Linear Vs Nonlinear TH analysis - Chopra chapter 7.4.1

[WaisAu]

Hello everyone
I am trying to redo an example from Anil K. Chopra book, where he finds the Response of Linear Elastic and Elastolastic system with Tn=0.5 s and no damping, to El Centro ground motion. He finds the displacement u=3.34in for Linear system and 1.71in for Elastoplastic system.

So I succeded to find almost same result for the Elastic system, but when I do Non Linear time History Analysis, my results are almost the same as the elastic system. I have used 3 hinges in beam and 2 hinges in columns.

Could some one please look at the attached file and look at the load, Modal and time history cases and check if there is anything wrong.

I did read here on this forum that you can use hinges with TH Analysis.


Kind Regards
Wais

 

[stressed]

I took a quick look at your model. First of all, in order to consider material NL behavior you need to run NL Direct Integration time history analysis. Your model only had FNA time history which will not work. Second, you assigned negative joint mass number in the 3 direction which seems to produce an error during analysis. Assigning a negative mass is usually incorrect. This mass was assigned in addition to the selfweight of the members. It's usually easiest to assign additional mass as a load in the gravity direction and then use Define>mass source to specify loads to be used in the mass model instead of default mass of selfweight + assigned mass. That way, SAP2000 will automatically convert loads into mass which saves time and minimizes the possibility of error. The DEAD case by default includes selfweight.

The time history analysis has 1 G scale factor (9.8 m/s/s). Is that scale factor adequate to cause yielding at the hinges? I did not investigate further. Also, your hinges were assigned at frame stations 0 and 1. I was taught to assign hinges slightly offset from the end points, relative distance .02 and .98 for example instead of 0 and 1.