How do I properly define boundary conditions for multi-cell object in Matlab using the structuralBC

my question is very similar to one asked by Harrison Gardner in 2018. How do I get matlab to view the U-beam shape shown here

as one solid shape. Currently Matlab only looks at one cell at a time as shown below

The Geometry must be kept with mutiple cells as the geometry is made from multiple different materials.

some background:

I am using GMSH to create .MSH files then reading the resulting files into matlab and using the GeometrytoMesh function to create the resulting geometry. I have included the .MSH file used in this example (it has been renamed to a txt file a mathworks does not let you upload MSH files.)