Hi
the resulting Hysteretic curve I get for a reinforced concrete structure doesn't look like the typical ones in the published papers.
i.e. the curve is not degrading as it should look. Its stiffness, however, remains the same!
I shifted to a different constitutive model with a degrading strength, such as (con_cm and con_ma), but the hysteretic curve remained the same.
Do you know how to get such an important result for this a basic issue?
thank you
hysteresis loops
Re: hysteresis loops
Hi benamer.
You might check to see that, in fact the structure is being loaded beyond the elastic range. There could be a scale factor awry in your loading specification, in your properties, or something like that.
If the loadings all check out and the structure is indeed loaded well beyond the elastic range, you might check to ensure that you are plotting the correct degrees of freedom in your hysteresis curve. Sometimes it is quite easy to get degrees of freedom interchanged in your mind.
I hope this helps you to locate the problem benamer.
You might check to see that, in fact the structure is being loaded beyond the elastic range. There could be a scale factor awry in your loading specification, in your properties, or something like that.
If the loadings all check out and the structure is indeed loaded well beyond the elastic range, you might check to ensure that you are plotting the correct degrees of freedom in your hysteresis curve. Sometimes it is quite easy to get degrees of freedom interchanged in your mind.
I hope this helps you to locate the problem benamer.
Tim Huff
Re: hysteresis loops
Thank you Tim
But I am loading the structure with El-centro, 180-ground acceleration, with max PGA = 0.31g.
So, Yes, the structure is loaded beyond the elastic range, and
if I magnify the load (say by 1.5), numerical instability occurs because of severe distortion of the elements.
I suppose that properties and plotting DOF's are O.K.
However, when I use STATIC time-history analysis I get the degrading
stiffness hysteresis shape ! i.e. using cyclic loading.
should this be the loading type with all of what's been published about Hyestersis loops for reinfo. concrete structures?
Please, let me know, as soon as you can, if you or some one else
has got any idea about this 'major' inquiry ....
thank you Tim
But I am loading the structure with El-centro, 180-ground acceleration, with max PGA = 0.31g.
So, Yes, the structure is loaded beyond the elastic range, and
if I magnify the load (say by 1.5), numerical instability occurs because of severe distortion of the elements.
I suppose that properties and plotting DOF's are O.K.
However, when I use STATIC time-history analysis I get the degrading
stiffness hysteresis shape ! i.e. using cyclic loading.
should this be the loading type with all of what's been published about Hyestersis loops for reinfo. concrete structures?
Please, let me know, as soon as you can, if you or some one else
has got any idea about this 'major' inquiry ....
thank you Tim
-
seismosoft
- Posts: 1272
- Joined: 06 Jul 2007, 04:55
Re: hysteresis loops
Dear Benamer,
The fact that you are loading the structure with "El Centro 180 with max PGA = 0.31g" does not necessarily mean that the structure is going into the inelastic range, since the latter depends on the characteristics of the structure itself.
In order to check if the response of the structure is inelastic or not, you should check the strain response history of the materials, and check if these ever go above their yielding values. If they do, then, yes, your response is inelastic.
From your description of the problem, our suspicion is that there is a modelling error somewhere that is preventing the structure to respond as expected. Have you tried using the 'Wizard' to get SeismoStruct to quickly put together a nonlinear dynamic analysis model that you could then compare with your own model, with a view to identify possible errors?
Seismosoft Support
The fact that you are loading the structure with "El Centro 180 with max PGA = 0.31g" does not necessarily mean that the structure is going into the inelastic range, since the latter depends on the characteristics of the structure itself.
In order to check if the response of the structure is inelastic or not, you should check the strain response history of the materials, and check if these ever go above their yielding values. If they do, then, yes, your response is inelastic.
From your description of the problem, our suspicion is that there is a modelling error somewhere that is preventing the structure to respond as expected. Have you tried using the 'Wizard' to get SeismoStruct to quickly put together a nonlinear dynamic analysis model that you could then compare with your own model, with a view to identify possible errors?
Seismosoft Support
Re: hysteresis loops
Support Team
Hello
Thank you for your e-mail. it was helpful.
To get a Hysteresis curve with the degrading stiffness,
I had to (lower) the limiting values set for concrete crushing criterion and reinforcement yielding criterion, from the Performance page.
The default ultimate crushing strain 0.002, But I used 0.00002.
the default ratio between yield strength and modulus of elasticity of the steel material is 0.0025, But I used 0.00025
This is to include (more elements) under these limits in order to get the degrading shape of the hysteresis.
My question is: how to verify such limits for a reinforced concrete column under a seismic loading? And wether I should use Dynamic or Static loading for a realistic behavior of the analysis.
Thank you for your support
Mohamed Benamer
Hello
Thank you for your e-mail. it was helpful.
To get a Hysteresis curve with the degrading stiffness,
I had to (lower) the limiting values set for concrete crushing criterion and reinforcement yielding criterion, from the Performance page.
The default ultimate crushing strain 0.002, But I used 0.00002.
the default ratio between yield strength and modulus of elasticity of the steel material is 0.0025, But I used 0.00025
This is to include (more elements) under these limits in order to get the degrading shape of the hysteresis.
My question is: how to verify such limits for a reinforced concrete column under a seismic loading? And wether I should use Dynamic or Static loading for a realistic behavior of the analysis.
Thank you for your support
Mohamed Benamer
-
seismosoft
- Posts: 1272
- Joined: 06 Jul 2007, 04:55
Re: hysteresis loops
Dear Mohamed Benamer,
If you are using artificial and unrealistic values of material properties in order to get expected structural responses, then there is certainly something flawed with your model, which we again advise you to carefully review and revise.
Both static and dynamic analyses may be used to realistically simulate the response of your structure. It depends on what you are trying to achieve and also on the accuracy of your models.
We suggest you to study further the literature on this subject (the Help System of SeismoStruct features an extensive bibliography listing) and seek the local assistance of someone with past experience on nonlinear analysis of structures.
Seismosoft Support
If you are using artificial and unrealistic values of material properties in order to get expected structural responses, then there is certainly something flawed with your model, which we again advise you to carefully review and revise.
Both static and dynamic analyses may be used to realistically simulate the response of your structure. It depends on what you are trying to achieve and also on the accuracy of your models.
We suggest you to study further the literature on this subject (the Help System of SeismoStruct features an extensive bibliography listing) and seek the local assistance of someone with past experience on nonlinear analysis of structures.
Seismosoft Support