how to calculate the seismic force for pipe?

[hello2006]

Hi Good morning everybody!

I am calculating the force of seismic for designing pipe support.

I have HPGA =0.44 g. Can I simply use F= 0.44*g*weight of pipe? Because I think F=am, here a=0.44*386 (g=386 in/s2), therefore, F=0.44*386*weight, Is that correct or I should use what formula to calculate the force of seismic?

thanks very much!

 

[JStephen]

Generally, the seismic load is not the peak ground acceleration. You might check ASCE 7 and see if it addresses pipelines. I seem to call that ASCE has had books out before on seismic design of piping.

 

[rconner]

Aren't acronyms grand!! While not professing to know a great deal about this specific subject, I agree with JStephen that the force on a particular pipe support might well not simply be the mass or weight of the pipe and contents multiplied by a “Ground” (the “G” in your acronym?) acceleration, but could conceivably also be influenced by the reactions (sway etc.) of the structure to which the pipeline is attached. I suspect discussions of this can perhaps be found in many references including by googling e.g.

http://www.crid.or.cr/crid/CD_Agua/pdf/eng/doc14611/doc14611-4.pdf.

I realize this likely doesn’t immediately solve your problem, but it would appear to me you might also need some input from the structural engineer, involving specifically how the structure to which the pipeline is attached will react to the horizontal (and vertical?) ground accelerations expected and maybe even from your local governing authorities or codes. Once you get to that point, it would appear the supports and their anchorage/structure must withstand the magnitude and direction of force in appropriate units applied, and incidentally also that the pipe wall must withstand the localized etc. level of force applied (due to its strapping etc. contact w/ the support) at that location/direction.
[I noticed you apparently also posted inquiry with maybe more info at

http://www.eng-tips.com/viewthread.cfm?qid=179404&page=2.

]

 

[civilperson]

You have mixed up weight and mass, use 0.44 of the weight as a force in the horizontal direction. If you use the 386 inch/sec<2 as acceleration of gravity, you must apply it to mass, (slugs), and the result is back to pounds force.

 

[hello2006]

Hi thanks civilperson,

I am thinking that pounds is an unit of mass, but not weight, right?

In my calculation, I use the pounds as unit for pipe and other conponents. Actually that is mass of pipe and others too, right?

When I was choosing hanger rod, the catalog also shows the pounds as the maximum strength the hanger rods can arrord. So I just calculated how much pounds the PHGA put to the pipe, but do not need to apply the gravity acceleration again. Is this correct?

For example, the hanger catalog shows 7/8" diameter rod can arrord the maximum strongth of 4480 lbs. Therefore, I need to calculate how much pounds the PHGA put to the pipe.

Therefore, Pounds of PHGA = 0.44 * pound of pipe,

but not Pounds of PHGA = 0.44 *pounds of pipe * 386 in/s2

because the calculation applied by 386in/s2 has the unit of Newton, but not pounds any more. Therefore, I can not use this value to choose which rod I have to choose. Is that correct?