Strange Response Spectrum

[Anonymous]

Hello dear engineers

I just done a response spectrum analysis on my lovely bridge, and although all the parameters are set correctly the first part of the spectrum (0<T<TB) has a downward slope.... can somebody please check the model and tell me what the issue is ?

Thanks

[mustafahesenow]

This is happened because of behavior factor the one you set it as 3.9 please be sure about this number.

[Anonymous]

Thanks buddy

I just realized that robot did not show the negative sign after e. and for the elastic spectrum it looks perfectly fine. a random question, do you know how to generate moment-curvature for a concrete element for nonlinear analysis in robot ?

Regards

[Artur.Kosakowski]

Hi @Anonymous

Could you attach a sample of such diagram/ I'm not sure if I understand what you need. 

[Anonymous]

Thanks Artur

I got that sorted, however I attached the diagram here.

Regards

[Artur.Kosakowski]

Hi @Anonymous

I do apologize for my limited knowledge in seismic design - could you attach the 'right' diagram too so that I'm sure I understand the situation correctly? Thank you.

[Anonymous]

Dear Artur

I made a mistake while putting PGA in Robot (ag=0.912 instead of ag=1.88 m/s2) so the diagram showed values with decimals in vertical axis (for example 1.3e-2), however the minus sign was hidden due to poor quality of font. Now in the correct file you won't be able to see as it shows proper figures. By the way I attached the correct diagram.

I have another post which I desperately look for a solution ASAP. My model is 99% complete, no error, everything is well-set but I don't get correct capacity curve, demand spectrum and performance point in pushover analysis. My deadline is in few days and all my thesis depends on this nonlinear analysis. I would appreciate if you could help me out.

Best Regards

[Artur.Kosakowski]

Hi @Anonymous

Thank you for the picture.

I'm sorry but I have no knowledge about the  pushover analysis. The Performance point & Demand spectra have not been computed warning indicates missing intersection between capacity and selected demand spectra however I'm not able to tell why the demand spectrum is not displayed and if it has anything to do with Ca and Cv values or other parameters. 

[Anonymous]

Thank you Artur

To be honest, I watched all the tutorials and read Robot documentation as well, I followed all the necessary steps but unfortunately it does not give me spectrum and curve properly. I am using CSI-bridge as well which is far easier than Robot in this particular case. I am going to upload screenshots of all the settings that I used in nonlinear pushover in another post to see if I can get it work.

Best Regards