problem description
title="Classical Truss-Spring Nonlinear Problem"
nodes=3 elements=2 analysis=static-substitution

analysis parameters
iterations = 500
tolerance  = 1e-6
load-steps = 50

nodes
1 x=0	  y=0	constraint=pin
2 x=100   y=1	constraint=roller		force=P
3 x=100	  y=-1	constraint=pin

truss elements
1 nodes=[1,2]	material=EA
2 nodes=[2,3]	material=k

material properties
EA	E=1	A=1e7
k	E=2	A=6   Kx=6

forces
P	Fy=-5

constraints
pin    Tx=c Ty=c Tz=c
roller Tx=c Ty=u Tz=c

end
