torsional stiffness

[hosiensg]

hi
in example 7 ( http://opensees.berkeley.edu/wiki/index ... _W_Section)
in file " Ex7.Frame3D.build.Wsec " introduce "Ubig" as magnitude of torsional stiffness , but i don't how compute this for every member ( for example W12x114 )?

[fmk]

Ubig is just a variable she uses in her scripts for anytime a large number is called for, it's not an element, material, calculated thing.

GJ is the number she is supplyin, G a material property and J the scetion property which can be found in tables or simple formulas on-line, e.g.
http://www.roymech.co.uk/Useful_Tables/ ... rsion.html

[civil]

hi
so how could define torsional stiffness for W12x114 in this example?

thanks in advance

[fmk]

did you Google the question before you asked it? get the section properties and do the math!!

http://www.scribd.com/doc/28133413/Tors ... eel-Shapes

or

http://www.roymech.co.uk/Useful_Tables/ ... rsion.html

or

......

[Panos]

On account of this topic, I would like to ask the reason for customarily assigning large values of torsional stiffness when modelling 3D buildings (like the example you posted above), instead of the actual stiffness calculated using the equations of engineering mechanics.