The weights of the main members of the two structures are as follows: Two-hinged arch ......... 72,000 lb per truss Three-hinged arch ....... 85,900 lb per truss Considering the weights of details and laterals to vary in the same ratio as the main members of the respective arch trusses, it was found that the three-hinged arch was lighter than the two-hinged arch by 8.5%.

The maximum deflection for each arch structure was found at the center with the live load across the entire span. They compare ae follows: Two-hinged arch ......... 0.90 in. Three-hinged arch ....... 1.28 in.

An inspection of Tables 8 and 10 indicates that for the two-hinged arch, a relative lateral yielding of supports of small magnitude (0.25 in.) produces no critical stresses, whereas, a lateral displacement of larger magnitude would over-stress upper chord and diagonal members.