Apply gravity load by applying constant acceleration g?

[foxchameleon]

Hi, Guys

When we apply gravity loads for a structure in OpenSees, did you try to apply a constant acceleration "g" instead of applying the loads by any chance, which may save us lots of trouble. But I did not see much of this in OpenSees, which can work in other software like ANSYS

How did you think of it? Experience are welcomed to be shared.

Yong

[vesna]

In OpenSees there is such an option. You need to define gravity loads yourself.

[foxchameleon]

Hey vesna

Thanks for your reply, but I did not get whether you agree or not.

Yes, in OpenSees we need to define gravity loads. But the gravity loads can also be obtained by applying constant acceleration of g, without defining gravity load directly, right?


vesna wrote:
> In OpenSees there is such an option. You need to define gravity loads
> yourself.

[foxchameleon]

For now, it works fine according to the check I did.
So we can save lots of trouble to define gravity load directly. Instead, we just need to define mass, and then define constant acceleration g.

[seu]

Could you show me an example about this question or tell me how you do?
I'm also confused with this problem.
I use the pattren load to apply gravity,it's not convenient.

[foxchameleon]

# For check applying gravity option by Yong Li
set m 10;
set g 9.8;

wipe
model BasicBuilder -ndm 2 -ndf 2
node 1 0.0 0.0
node 2 144.0 0.0
node 3 168.0 0.0
node 4 72.0 96.0 -mass $m $m;
fix 1 1 1
fix 2 1 1
fix 3 1 1
uniaxialMaterial Elastic 1 3000.0
element truss 1 1 4 10.0 1
element truss 2 2 4 5.0 1
element truss 3 3 4 5.0 1

set ApplyGrvityOption "viaConstantG"; # viaDirectLoad or viaConstantG

if {$ApplyGrvityOption == "viaDirectLoad"} {
pattern Plain 1 Linear {
load 4 0 [expr -$m*$g];
}
} elseif {$ApplyGrvityOption == "viaConstantG"} {
timeSeries Constant 1 -factor $g;
pattern UniformExcitation 1 2 -accel 1;
} else {
puts "No Gravity Load Applied"
}

# --- static analysis ---

constraints Transformation
numberer RCM
system BandGeneral
test NormDispIncr 1.0e-6 6 2
algorithm Newton
integrator LoadControl 0.1
analysis Static
analyze 10

puts "After Gravity Analysis while applying gravity load by Approach of $ApplyGrvityOption"
set d [nodeDisp 4 2]
puts "$d"

# OUTPUT ON THE DOS WINDOW for two approaches.:
# After Gravity Analysis while applying gravity load by Approach of viaDirectLoad
# -0.33206408631820522000

#After Gravity Analysis while applying gravity load by Approach of viaConstantG
# -0.33206408631820528000