Dear Vesna, all
I have read some literature on pushover analysis and have researched the community board on this topic, however I would be happy to get the answers to some of the following questions:
1. If I have a bridge structure (modeled as 3D, 6DOF) with piers of varying height, is it advisable to apply lateral load at only one free node or is it better to apply the load at all free nodes?. I am thinking that application of this load at one node is sufficient. However, I have seen some researchers who have applied lateral load at only one node but others have applied loads at all free nodes in a structure.
2. In examples posted by OpenSees, the lateral load is called a reference load. I have also tried varying the value of the lateral load in the analysis but regardless of the value of load applied, the output is the same. Why is this so, and why is it called a reference load. Does this mean that the pushover is dictated by the axial load only?
3. I have asked for element and node recorders for reaction at column bases and displacements. How do I know which of the outputs is base shear.
I am sorry if my questions sounded too fundamental, but I would appreciate any help on this to understand the analysis further.
Thank you in advance for any help or suggestions.
zsherliza
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Lateral force in pushover analysis
Moderators: silvia, selimgunay, Moderators
Re: Lateral force in pushover analysis
1. It is on you to decide where and how to apply the load. Sometimes, depending on the structure and the direction of loading it might be sufficient to apply load at one node only, but not always.
2. The values of the loads defined through the load pattern are called reference loads. The load that is actually applied at the node is the reference load times the load factor, where the load factor is provided by the time series.
3. To get what each column of recorded file is use -xml $fileName instead of -file $fileName in the recorder command.
2. The values of the loads defined through the load pattern are called reference loads. The load that is actually applied at the node is the reference load times the load factor, where the load factor is provided by the time series.
3. To get what each column of recorded file is use -xml $fileName instead of -file $fileName in the recorder command.
Re: Lateral force in pushover analysis
Dear Vesna,
Thanks for your reply but I am still confused about the value of lateral load to be applied at nodes. Instead of the reference load, what I have done further in my analysis is applying, for example, 0.2*weight of the structure at all free nodes. This is because I am assuming that lateral load is equivalent to 0.2*W. Is my method correct?. If this is incorrect, how do we assume the value of reference load then?
Thank you.
zsherliza
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Thanks for your reply but I am still confused about the value of lateral load to be applied at nodes. Instead of the reference load, what I have done further in my analysis is applying, for example, 0.2*weight of the structure at all free nodes. This is because I am assuming that lateral load is equivalent to 0.2*W. Is my method correct?. If this is incorrect, how do we assume the value of reference load then?
Thank you.
zsherliza
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Re: Lateral force in pushover analysis
Are you trying to perform pushover analysis or just static analysis with a fixed value of the lateral force?
Re: Lateral force in pushover analysis
Dear Vesna,
My aim is to plot pushover curve. From the pushover curve, I hope to find the value of maximum lateral load that the structure is able to withstand.
I hope I have done the right thing.
Thank you.
My aim is to plot pushover curve. From the pushover curve, I hope to find the value of maximum lateral load that the structure is able to withstand.
I hope I have done the right thing.
Thank you.
Re: Lateral force in pushover analysis
Yes, what you are doing is right.
In the case of pushover analysis, the load that you defined (0.2W) is a reference load. During pushover analysis the load applied on the structure will increase in magnitude (reference load x coefficient) but the values of the forces are going to be the same at all nodes (this is based on your reference load that is same at all nodes).
In the case of pushover analysis, the load that you defined (0.2W) is a reference load. During pushover analysis the load applied on the structure will increase in magnitude (reference load x coefficient) but the values of the forces are going to be the same at all nodes (this is based on your reference load that is same at all nodes).
Re: Lateral force in pushover analysis
Dear Vesna,
Thanks for helping, you have been great.
zsherliza
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Thanks for helping, you have been great.
zsherliza
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Re: Lateral force in pushover analysis
Dear Vesna,
I want to plot a pushover curve and i am new user of opensees, the results i get are ploting load steps versus displacement, could you explain a bit what that means and how do get the base shear plotted (saved in other output file) versus displacements?
I want to plot a pushover curve and i am new user of opensees, the results i get are ploting load steps versus displacement, could you explain a bit what that means and how do get the base shear plotted (saved in other output file) versus displacements?
Re: Lateral force in pushover analysis
Hi,
You can plot pushover plots in different ways. The most common form is to plot base shear against roof displacements or drifts.
You can record the base shear as reaction at nodes at the base .. If you have a one bay, one story frame structure, then the base shear will be the total of the reaction recorded at the two nodes at the base of the columns. You can use the recorder Node command to find the reactions. Or you can record the element forces at the base story and sum the shear force at the lower end of the elements.
You can either record the displacements at the roof or drift at the roof level using the recorder Node or Drift command for this.
You can then plot the base shear (found as reactions) against the displacements.
If you plot base shear (in Y axis) against roof displacements (in X axis), technically any point (x,y) in the plot gives the base shear 'y' at particular level of displacement 'x' imposed at the roof level.
Please check the following example.
http://opensees.berkeley.edu/wiki/index ... trated.tcl
Thanks,
Jeena
You can plot pushover plots in different ways. The most common form is to plot base shear against roof displacements or drifts.
You can record the base shear as reaction at nodes at the base .. If you have a one bay, one story frame structure, then the base shear will be the total of the reaction recorded at the two nodes at the base of the columns. You can use the recorder Node command to find the reactions. Or you can record the element forces at the base story and sum the shear force at the lower end of the elements.
You can either record the displacements at the roof or drift at the roof level using the recorder Node or Drift command for this.
You can then plot the base shear (found as reactions) against the displacements.
If you plot base shear (in Y axis) against roof displacements (in X axis), technically any point (x,y) in the plot gives the base shear 'y' at particular level of displacement 'x' imposed at the roof level.
Please check the following example.
http://opensees.berkeley.edu/wiki/index ... trated.tcl
Thanks,
Jeena
Re: Lateral force in pushover analysis
Dear all,
i am doing pushover analysis of a 1 storey 1 bay rc frame, the problem i am encountered with is that if i apply lateral load from left to right and run the analysis it comes out to be successful....but just to check if i input the load at the opposite top node from right to left analysis failed....everything is identical the columns and the beam...could you please guide me why is this happening????
Thankyou
i am doing pushover analysis of a 1 storey 1 bay rc frame, the problem i am encountered with is that if i apply lateral load from left to right and run the analysis it comes out to be successful....but just to check if i input the load at the opposite top node from right to left analysis failed....everything is identical the columns and the beam...could you please guide me why is this happening????
Thankyou