About applying displacement control analysis

[deepak]

Dear Silvia,
I want to test a column under bi-axial loading using displacement control. I need to apply different displacement history in x and y direction( x and y are the axes for applying displacement control to the column). In my loading history, first loading will be applied to x direction at that time loading history at y direction will be zero and then in second step I will apply displacement to y- direction without applying displacement in x direction.

'''''''''''''''''''''''''''''''' Y
'''''''''''''''''''''''''''''''' |
'''''''''''''''''''''''''''''''' |
''''''''''''''''LLLLLLLLLLLLLLLL
''''''''''''''' L'''''''''''''' |''''''''''''''' L
--------- L--------------------L--------- X
''''''''''''''' L'''''''''''''' |''''''''''''''' L
''''''''''''''''LLLLLLLLLLLLLLLLL
'''''''''''''''''''''''''''''''''|
'''''''''''''''''''''''''''''''' |

*--L is loading path

This is my displacement loading history to column. I will have 5 such cycle.


One more thing, is it possible to change load pattern in x direction after completing the first step of applying displacement in x and then apply load pattern in y direction for displacement at y-direction. so on ( keep changing load pattern).
I want to apply load pattern only those direction where I am applying displacement because If I apply load displacement at both direction at the beginning it will run the analysis but do not give the correct result ???

I hope I will get some reply.

Thank you

[silvia]

this is tricky, i have never done it, play around with the sp command in the load pattern.

do try it on a simple sdof elastic system first.

[seocy]

I tried MultipleSupport to impose bi-directional displacement history to a node long ago.

Code: Select all

# impose displacement history 
   set dispSeriesX "Series -fileTime time.txt -filePath pathX.txt"
   set dispSeriesY "Series -fileTime time.txt -filePath pathY.txt"

   pattern MultipleSupport 1 {
       groundMotion 1  Series -disp $dispSeriesX 
       groundMotion 2  Series -disp $dispSeriesY 

      imposedSupportMotion $nd $X 1
      imposedSupportMotion $nd $Y 2
}

Hope this works !

[silvia]

that's for dynamic analysis.
use the sp command and analyze under load control.

[fmk]

MultiSupport will work fine .. just use load control in a static analysis.

[silvia]

cool, i didn't know that....

[deepak]

Thanks a lot!!!
Silvia: If I use SP command. I got one problem. SP command work for first cycle when I applied the displacement in x direction but when I changed the displacement to y direction (Next cycle). It applied the displacement in y but at the same to it applied also in x direction even though I didn't in x direction .


Frank: I have a question using multiple support excitation. Since I want to test my specimen for cyclic loading. If I use the multiple Support excitation Should I have to include mass??? and also what time interval I should applied the displacement( It depends upon time period of column???)
Actually, for cyclic loading I don't need mass and time period.

Thank you.

[silvia]

likely, you could use either.
if you want to hold the "load" in x direction constant, use the loadConst command..

[fmk]

you don't need mass if you are doing a static analysis .. you use load control and the the increment in load you specify you set equalk to the time interval between the points when creating the gound motions.

also if you want to remove an sp use remove sp nodeTag? dofTag? if you do this using sp's

[silvia]

careful, if you remove the sp on that one, though, you are releasing that node.
if you want to keep it zero, you are still controlling that dof -- set it as zero, or bring it to zero and set it constant.

[hrodrigues]

I’m doing biaxial analysis of RC columns also, and I use the to run SP command to load the discplacement history and works fine with me

Code: Select all

#recorder plot BaseShearx.out PushICurvex 100 100 400 400 -columns 2 1 

set SeriesPath1 "Path Series -dt 1 -filePath path1x.txt"
set SeriesPath2 "Path Series -dt 1 -filePath path2y.txt"

recorder Node -file disp.out -time -node 2 -dof 1 2 3 disp
recorder Element -file Force.out -ele 1 globalForce

pattern Plain 2 $SeriesPath1 {
# sp $node $DOF $Reference
 sp 2 1 1
}

pattern Plain 3 $SeriesPath2 {
 sp 2 2 1
}

# Define analysis parameters
integrator LoadControl 1
system SparseGeneral -piv
test NormDispIncr 1.0e-8 300 1
numberer Plain
constraints Transformation
algorithm KrylovNewton
analysis Static

# Apply the 2400 points in the files.
analyze 2400