Load distribution in hold down bolts for circular base plates 1

[sbnz]

Hi,

I have to select the hold down (anchor) bolts for a pressure vessel (designed and supplied by others) having circular base (and large [pockets for the HD bolts).

I have the foundation loads, the critical load being a horizontal pipe load applied at a height resulting in a significant bending moment at base.

My question is can someone explain me in simple terms how to determine the nominal bolt loads for this bending moment. I know that the bolts will not be uniformly loaded (will depend on proximity to the neutral axes) but not sure how to calculate.

thanks in advance

 

[JoeTank]

The max bolt load will be [4M/(ND)]-(W/N)
M=moment
N=number of bolts
D=bolt circle diameter
W=weight of vessel

Joe Tank

 

[MJCronin]

sbnz,

Where are you located and where will the vessel be located ?

Joe Tank's answer is simplified, but may not be applicable in all cases. It does not account for any flexibility in the vessel base or the stiffness of the supporting foundation.

Both the Bednar text and the "Pressure Vessel Handbook" discuss calculation of anchor bolt loads.

-MJC

 

[doct9960]

sbnz,

The usual procedure is for the vessel engineer to design the base support and come up with the required size, number and BCD of the anchor bolts. His design should be based on the worst case combined loading of weight, wind/seismic, and eccentric loads such as that horizontal pipe load you mentioned. He should be familiar with the vessel location's building code, foundation strength, acceptable anchor bolt material and other required structural requirements like bolt preloads, etc. A civil/structural engineer also verifies the vessel engineer's design since they are ones who are going to design the foundation (or steel structure) where the vessel will be installed. If the vessel sits on a concrete foundation, civil will set the bolts. If the vessel is on a steel structure, mechanical sets the bolts, with the approval of structural.

Your profile says you are Mechanical and you said that the pressure vessel & support was designed by others. Why are you trying to "select" and design the anchor bolts? Didn't the vessel engineer design the anchor bolts?

 

[JoeTank]

No matter who sets anchors bolts, it is often very useful to have the vessel manufacturer provide an anchor bolt template for their use. Nothing worse that anchor bolts not at same location as base plate holes!!!

Joe Tank

 

[desertfox]

Hi sbnz

Have a look at this link:-

http://www.mech.uwa.edu.au/DANotes/threads/fatigue/exampleB.html#top

I don't know if any pressure vessel codes cover your situation but the above link may help.
If your baseplate deflects under this moment load you may need to consider bolt prying if you do try this site but it only covers angles and T sections.

http://www.webcivil.com/prying.aspx

 

[sbnz]

Thanks all - every reply to the posting has been helpful.

doct9960 - I am indeed a Mechanical, more precisely a piping engineer. I have a process pressure vessel where dimesional parameters are specified by us and piping nozzle loads estimated as per our piping design. The supplier has designed the pressure vessel as per our specifications. Based on the foundation loads furnished and considering the BCD furnished by them we will select the HD bolts (sizes of MS bars).

May be the common practice would be a civil engineer design the HD bolts - but this is the way it has usually been done in our company (in New Zealand).

thanks