*HEADING
 UNDERWOOD & PARK 2 D.O.F. SYSTEM       
*NODE,NSET=FILE
2,10,,
3,20,,
*ELEMENT,TYPE=SPRING1,ELSET=SPRING1
1,2
*ELEMENT,TYPE=MASS,ELSET=MASS
2,2
*ELEMENT,TYPE=SPRING2,ELSET=SPRING2
3,2,3
*ELEMENT,TYPE=DASHPOT2,ELSET=DASHPOT
4,2,3
*ELEMENT,TYPE=MASS,ELSET=MASS
5,3
*ELEMENT,TYPE=SPRING1,ELSET=SPRING3
6,3
*ELSET,ELSET=MODEL,GENERATE
1,6
*MASS,ELSET=MASS
1.0, 
*DASHPOT,ELSET=DASHPOT
1,1
5.0, 
*SPRING,ELSET=SPRING2
1,1
100., 
*SPRING,NONLINEAR,ELSET=SPRING1
1, 
-999.909,-5,
-999.329,-4,
-995.0547,-3,
-964.0275,-2
-941.375,-1.75,
-905.148,-1.5,
-848.2836,-1.25,
-761.5941,-1.0
-635.148,-0.75,
-462.117,-0.5,
-244.919,-0.25,
0.0,0.0
244.919,0.25,
462.117,0.5,
635.148,0.75,
761.5941,1.0
848.284,1.25,
905.148,1.5,
941.375,1.75,
964.0275,2.0
995.0547,3,
999.329,4.0,
999.909,5
*SPRING,NONLINEAR,ELSET=SPRING3
 1, 
-74203.2,-5.0,
-57787.816,-4.75,
-45003.0115,-4.5,
-27289,-4.0
-16542.6,-3.5,
-10017.87,-3.0,
-6050.204,-2.5,
-3626.86,-2.0
-2129.28,-1.5,
-1175.201,-1.0,
-521.095,-0.5,
0.0,0.0
521.095,0.5,
1175.201,1.0,
2129.28,1.5,
3626.86,2.0
6050.204,2.5,
10017.87,3.0,
16542.6,3.5,
27289,4.0
45003,4.5,
57787.82,4.75,
74203.2,5.0
*INITIAL CONDITIONS,TYPE=VELOCITY
2,1,100.0
*BOUNDARY
2,2,3
3,2,3
*STEP,NLGEOM,INC=50
*DYNAMIC,DIRECT
0.01,0.5
*PRINT,RESIDUAL=NO,FREQUENCY=5
*ENERGY PRINT,FREQUENCY=5
*EL PRINT,FREQUENCY=25,SUMMARY=NO
*NODE PRINT,FREQUENCY=5,SUMMARY=NO
U1,V1,A1,RF1
*NODE FILE,NSET=FILE
U, 
V, 
*MONITOR,NODE=2,DOF=1,FREQUENCY=5
*FILE FORMAT,ZERO INCREMENT
*CONTROLS, PARAMETERS=FIELD

,0.0,
*END STEP
*STEP,NLGEOM,INC=50
*DYNAMIC,DIRECT
0.001,0.05
*CLOAD
3,1,3000.0
*END STEP
*STEP,NLGEOM,INC=50
*DYNAMIC,DIRECT
0.01,0.45
*CLOAD,OP=NEW
*END STEP