Force-displacement plot not starting from zero

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elescher
Posts: 2
Joined: Wed Apr 01, 2020 7:21 am

Force-displacement plot not starting from zero

Post by elescher »

I am running a code for a 3D bridge and my transverse force-displacement plot is not starting from zero, but my longitudinal force-displacement plot is. If I turn off the gravity loading and just apply the masses to each node, the plots look fine, but the transverse direction starts at 6.1 kips when I apply linear gravity load. Here is the part of the code for gravity analysis (units are kips and inches):

Code: Select all

 
 #Define Gravity Load and Analysis
#================================

#Define Loads
set g 386.4;									#gravity (in/s2)
set WtCol [expr -37.*$kip];					#Total weight per column (kip)
set WtBeam [expr -210.*$kip];					#Total weight of cap beam (kip)
set WtSAP [expr -1794.*$kip];					#Total weight of panels + girders from SAP2000 (kip)
set WtDeck [expr $WtSAP]; 						#Total deck weight to be distributed to nodes (kip)
set NumNodes 40;								#number of bridge nodes for lumping mass *39 nodes and end nodes use 1/2 load
set DNodeLoad [expr $WtDeck/$NumNodes]; 		#Load at deck nodes
set BNodeLoad [expr $WtBeam/10.];					#beam weight distributed over nodes  *9 nodes and end nodes use 1/2 load
set CNodeLoad [expr $WtCol/2.]; 					#Load at bottom column nodes *2 nodes per column

#Define Masses 
set CNodeMass [expr abs($CNodeLoad/$g)];		#Lumped mass at column nodes
set BNodeMass [expr abs($BNodeLoad/$g)];		#Lumped mass at beam nodes
set DNodeMass [expr abs($DNodeLoad/$g)];		#Lumped mass at deck nodes

#mass nodetag Mx My Mz MRx MRy MRz
#Column Nodes
mass 63373 $CNodeMass $CNodeMass $CNodeMass 0 0 0;
mass 63374 $CNodeMass $CNodeMass $CNodeMass 0 0 0;

#Beam Nodes
mass 63375 [expr $BNodeMass/2.] [expr $BNodeMass/2.] [expr $BNodeMass/2.] 0 0 0; #1/2 beam 
mass 63376 $BNodeMass $BNodeMass $BNodeMass 0 0 0;
mass 63377 [expr $CNodeMass+$BNodeMass] [expr $CNodeMass+$BNodeMass] [expr $CNodeMass+$BNodeMass] 0 0 0;  # Beam + column
mass 63378 $BNodeMass $BNodeMass $BNodeMass 0 0 0;
mass 63379 $BNodeMass $BNodeMass $BNodeMass 0 0 0;
mass 63380 [expr $DNodeMass+$BNodeMass] [expr $DNodeMass+$BNodeMass] [expr $DNodeMass+$BNodeMass] 0 0 0; #deck + beam
mass 63381 $BNodeMass $BNodeMass $BNodeMass 0 0 0;
mass 63382 $BNodeMass $BNodeMass $BNodeMass 0 0 0;
mass 63383 [expr $CNodeMass+$BNodeMass] [expr $CNodeMass+$BNodeMass] [expr $CNodeMass+$BNodeMass] 0 0 0;  # Beam + column
mass 63384 $BNodeMass $BNodeMass $BNodeMass 0 0 0;
mass 63385 [expr $BNodeMass/2.] [expr $BNodeMass/2.] [expr $BNodeMass/2.] 0 0 0; #1/2 beam 

#Deck Nodes
#SPAN 1
mass 63386	[expr $DNodeMass/2.] [expr $DNodeMass/2.] [expr $DNodeMass/2.] 0 0 0; #1/2 deck
mass 63387	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63388	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63389	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63390	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63391	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63392	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63393	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63394	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63395	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63396	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63397	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63398	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63399	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63400	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63401	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63402	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63403	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63404	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63405	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
#SPAN 2
mass 63406	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63407	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63408	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63409	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63410	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63411	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63412	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63413	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63414	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63415	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63416	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63417	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63418	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63419	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63420	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63421	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63422	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63423	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63424	$DNodeMass $DNodeMass $DNodeMass 0 0 0;
mass 63425	[expr $DNodeMass/2.] [expr $DNodeMass/2.] [expr $DNodeMass/2.] 0 0 0; #1/2 deck

puts "Masses Defined"

#create load pattern for gravity load
pattern Plain 1 Linear {
#Column Nodes, concentrated in the y-direction
load 63373 0 $CNodeLoad 0 0 0 0;
load 63374 0 $CNodeLoad 0 0 0 0;

#Beam Nodes
load 63375 0 [expr $BNodeLoad/2] 0 0 0 0;				#1/2 beam load
load 63376 0 $BNodeLoad 0 0 0 0;
load 63377 0 [expr $CNodeLoad +$BNodeLoad] 0 0 0 0;	# Beam + column 
load 63378 0 $BNodeLoad 0 0 0 0;
load 63379 0 $BNodeLoad 0 0 0 0;
load 63380 0 [expr $BNodeLoad+$DNodeLoad] 0 0 0 0;	# Midspan node 
load 63381 0 $BNodeLoad 0 0 0 0;
load 63382 0 $BNodeLoad 0 0 0 0;
load 63383 0 [expr $CNodeLoad +$BNodeLoad] 0 0 0 0;	# Beam + column
load 63384 0 $BNodeLoad 0 0 0 0;
load 63385 0 [expr $BNodeLoad/2] 0 0 0 0;				#1/2 beam load

#Deck Nodes, concentrated in the y-direction
#SPAN 1
load 63386	0 [expr $DNodeLoad/2.] 0 0 0 0;				#1/2 deck load
load 63387	0 $DNodeLoad 0 0 0 0;
load 63388	0 $DNodeLoad 0 0 0 0;
load 63389	0 $DNodeLoad 0 0 0 0;
load 63390	0 $DNodeLoad 0 0 0 0;
load 63391	0 $DNodeLoad 0 0 0 0;
load 63392	0 $DNodeLoad 0 0 0 0;
load 63393	0 $DNodeLoad 0 0 0 0;
load 63394	0 $DNodeLoad 0 0 0 0;
load 63395	0 $DNodeLoad 0 0 0 0;
load 63396	0 $DNodeLoad 0 0 0 0;
load 63397	0 $DNodeLoad 0 0 0 0;
load 63398	0 $DNodeLoad 0 0 0 0;
load 63399	0 $DNodeLoad 0 0 0 0;
load 63400	0 $DNodeLoad 0 0 0 0;
load 63401	0 $DNodeLoad 0 0 0 0;
load 63402	0 $DNodeLoad 0 0 0 0;
load 63403	0 $DNodeLoad 0 0 0 0;
load 63404	0 $DNodeLoad 0 0 0 0;
load 63405	0 $DNodeLoad 0 0 0 0;
#SPAN 2
load 63406	0 $DNodeLoad 0 0 0 0;
load 63407	0 $DNodeLoad 0 0 0 0;
load 63408	0 $DNodeLoad 0 0 0 0;
load 63409	0 $DNodeLoad 0 0 0 0;
load 63410	0 $DNodeLoad 0 0 0 0;
load 63411	0 $DNodeLoad 0 0 0 0;
load 63412	0 $DNodeLoad 0 0 0 0;
load 63413	0 $DNodeLoad 0 0 0 0;
load 63414	0 $DNodeLoad 0 0 0 0;
load 63415	0 $DNodeLoad 0 0 0 0;
load 63416	0 $DNodeLoad 0 0 0 0;
load 63417	0 $DNodeLoad 0 0 0 0;
load 63418	0 $DNodeLoad 0 0 0 0;
load 63419	0 $DNodeLoad 0 0 0 0;
load 63420	0 $DNodeLoad 0 0 0 0;
load 63421	0 $DNodeLoad 0 0 0 0;
load 63422	0 $DNodeLoad 0 0 0 0;
load 63423	0 $DNodeLoad 0 0 0 0;
load 63424	0 $DNodeLoad 0 0 0 0;
load 63425	0 [expr $DNodeLoad/2.] 0 0 0 0;				#1/2 deck load
}
puts "Loads Defined"

constraints Plain;                 # how it handles boundary conditions (single and multi-point constraints)
numberer RCM;			             		# renumber dof's to minimize band-width (optimization)
system BandGeneral;		                	# how to store and solve the system of equations in the analysis

#Convergence Test
set TestTypeGravity NormDispIncr;	        # Convergence Test: type
set TolGravity 1.0e-10;		      			# Convergence Test: tolerance
set maxNumIterGravity 10;             		# Convergence Test: max number of iterations
set printFlagGravity 0;		      			# Convergence Test: flag used to print information on convergence (optional)        # 1: print information on each step; 
test $TestTypeGravity $TolGravity $maxNumIterGravity $printFlagGravity;

#Integrator
set NstepGravity 10;  		          		# apply gravity in 20 steps
set DGravity [expr 1./$NstepGravity]; 		# Gravity load increment;
integrator LoadControl 0.1;	  		# Determine the next time step for an analysis

#Algorithm
set algorithmTypeGravity Linear;      		# use Newton's solution algorithm: updates tangent stiffness at every iteration
algorithm $algorithmTypeGravity;

#Analysis
set  InTG [clock microseconds]
analysis Static;		              		# define type of analysis static or transient
analyze $NstepGravity;		         		# Apply Gravity load

set FiTG [clock microseconds]
set ComT [expr ($FiTG-$InTG)/1.e6]
puts "Computational time for Gravity Analysis: $ComT"
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