BESO + Cross Section Optimisation

Hello Karamba Community

I have been working on a project using BESO and Cross Section Optimization, during which I encountered something counterintuitive and thought I’d share it with the community here to get some feedback. I designed a structure as shown in the attached video, which initially undergoes BESO and then Cross Section Optimization. I observed that the Cross Section Optimization tends to modify cross sections that exhibit less displacement (as shown in the animation), seemingly without considering the overall structural performance. For instance, it would make more sense to have thinner cross sections at the top of the structure, but these are never adjusted or replaced with thinner ones (see animation). I’m curious about why this happens and if there’s any way to address this issue. I attached the file to this thread too if anyone wants to have a look, Many thanks (45.2 KB)

Hi, there are “high” bending moments in those beams and therefore the utilisation is also higher in those members. Also, there seems to be problems in the geometry with the LDist - you should switch this to 0.005

Thank you Mathew for your response. Regarding the logic behind the cross section optimization workflow, I’m curious to know if it would make more sense to alter those cross sections with high bending moments to thinner ones?
Just to better understand the workflow of cross section optimization in Karamba; does it consider the overall structural performance and try to optimize the cross sections ( for instance lighter on the top and heavier in the bottom) ? Or does it focus on optimizing each individual cross section (minimizing the thickness in this example) until it reaches the critical moment of failure per element?

Hi Milad,

well the Optimisation Procedure can take deformation into account, but on the first basis it takes utilisation of each individual element into account. Therefore elements which have higher bending stresses typically will have larger cross sections.

However if you want to actually have smaller cross sections in your elements, I would suggest you start with the smallest one in your list as typically the optimisation procedure goes down your list of cross sections and when your starting cross section is already quite large, then it might not pick the the most appropriate cross section as a larger cross section might already fulfill the optimisation criteria.

You can find more information here: 3.6.8: Optimize Cross Section :large_blue_diamond: | English 英文 | Karamba3D 2.2.0

Thank you Mathew for the clarification