IDA not yielding results

04-Unexpected behaviour/errors
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Spyros Resvanis
Posts: 3
Joined: 31 Aug 2020, 02:44

IDA not yielding results

Post by Spyros Resvanis »

Hello all,
I hope you are well! I am running an IDA analysis with Seismostruct for a bridge model and I am using the software's code-based checks for chord rotation and shear. I am applying a suite of ground motions and for many of them, it seems to produce results, while for others it doesn't. As an example I will note that I have applied an excitation of a peak PGA value of 0.33g scaled with factors ranging from 1 to 10. However, the model appears to be intact in every case which i believe to be a mistake given the value of these factors. The other excitations for which my model does not produce results have been similarly scaled. I also noticed that the relative displacements of the structure in the aforementioned cases are very low. I have reviewed both models in terms of: constraints, the application and import of the time histories, material strength, element connectivity and classes and checks performed. I have also tried increasing the convergence tolerance of the model and the relevant parameters outlined in the relevant section of the Seismostruct manual and increased the fibers in the used elements but unfortunately to no avail. Moreover, i tried performing a more simple DTH analysis to the entire model and to more simplified model (i.e just one pier with the acceleration loads applied at the fixed footing) with all my efforts being equally unfruitful.I would greatly appreciate your help and your quick response.
Kind Regards
Spyros Resvanis
huffte
Posts: 892
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: IDA not yielding results

Post by huffte »

This looks as though it could be a units problem. I typically load accelerograms in units of g. I typically use units of inches and seconds. So, when I apply a particular accelerogram as a nodal loading, I have to specify a factor of 386. Just a thought, but double-check the scale factor you applied to the accelerograms when they were specified as dynamic time history loads on nodes. Best of luck.
Tim Huff
Spyros Resvanis
Posts: 3
Joined: 31 Aug 2020, 02:44

Re: IDA not yielding results

Post by Spyros Resvanis »

Dear huffte,

Thank you for your reply but I believe my units are correct. The accelerogram i am introducing in in cm/s2 and i am multiplying it by 0.01 to make it m/s2 which are the units that i work in. I also considered that the accelerogram itself might be faulty so I did the same using the ones available by seismosoft which are in units of g and which i multiplied by 9.81 but the issue persists. Thank you for your help.

Kind Regards,
Spyros Resvanis
huffte
Posts: 892
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
Contact:

Re: IDA not yielding results

Post by huffte »

Just to be clear and rule out the potential units issue:

1. When you define the time history curve, you specify a factor of 0.01 to get cm to m.
2. When you define the loading, you specify a factor of 1.0, since you converted the units in defining the curve.

If these are true, I believe you are correct and the units are fine. Just making certain you did not use the 0.01 factor both times.
Tim Huff
Spyros Resvanis
Posts: 3
Joined: 31 Aug 2020, 02:44

Re: IDA not yielding results

Post by Spyros Resvanis »

Indeed, I am importing the time history with a factor of one but change my loading factor to 0.01, which is the same thing.
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