Seismic design of concrete stairs

[RafikCGS]

Can anyone give me some guidance for seismic design of concrete stairs attached to the main structure?

Some questions I have included:

Shall we consider stairs as non-structural elements?
If yes, how calculate the seismic forces?
Can the stair pans be assumed to act as a diaphragm to resist lateral loads?
Shall we consider stairs stiffness for the evaluation of the centre of rigidity?
Are there any special requirements for support attachments to the main structure?
Are there any design references or guidelines published for the seismic design of stairs?

Thank you.

 

[PEinVA]

Why would you be designing stairs for Seismic Load? Are you planning on transferring load through your stair?

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[slickdeals]

Interesting. I had never thought about this yet. Do you folks in the west coast have to do something to take care of the serviceability of the stairs in a seismic event? Like connections at the landing etc.

Thanks

 

[PEinVA]

Stairs typically wouldn't absorb any load from an event like this, correct? I could be wrong, but unless you plan on making the stair part of your lateral system in your building, it is most likely something you can ignore.

RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[drile007]

Why don't you separate the stairs from the main building with some kind of movement joint to freely vibrate in their own mode. If you attach them to the main structure there will be a huge "jump" in stiffness and consequently attractive point for damages during earthquake...

 

[RafikCGS]

Build

In this case, the stairs must be attached to the main structures, and it is clear that stairs will be attractive point of seismic forces, but many seismic codes consider that stairs as secondary element (seismic codes says any think about if stairs must be or not attached to the main structure)

In my opinion, it is interesting to make a “U” enclosure shear wall to protect stairs (when attached to the structural system), shear walls attracts seismic forces, and no seismic forces to the stairs (secondary element),

Is this correct?

Thank

 

[dik]

I would probably secure the stairs to the structure for a seismic force to make sure that they don't collapse and prevent people from exiting the structure.

Dik

 

[ronstruc]

As far as seismic design of the stair goes - you need to look at ASCE 7-05 chapter 15, which will reference you to chapter 13 if the weight of the stairs is less than 25 percent of the combined weight of the stairs and the building. If that is the case, chapter 13 will give you the information you need for determining the seismic forces on the stairs. You could then use the building to resist some of these forces if it is attached to the building in such a fashion.