Dear seismosoft,
I want to know about <run with linear elastic properties> in analysis tab. I have some elfrm in my model. and when I use this capability the results are different. I read the manual and searched in forums but it didn't help.
thanks for your attention
run with linear elastic properties
Re: run with linear elastic properties
Hi jackrussel.
I will simply paste an excerpt form the Seismostruct Help system found in the "Project Settings" -> "Analysis" section in the Contents:
"Note: When users decide to run an analysis considering the linear elastic properties of materials (see the option described above), they should keep in mind that, if the elements are modelled using r.c. sections and 'infrm' elements, the infrm elements will account for the reinforcement; on the contrary, if 'elfrm' elements are employed, their properties are calculated using the concrete modulus of elasticity and the section dimensions, thus neglecting the effect of the reinforcement."
So, I think the differences in results should certainly be expected. Material non-linearity is ignored with the subject option checked.
By the way, what type of analysis are you running?
Best of luck.
I will simply paste an excerpt form the Seismostruct Help system found in the "Project Settings" -> "Analysis" section in the Contents:
"Note: When users decide to run an analysis considering the linear elastic properties of materials (see the option described above), they should keep in mind that, if the elements are modelled using r.c. sections and 'infrm' elements, the infrm elements will account for the reinforcement; on the contrary, if 'elfrm' elements are employed, their properties are calculated using the concrete modulus of elasticity and the section dimensions, thus neglecting the effect of the reinforcement."
So, I think the differences in results should certainly be expected. Material non-linearity is ignored with the subject option checked.
By the way, what type of analysis are you running?
Best of luck.
Tim Huff
-
jackrussel
- Posts: 33
- Joined: 21 Sep 2013, 12:37
Re: run with linear elastic properties
Hi Huffte,
I have read the note before. my model is a steel braced structure. when I check the option 'run with linear elastic properties' sometimes the difference between displacements is about 10cm!!
I have read the note before. my model is a steel braced structure. when I check the option 'run with linear elastic properties' sometimes the difference between displacements is about 10cm!!
Re: run with linear elastic properties
When you run without the box checked - that is to say, with material nonlinearity included in the analysis - do you observe strains and displacements well beyond the elastic limit? I suspect so, and a difference of 10 cm doesn't sound particularly surprising. Can you estimate the yield displacement? For example, if the yield displacement were 5 cm and the inelastic displacement were 15 cm, then a displacement ductility demand of 15/5 = 3 would be indicated.
(Note that displacement ductility and curvature ductility demands are not the same.)
The old so-called "equal-displacement rule" in which one assumes that the displacement experienced by a yielding structure equals the displacement experienced by the same structure, but without material nonlinearity included, is now known to be invalid for many cases of structures.
So, I am still not surprised that the difference in responses between an analysis which incorporates material nonlinearity and one which does not incorporate material nonlinearity are significant.
(Note that displacement ductility and curvature ductility demands are not the same.)
The old so-called "equal-displacement rule" in which one assumes that the displacement experienced by a yielding structure equals the displacement experienced by the same structure, but without material nonlinearity included, is now known to be invalid for many cases of structures.
So, I am still not surprised that the difference in responses between an analysis which incorporates material nonlinearity and one which does not incorporate material nonlinearity are significant.
Tim Huff
-
jackrussel
- Posts: 33
- Joined: 21 Sep 2013, 12:37
Re: run with linear elastic properties
huffte,
in the part of manual that you wrote in this forum there is a difference between elfrm and infrm. I said that I have both infrm and elfrm in my model.should I check this option in my model? I think this ambiguity is in the manual. we can read the manual in another way: when you check this option all of the materials are linear elastic.
in the part of manual that you wrote in this forum there is a difference between elfrm and infrm. I said that I have both infrm and elfrm in my model.should I check this option in my model? I think this ambiguity is in the manual. we can read the manual in another way: when you check this option all of the materials are linear elastic.
Re: run with linear elastic properties
Yes, I believe you have interpreted the manual correctly jackrussel.
So I must confess that I still don't see where the problem lies.
By checking the "Run with linear elastic properties" box, all material non-linearity will be ignored.
The fact that you have both infrm and elfrm elements in your model only reinforces the notion that you would get different results when the analysis is run with the box checked than without.
In general, Seismostruct, at least in my experience, is such a great tool for analyzing inelastic behavior, so I virtually never run models with the "Run with linear elastic properties" box checked.
That said, the feature provides an ideal means of comparing inelastic response to the response which would be obtained had the structure remained elastic.
The answer as to whether or not to check the feature in your model can only be answered by you. What are you trying to model? Are you trying to determine how much damage, as measured by inelastic strains, your structure will experience when subjected to a certain loading? If so, then you would certainly NOT want to check the box. I would say that any time you have accurately modeled the structure in question and you wish to estimate real response, you would not check the box. As mentioned earlier, running with the box checked could provide a means of comparing displacements of the actual structure to those of the fictitious case in which all materials remain elastic.
Of course, if you have infrm elements which never yield, you should get very close to the same answer whether the box is checked or not.
I hope this makes sense jackrussel. I am still not seeing where the problem lies, so pardon me if I have missed something along the way and I wish you much success in your work.
So I must confess that I still don't see where the problem lies.
By checking the "Run with linear elastic properties" box, all material non-linearity will be ignored.
The fact that you have both infrm and elfrm elements in your model only reinforces the notion that you would get different results when the analysis is run with the box checked than without.
In general, Seismostruct, at least in my experience, is such a great tool for analyzing inelastic behavior, so I virtually never run models with the "Run with linear elastic properties" box checked.
That said, the feature provides an ideal means of comparing inelastic response to the response which would be obtained had the structure remained elastic.
The answer as to whether or not to check the feature in your model can only be answered by you. What are you trying to model? Are you trying to determine how much damage, as measured by inelastic strains, your structure will experience when subjected to a certain loading? If so, then you would certainly NOT want to check the box. I would say that any time you have accurately modeled the structure in question and you wish to estimate real response, you would not check the box. As mentioned earlier, running with the box checked could provide a means of comparing displacements of the actual structure to those of the fictitious case in which all materials remain elastic.
Of course, if you have infrm elements which never yield, you should get very close to the same answer whether the box is checked or not.
I hope this makes sense jackrussel. I am still not seeing where the problem lies, so pardon me if I have missed something along the way and I wish you much success in your work.
Tim Huff
-
jackrussel
- Posts: 33
- Joined: 21 Sep 2013, 12:37
Re: run with linear elastic properties
huffte,
thank you very much.
thank you very much.