An elliptical cross section is superior to a circular section at an unstiffened edge because of the greater curvature of the ellipse, making the shell stiffer at the lower edge. Also, the shell with a complete half circle will be more rigid than one with only a segment of a circle.
The end stiffeners in this example are rigid frames which give a much lighter appearance than the girder shown in the previous example. The columns must be large however, because of the high thrust from the vault. A steel tie disguised as a thin horizontal window mullion will overcome some of this disadvantage.