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Gravity loads are independent of the type of lateral loading and are considered part of the structural model. These loads are first defined:
# apply constant gravity load (and other constant loads)
set Pdl [expr $Weight]; # gravity axial load per column
pattern Plain 1 Linear {
load 2 0.0 -$Pdl 0.0
}
The above defines the gravity load (ID=1) as a load in the negative y-direction at node 2 with a magnitude Pdl
And then applied:
# set up solution procedure
system UmfPack; # solution procedure, Super-LU, how it solves system of equations
constraints Plain; # how it handles boundary conditions, enforce constraints through the transformation
# set up convergence criteria
test NormDispIncr 1.0e-5 10 0; # tolerance, max no. of iterations, and print code , 1: every iteration
algorithm Newton; # use Newton's solution algorithm: updates tangent stiffness at every iteration
numberer RCM; # renumber dof's to minimize band-width (optimization)
# set up load steppring
integrator LoadControl 0.1 1 0.1 0.1; # variable load-stepping: Do initial incr., desred no. of iterations to converge, Dmax, Dmin
# set up type of analysis, static for gravity
analysis Static
initialize
# RUN GRAVITY ANALYSIS
analyze 10
loadConst -time 0.0
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