Direct Analysis Method (DAM) - Effective Buckling Lenght Calculation

[umut.akparlar]

Hi,

I was using the DAM for a steel frame structure, and I saw the following statement in knowledge base documents:

The primary benefit of this approach is the possibility to check the section capacity during the des...

It is very handy to check the design capacity without using effective member lengths, but after I check couple of vertical members, it still calculates effective lengths. Are those calculations can be ignored, or should I turn off buckling check from member definition parameters?

And for some reason this member has instability, but checks are lower than 1.

Kindly provide input.

Thanks

[CaioSaporito]

Hi @umut.akparlar.

You still have to apply "load parameters" but  Ky and Kz equal to 1. (k=1)

Best regards,

Caio

[umut.akparlar]

Thank you, @CaioSaporito

I tried to change the effective length factor to 0.5 instead of default 1 value and the utilization is not affected by this. So the input value for effective length factor seems to have no effect on member verification when DAM is active.

Do you have any thoughts about how RSA handles K for different user inputs during DAM? Just fully ignores it and assumes a default value independent of user input?

Regards

[CaioSaporito]

Hi @umut.akparlar.

The resistance calculation is the same as we are used to, but only with k=1. What will change are the forces that will be amplified by second order effects and stiffness reductions. It may be that your column is compact, and the failure is not happening due to global buckling but rather due to yielding.

Best regards,

Caio

[CaioSaporito]

Thinking about it, it's not your case, but the compression resistance in Y and Z must have increased.

And maybe the Ned/Nrd  is too low for the final ratio

Best regards,

Caio