wuhaoshrek wrote:
> vesna wrote:
> > At the bottom of the command manual for the forceBeamColumn element you can
> > find some info on integration schemes and their integration weights.
> >
> > Plastic hinge length depends on the structural system, component, material.
> > There are empirical formulas that mostly used to estimate the plastic hinge
> > length. Plastic hinge occurs at a concentrated section only in cases of
> > very bad design. The intent of modern building codes is to spread
> > plasticity over a length of the element and this length is called plastic
> > hinge length.
> >
> > Yes, "wt(0)/2*L" applies only to the case that plastic hinges
> > develop at the element ends.
> >
> > Remember, this is important only if local response is important for your
> > study.
>
>
> Hi vesna,
>
> 1. If you let the weight of the bottom int. point to be the same as plastic hinge,
> for Lobatto int. method
> where the int. is on the end of the element, I think this would overestimate the
> integration result since
> deformation at the end would usually be largest. So i suggest use one element
> with its length equal to
> the plastic hinge length, and use more int. points within that element as long as
> it converges.
>
> 2. The plastic hinge concentrates at the bottom critical section occurs when we use
> Elastic of softening material
> in a cantilever column model. Acctually I'm modeling on such a simple model right
> model. I was wondering
> what would be the EXACT solution to such a problem? My personal view is there
> would be no answer to such
> a problem since plastic hinge length would be zero after yield.
>
> 3. By the way I am trying to use user default integration method, with 1 int. point
> in the middle and weights=1.0
> on an element with its length equal to the plastic hinge length. The idea is
> straightforward, just to check if
> in this way we can accuarately capture the behavior in plastic hinge. BUT I
> cannot get converged. OpenSees
> failed to converge at the very beginning and prompts that the cannot find
> compatible force and deformation
> for that very element representing the plastic hinge. Vesna, Can you explain why?
> and give me some suggestions?
>
> Thanks.
Personal view:
1. Setting the weight of the end IP to be the plastic hinge length is right for softening member but the non-objectivity is not solved since the results will be different using different # of IPs. That's why element-with-hinges is proposed.
2. The plastic hinge length is actually a very empirical parameter which is proposed for calculating the global member responses. It is usually calculated based on the yield moment of the section as proposed by Park and Priestley.
3. This is zero-length element in Opensees: unit length with only one IP. You can just base on it.
the difference between the dispbeamcolumn and nonlinearbeamc
Moderators: silvia, selimgunay, Moderators
-
linguan118
- Posts: 140
- Joined: Sun Oct 03, 2010 11:36 pm
- Location: Hong Kong
Re: the difference between the dispbeamcolumn and nonlinearb
Research Assistant Professor, The Hong Kong Polytechnic University
guanlin@polyu.edu.hk
guanlin@polyu.edu.hk
-
wuhaoshrek
- Posts: 122
- Joined: Tue Oct 28, 2008 4:01 am
Re: the difference between the dispbeamcolumn and nonlinearb
linguan118,
Thanks for you reply.
For beam with hinges, the # of IPs is also fixed, you can refer to the paper
by Scotts et al. 2006. As we can imagine deformation localization would always
concentrate on the maximum moment section(int. point), so all the other int. point
in the plastic hinge would unload.So, actually I don't quite understand the meaning
of non-objectivity, I am not sure it is with # IPs.
For 2, what I really mean is for such a ideal bi-linear EPP model, do we
have exact theoretical solution to it? if not, how can we check the result
from OpenSees.
For 3, I'll try use zero-length element later, but there is 1-point Legendre
option in FBE, you can check it in its source code. The problem now is I
cannot get converged result with 1 Legendre point. I was wondering if
opensees cannot deal with if there is only 1 int. point in an element since
it may not be able to calculate the inertial force for static equalibrium for
the element? I don't know, just guess.
Hao
linguan118 wrote:
> wuhaoshrek wrote:
> > vesna wrote:
> > > At the bottom of the command manual for the forceBeamColumn element you can
> > > find some info on integration schemes and their integration weights.
> > >
> > > Plastic hinge length depends on the structural system, component, material.
> > > There are empirical formulas that mostly used to estimate the plastic hinge
> > > length. Plastic hinge occurs at a concentrated section only in cases of
> > > very bad design. The intent of modern building codes is to spread
> > > plasticity over a length of the element and this length is called plastic
> > > hinge length.
> > >
> > > Yes, "wt(0)/2*L" applies only to the case that plastic hinges
> > > develop at the element ends.
> > >
> > > Remember, this is important only if local response is important for your
> > > study.
> >
> >
> > Hi vesna,
> >
> > 1. If you let the weight of the bottom int. point to be the same as plastic
> hinge,
> > for Lobatto int. method
> > where the int. is on the end of the element, I think this would overestimate
> the
> > integration result since
> > deformation at the end would usually be largest. So i suggest use one
> element
> > with its length equal to
> > the plastic hinge length, and use more int. points within that element as
> long as
> > it converges.
> >
> > 2. The plastic hinge concentrates at the bottom critical section occurs when we
> use
> > Elastic of softening material
> > in a cantilever column model. Acctually I'm modeling on such a simple model
> right
> > model. I was wondering
> > what would be the EXACT solution to such a problem? My personal view is
> there
> > would be no answer to such
> > a problem since plastic hinge length would be zero after yield.
> >
> > 3. By the way I am trying to use user default integration method, with 1 int.
> point
> > in the middle and weights=1.0
> > on an element with its length equal to the plastic hinge length. The idea is
> > straightforward, just to check if
> > in this way we can accuarately capture the behavior in plastic hinge. BUT I
> > cannot get converged. OpenSees
> > failed to converge at the very beginning and prompts that the cannot find
> > compatible force and deformation
> > for that very element representing the plastic hinge. Vesna, Can you explain
> why?
> > and give me some suggestions?
> >
> > Thanks.
> Personal view:
> 1. Setting the weight of the end IP to be the plastic hinge length is right for
> softening member but the non-objectivity is not solved since the results will be
> different using different # of IPs. That's why element-with-hinges is proposed.
> 2. The plastic hinge length is actually a very empirical parameter which is proposed
> for calculating the global member responses. It is usually calculated based on the
> yield moment of the section as proposed by Park and Priestley.
> 3. This is zero-length element in Opensees: unit length with only one IP. You can
> just base on it.
Thanks for you reply.
For beam with hinges, the # of IPs is also fixed, you can refer to the paper
by Scotts et al. 2006. As we can imagine deformation localization would always
concentrate on the maximum moment section(int. point), so all the other int. point
in the plastic hinge would unload.So, actually I don't quite understand the meaning
of non-objectivity, I am not sure it is with # IPs.
For 2, what I really mean is for such a ideal bi-linear EPP model, do we
have exact theoretical solution to it? if not, how can we check the result
from OpenSees.
For 3, I'll try use zero-length element later, but there is 1-point Legendre
option in FBE, you can check it in its source code. The problem now is I
cannot get converged result with 1 Legendre point. I was wondering if
opensees cannot deal with if there is only 1 int. point in an element since
it may not be able to calculate the inertial force for static equalibrium for
the element? I don't know, just guess.
Hao
linguan118 wrote:
> wuhaoshrek wrote:
> > vesna wrote:
> > > At the bottom of the command manual for the forceBeamColumn element you can
> > > find some info on integration schemes and their integration weights.
> > >
> > > Plastic hinge length depends on the structural system, component, material.
> > > There are empirical formulas that mostly used to estimate the plastic hinge
> > > length. Plastic hinge occurs at a concentrated section only in cases of
> > > very bad design. The intent of modern building codes is to spread
> > > plasticity over a length of the element and this length is called plastic
> > > hinge length.
> > >
> > > Yes, "wt(0)/2*L" applies only to the case that plastic hinges
> > > develop at the element ends.
> > >
> > > Remember, this is important only if local response is important for your
> > > study.
> >
> >
> > Hi vesna,
> >
> > 1. If you let the weight of the bottom int. point to be the same as plastic
> hinge,
> > for Lobatto int. method
> > where the int. is on the end of the element, I think this would overestimate
> the
> > integration result since
> > deformation at the end would usually be largest. So i suggest use one
> element
> > with its length equal to
> > the plastic hinge length, and use more int. points within that element as
> long as
> > it converges.
> >
> > 2. The plastic hinge concentrates at the bottom critical section occurs when we
> use
> > Elastic of softening material
> > in a cantilever column model. Acctually I'm modeling on such a simple model
> right
> > model. I was wondering
> > what would be the EXACT solution to such a problem? My personal view is
> there
> > would be no answer to such
> > a problem since plastic hinge length would be zero after yield.
> >
> > 3. By the way I am trying to use user default integration method, with 1 int.
> point
> > in the middle and weights=1.0
> > on an element with its length equal to the plastic hinge length. The idea is
> > straightforward, just to check if
> > in this way we can accuarately capture the behavior in plastic hinge. BUT I
> > cannot get converged. OpenSees
> > failed to converge at the very beginning and prompts that the cannot find
> > compatible force and deformation
> > for that very element representing the plastic hinge. Vesna, Can you explain
> why?
> > and give me some suggestions?
> >
> > Thanks.
> Personal view:
> 1. Setting the weight of the end IP to be the plastic hinge length is right for
> softening member but the non-objectivity is not solved since the results will be
> different using different # of IPs. That's why element-with-hinges is proposed.
> 2. The plastic hinge length is actually a very empirical parameter which is proposed
> for calculating the global member responses. It is usually calculated based on the
> yield moment of the section as proposed by Park and Priestley.
> 3. This is zero-length element in Opensees: unit length with only one IP. You can
> just base on it.
-
linguan118
- Posts: 140
- Joined: Sun Oct 03, 2010 11:36 pm
- Location: Hong Kong
Re: the difference between the dispbeamcolumn and nonlinearb
wuhaoshrek wrote:
> linguan118,
>
> Thanks for you reply.
>
> For beam with hinges, the # of IPs is also fixed, you can refer to the paper
> by Scotts et al. 2006. As we can imagine deformation localization would always
> concentrate on the maximum moment section(int. point), so all the other int. point
> in the plastic hinge would unload.So, actually I don't quite understand the meaning
> of non-objectivity, I am not sure it is with # IPs.
>
> For 2, what I really mean is for such a ideal bi-linear EPP model, do we
> have exact theoretical solution to it? if not, how can we check the result
> from OpenSees.
>
> For 3, I'll try use zero-length element later, but there is 1-point Legendre
> option in FBE, you can check it in its source code. The problem now is I
> cannot get converged result with 1 Legendre point. I was wondering if
> opensees cannot deal with if there is only 1 int. point in an element since
> it may not be able to calculate the inertial force for static equalibrium for
> the element? I don't know, just guess.
>
> Hao
>
> linguan118 wrote:
> > wuhaoshrek wrote:
> > > vesna wrote:
> > > > At the bottom of the command manual for the forceBeamColumn element
> you can
> > > > find some info on integration schemes and their integration weights.
> > > >
> > > > Plastic hinge length depends on the structural system, component,
> material.
> > > > There are empirical formulas that mostly used to estimate the plastic
> hinge
> > > > length. Plastic hinge occurs at a concentrated section only in cases
> of
> > > > very bad design. The intent of modern building codes is to spread
> > > > plasticity over a length of the element and this length is called
> plastic
> > > > hinge length.
> > > >
> > > > Yes, "wt(0)/2*L" applies only to the case that plastic
> hinges
> > > > develop at the element ends.
> > > >
> > > > Remember, this is important only if local response is important for
> your
> > > > study.
> > >
> > >
> > > Hi vesna,
> > >
> > > 1. If you let the weight of the bottom int. point to be the same as plastic
> > hinge,
> > > for Lobatto int. method
> > > where the int. is on the end of the element, I think this would
> overestimate
> > the
> > > integration result since
> > > deformation at the end would usually be largest. So i suggest use one
> > element
> > > with its length equal to
> > > the plastic hinge length, and use more int. points within that element
> as
> > long as
> > > it converges.
> > >
> > > 2. The plastic hinge concentrates at the bottom critical section occurs
> when we
> > use
> > > Elastic of softening material
> > > in a cantilever column model. Acctually I'm modeling on such a simple
> model
> > right
> > > model. I was wondering
> > > what would be the EXACT solution to such a problem? My personal view is
> > there
> > > would be no answer to such
> > > a problem since plastic hinge length would be zero after yield.
> > >
> > > 3. By the way I am trying to use user default integration method, with 1
> int.
> > point
> > > in the middle and weights=1.0
> > > on an element with its length equal to the plastic hinge length. The
> idea is
> > > straightforward, just to check if
> > > in this way we can accuarately capture the behavior in plastic hinge.
> BUT I
> > > cannot get converged. OpenSees
> > > failed to converge at the very beginning and prompts that the cannot
> find
> > > compatible force and deformation
> > > for that very element representing the plastic hinge. Vesna, Can you
> explain
> > why?
> > > and give me some suggestions?
> > >
> > > Thanks.
> > Personal view:
> > 1. Setting the weight of the end IP to be the plastic hinge length is right for
> > softening member but the non-objectivity is not solved since the results will be
> > different using different # of IPs. That's why element-with-hinges is proposed.
> > 2. The plastic hinge length is actually a very empirical parameter which is
> proposed
> > for calculating the global member responses. It is usually calculated based on
> the
> > yield moment of the section as proposed by Park and Priestley.
> > 3. This is zero-length element in Opensees: unit length with only one IP. You
> can
> > just base on it.
Yes, the # of IPs is fixed in Beam-with-hinges, but the weight of the end iP can be changed, so there is no non-objectivity problem. The curvature (deformation) within the weight length (=plastic hinge length) of the end IP (end section) is constant as Scotts used modified Gauss–Radau plastic hinge integration methods.
There is of course exact solution, the problem derives from FE analysis which uses finite elements with integration points and weights for the purpose of fitting real deformation field.
I think Opensees can deal with element with one IP, since zero-length element uses only 1 IP.
> linguan118,
>
> Thanks for you reply.
>
> For beam with hinges, the # of IPs is also fixed, you can refer to the paper
> by Scotts et al. 2006. As we can imagine deformation localization would always
> concentrate on the maximum moment section(int. point), so all the other int. point
> in the plastic hinge would unload.So, actually I don't quite understand the meaning
> of non-objectivity, I am not sure it is with # IPs.
>
> For 2, what I really mean is for such a ideal bi-linear EPP model, do we
> have exact theoretical solution to it? if not, how can we check the result
> from OpenSees.
>
> For 3, I'll try use zero-length element later, but there is 1-point Legendre
> option in FBE, you can check it in its source code. The problem now is I
> cannot get converged result with 1 Legendre point. I was wondering if
> opensees cannot deal with if there is only 1 int. point in an element since
> it may not be able to calculate the inertial force for static equalibrium for
> the element? I don't know, just guess.
>
> Hao
>
> linguan118 wrote:
> > wuhaoshrek wrote:
> > > vesna wrote:
> > > > At the bottom of the command manual for the forceBeamColumn element
> you can
> > > > find some info on integration schemes and their integration weights.
> > > >
> > > > Plastic hinge length depends on the structural system, component,
> material.
> > > > There are empirical formulas that mostly used to estimate the plastic
> hinge
> > > > length. Plastic hinge occurs at a concentrated section only in cases
> of
> > > > very bad design. The intent of modern building codes is to spread
> > > > plasticity over a length of the element and this length is called
> plastic
> > > > hinge length.
> > > >
> > > > Yes, "wt(0)/2*L" applies only to the case that plastic
> hinges
> > > > develop at the element ends.
> > > >
> > > > Remember, this is important only if local response is important for
> your
> > > > study.
> > >
> > >
> > > Hi vesna,
> > >
> > > 1. If you let the weight of the bottom int. point to be the same as plastic
> > hinge,
> > > for Lobatto int. method
> > > where the int. is on the end of the element, I think this would
> overestimate
> > the
> > > integration result since
> > > deformation at the end would usually be largest. So i suggest use one
> > element
> > > with its length equal to
> > > the plastic hinge length, and use more int. points within that element
> as
> > long as
> > > it converges.
> > >
> > > 2. The plastic hinge concentrates at the bottom critical section occurs
> when we
> > use
> > > Elastic of softening material
> > > in a cantilever column model. Acctually I'm modeling on such a simple
> model
> > right
> > > model. I was wondering
> > > what would be the EXACT solution to such a problem? My personal view is
> > there
> > > would be no answer to such
> > > a problem since plastic hinge length would be zero after yield.
> > >
> > > 3. By the way I am trying to use user default integration method, with 1
> int.
> > point
> > > in the middle and weights=1.0
> > > on an element with its length equal to the plastic hinge length. The
> idea is
> > > straightforward, just to check if
> > > in this way we can accuarately capture the behavior in plastic hinge.
> BUT I
> > > cannot get converged. OpenSees
> > > failed to converge at the very beginning and prompts that the cannot
> find
> > > compatible force and deformation
> > > for that very element representing the plastic hinge. Vesna, Can you
> explain
> > why?
> > > and give me some suggestions?
> > >
> > > Thanks.
> > Personal view:
> > 1. Setting the weight of the end IP to be the plastic hinge length is right for
> > softening member but the non-objectivity is not solved since the results will be
> > different using different # of IPs. That's why element-with-hinges is proposed.
> > 2. The plastic hinge length is actually a very empirical parameter which is
> proposed
> > for calculating the global member responses. It is usually calculated based on
> the
> > yield moment of the section as proposed by Park and Priestley.
> > 3. This is zero-length element in Opensees: unit length with only one IP. You
> can
> > just base on it.
Yes, the # of IPs is fixed in Beam-with-hinges, but the weight of the end iP can be changed, so there is no non-objectivity problem. The curvature (deformation) within the weight length (=plastic hinge length) of the end IP (end section) is constant as Scotts used modified Gauss–Radau plastic hinge integration methods.
There is of course exact solution, the problem derives from FE analysis which uses finite elements with integration points and weights for the purpose of fitting real deformation field.
I think Opensees can deal with element with one IP, since zero-length element uses only 1 IP.
Research Assistant Professor, The Hong Kong Polytechnic University
guanlin@polyu.edu.hk
guanlin@polyu.edu.hk
-
tahakhalifa
- Posts: 1
- Joined: Mon Nov 12, 2012 3:40 am
- Contact:
-
wuhaoshrek
- Posts: 122
- Joined: Tue Oct 28, 2008 4:01 am
Re: the difference between the dispbeamcolumn and nonlinearb
linguan118 wrote:
> wuhaoshrek wrote:
> > linguan118,
> >
> > Thanks for you reply.
> >
> > For beam with hinges, the # of IPs is also fixed, you can refer to the paper
> > by Scotts et al. 2006. As we can imagine deformation localization would always
> > concentrate on the maximum moment section(int. point), so all the other int.
> point
> > in the plastic hinge would unload.So, actually I don't quite understand the
> meaning
> > of non-objectivity, I am not sure it is with # IPs.
> >
> > For 2, what I really mean is for such a ideal bi-linear EPP model, do we
> > have exact theoretical solution to it? if not, how can we check the result
> > from OpenSees.
> >
> > For 3, I'll try use zero-length element later, but there is 1-point Legendre
> > option in FBE, you can check it in its source code. The problem now is I
> > cannot get converged result with 1 Legendre point. I was wondering if
> > opensees cannot deal with if there is only 1 int. point in an element since
> > it may not be able to calculate the inertial force for static equalibrium for
> > the element? I don't know, just guess.
> >
> > Hao
> >
> > linguan118 wrote:
> > > wuhaoshrek wrote:
> > > > vesna wrote:
> > > > > At the bottom of the command manual for the forceBeamColumn
> element
> > you can
> > > > > find some info on integration schemes and their integration
> weights.
> > > > >
> > > > > Plastic hinge length depends on the structural system, component,
> > material.
> > > > > There are empirical formulas that mostly used to estimate the
> plastic
> > hinge
> > > > > length. Plastic hinge occurs at a concentrated section only in
> cases
> > of
> > > > > very bad design. The intent of modern building codes is to spread
> > > > > plasticity over a length of the element and this length is called
> > plastic
> > > > > hinge length.
> > > > >
> > > > > Yes, "wt(0)/2*L" applies only to the case that plastic
> > hinges
> > > > > develop at the element ends.
> > > > >
> > > > > Remember, this is important only if local response is important
> for
> > your
> > > > > study.
> > > >
> > > >
> > > > Hi vesna,
> > > >
> > > > 1. If you let the weight of the bottom int. point to be the same as
> plastic
> > > hinge,
> > > > for Lobatto int. method
> > > > where the int. is on the end of the element, I think this would
> > overestimate
> > > the
> > > > integration result since
> > > > deformation at the end would usually be largest. So i suggest use
> one
> > > element
> > > > with its length equal to
> > > > the plastic hinge length, and use more int. points within that
> element
> > as
> > > long as
> > > > it converges.
> > > >
> > > > 2. The plastic hinge concentrates at the bottom critical section
> occurs
> > when we
> > > use
> > > > Elastic of softening material
> > > > in a cantilever column model. Acctually I'm modeling on such a
> simple
> > model
> > > right
> > > > model. I was wondering
> > > > what would be the EXACT solution to such a problem? My personal
> view is
> > > there
> > > > would be no answer to such
> > > > a problem since plastic hinge length would be zero after yield.
> > > >
> > > > 3. By the way I am trying to use user default integration method, with
> 1
> > int.
> > > point
> > > > in the middle and weights=1.0
> > > > on an element with its length equal to the plastic hinge length.
> The
> > idea is
> > > > straightforward, just to check if
> > > > in this way we can accuarately capture the behavior in plastic
> hinge.
> > BUT I
> > > > cannot get converged. OpenSees
> > > > failed to converge at the very beginning and prompts that the
> cannot
> > find
> > > > compatible force and deformation
> > > > for that very element representing the plastic hinge. Vesna, Can
> you
> > explain
> > > why?
> > > > and give me some suggestions?
> > > >
> > > > Thanks.
> > > Personal view:
> > > 1. Setting the weight of the end IP to be the plastic hinge length is right
> for
> > > softening member but the non-objectivity is not solved since the results
> will be
> > > different using different # of IPs. That's why element-with-hinges is
> proposed.
> > > 2. The plastic hinge length is actually a very empirical parameter which is
> > proposed
> > > for calculating the global member responses. It is usually calculated based
> on
> > the
> > > yield moment of the section as proposed by Park and Priestley.
> > > 3. This is zero-length element in Opensees: unit length with only one IP.
> You
> > can
> > > just base on it.
>
> Yes, the # of IPs is fixed in Beam-with-hinges, but the weight of the end iP can be
> changed, so there is no non-objectivity problem. The curvature (deformation) within
> the weight length (=plastic hinge length) of the end IP (end section) is constant as
> Scotts used modified Gauss–Radau plastic hinge integration methods.
> There is of course exact solution, the problem derives from FE analysis which uses
> finite elements with integration points and weights for the purpose of fitting real
> deformation field.
> I think Opensees can deal with element with one IP, since zero-length element uses
> only 1 IP.
Hi,linguan118,
So far what I understand for the meaning of non-objectivity is the element response
would be changed as a function of # IPs. Non-objectivity issue derives from localizaion
phenomenon which introduce one-point integration method and so we should be carefully
choose the appropriate end int. weight, which is aiming to match the localized deformation
length. Scott use Modified Radau int. which introduce the plastic length into the integration
and let the weight of end int. point to be the same as plastic hinge length. From the definition
of non-objectivity as I understand above, it of course omit non-objectivity problem, since
user can only change the # of IPs within elastic segment of the element.
For element using EPP and softening material, what happened exactly is only one section
get into plastic range(zero length), so you would never integrate it since it contribute zero
to the total deflection of the element(deformation distribution is a dirichlet function), which
means you would never find a exact solution to such a problem.
I still cannot get converged solution with 1 IPs in opensees,but with 2, it is OK.
Thanks.
> wuhaoshrek wrote:
> > linguan118,
> >
> > Thanks for you reply.
> >
> > For beam with hinges, the # of IPs is also fixed, you can refer to the paper
> > by Scotts et al. 2006. As we can imagine deformation localization would always
> > concentrate on the maximum moment section(int. point), so all the other int.
> point
> > in the plastic hinge would unload.So, actually I don't quite understand the
> meaning
> > of non-objectivity, I am not sure it is with # IPs.
> >
> > For 2, what I really mean is for such a ideal bi-linear EPP model, do we
> > have exact theoretical solution to it? if not, how can we check the result
> > from OpenSees.
> >
> > For 3, I'll try use zero-length element later, but there is 1-point Legendre
> > option in FBE, you can check it in its source code. The problem now is I
> > cannot get converged result with 1 Legendre point. I was wondering if
> > opensees cannot deal with if there is only 1 int. point in an element since
> > it may not be able to calculate the inertial force for static equalibrium for
> > the element? I don't know, just guess.
> >
> > Hao
> >
> > linguan118 wrote:
> > > wuhaoshrek wrote:
> > > > vesna wrote:
> > > > > At the bottom of the command manual for the forceBeamColumn
> element
> > you can
> > > > > find some info on integration schemes and their integration
> weights.
> > > > >
> > > > > Plastic hinge length depends on the structural system, component,
> > material.
> > > > > There are empirical formulas that mostly used to estimate the
> plastic
> > hinge
> > > > > length. Plastic hinge occurs at a concentrated section only in
> cases
> > of
> > > > > very bad design. The intent of modern building codes is to spread
> > > > > plasticity over a length of the element and this length is called
> > plastic
> > > > > hinge length.
> > > > >
> > > > > Yes, "wt(0)/2*L" applies only to the case that plastic
> > hinges
> > > > > develop at the element ends.
> > > > >
> > > > > Remember, this is important only if local response is important
> for
> > your
> > > > > study.
> > > >
> > > >
> > > > Hi vesna,
> > > >
> > > > 1. If you let the weight of the bottom int. point to be the same as
> plastic
> > > hinge,
> > > > for Lobatto int. method
> > > > where the int. is on the end of the element, I think this would
> > overestimate
> > > the
> > > > integration result since
> > > > deformation at the end would usually be largest. So i suggest use
> one
> > > element
> > > > with its length equal to
> > > > the plastic hinge length, and use more int. points within that
> element
> > as
> > > long as
> > > > it converges.
> > > >
> > > > 2. The plastic hinge concentrates at the bottom critical section
> occurs
> > when we
> > > use
> > > > Elastic of softening material
> > > > in a cantilever column model. Acctually I'm modeling on such a
> simple
> > model
> > > right
> > > > model. I was wondering
> > > > what would be the EXACT solution to such a problem? My personal
> view is
> > > there
> > > > would be no answer to such
> > > > a problem since plastic hinge length would be zero after yield.
> > > >
> > > > 3. By the way I am trying to use user default integration method, with
> 1
> > int.
> > > point
> > > > in the middle and weights=1.0
> > > > on an element with its length equal to the plastic hinge length.
> The
> > idea is
> > > > straightforward, just to check if
> > > > in this way we can accuarately capture the behavior in plastic
> hinge.
> > BUT I
> > > > cannot get converged. OpenSees
> > > > failed to converge at the very beginning and prompts that the
> cannot
> > find
> > > > compatible force and deformation
> > > > for that very element representing the plastic hinge. Vesna, Can
> you
> > explain
> > > why?
> > > > and give me some suggestions?
> > > >
> > > > Thanks.
> > > Personal view:
> > > 1. Setting the weight of the end IP to be the plastic hinge length is right
> for
> > > softening member but the non-objectivity is not solved since the results
> will be
> > > different using different # of IPs. That's why element-with-hinges is
> proposed.
> > > 2. The plastic hinge length is actually a very empirical parameter which is
> > proposed
> > > for calculating the global member responses. It is usually calculated based
> on
> > the
> > > yield moment of the section as proposed by Park and Priestley.
> > > 3. This is zero-length element in Opensees: unit length with only one IP.
> You
> > can
> > > just base on it.
>
> Yes, the # of IPs is fixed in Beam-with-hinges, but the weight of the end iP can be
> changed, so there is no non-objectivity problem. The curvature (deformation) within
> the weight length (=plastic hinge length) of the end IP (end section) is constant as
> Scotts used modified Gauss–Radau plastic hinge integration methods.
> There is of course exact solution, the problem derives from FE analysis which uses
> finite elements with integration points and weights for the purpose of fitting real
> deformation field.
> I think Opensees can deal with element with one IP, since zero-length element uses
> only 1 IP.
Hi,linguan118,
So far what I understand for the meaning of non-objectivity is the element response
would be changed as a function of # IPs. Non-objectivity issue derives from localizaion
phenomenon which introduce one-point integration method and so we should be carefully
choose the appropriate end int. weight, which is aiming to match the localized deformation
length. Scott use Modified Radau int. which introduce the plastic length into the integration
and let the weight of end int. point to be the same as plastic hinge length. From the definition
of non-objectivity as I understand above, it of course omit non-objectivity problem, since
user can only change the # of IPs within elastic segment of the element.
For element using EPP and softening material, what happened exactly is only one section
get into plastic range(zero length), so you would never integrate it since it contribute zero
to the total deflection of the element(deformation distribution is a dirichlet function), which
means you would never find a exact solution to such a problem.
I still cannot get converged solution with 1 IPs in opensees,but with 2, it is OK.
Thanks.
-
linguan118
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- Location: Hong Kong
Re: the difference between the dispbeamcolumn and nonlinearb
Hi, Wu,
The # of IPs within elastic portion of Beam-with-hinge element is fixed by default; only weights of end section can be changed.
What I mean by exact solution is analytic solution instead of numerical results.
Why do you want to use element with 1 ips (with length = empirical plastic hinge length)? The deformation along the element will be constant with only 1 IP, which is the same case for beam-with-hinge element with constant deformation within the plastic hinge region.
The # of IPs within elastic portion of Beam-with-hinge element is fixed by default; only weights of end section can be changed.
What I mean by exact solution is analytic solution instead of numerical results.
Why do you want to use element with 1 ips (with length = empirical plastic hinge length)? The deformation along the element will be constant with only 1 IP, which is the same case for beam-with-hinge element with constant deformation within the plastic hinge region.
Research Assistant Professor, The Hong Kong Polytechnic University
guanlin@polyu.edu.hk
guanlin@polyu.edu.hk
-
wuhaoshrek
- Posts: 122
- Joined: Tue Oct 28, 2008 4:01 am
Re: the difference between the dispbeamcolumn and nonlinearb
linguan118:
I know the exact solution refer to the analytical rather than numerical, with numerical
you have corresponding weight, but with analytical the weight is zero, so no exact
solution is able to be found.
I just try to understand it more.
I know the exact solution refer to the analytical rather than numerical, with numerical
you have corresponding weight, but with analytical the weight is zero, so no exact
solution is able to be found.
I just try to understand it more.
-
linguan118
- Posts: 140
- Joined: Sun Oct 03, 2010 11:36 pm
- Location: Hong Kong
Re: the difference between the dispbeamcolumn and nonlinearb
wuhaoshrek wrote:
> linguan118:
>
> I know the exact solution refer to the analytical rather than numerical,
> with numerical
> you have corresponding weight, but with analytical the weight is zero, so
> no exact
> solution is able to be found.
>
> I just try to understand it more.
Sorry, I misunderstood your statement. For softening behavior, there is no closed-form solution (that is what you mean by "exact solution"), but for hardening behavior, there is. You're right, no integration of curvature can be obtained at the end. Closed-form solution doesn't represent exact solution (realistic I mean), that's why the proposed beam-with-hinge element is validated by experimental results.
> linguan118:
>
> I know the exact solution refer to the analytical rather than numerical,
> with numerical
> you have corresponding weight, but with analytical the weight is zero, so
> no exact
> solution is able to be found.
>
> I just try to understand it more.
Sorry, I misunderstood your statement. For softening behavior, there is no closed-form solution (that is what you mean by "exact solution"), but for hardening behavior, there is. You're right, no integration of curvature can be obtained at the end. Closed-form solution doesn't represent exact solution (realistic I mean), that's why the proposed beam-with-hinge element is validated by experimental results.
Research Assistant Professor, The Hong Kong Polytechnic University
guanlin@polyu.edu.hk
guanlin@polyu.edu.hk
-
wuhaoshrek
- Posts: 122
- Joined: Tue Oct 28, 2008 4:01 am
Re: the difference between the dispbeamcolumn and nonlinearb
Hi linguan118,
Beam with hinge element use elastic section property for the middle part. When force beamcolumn
element use modified Radau Int. method, what do you think is the difference between them? For me,
I think the latter would be more reasonable.
Beam with hinge element use elastic section property for the middle part. When force beamcolumn
element use modified Radau Int. method, what do you think is the difference between them? For me,
I think the latter would be more reasonable.
-
linguan118
- Posts: 140
- Joined: Sun Oct 03, 2010 11:36 pm
- Location: Hong Kong
Re: the difference between the dispbeamcolumn and nonlinearb
For softening behavior, I think they're the same if the same plastic hinge length is assigned. But in the concept of plastic hinge, there is no inelastic deformation outside the plastic hinge region. So this facilitates the calculation of beam-with-hinge element as it only captures the inelastic deformation at two ends (only two monitoring sections). Of course we can use force-element with modified G-R integration for softening behavior by also assigning the empirical plastic hinge length. But the computational effort is larger than beam-with-hinge element because the former has four monitoring sections. For the accuracy, it isn't necessarily improved.
BTW, I'm not sure if the modified G-R integration method can be directly used by force-beam element?
BTW, I'm not sure if the modified G-R integration method can be directly used by force-beam element?
Research Assistant Professor, The Hong Kong Polytechnic University
guanlin@polyu.edu.hk
guanlin@polyu.edu.hk
-
wuhaoshrek
- Posts: 122
- Joined: Tue Oct 28, 2008 4:01 am
Re: the difference between the dispbeamcolumn and nonlinearb
linguan118 wrote:
> For softening behavior, I think they're the same if the same plastic hinge
> length is assigned. But in the concept of plastic hinge, there is no
> inelastic deformation outside the plastic hinge region. So this facilitates
> the calculation of beam-with-hinge element as it only captures the
> inelastic deformation at two ends (only two monitoring sections). Of course
> we can use force-element with modified G-R integration for softening
> behavior by also assigning the empirical plastic hinge length. But the
> computational effort is larger than beam-with-hinge element because the
> former has four monitoring sections. For the accuracy, it isn't necessarily
> improved.
> BTW, I'm not sure if the modified G-R integration method can be directly
> used by force-beam element?
Thanks, I think so. Modified G-R method can be directly applied to FBE, although
there is no instruction on OpenSees website, but you can find it in the source
code. There is a pdf file linked on the page of FBE website, you can check it.
> For softening behavior, I think they're the same if the same plastic hinge
> length is assigned. But in the concept of plastic hinge, there is no
> inelastic deformation outside the plastic hinge region. So this facilitates
> the calculation of beam-with-hinge element as it only captures the
> inelastic deformation at two ends (only two monitoring sections). Of course
> we can use force-element with modified G-R integration for softening
> behavior by also assigning the empirical plastic hinge length. But the
> computational effort is larger than beam-with-hinge element because the
> former has four monitoring sections. For the accuracy, it isn't necessarily
> improved.
> BTW, I'm not sure if the modified G-R integration method can be directly
> used by force-beam element?
Thanks, I think so. Modified G-R method can be directly applied to FBE, although
there is no instruction on OpenSees website, but you can find it in the source
code. There is a pdf file linked on the page of FBE website, you can check it.
-
linguan118
- Posts: 140
- Joined: Sun Oct 03, 2010 11:36 pm
- Location: Hong Kong
Re: the difference between the dispbeamcolumn and nonlinearb
If the length of the element is long enough while the assigned plastic hinge length is relatively short, there will be no Ips within the middle region of the element. Will that lead to some inaccuracy?
Research Assistant Professor, The Hong Kong Polytechnic University
guanlin@polyu.edu.hk
guanlin@polyu.edu.hk
-
wuhaoshrek
- Posts: 122
- Joined: Tue Oct 28, 2008 4:01 am
Re: the difference between the dispbeamcolumn and nonlinearb
linguan118 wrote:
> If the length of the element is long enough while the assigned plastic
> hinge length is relatively short, there will be no Ips within the middle
> region of the element. Will that lead to some inaccuracy?
You mean with BWH ? BWH has only 1 Ips at each end of the element, and the
other Radau Ips is elastic in the middle region. So, whatever elastic element
region is how long, it is always with elastic property.
> If the length of the element is long enough while the assigned plastic
> hinge length is relatively short, there will be no Ips within the middle
> region of the element. Will that lead to some inaccuracy?
You mean with BWH ? BWH has only 1 Ips at each end of the element, and the
other Radau Ips is elastic in the middle region. So, whatever elastic element
region is how long, it is always with elastic property.
-
linguan118
- Posts: 140
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- Location: Hong Kong
Re: the difference between the dispbeamcolumn and nonlinearb
I mean force beam with modified G-R integration method
Research Assistant Professor, The Hong Kong Polytechnic University
guanlin@polyu.edu.hk
guanlin@polyu.edu.hk
-
wuhaoshrek
- Posts: 122
- Joined: Tue Oct 28, 2008 4:01 am
Re: the difference between the dispbeamcolumn and nonlinearb
linguan118 wrote:
> I mean force beam with modified G-R integration method
The effect is same when you apply modified G-R to FBE, compared with BWH.
Only int. point at the end account nonlinear behavior, other Ips would only be
elastic, and with 2 elastic Ips, you can accurately capture the behavior of middel
region, whatever how long it is.
> I mean force beam with modified G-R integration method
The effect is same when you apply modified G-R to FBE, compared with BWH.
Only int. point at the end account nonlinear behavior, other Ips would only be
elastic, and with 2 elastic Ips, you can accurately capture the behavior of middel
region, whatever how long it is.