Modeling & Analyzing a moving load with constant speed

[navidsalamipargoo]

Hi dear McKenna and Silvia,

I am trying to apply a moving load with a constant speed to a beam and perform relevant transient analysis.
There are two problem I am facing:

1) It seems that the defined load in each step (each load location) is being added to that of the previous step rather than being replaced, though using "remove loadPattern" command. How can I make the load to move? Also, I think effects of the speed is not applied in my codes, I wonder how it can be included!

2) I am not sure how to define transient analysis to have the output of the recorder object in a dynamic analysis format. I'd like to have the displacement response of a specific node over the time due to the moving load.

I highly appreciate your kind reply,

Thanks


My codes are as below. Please help me how they should be modified. Thanks a lot



# UNITS: kg - cm - sec

wipe;
model BasicBuilder -ndm 2 -ndf 3;
set dataDir Data;
file mkdir $dataDir;

node 1 0. 0.
node 2 75. 0.
node 3 150. 0.

fix 1 1 1 0;
fix 3 1 1 0;

set IDsteel02 1;
set Fy [expr 2400.0];
set Es [expr 2.e6];
set bs [expr 0.01];
set R0 [expr 18];
set cR1 [expr 0.925];
set cR2 [expr 0.15];

uniaxialMaterial Steel02 $IDsteel02 $Fy $Es $bs $R0 $cR1 $cR2;

set D3_34Tag 1;
section Fiber $D3_34Tag {
patch circ $IDsteel02 36 3 0. 0. 1.41 1.67 0. 360.
}

geomTransf Linear $D3_34Tag;

set np 5;
element nonlinearBeamColumn 1 1 2 $np $D3_34Tag $D3_34Tag;
element nonlinearBeamColumn 2 2 3 $np $D3_34Tag $D3_34Tag;

mass 1 0.0005 0.0005 0.000000000000001;
mass 2 0.0005 0.0005 0.000000000000001;
mass 3 0.0005 0.0005 0.000000000000001;

recorder Node -file $dataDir/MidSpan.out -time -node 2 -dof 1 2 3 disp;

for {set i 0} {$i <=1} {incr i 1} {
for {set j 0} {$j <10} {incr j 1} {
pattern Plain 101 Linear {
eleLoad -ele [expr $i+1] -type -beamPoint -20 [expr $j/10.];

puts "current element is [expr $i+1] and point load is at [expr $j/10.]"
constraints Transformation;
numberer Plain;
system SparseGeneral;
test EnergyIncr 1.0e-8 100;
algorithm Newton;
set NewmarkGamma 0.5;
set NewmarkBeta 0.25;
integrator Newmark $NewmarkGamma $NewmarkBeta;
analysis Transient;
analyze 200 0.1;

remove loadPattern 101;
}
}
}
loadConst -time 0.0
puts "model built!"

[navidsalamipargoo]

In fact, I am trying to model a truss bridge in order to compare the acceleration response of the bridge in healthy and damaged conditions. I wonder how i can model a moving load on a given beam with constant speeds of different values in order to record acceleration and vibration responses.
I highly appreciate any comments which help me to do so.
Thanks

[selimgunay]

In your tcl syntax, you seem to analyze the 200 time steps with the same load pattern and then remove the load pattern. You should have a loop in the analyze commend where you analyze one step with a load pattern and then remove it and add a new pattern. You need to compute the new location of the load according to the seed and arrange the nodes that are loaded during each load pattern accordingly.

[fmk]

1. you need to change to a constant time series, a linera one just increases the load factor as the time increases. you want load factor to remain constant.

2. to change the speed you would need to change the number of steps in the last analyze .. by keeping the 200 .1 constant you are applying the load for the same a mount of time

[navidsalamipargoo]

fmk wrote:
> 1. you need to change to a constant time series, a linera one just
> increases the load factor as the time increases. you want load factor to
> remain constant.
>
> 2. to change the speed you would need to change the number of steps in the
> last analyze .. by keeping the 200 .1 constant you are applying the load
> for the same a mount of time

Thank you McKenna
Another point is that I can see no vibrations in displacement outputs of recorder due to this moving load. It is known that a moving load on a beam causes some vibrations too, but the results obtained are not containing vibrational effets. I need the displacement outputs to include some vibrational components, could you please tell me how I can see such results?

[Mohammadf]

Hi Dear Navid
I have this example in my book. I suggest you to read my book titled "The Most Complete Applied Reference of OpenSEES" in Persian.
Best

[selimgunay]

You need to use a transient integrator to see the vibrations:

http://opensees.berkeley.edu/wiki/index ... or_Command