Change properties

[Salarson]

Hi
I've modeled a 2D frame, with beams and columns.
Is it possible to reduce the mass of a beam after 3.23 second?
this is the beam:
element nonlinearBeamColumn 1 1 6 10 14 1 5
which means the mass is 5
how is it possible to reduce %30 of it after 3.23 second?
and what about to add %30 of mass after 3.24 second?

[Jeena]

Hi,

Did you mean after 3.23 seconds in a time history (for a transient analysis) ?

If you meant 3.23 second in a time history, the following may (or may not) works for your case,

Do the transient analysis in a for loop through the number of ground acceleration points,

for {set i 0} {$i < $Nsteps} {incr i} {
# loop through each data point, Nstep is the total number of points

t = i*$DtAnalysis # current time

if {$t <= 3.23} {
element nonlinearBeamColumn 1 1 6 10 14 1 5 # for all t <= 3.23 sec, take the actual mass
}
if {$t == 3.24} {
element nonlinearBeamColumn 1 1 6 10 14 1 [expr 5*0.70] # reduce mass by 30% at 3.24 sec
}
if {$t > 3.24} {
element nonlinearBeamColumn 1 1 6 10 14 1 5 # mass
}

#Define here damping and any property that is dependent on the mass.
set ok [analyze 1 $DtAnalysis] # do analysis for the current step
}

[fmk]

you will loose the stress-strain history in the materials if it goes nonlinear .. the easiest approach would be to use nodal masses and issu ethe mass command at any point you want the masses to change