pushover curve

[zthaer]

dear all;
I'm pushing a 4 story building with rigid diaphragm and i got a very strange capacity curve with no softening and post- yield capacity , the attached photo :


Please any help;
best;
Thaer;

https://drive.google.com/file/d/0BzZ5tJ ... sp=sharing

[z.gronti]

Dear Thaer,

Having seen the attached screenshot, i would advise you to check the following:
1. Increase the steps in the loading phase
2. Check the strength degradation in the performance criteria, if you have assigned any.
3. Check the assigned fracture/buckling strain in the steel/reinforcement model.

[zthaer]

hi zoi;
i got this response:


where is the problem?
best;
Thaer;
https://drive.google.com/open?id=0BzZ5t ... ElIQ1V3UVk

[huffte]

It is difficult to make an accurate assessment without seeing the model, zthaer. I would note that your performance criteria concrete strains are quite low (-0.005), but you may be assessing a lightly reinforced structure. You appear to be failing some very weak elements early on, with more resilient elements picking up load thereafter? I wonder if you might need to double-check your geometry, sections, performance criteria, material properties, permanent loads?

[zthaer]

Dear Tim,
thank you for your answer, but I made a shear capacity check in the performance criteria section since i got a feeling that this type of zigzag curve had something to do with brittle shear failure then i surprised when i see many of elements (almost a half of the total number ) have reached the shear capacity even before start pushing the structure.
So i m really got lost with that .
Please any help
Best,
Thaer,

[huffte]

There may be some erratic behavior of the automatically computed shear capacities. Can you calculate shear capacities by hand and input them instead of having SeismoStruct auto-compute and see if that makes any difference? Keep at it zthaer. You'll get it resolved with a little sweat and perseverance.

[seismosoft]

Hi Thaer,
1) If you reach the shear capacity even before you start pushing the building, probably this means that you have shear failure from the gravity loads.
2) Can the zigzags in the curve mean that you use a very loose convergence criterion?
3) From the general shape of the pushover curve, it seems that the second ascending branch is derived with the structure being under pure tension.

Regards,
Seismosoft Support