I tend to think the "Unless otherwise calculated, the minimum displacements in Table 15.7-1 shall be assumed." as not a way out, but as a way to actually increase the displacements if additional info is available (like a soils report).
I disagree. If you were to pick the location in America with the worst seismic events, and then use the worst possible "normal" piping arrangement, this singular chart is supposed to cover that much... and then some more. My opinion is "unless otherwise calculated" here means "you take responsibility for determining better/useful/realistic numbers."
All our codes inevitably push some amount of "engineering judgement" onto the engineer at some point.
Piping to nozzle connection displacements differs from calculated accelerations. The accelerations would apply to ASCE-7 section 13 for piping, right?
Unless a crack in the ground opens up between the tank and the first support, it's problematic to think that the original input to the free body diagram should be a displacement.
Instead, the displacement itself is either:
a) a displacement caused by a singular thrust of acceleration of the entire system and
i) can itself be calculated and then input into caesar or
ii) can simply be included into CAESAR and have CAESAR calculate the displacement
b) a final or worst case scenario location of where the pipe lands after an extended sequence of random thrusts and vibrations during a seismic event. The only way I've seen this addressed is through a dynamic study where you physically input seismograph data into CAESAR.
As you seem to also be aware, some of these displacements are enormous and every facility I've ever seen obviously appears to be completely designed without applying the requirements of Table 15.7-1. Which I totally understand. It is generally not feasible, economical, nor practical to design every single connection to a vessel or tank to these measures.
Hence, my question since it is considered law. So I'm curious how others in the industry view this topic.
I can't say at what point in which state it became law or what point ASCE-07 included this table. Some simply become grandfathered in.
Those that did try to comply with either these or other onerous requirements frequently circumvented the problem via flex hoses, that may or may not have been replaced by hard piping after the flex hose expired.
By the way, UTS = Ultimate Strength I presume?
Yes. This would be my first "sanity check" for "won't rupture." If the stresses exceed UTS, then we can say without hesitation that this pipe or nozzle should not be able to withstand this scenario. Brand new? Perfectly installed? Not even one single time.
Of course, simply exceeding YS means you're likely dealing with material that needs to be replaced.
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