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Preliminary Earthquake Loads for Universal Frames

Preliminary Earthquake Loads for Universal Frames

Preliminary Earthquake Loads for Universal Frames


I'm designing a 1-story platform that can pretty much be located anywhere in the world. As a rule of thumb, I was informed to use seismic load of 40% times the Dead Weight of the structure. There will be cases where there is/isn't earthquake (50-50). Since there are no PE's in the company, and that our firm usually outsources the PE procedures, is it ok to follow this type of procedure for initial design phase?


RE: Preliminary Earthquake Loads for Universal Frames

I think you'll need to give us a little more information.  I'm assuming this is a platform that will be located at the ground level?

What I've done in the past when unsure of where something (equipment for example) will be located I have designed using the highest SDS that I have found in ASCE 7 which I believe is somewhere around 3.0 g.  This is obviously conservative and may be overly so for you.  I would then suggest calculating the seismic forces in ASCE 7 using that SDS.  Your R value that you use for your structure will have a huge impact on whether or not 40% times the dead weight is reasonable or not.

I would then very EXPLICITLY write on the drawings the exact seismic design values that you used for the calculations.  I would then box this information on your drawings with a big bold note that the Engineer of Record for the building is to verify that your assumed seismic loading is applicable to the installation for their region.

If you are just looking at cost estimating purposes 40% may not be off depending on what type of platform it is (i.e. moment frame, tension bracing, etc).

RE: Preliminary Earthquake Loads for Universal Frames


Besides the lateral force demand that you use there are other, more important aspects of seismic design.  Specifically the connections need to be properly designed, more robust than the members.  The braces too must be upsized.  All of this depends a lot on the type of bracing system or moment frame system you use.  

For initial design phase, though, the 40% sounds "enough".  jdgengineer's suggestions are good.


RE: Preliminary Earthquake Loads for Universal Frames

Thanks JAE and jdgengineer.

Yea, I remember using ASCE 7 for calculating the base shear for this matter. I just wasn't sure of what a conservative SDS value was. During school, I've used SDS values close to 1.0g for downtown San Diego.

Appreciate the help!


RE: Preliminary Earthquake Loads for Universal Frames

My guess is 40% would cover at least 99% of you apps.  But do as JD and JAE suggest.... Check it out.

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