

 

[BAretired]

In the National Building Code of Canada (NBC), the minimum horizontal load applied inward or outward at the top of every required guard shall be 3.0 kN/m for means of egress in grandstands, stadia, bleachers and arenas. The balustrade around the landing and on the edge of the stair is deemed to be a required guard in NBC.

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

 

[hokie66]

Just so you guys know, the grandstand is in Australia. And knowing architects here like I do, he wants brick on both sides. After all, kslee, both sides of the balustrade are exposed.

 

[BAretired]

hokie66,

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

 

[kslee1000]

Hokie:

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.

 

[asixth]

Hi guys,

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.

 

[hokie66]

Looks good to me. Just my pedantic checking persona, but you have the bars in different layers in your two sections. Should have the short direction bars in the bottom layer.

 

[BAretired]

My eyesight is not as good as it used to be so I did not catch all of the detail mentioned by hokie. I have concerns about relying on two 6" masonry walls for "notional horizontal forces". Not so notional when you get a bunch of crazed soccer fans trying to find the natural frequency of the structure. Can't you get a couple of stiff columns at the right end of the walls?

I would prefer to see 8" concrete walls below the stair too.

BA

 

[asixth]

hokie,

I also realized that after I sketched it up, I will make sure the cad-techs get it right.

 

[apsix]

BA
It's a rigid box structure with 1 wall missing, I can't see stability being a problem.

 

[BAretired]

apsix,

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 am relying on the block wall to cantilever out-of-plane in order to brace the stair against any notional horizontal forces.

I don't think he should rely on those walls in that way.



BA