Earthquake or Wind

[SalinaMh]

Hi everyone,
I need to calculate the earthquake load for the staircase that is attached to a building located almost to the top and outside of the building. Just an access from one room to another. Not considering the whole building effect, just the staircase , how to calculate the earthquake effect on the staircase? I have the peak ground acceleration of 1.86m/s2. And this i need to compare with the windload effect and see which is the primary Load type i need to use to design the staircase.

 

[EngDM]

Not sure what code you are governed by, but for the NBCC it gives a fairly straightforward solution to this. I'd imagine other governing code bodies do as well.

 

[SalinaMh]

It is Eurocode. Staircase has a raincover over the staircase as well.

 

[milkshakelake]

I think you just follow the code, right? Like find the part of the code that pertains to this, and go through it line by line until you have the force distribution. The code would tell you if this is a building or non-building structure, and what coefficients/variables to use.

It's kind of a vague question. Maybe if you're getting stuck on something particular, I'd have a better answer.

If you want to estimate it, take 12% of its mass and apply it laterally. That's your extremely rough seismic load. Now apply 2.5 kN/m2 wind load to its face. That's your extremely rough wind load. Don't use this to design it, but it answers your question.

 

[SalinaMh]

Thank you for your answer. According to my understanding, i only take the self weight or mass of the staircase and use F=ma and i get the Earthquake force for the staircase. Now again, i multiply the wind pressure for that region to the area of the staircase (in the direction of z shape of the staircase) and i get a wind load that acts on the staircase. This way now i compare both the loads.

 

[EngDM]

I'm not sure if it is perhaps different in Eurocode, but the peak ground acceleration is not used in the way you describe for the NBCC procedure in Canada. After a quick review of Eurocode 8, I believe you should be using the procedure outlined in section 4.3.3.2 of Eurocode 8.

 

[JAE]

And just to be a bit nit-picky - proper engineering procedure is to NOT compare wind and seismic overall loads and choose the larger and go with that.

Seismic design has special requirements for diaphragms, fasteners, braces, brace connections, etc. that sometimes increase the seismic load OVER that of wind even if the overall wind is larger.

So be careful. The proper procedure is to check BOTH wind and seismic through the entire load path and for all the parts.

Now admittedly for some cases it becomes quite apparent which one controls throughout - but saying you'll compare the overall load and just go with that one isn't correct.

 

[ThomasH]

i only take the self weight or mass of the staircase and use F=ma and i get the Earthquake force for the staircase.

What value would you use for a? You mentioned peak ground acceleration but that is probably not relevant near the top of the building.