Design of Built-up section.

[Wani_1]

Hi, I was wondering what ways one would use to get an equal radius of gyration in both yy & zz axis of given cross sections.

I tried using 2 flat plates and I beam to achieve this by equating the desired radius of gyration to that of the highest radius of gyration of the I beam.
After some algebra, I got an uneconomical plate thickness (106mm).

Are there any other consideration made to achieve equal radius of gyration and reasonable thickness in my case?

Thanks.

 

[rb1957]

so I imagine you have an I beam with two "vertical" plates closing the section, creating a box.

I assume you have a narrow tall I beam, as opposed to a short squat one. I think the flanges should be as wide as the beam web is tall ... it doesn't Have to be, but I is going to be mostly Aflange*height^2/2 on one side and Aplate*width^2/2 on the other ... rough and approximate ... so if you're getting a very thick plate, you need to increase the width.

why are you doing this (an equal radius of gyration in both yy & zz axis of given cross sections) ?

 

[GregLocock]

You've got 2 equations and 2 unknowns, assuming thickness is constant and the other dimensions are in multiples of t. Presumably you know how to calculate Iyy and Izz? parallel axis theorem and all that.