Period changed after gravity load analysis

andrewfirst · Post by **andrewfirst** » Sat Aug 15, 2009 6:41 pm

Dear all
I'm analyzing a RC frame structure, and wondering why the structural period changed after gravity load analysis. If it should change as a result of change of material stiffness, then it should increase or decrease? Thank you.

andrewfirst · Post by **andrewfirst** » Sun Aug 16, 2009 5:39 pm

In the Example5, the structural period decreases after gravity analysis, which means the stiffness increases. This is too weird for me. Anyone help me?

andrewfirst · Post by **andrewfirst** » Mon Aug 17, 2009 4:58 pm

I suspect this may be a bug in OpenSees. Very disappointed.

silvia · Post by **silvia** » Tue Aug 18, 2009 3:45 pm

more likely to be a bug in the example.
also,
many materials have different stiffnesses in tension and/or compression, therefore a period should never be checked at zero loading.

andrewfirst · Post by **andrewfirst** » Tue Aug 18, 2009 4:46 pm

Thank you Dr. Silvia.