Beam Fiber Section Editor

[Lei Lei]

Dear STKO Team,

I am using the Beam Fiber Section Editor to define a custom fiber cross-section, and I’ve noticed that the center of the cross-section is defined by the y,z origin, not the x,y origin. Could you clarify how the center of the section is calculated? Is it based on the centroid of the section? Additionally, is there a way to automatically calculate the centroid of the section, and can I customize the center according to my needs?

Thank you for your assistance!

097b379c66654938d0a4c45663b8505.png (47.59 KiB) Viewed 604 times

[kesavapraba]

Hi, cross section coordinates are always defined in local y and z axes - the element's longitudinal direction is represented by local x axis. The axes system (Red Green Blue) that you showed on figure is global coordinate system in STKO, not local system.
Regarding the centroid of the fiber section, it is automatically calculated by OpenSees, so it does not matter where you keep the origin of the local y and z axes. The response (axial and curvature line) are determined with respect to the centroid axes calculated so. You are not required to explicitly calculate the centroid here.

Additionally, you can know that there an option to specify -noCentroid in OpenSees for the fiber section - which may be useful for unsymmetrical section and angled loads.

Please watch the video below to understand local coorinates system in OpenSees
https://youtu.be/Zeupc5xMWIc

[Lei Lei]

Thanks!

Hi, cross section coordinates are always defined in local y and z axes - the element's longitudinal direction is represented by local x axis

Since the local origin of the section is always at the centroid, for asymmetric sections, I might need the centroid's coordinates to determine its distance from the target origin for proper offset adjustments. Perhaps I can use the Query Geometry tool to find it.

Additionally, you can know that there an option to specify -noCentroid in OpenSees for the fiber section - which may be useful for unsymmetrical section and angled loads.

By the way, if I use the -noCentroid option, where is the origin of the section?

Looking forward to your reply!

[kesavapraba]

Hi,

By the way, if I use the -noCentroid option, where is the origin of the section?

With the option -noCentroid, the reference is made with where the origin (y=0, z=0) is defined for the cross-section. Without the option, the reference of the section under bending is made with centroid, eventhough the origin of the axes is not located at the centroid. Please have a look at the following article on this aspect. https://portwooddigital.com/2021/01/24/ ... centroids/

[Lei Lei]

Thanks for your reply！
Best Wishes!