PUSHOVER ANALYSIS

03-Analytical/modelling capabilities
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Ghadeer Mattar
Posts: 4
Joined: 15 Feb 2021, 22:15

PUSHOVER ANALYSIS

Post by Ghadeer Mattar »

Hello,
Hope that you are doing well.

I am facing some problems in analyzing high rise buildings by pushover, i increased the iterations to 100, and took 1.2% of height as target displacement as per the convergence tips but the model took more than 12 hours to complete the run! Is this normal for a 36 floors structure?
More over, the resulted performance point changes from life safety to operational only by clicking the per-processor button then going back to the processor , could you advise?

Finally, i really could not determine the base that the program take in consideration when determining the resulted performance category( operational,life safety...), is it the chord rotations check ?

Thanks in advance
Ghadeer
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seismosoft
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Joined: 06 Jul 2007, 04:55

Re: PUSHOVER ANALYSIS

Post by seismosoft »

12h is a lot even for a 26 floor structure. It seems that you are facing some convergence difficulties in the nonlinear range (please confirm).
Note that 1.2% for a 100-150m structure is almost 2m, which is a lot. You might want to decrease this a bit (to say 0.8%).The number of iterations seems excessive, you should better increase the number of steps.
I am not sure that understand your two questions on the perfromance points however.
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Ghadeer Mattar
Posts: 4
Joined: 15 Feb 2021, 22:15

Re: PUSHOVER ANALYSIS

Post by Ghadeer Mattar »

Thanks a lot. I had some convergence problems as you said.
I increased number of steps to 75 and decreased the iterations to 70, it became much better and took a round 1 hr to complete the analysis, i also increased the number of modes to be the same of the floors number however i got " unknown error" in the analysis log but the analysis completed.
However, i still have the same problem which is that the resulted performance level for the same model is once life safety and once operational even so i did not change any thing, so i was wondering if SeismoStruct determines the performance level based on the number of hinges that lie in the performance category" Like ETABS" because i could not find a way to track how the performance category is determined.

Thanks in advance
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seismosoft
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Joined: 06 Jul 2007, 04:55

Re: PUSHOVER ANALYSIS

Post by seismosoft »

In any assessment methodology, the performance level is chosen by the engineer, when setting performance objectives, it is the performance level of the structure to checked for the selected Hazard level (see ASCE-41 for more details).
In SeismoStruct, the performance levels are selected by the user in the Target Displacement module of the pre-processor. These are the performance levels for which the target displacement is automatically calculated. Note also that in the code-based checks you are able to define checks for frame and masonry elements for any performance level.
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Ghadeer Mattar
Posts: 4
Joined: 15 Feb 2021, 22:15

Re: PUSHOVER ANALYSIS

Post by Ghadeer Mattar »

Thanks a lot. However, i only have two more queries.

What could be the reason behind getting exactly the same value for target displacement despite of changing the performance level( operational, immediate, life safety or collapse prevention) for the same seismic hazard?

Moreover, i had more than case where the resulted target displacement value was allocated far a way from the linear part of the displacement- shear force curve , but the SeismoStruct still give the operational level for the resulted target displacement ?

Thanks in advance.
Ghadeer
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seismosoft
Posts: 904
Joined: 06 Jul 2007, 04:55

Re: PUSHOVER ANALYSIS

Post by seismosoft »

The performance level is associated with the damage expected to the structure. The target displcement (which is the approximation of the displacement expected in the design earthquake) depends on the hazard level. It seems that you need to study a bit the performance objectives and how these combine the hazard levels and the limit states (or performance levels). I believe that Chapter 2 of ASCE 41-17 (and its commentary) is the best guidelines on the issue. In any case, note that this forum is on the use of Seismosoft's programs, not a general forum on earthuake engineering.
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Ghadeer Mattar
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Joined: 15 Feb 2021, 22:15

Re: PUSHOVER ANALYSIS

Post by Ghadeer Mattar »

Noted.
Thanks for your help.
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