PV ELITE ANCHOR BOLT DESIGN FOR VERTICAL VESSEL

[roca]

Question:
Attached is a clip (apologies for the quality) from a PV Elite calculation for a vertical skirt supported vessel anchor bolt design which I have been checking. All units are in N (Newtons) and mm.
The formula for the anchor bolt load per bolt is: = (4*M/DC - W) / RN
Where:
M = moment at base Nmm
DC = Anchor Bolt Circle Diameter
W = Vessel weight
RN = number of anchor bolts

In the PV Elite calculation the vessel weight is shown as 49616.1N, yet in the anchor bolt calculation the weight is shown as 12404N
e.g. the weight has been divided by a factor of 4 in the calculation.

Why is this as this is not correct in my opinion – or am I missing something……..??

 

[PreVes]

Roca,

You should send it to the Tech Support at COADE. I can barely see your image so it doesn't help.

 

[roca]

will add a better clip tomorrow.
However the question is still the same as above, why is the weight divided by 4?
I can't contact PVElite as we do not have the software where I work and this is a supplier / manufacturer calculation

 

[Aconnell]

Hi Roca,

Have a look in the Pressure Vessel Design Manual by Henry Bednar Page 82 (my addition). The four comes from the linear section modulus of the bolt circle which is part of the derivation. If you work alot with pressure vessels I suggest this book, it is an very good reference.

Regards,

Alex C

 

[roca]

Hi Aconnell
I have Bednar 2nd Edition (I believe that there is no higher version).
On page 93 the required anchor bolt area = Ab = ((4M/d)-W) / NSa
The weight is not divided by 4.

I have attached a better copy of the calculation

Moss 3rd Edition, page 201 also uses the above formula (albeit in imperial units), but it is the same.

There must be simple answer to this that I am missing…..

 

[gr2vessels]

roca,
in the PV Elite, the calculation window of the number of bolts resisting the overturning moment is half of the total bolts, ie 4 only bolts (this is a simplistic and conservative assumption made by PV Elite). The same assumption is applied for the bolts resisting the overturning moment on the saddles calculated per PV Elite 2008 edition. I suspect that is the case, but I would ask Mandeep Singh in the COADE forum to confirm the above.
I could run the calculation for you and check on this, let me know if you need my help.
Cheers,
gr2vessels

 

[roca]

Thanks gr2vessels - at least someone reads / knows the program rather than just inputting and not looking att he end result.
The reason I found this is that I am checking an existing vertical vessel design in which the top nozzle loads have been increased. The skirt anchor bolts are already at their limit (design wise) and I couldn’t work out why the weight had been divided by 4.
This is very conservative on an already simple anchor bolt design.
Do you know if COMPRESS takes the same approach?
Ta

 

[Mandeep1]

Roca,

I do not get this, see below,

Dead Weight of Vessel DW 40849.7 N
Operating Weight of Vessel ROW 40849.7 N
Earthquake Moment on Basering EQMOM 60532132.0 N-mm
Wind Moment on Basering WIMOM 34932092.0 N-mm
Percent Bolt Preload ppl 100.0

Use AISC A5.2 Increase in Fc and Bolt Stress No
Use Allowable Weld Stress per AISC J2.5 No

Factor for Increase of Allowables Fact 1.0000

Results for Basering Analysis : Analyze Option

Basering Thickness Calculation method used : Simplified (Steel on Steel)

Calculation of Load per Bolt [W/Bolt], Earthquake + Operating Condition:
W = ROW - Yforce (from gy Acceleration or user force), M = EQMOM

= (( 4 * M/DC ) - W ) / RN per Jawad & Farr, Eq. 12.3
= (( 4 * 60532132 / 2590.800 ) - 40849 ) / 8
= 6571.1821 N

Check if the user specified a +gy acceleration. In PV Elite +ve gy can act against the weight of the vessel.

Whoever has the PV Elite input file can send that our technical support. We can review it and let you know.


best regards,
Mandeep Singh