effect of rebar

[bshad]

It steams that Seismostruct considers longitudinal reinforcement in period and with changing of rebar the location of stiffness center is changing & if you change confinement factor (i.e. changing stirrups) period has no change and this is contradict with help manual (page 186)
Etabs or any other software believes that stiffness and location of its center is independent of rebar (longitudinally or horizontally)
is this problem of Siesmo or other software?& why when you changing the confinement factor (e.g. 4times!!!!) we don't have any any change in period- contradict with Manual

[huffte]

I have observed this same behavior. It may simply be that the Young's Elastic Modulus, E, for the concrete is being calculated as:

4700(fc)^0.5

Whereas, it would seem that the value should be:

4700(kc x fc)^0.5

My comments apply for the con_ma material model.

[bshad]

what is kc & how can I calculate it??

[huffte]

When you select the con_ma material model, you will see a button to the left of the confinement factor. The confinement factor is kc. If you click on the button, you will be presented with a set of input variables which are used to calculate the confinement factor, kc.

If you are doing only an Eigenvalue Analysis, then you can manually increase the input concrete strength to kc x fc to investigate the efects of confined concrete on natural periods. However, I would not recommend this if you are doing any other type of analysis in which inelastic effects are being considered.

Please refer to the Help System on confinement factor for references in the literature if you need further information on the details of calculating kc.

Best of luck bshad.

[bshad]

tanx
but did you exam it! or just you say
I know what you say but if you change confinement factor from 1.2 to 10! you can see that you don't have any any change in your periods contradiction with manual,but Seismo consider longitudinal reinforcement in period inversely of SAP2000 or Etabs

[huffte]

Yes, I did examine it. If you will read my first reply you will find that I am not disagreeing with you. There does seem to be a problem. And if you will read my second reply you will find that I was simply answering your question regarding kc and it's computation.

[bshad]

Thanks huffte
I was wondering if Seismostruct remove this bug about confinement factor and its effect on period of structure.
but Now I dont know about longitudinal reinforcement,I tell again that in Etabs and Sap2000 and perform they dont consider rebar in period but Seismostruct consider it which of them is accurate, I was wondering if Seismosoft support team answer these qustions...

[seismosoft]

Dear bshad,

We will indeed address the issue you (and huffte) raised in the next release of SeismoStruct.

For what concerns your question on if consideration of rebars is an accurate option or not, well, if the rebars do exist in your real structure, then it would seem to us that their consideration in the model is an appropriate thing to do.

Seismosoft Support

[seismosoft]

A quick corrective note on the fact that the stiffness calculation is based on the unconfined compressive strength, hence, changing the confinement factor will indeed not have an effect on the stiffness.

Seismosoft Support