How to calculate base shear for time period more than 0.06 sec

[maverick29]

Hi,

I will really appriciate if somebody can tell me how to calcullate base shear of non building structure when fundamental time period is more than 0.06sec.

I can find V = 0.30SdsWI (Eq 15.4.5-ASCE7-05 ) fundamental time period less than 0.06 sec.

can we just use V=0.03XW ( section 15.4.1)

Thanks in advance

 

[JStephen]

What kind of non-building structure is it?

 

[maverick29]

Stephen,

It is tank of 5' dia radius, 36 ' high made of steel.Tank will store argon gas.

 

[JStephen]

Just looking through this fairly quickly, it looks like you've got an ASME pressure vessel, falling under 15.7.11.2, which refers back to 15.4 for a free-standing structure, which refers back to 12.8, but with limitations on Cs as noted in 15.4. Note also that you may be able to multiply the seismic load by a 0.7 load factor for allowable stress design per 2.4.1.

ASCE 7 seems to be very poorly written for applications such as this, and it is not always clear what the meaning, if any, is.

 

[maverick29]

Stephen,

Thanks for replying back. Let me rephrase may questin, may be I was not very clear in my first post. It is not the tank I am designing. It is the support system , as these tanks are elevated 1.5' above the ground by steel coulmn.

I need to have base shear of the tank to design base plate and hilti anchor bolts.

Thanks in advance

 

[JKW05]

maverick,

It looks to me like you found a hole in the ASCE standard. As the section you cite is titled "Rigid Nonbuilding Structures", my first inclination was that there must be a section for "flexible nonbuilding structures". But I haven't been able to find anything to help you out. The commentary is pretty useless.

If I do find something, I will post again.

 

[JStephen]

I think you'd still wind up with 12.8.1, with base shear given by Eq. 12.8-1.

You might also want to confirm with the vessel designer if there is any anticipated loading or horizontal movement at the base plates due to pressurization, vertical loading, or temperature changes in the tank.