# Reinforced Concrete Frame Earthquake Analysis
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In this example the reinforced concrete portal frame which has undergone the gravity load analysis is now be subjected to a pushover analysis.
Files Required:
NOTES:
necessary to step through the analysis, checking for convergence at each step and trying different options if the analysis fails at any particular step. This script makes use of the fact that many OpenSees commands actually return values that can be used in the script.
The RCFrameGravity script is first run using the "source" command. The model is now under gravity and the pseudo-time in the model is 1.0. The existing loads in the model are now set to constant and the time is reset to 0.0. Mass terms are added to nodes 3 and 4.
The ReadRecord script is also sourced. This script contains the ReadRecord procedure. This procedure takes as arguments the name of the file containing the record, another file name to which the data points in the record will be written, and two variables which will be set on exit to be equal to the time interval between recorder data points and the number of points in the record.
A Path time series is then created with the name of the file containing the data points, the time interval between these points and a scaling factor to apply to the points, in this case the gravitational constant. This Path is used in the Uniform Excitation
We will also add damping to the model. We will use rayleigh damping and specify that the damping term will be based on the last committed stifness of the elements, i.e. C = ac Kcommit with ac = 0.000625.
<pre>
source RCFrameGravity.tcl
loadConst -time 0.0
set g 386.4 set m [expr $P/$g]; # expr command to evaluate an expression
mass 3 $m $m 0 mass 4 $m $m 0
set record ARL360
source ReadRecord.tcl
ReadRecord $record.at2 $record.dat dt nPts
timeSeries Path 1 -filePath $record.dat -dt $dt -factor $g
pattern UniformExcitation 2 1 -accel 1
rayleigh 0.0 0.0 0.0 0.000625 </pre>
<pre>
recorder Node -time -file disp.out -node 3 4 -dof 1 2 3 disp
recorder Element -time -file ele1secForce.out -ele 1 section 1 force recorder Element -time -file ele1secDef.out -ele 1 section 1 deformation </pre>
For the Pushover analysis we will use a displacement control strategy. In displacement control we specify a incremental displacement that we would like to see at a nodal dof and the strategy iterates to determine what the pseudo-time (load factor if using a linear time series) is required to impose that incremental displacement. For this example, at each new step in the analysis the integrator will determine the load increment necessary to increment the horizontal displacement at node 3 by 0.1 in. A target displacement of $maxU (15.0 inches) is sought.
As the example is nonlinear and nonlinear models do not always converge the analysis is carried out inside a while loop. The loop will either result in the model reaching it's target displacement or it will fail to do so. At each step a single analysis step is performed. If the analysis step fails using standard Newton solution algorithm, another strategy using initial stiffness iterations will be attempted.
<pre>
wipeAnalysis
system BandGeneral
constraints Plain
test NormDispIncr 1.0e-12 10
algorithm Newton
numberer RCM
integrator Newmark 0.5 0.25
analysis Transient
puts "eigen values at start of transient: [eigen 2]"
set tFinal [expr $nPts * $dt] set tCurrent [getTime] set ok 0
while {$ok == 0 && $tCurrent < $tFinal} {
set ok [analyze 1 .01]
if {$ok != 0} { puts "regular newton failed .. lets try an initail stiffness for this step" test NormDispIncr 1.0e-12 100 0 algorithm ModifiedNewton -initial set ok [analyze 1 .01] if {$ok == 0} {puts "that worked .. back to regular newton"} test NormDispIncr 1.0e-12 10 algorithm Newton }
set tCurrent [getTime] }
if {$ok == 0} { puts "Transient analysis completed SUCCESSFULLY"; } else { puts "Transient analysis completed FAILED"; }
puts "eigen values at end of transient: [eigen -Umfpack 2]"
print node 3
</pre>
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