Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Cb value in columns ?
- Thread starter hebert53
- Start date
JoshPlumSE
Structural
That will depend on your moment diagram, your design code, and your bracing.....it may even depend on your member type.
- Thread starter
- #3
Thanks Josh ..
But ,, talking about Cb ,, When I leave blank de Cb value at Risa 3d , the results show me a value of 2 , I am worry about if that means that I am lack of steel , I mean , needs a better shape even the UC values are below of 1 and the relative deforation member ratio is above n=360 .. ??? Will you help me to uderstand this topic better . I am from mexico and do frabicate steel structuras . Iam learning fron Risa 3 demostration version and I am very happy with this program .. Thanks again
But ,, talking about Cb ,, When I leave blank de Cb value at Risa 3d , the results show me a value of 2 , I am worry about if that means that I am lack of steel , I mean , needs a better shape even the UC values are below of 1 and the relative deforation member ratio is above n=360 .. ??? Will you help me to uderstand this topic better . I am from mexico and do frabicate steel structuras . Iam learning fron Risa 3 demostration version and I am very happy with this program .. Thanks again
JoshPlumSE
Structural
In AISC, the beam buckling equations are put together assuming that the moment in the beam is constant throught the length of the beam between segments. In reality, obviously, this is not the case as our bending moment diagrams vary greatly.
The Cb factor is a way to determine the increase in bending moment capacity that would result from the fact that the bending moment diagram varies. For a linear moment diagram with a zero value at one end, the Cb value would be approximately 1.67. Therefore, a value of 2.0 is not unreasonable.
I should point out that RISA does allow you to enter in a user defined value of Cb for those cases where you do not want the program to calculate it automaticallly. If you enter in this value as 1.0, then you would be conservatively ignoring this effect.
The Cb factor is a way to determine the increase in bending moment capacity that would result from the fact that the bending moment diagram varies. For a linear moment diagram with a zero value at one end, the Cb value would be approximately 1.67. Therefore, a value of 2.0 is not unreasonable.
I should point out that RISA does allow you to enter in a user defined value of Cb for those cases where you do not want the program to calculate it automaticallly. If you enter in this value as 1.0, then you would be conservatively ignoring this effect.
- Thread starter
- #5
- Status
Similar threads
- Locked
- Question