Concrete Stair - Seismic Design

[ztengguy]

Would you consider a stair a non structural component, or structural component?

 

[concretemasonry]

Does it have a code requirement for a specific loading?

Since it is critical for access, egress, and supporting people, I would think it is a structural element. The connection to the major structure is up to you.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[wannabeSE]

For seismic design, stairs are commonly considered to be non-structural components. They typically do not contribute to stability or strength of the building (gravity or lateral).

 

[MiketheEngineer]

But I would check them as an individual element to make sure they are OK!!

Whats the first thing people do during an earthquake or fire - bail out of the building.

Hope I have stairs when the elevators shut off!!

 

[connectegr]

This is a building code issue. We frequently design stair structures for seismic lateral forces.

http://www.FerrellEngineering.com

 

[connectegr]

Reference ASCE 7, Chapter 13, Seismic Design Requirements for Nonstructural Components, 13.1.4

This provides exceptions for Architectural components, in Seismic Design Category B. Therefore stairs in categories C, D, and E should consider seismic forces. Our reasoning has been similar to the comment above. These structures are critical in a seismic event.

http://www.FerrellEngineering.com

 

[wannabeSE]

Also, egress stairs should be designed (as a non-stuctural component) with an importance factor of 1.5 because they are required for life saftey purposes.

 

[ztengguy]

Im design cat A, so im getting like 4% W for design. Just going to make sure I have a couple welded connections at each stair to cover any lateral load. Thanks

 

[Teguci]

Structural component. Had a cast in place disconnected elevator/stairtower where I needed to transfer diaphragm loads through the stairs to a shearwall at the midlevel landing (LOVE architects!). The design included torsional ties and additional longitudinal bars for chord and torsion action. These were definitely structural components!

 

[ztengguy]

I can see that, where its detailed to be a structural component. These are just run of the mill stairs, base connection, and top connection. Everything is adequate for non building component architectural loads, but just wondered if they really needed.

 

[SAIL3]

As others have pointed out the stairs would be critical for egress and personnel safety, so use your engineering judgement accordingly. Connection of the stairs to the different elements of the structure should be given special attention as ithe stairs may be connecting different portions of the structure where relative movement of these portions could impart significant loads to the stairs or at least to it's connection.