ASCE "Anchorage Design for Petrochemical Facilities" ?
ASCE "Anchorage Design for Petrochemical Facilities" ?
(OP)
I am interested in analysis of anchor bolt tensile loads for vertical pressure vessels. ASCE has a publication "Anchorage Design for Petrochemical Facilities". The initial edition was published in 1997 (combined as "Wind Loads and Anchor Bolt Design for Petrochemical Facilities", two books in one: wind design, then anchor bolt design). The new, second edition was published in 2013 as a highly-expanded document "Anchorage Design for Petrochemical Facilities".
The original edition discusses the case of vessels supported on skirts with a circular pattern of anchor bolts (para. 3.5.1.1). It provides the usual formula for bolt tension: T = 4M / (N*BC) - W/N (3.1)
It describes the conservative assumptions built into this analysis. Basically, the neutral axis of the resisting forces of compression on the concrete foundation and tension on the anchor bolts shifts away from the geometric centerline of the vessel, due to the differing material stiffness of the steel and concrete. It goes on to describe that this effect can be considered in the design (sizing) of the anchor bolts, and "may...be worth undertaking when the above equation yields large anchor bolt sizes and embedments."
The second edition of the "report" (as ASCE calls them) eliminates any reference to the "advanced" analysis of tensile load acting on the anchor bolts by considering the differing material stiffnesses. (For that matter, they have relegated formula (3.1) to an example, Example 2 Step 4).
Any ideas as to "why" they have eliminated reference to the advanced analysis? The whole report seems to be more focused on what happens below the concrete's surface, rather than what happens above. Is this why?
[The "advanced" analysis is that discussed in numerous pressure design texts, such as "Moss", "Bednar", "Megyesy", "Brownell & Young", etc, so it has certainly been accepted in industry for a very long time.)
The original edition discusses the case of vessels supported on skirts with a circular pattern of anchor bolts (para. 3.5.1.1). It provides the usual formula for bolt tension: T = 4M / (N*BC) - W/N (3.1)
It describes the conservative assumptions built into this analysis. Basically, the neutral axis of the resisting forces of compression on the concrete foundation and tension on the anchor bolts shifts away from the geometric centerline of the vessel, due to the differing material stiffness of the steel and concrete. It goes on to describe that this effect can be considered in the design (sizing) of the anchor bolts, and "may...be worth undertaking when the above equation yields large anchor bolt sizes and embedments."
The second edition of the "report" (as ASCE calls them) eliminates any reference to the "advanced" analysis of tensile load acting on the anchor bolts by considering the differing material stiffnesses. (For that matter, they have relegated formula (3.1) to an example, Example 2 Step 4).
Any ideas as to "why" they have eliminated reference to the advanced analysis? The whole report seems to be more focused on what happens below the concrete's surface, rather than what happens above. Is this why?
[The "advanced" analysis is that discussed in numerous pressure design texts, such as "Moss", "Bednar", "Megyesy", "Brownell & Young", etc, so it has certainly been accepted in industry for a very long time.)






RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
Are you referring to a cyclic load on the anchors?
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
But it should be pointed out that this effect (shift in neutral axis) occurs only when there is a bending moment applied to the pressure vessel.
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
The impression I had was that it was based on treating the bolts and concrete around them as a composite beam, whereas the normal analysis treated the bolts only as an equivalent beam. But neither assumption is necessarily better than the other, so it was always questionable in my mind whether you were really getting a more accurate number or just cooking the numbers to give you a more favorable result.
I would be curious as to whether anyone has actually tested bolt loads in an actual vessel or tank or stack to see how they compared to either theory? It wouldn't be hard to do, just a matter of spending time and money to do it.
In the tank standards, they have added allowances for using higher-strength anchor bolts, and meanwhile, Appendix D has been added to ACI 318, and it's possible those changes just negated the need for that analysis rather than rendering it void. (The higher strength bolts are also pre-tensioned.)
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
I can see how you might treat the concrete as an elastic solid, consider elasticity of the bolts above that, etc., and come up with a more accurate distribution of bolt force, but that isn't what's done in Megyesy.
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
How specific are they expecting the pre-load/pre-tensioning to be? I've only ever seen them calibrate a run of the mill torque wrench and use that. It gets close enough for anything I need.
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
It is described (or not, in one case) in the following texts:
- Moss – “Pressure Vessel Design Manual” (third edition) – Procedure 3-14
- Bednar – “Pressure Vessel Design Handbook” (second edition) – page 98 “Initial Tension in Bolts Neglected”
- Megyesy – “Pressure Vessel Handbook” (eleventh edition) – page 80
- Brownell & Young – “Process Equipment Design” (1959) - Chapter 10 (section 10.1b)
- Jawad & Farr – “Structural Analysis and Design of Process Equipment” Section 12.2 (see page 424 second edition)
- Troitsky (Lincoln Welding Institute) – “Tubular Steel Structures – Theory and Design” (second edition), Section 5.5
- Harvey - “Theory and Design of Modern Pressure Vessels” – doesn’t seem to address this issue [otherwise, about the best textbook on vessel analysis around]
It seems to come down to needing to contact the ASCE report's authors for an explanation why this was omitted in the new edition. It may be because the current edition doesn't really seem to care how the loads on the anchor bolts are determined, it's more concerned with how the anchor bolts are embedded in the foundation.ETA: the only texts that give a fully comprehensible discussion of this method, IMO, are Brownwell & Young, and Troitsky. I would never have been able to understand it from just the Jawad & Farr text or Megyesy.
RE: ASCE "Anchorage Design for Petrochemical Facilities" ?
In the derivation, he assumes strain is proportional to distance from the neutral axis. Which is based on plane-sections-remain plain. And as I recall from beam theory, that is true away from supports or discontinuities. So it seems to violate the assumptions used in its derivation. I don't know that that makes it any less accurate than the alternative method (which assumes the same thing). The obvious solution is to put strain gauges on some anchor bolts and see how reality compares to the different derivations. I've not heard of that being done, and would be curious if any of those references had any additional justification for the method.
In some of the current tank standards, they have requirements for prestressing of bolts, generally only applicable to higher-strength bolts. So Gr. 36 bolts aren't prestressed, but others are. I assume they have special equipment just for this, but haven't dealt with it.