Do you apply load or displacement control? With arc length only load should be applied.

Also try to subdivide the step which doesn't converge.

I have been examining 3D shell model for bridge deck. However I have problem with convergence and consequently with L-D diagram in a way that after the peak load is reached the convergence can not be reached and values in L-D diagram are faulty. I am using arc-length and I have increased the mesh units in thickness of the shell to 4. Since I am modelling just 1/4 of the bridge deck I have translation constraints for symmetry planes and translation constraint in z direction where the grider is supposed to be. I am also applying load on surface. I am following the load and displacement for the mid point of the slab.

https://drive.google.com/file/d/1lmuOkF … sp=sharing