force control pushover analysis

[mojtaba_khodayari]

Dear Dr.Silvia

I want to do force control pushover analysis but it can't give me negative branch of base shear vs. drift curve. i use a for loop and in each step increment a little my force with inverse TRIANGLE distrubution.
please guid me. if something like your examples in manual for pushover with force control insted of displacment control, exit , can i have it.

with best wishes

[fmk]

you place reference loads in a pattern and make the timeseries vary depending on how you want the loads to vary. here is a simple example.
[code]
model basic -ndm 2 -ndf 2

# model
set periodStruct 1.0;
set L 1.0
set A 1.0;
set m 1.0;

#derived quantaties
set PI 3.14159

set fStruct [expr 1.0/$periodStruct]
set wStruct [expr 2.0 * $PI / $periodStruct]
set K [expr $wStruct * $wStruct * $m]
set E [expr $L * $K / $A]

wipe
model basic -ndm 1 -ndf 1

node 1 0.0
node 2 $L -mass $m
uniaxialMaterial Elastic 1 $E
element truss 1 1 2 $A 1

fix 1 1

timeSeries Path 1 -dt 1.0 -values {0.0 1.0 2.0 1.0 0.0 -1.0 -2.0 -1.0 0.0} -factor 2.0

pattern Plain 1 1 {
load 2 1.0
}

integrator LoadControl 1.0
constraints Plain
system BandGen
algorithm Linear
numberer Plain
constraints Plain
analysis Static

recorder Node -file rxn.out -time -node 1 -dof 1 reaction

for {set i 1} {$i <= 8} {incr i 1} {
analyze 1
set reaction [eleResponse 1 localForce]
puts "$i $reaction"
}
[/code]

note that the analysis starts at time 1.0, the second point of the time series.

the time series path could also be placed in a file.