from sectionproperties.pre.library import rectangular_hollow_section
from sectionproperties.analysis import Section

geom = rectangular_hollow_section(d=100, b=100, t=6, r_out=15, n_r=8)
geom.create_mesh(mesh_sizes=[5.0])

sec = Section(geom)
sec.calculate_geometric_properties()
sec.calculate_warping_properties()
stress = sec.calculate_stress(vx=20e3, mxx=15e6, mzz=15e6)

stress.plot_stress(stress="vm", cmap="viridis", normalize=False)