In a polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes, {HEAD ~ a thickened central portion} located at {TAIL ~ a substantially central portion} in the longitudinal direction of each side of the polygonal rib is bisected 
located at
In a polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes , { HEAD ~ a thickened central portion } located at { TAIL ~ a substantially central portion } in the longitudinal direction of each side of the polygonal rib is bisected
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH