Design of stair supported on walls 2

[benjaman]

Hi,

I am designing a stair supported by RCC walls on both sides. Now, in a few articles I saw that connecting stairs to walls on both sides is not a good practice in case of seismic design.

Any comments regarding this will be appreciated.

Thanks.

 

[Bagman2524]

Are the walls supported from the same floor? If the seismic deplacement of the walls is not in sync there will be additional seismic forces on the stairs.

 

[BAretired]

Please define RCC.

BA

 

[benjaman]

Hi, one of the walls form the lift core and the other the stair well.

So, there are chances that their displacements might no be in sync. So probably it's better to design the stair as cantilever from any of the walls.

 

[pwht1]

RCC means reinforced concrete doesn't it?

How wide are the stairs, how many storeys in the building and what's the floor to floor spacing?

 

[benjaman]

The stairs are 2m long. Floor to floor spacing is 3.0m and there are a total no. of eight storeys.

 

[BAretired]

RC means reinforced concrete. What does RCC mean?

BA

 

[engineertipsman]

I would not cantilever, perhaps a slip connection or just a bearing connection that can allow movement

 

[Bagman2524]

Agree with tipsman. A connection on one end that allows movement seems like a better choice than a cantilever.

 

[benjaman]

Dear tipsman,

could you please explain a bit more about providing bearing connection?

 

[cvg]

BA
RCC is roller compacted concrete

 

[BAretired]

Thanks, cvg. I have never used roller compacted concrete, so I am not familiar with it. Are the walls rolled flat on grade, then tilted up to support the stair?

BA

 

[benjaman]

Dear BAretired,

RCC (Reinforced Cement Concrete) is a very common term used for reinforced concrete in my country. The stairs as well as the stairs are of reinforced concrete.

 

[BAretired]

Thanks, benjaman. You must be from India. As you have seen, RCC means something different in North America.

I am fortunate enough to live in an area of the world where seismic activity is not a major concern, so I am not speaking from experience and claim no expertise in this subject.

I agree with the others that a cantilever is a bad idea, but I do not see the value in allowing movement on one side of the stair either. During a seismic event, it seems me that the edge with the movement would batter the wall. I would be inclined to tie the stair slab to both walls such that they are forced to move in sync.

BA

 

[a2mfk]

Since the stairs and walls are all reinf concrete, can you design the stairs as a strut or diaphgram as BA suggested and incorporate it into your seismic design? You may also need the stairs to brace the walls for out-of-plane seismic and wind forces. I have had to do this on a CMU stair tower with steel stairs, otherwise the CMU was overstressed.