Participation Factors For a Bridge-Ground-Foundation System

bayram_aygun · Post by **bayram_aygun** » Fri Oct 31, 2008 6:42 pm

Hi,

I have a 2D bridge-soil-pile foundation model in OpenSees. I can get the eigen file which has the mode shapes and the mass matrix which has all the nodal masses along their DOFs.

Somehow when I apply the ordinary structural dynamics rules to get the mass participation factors, I don't seem to get the correct results. I get "relative weights" though which point to the dominant modes. My soil domain is 2DOF whereas my structural domain is 6DOF but I don't think this can cause a problem, right? Whether my model has a heterogeneous DOF all over the model or not it shouldn't prevent OpenSees from giving me the right eigen file, right?

Lastly, the funny part is when I set the soil nodal masses to zero in mass matrix the "relative weights" look better and get closer to being actual participation factors (their sum approaches to 100%)

Any suggestion or insight is greatly appreciated!

ebe79442114 · Post by **ebe79442114** » Sat Nov 01, 2008 3:56 am

refer to this part of book:

www.csiberkeley.com/Tech_Info/16.pdf

page 5, equation (16.7).

bayram_aygun · Post by **bayram_aygun** » Sat Nov 01, 2008 12:18 pm

Thanks a lot. Let me read through this document and I hope I'll gain some theoretical insight and reassurance about what I have experimentally observed