Hi,
I have a question about Plastic-hinge.
The plastic hinge can be considered by using the inelastic plastic hinge frame element(infrmFBPH), and the analysis result shows that the columns produce large deformation that those columns using infrmDB/infrmFB. However, the plastic hinges are less obvious than lumped plastic hinge. So, I want to know how to make the plastic hinge much more obviously?
lumped plastic hinge
Re: lumped plastic hinge
I'm not quite clear on what your question is bc863. It is likely not a surprise that the infrmFBPH plasticity strategy produced larger displacements than the distributed plasticity modeled with infrmDB/infrmFB elements. It could actually go either way I believe, depending upon the plastic hinge length and section fibers specified for the infrmFBPH elements.
As far as post-processing the results, I don't immediately see a difference between the two. I can plot chord rotations and hysteretic curves for each element type and they look very similar, both showing the inelastic nature of the response.
So I'll respond with another question - what do you mean when you say "I want to know how to make the plastic hinge much more obviously"?
As far as post-processing the results, I don't immediately see a difference between the two. I can plot chord rotations and hysteretic curves for each element type and they look very similar, both showing the inelastic nature of the response.
So I'll respond with another question - what do you mean when you say "I want to know how to make the plastic hinge much more obviously"?
Tim Huff
Re: lumped plastic hinge
Dear huffte.
Thanks for your prompt reply.
I just want to know whether the lumped plastic hinge can be set like SAP2000 or not?
Thank you.
Thanks for your prompt reply.
I just want to know whether the lumped plastic hinge can be set like SAP2000 or not?
Thank you.
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seismosoft
- Posts: 1263
- Joined: 06 Jul 2007, 04:55
Re: lumped plastic hinge
Hi bc863,
In SAP2000 the user is able to derive (based on a given axial force), and adapt the moment-curvature curve of each section, however this M-r curve is kept constant during the analysis (which is not very accurate).
On the contrary, with the infrmFBPH element of SeismoStruct, the moment-curvature curve is derived at each step of the analysis, based on the current (at that step) axial load. For this reason, it is not possible for the user to pre-define the M-r curve.
SeismoSoft Support
In SAP2000 the user is able to derive (based on a given axial force), and adapt the moment-curvature curve of each section, however this M-r curve is kept constant during the analysis (which is not very accurate).
On the contrary, with the infrmFBPH element of SeismoStruct, the moment-curvature curve is derived at each step of the analysis, based on the current (at that step) axial load. For this reason, it is not possible for the user to pre-define the M-r curve.
SeismoSoft Support
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fakharifar.mostafa
- Posts: 124
- Joined: 06 Jan 2010, 05:34
Re: lumped plastic hinge
Such a nice concept was brought up about FE element formulations and its use in SStruct. However, neither Fiber based element nor lumped plasticity model could be stated being BETTER THAN THE OTHER. Let's say for an RC frame, it is well studied while Fiber type elements are appropriate for strength degradation due to concrete deteriorating component, such formulation can not fully capture the degrading response due to different sources of strength degradation such as bar buckling and transverse bar yielding causing collapse.
Overall, if you need to capture the "structural failure" the lumped plasticity model is the preferred option to re-produce such behavior. Hope this helps for your model development.
Overall, if you need to capture the "structural failure" the lumped plasticity model is the preferred option to re-produce such behavior. Hope this helps for your model development.
Re: lumped plastic hinge
Hi fakharifar.mostafa,
It is probably better not to dwell too much on this topic, which is more of a general earthquake engineering nature, rather than about SeismoStruct modelling capabilities.
In any case, I just wanted to note that I do agree with you that it is not wise to claim that one modelling approach (concentrated plasticity vs. distributed inelasticity) is better than another, since both have pros and cons, and, exactly because of that, I would argue against your closing statement regarding the superiority of plastic hinge modelling when one is trying to model structural collapse, especially when it comes to cyclic/dynamic loading.
The correct calibration (without experimental data, as happens when dealing with real existing structures) of the hysteretic constitutive relationship for a plastic hinge that attempts to represent the inelastic flexural/shear/slippage/contact deformation of a RC member under cyclic loading is extremely difficult (I have seen over the years many highly experienced academics/engineers still getting it wrong), hence I would hesitate in stating that this is the best approach to model structural collapse.
I would say that the best way in which model structural collapse is that with which a given modeller feels more comfortable and experienced with. In my personal case it is through the employment a fibre beam element (coupled with a cap on shear capacity, possible in the upcoming SeismoStruct v7), whilst for others the use of a plastic hinge model adequately calibrated may result more intuitive.
Best,
Rui
It is probably better not to dwell too much on this topic, which is more of a general earthquake engineering nature, rather than about SeismoStruct modelling capabilities.
In any case, I just wanted to note that I do agree with you that it is not wise to claim that one modelling approach (concentrated plasticity vs. distributed inelasticity) is better than another, since both have pros and cons, and, exactly because of that, I would argue against your closing statement regarding the superiority of plastic hinge modelling when one is trying to model structural collapse, especially when it comes to cyclic/dynamic loading.
The correct calibration (without experimental data, as happens when dealing with real existing structures) of the hysteretic constitutive relationship for a plastic hinge that attempts to represent the inelastic flexural/shear/slippage/contact deformation of a RC member under cyclic loading is extremely difficult (I have seen over the years many highly experienced academics/engineers still getting it wrong), hence I would hesitate in stating that this is the best approach to model structural collapse.
I would say that the best way in which model structural collapse is that with which a given modeller feels more comfortable and experienced with. In my personal case it is through the employment a fibre beam element (coupled with a cap on shear capacity, possible in the upcoming SeismoStruct v7), whilst for others the use of a plastic hinge model adequately calibrated may result more intuitive.
Best,
Rui