Natural frequency in ASCE question
Natural frequency in ASCE question
(OP)
from ASCE 7-05, pg 294
eqn (c6-22a) reads : n1=(0.56/h^2)*sqrt(EI/m)
can anyone please tell me the units for
h, E, I, m?
I had h=ft, E=psi, I=in^4, m=lb/ft(mass per unit height according to the book)
however the answer yields in/ft^2 or 1/ft (w/ conversion)
my problem:
hss5x5x3/16
I=12.6, h=13', wt=11.96lb/ft
my answer: n1=0.56/13^2*sqrt(29e6*12.6/11.96)=18.32in/ft^2 =1.54/ft
thanks for you input.
eqn (c6-22a) reads : n1=(0.56/h^2)*sqrt(EI/m)
can anyone please tell me the units for
h, E, I, m?
I had h=ft, E=psi, I=in^4, m=lb/ft(mass per unit height according to the book)
however the answer yields in/ft^2 or 1/ft (w/ conversion)
my problem:
hss5x5x3/16
I=12.6, h=13', wt=11.96lb/ft
my answer: n1=0.56/13^2*sqrt(29e6*12.6/11.96)=18.32in/ft^2 =1.54/ft
thanks for you input.






RE: Natural frequency in ASCE question
RE: Natural frequency in ASCE question
No matter how I solve the equation, the result is 1/length.
So there has to be a conversion factor in the 0.56. Thus what are the proper units to use?
RE: Natural frequency in ASCE question
the m is mass, which is different
386 something
so the units of n1 is 1/s
RE: Natural frequency in ASCE question
11.96(lbm/ft)=11.96(lbf/ft)*32.174(lbm-ft/lbf-sec^2)/32.174(ft/sec^2)
11.96*32.174=384.8 (close to what you said) but why don't you divide by acceleration due to gravity to get pure lbm?
You've got to love the english units. . .
RE: Natural frequency in ASCE question
sqrt[lb/in^2*in^4/
(lb*s^2/in^2)]= sqart(in^4/s^2)=in^2/s
RE: Natural frequency in ASCE question
could you explain why you're only multiplying by 32.174 and not dividing by 32.174 also? one is acceleration due to gravity, the other is G sub c, an empirical conversion factor to convert pound force to pound mass.
Thanks for your efforts.
RE: Natural frequency in ASCE question
so
EI/M= mass*g*in^2/(mass/in)=g*in^3
g has units of in/s^2, it is the standard gravity
So for EI/M, the units should be in^4/s^2
the same thing.
I may confuse you by saying 386
RE: Natural frequency in ASCE question
In English units:
lbf=lbm*a/gc
or
lbf=slug*a
a slug = 32.174 lbm.
to further clarify:
11.96lbf*0.225=53.2N /9.807(acceleration due to gravity)=5.4kg
5.4kg*2.205=11.952lbm.
Therefore, the seconds are still eliminated.
Can anybody else shed some light on the subject?
RE: Natural frequency in ASCE question
You seem to be mixing soup from Barbados with soup from Ireland.
Try SI, has a more intuitive feel to it
Fe
RE: Natural frequency in ASCE question
Thanks for everyone's help.
RE: Natural frequency in ASCE question
I still don't see how you came to your answer?
Can you explain?
RE: Natural frequency in ASCE question
If anything needs clarification, let me know.
RE: Natural frequency in ASCE question
Sorry about that.
RE: Natural frequency in ASCE question
RE: Natural frequency in ASCE question
thanks for checking it out. In empirical units w/g = slugs. That's pretty much what was stumping me in the first place.
RE: Natural frequency in ASCE question