1) I am doing validation of non linear analysis of stiffened steel plate girder. When I use 1500kN the analysis converges . If I use 1800kN the analysis terminates at a substep and if I see the load corresponding to last substep it is less than 1500kN , although when the solution converged it reached 1500kN. It seems it is an intuitive process because the load at which there is failure that varies drastically. How can i correlate the applied load?

2) Where to input the ultimate tensile strength of steel while doing analysis . From my material model i am using bi linear plasticity which only requires yield strength and tangent modulus , How do i incorporate tensile strength of steel?

MPDATA,EX,1,,2e5

MPDATA,PRXY,1,,0.3

TB,BISO,1,1,2,

TBTEMP,0

TBDATA,,372.3,0.3,,,, !Yield strength of steel

3)If I add first buckling mode and factor it down as suggested by papers the load fails at a much lower value of 1250kN. Why is there so much difference . The factor i used is 0.001.