An elastic analysis gives a reinforcement ratio of approximately 4% at the center of the plate. This is high but still realistic. The elastic deformation of the plate under the design load is 41mm, which is L/250 and therefore on the high side of what is allowable.
Next I used fcFEM to load the plate to collapse. The material parameters are as follows (including the tough assumptions of full non-associated plasticity, psi=phi-30, and zero allowable tension):
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yield strength steel = 315.0 MPa compressive strength concrete = 15.75 MPa friction angle (phi) = 30.0 degrees dilation angle (psi) = 0.0 degrees material: Mohr-Coulomb tension cut off: principal stress tension strength concrete = 0.0 MPa reinforcement ratio: automatic from elastic analysis minimum reinforcement ratio = 0.001
The load-deflection curve shows a 10% margin between the elastic design load and the collapse load of the plate:
Note that the much larger elastic deformations are a result of assuming zero tension in the concrete from the start. The analysis should only be used to judge collapse load. When the incremental deformation of the plate at collapse (below) is compared to the elastic deformation (above) then it is clear that a collapse mechanism has developed (straight vs curved plate segments plus a small zone of rotation ... a plastic hinge):
and another representation of the same facts:
Although its still early days and much more testing and (speed and memory) optimising is required I think fcFEM holds promise as a robust (conceptual) design tool.
Next I will work on an idea for an alternative material model that should be faster and more stable. Stay tuned in.