Unbraced Length Ratio (Major and Minor)

[agps]

Dear colleagues,

Let's imagine that we're working on a metallic beam with 10 meters length and it was devided in 6 frames for a better analysis.

The working code is the Euro Code.

After running the Design/Check of structure, I verified that SAP2000 assume values, which I think they are for the worst case for each single frame element.

What is the correct length ratios for this case?

I´ve a note from college saying "the major length bending stands for the number of times the beam was divided".

Is this true? And what is the "minor length bending"?

I'll appreciate any answer explainning how to do it or WHERE in the SAP2000 manuals I can find this?

Thank you

agps

 

[masomenos]

For design, if you don't assign design parameters, SAP will make assumptions based on what you modeled based on moment releases, supports, connectivity and lengths of elements modeled. In your situation, you say that you divided your 10m frame elements for a "better analysis". Had you instead modeled the frame elements using their actual 10m lengths, and then Assigned frame automesh joints for a better analysis, SAP would have assumed different, probably more accurate length factors for design. In addition, you can select frame elements, then use the Design menu to assign frame overwrites to modify SAP default design parameters. As an alternative to using the Assign menu to assign internal automesh joints, you can draw 'special joints' along the frame. With both frame automesh and special joints, SAP meshes the frames internally based on special joint locations and automesh assignment, but then reformulates the output in order to report and design frame sections as they were originally modeled.

In your example, you wouldn't have to deal with 6 moment diagrams for one 10 meter frame if you instead Assign intermediate frame automesh joints. I'm pretty sure that SAP2000 V14, and maybe V12 too, have Eurocode design manuals in the 'Manuals' subdirectory which installs with SAP