equipment/component suppliers & 2003 IBC seismic

[SeanMD]

Hi! This is my first time on this forum. I'm a new structural engineer, 1 yr experience. I hope I can contribute something to this site, but for my first post I have a question...

I work in a multi-dicipline Industrial Manufacturing firm. Until this Jan we have been using the 1997 UBC. With the new IBC seismic requirements we are now giving site specific seismic critera to other diciplines (mechanical/process engineers) that need to order equipment and components for their design. I am working with an engineer that is trying to order a 2000+ gallon cone bottom tank, but we are having problems getting a tank that the supplier states is compliant with the new code. Seems it is no problem getting a tank that is compliant with zone 4, 1997 UBC. I can see this being a reoccuring problem for us.
Part of the problem is the seismic critera is now site specific instead of regional (zone xx). Another problem is there is significant differences in the new code when it comes to bracing requirements, and in the case of the cone bottom tank, the manufacturer supplies a braced-frame support structure. And I dont have any experience in actual tank design, there may be some issues there also. I could provide the manufacturer with the IBC seismic forces, or just compare them to the UBC myself, but that doesnt address the other issues such as bracing requirements.

Is anyone else having similar problems as a result of the IBC? Any suggestions or thoughts? Is this where engineering judgement comes in?

 

[mrMikee]

SeanMD,

The manufacturer should be able to tell you this; the problem might be that they just don't know. I was recently on a website of a company that seemed to be very knowledgeable technically, but in their specifications section they stated that they did not guarantee their bins to be compliant with the IBC because of the differing interpretations of that code. I can understand this somewhat, the IBC is a poorly written code.

Another consideration might be that the tank manufacturer doesn't have anyone on the staff that can check the design per current codes. Some of these companies just keep doing what they have been doing because, well, it was good enough before.

Regards,
-Mike

 

[JedClampett]

Everyone, including the design firms, are in a learning mode with respect to this issue. But if you provide in the contact documents the seismic parameters (Sds and Sd1) and make the responsibility the suppliers, they'll figure out a way to comply, especially if that puts them in a better position to make a sale. In the west, we see equipment suppliers have structural engineers analyze their equipment all the time for seismic, although it is still UBC.
I don't have any codes with me at home, so I'm not sure I understand the bracing issues. But if the supplier makes the specifications and drawings available, a sharp structural engineer can tailor his design to support conditions that occur. Or the design engineer can comment on this during the submittal review and correct any errors.

 

[mrMikee]

I think it used to be easier for manufacturers when there were only five seismic zones. Now there are two maps with more than 15 contour lines on each, and you don't know which one controls until you do some calculations.

As an aside, I would like to know if anyone has come up with a way to correlate the old seismic zones with an equivalent Sds and Sd1 value. It would be an approximation of course, but something like that might help with putting a perspective on this issue.

Regards,
-Mike