Seismic Design of Storage Tanks: EQ E.4.5.1-1b
Seismic Design of Storage Tanks: EQ E.4.5.1-1b
(OP)
I'm looking at the 11th ed. of API Std.650. I'm confused by the equation for Impuslive Natural Period (E.4.5.1-1b) given as:
Ti = 1/27.8 * CiH/sqrt(tu/D) * sqrt(E)
Units (by definition in Sec E.2.2): My values:
Ti: sec 1.23x10^6 s
Ci: unitless 7.20
H: ft 46.72 ft
tu: in 0.419 in
D: ft 150 ft
E: Definition gives kPa for U.S. Custom, I'm assuming psi
is what they meant, it's irrelevant to my question.
29x10^6 psi
First: How can period increase with an increase in elastic modulus? It seems to me that E should be somewhere in the denominator, not the numerator. Remarks?
Second: Does the coefficient out front account for the fact that the units, accourding to definitions, don't cancel out? For example tu/D is in units of in/ft. I would naturally want to convert one into the other by multiplying or dividing by 12 so that the units cancel out. But I don't know if the conversions are covered by that coeficient out front. It would make things easy to be able to just plug in a value based on the by definition units. For example if your thickness, tu, is 5/8" and your diameter, is 100 ft, then you plug into tu/D, (5/8)/100, and you're good. Would be nice, yes, but is it reality? School taught me to always cancel units, but by that logic, how does one arrive at units of seconds when none of the parameters have seconds in their units?
Third: What does "Rho = 9.35" mean?
Any remarks and/or insight would be much appreciated. Hopefully I'm just overanalyzing this thing and there's a simple solution to my problem.
HT
Ti = 1/27.8 * CiH/sqrt(tu/D) * sqrt(E)
Units (by definition in Sec E.2.2): My values:
Ti: sec 1.23x10^6 s
Ci: unitless 7.20
H: ft 46.72 ft
tu: in 0.419 in
D: ft 150 ft
E: Definition gives kPa for U.S. Custom, I'm assuming psi
is what they meant, it's irrelevant to my question.
29x10^6 psi
First: How can period increase with an increase in elastic modulus? It seems to me that E should be somewhere in the denominator, not the numerator. Remarks?
Second: Does the coefficient out front account for the fact that the units, accourding to definitions, don't cancel out? For example tu/D is in units of in/ft. I would naturally want to convert one into the other by multiplying or dividing by 12 so that the units cancel out. But I don't know if the conversions are covered by that coeficient out front. It would make things easy to be able to just plug in a value based on the by definition units. For example if your thickness, tu, is 5/8" and your diameter, is 100 ft, then you plug into tu/D, (5/8)/100, and you're good. Would be nice, yes, but is it reality? School taught me to always cancel units, but by that logic, how does one arrive at units of seconds when none of the parameters have seconds in their units?
Third: What does "Rho = 9.35" mean?
Any remarks and/or insight would be much appreciated. Hopefully I'm just overanalyzing this thing and there's a simple solution to my problem.
HT





RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
Joe Tank
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
http:
API does have a "draft" version of Addendum 1 somewhere on their website if you can find it. I think you have to look under "committees" and go from there.
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
Great Article
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
http://fatih.bazman.net
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
HT
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
-HT
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
Addendum 1 has been published and is available. In this version, equation E.4.5.1-1b appears to have the sqrt(E) in the denominator.
I use MathCAD and so usually use the SI version of the equations and always "prove" the equations using at least one USC example without units. Very occasionally I have to "fudge" an equation and artificially add a unit. Since the impulsive period is not used for tank design, I passed it by.
Where is th "rho" you are curious about?
RE: Seismic Design of Storage Tanks: EQ E.4.5.1-1b
The "rho" is in the 11th Edition, right out beside the impulsive period equation, it says "Rho = 9.35" for no apparent reason.