Every civilized jurisdiction, excepting Ontario, designs its concrete bridge slabs as elastic plates. Some model tests performed in Ontario show that an unreinforced bridge deck slab could carry as much as 80 percent of the maximum load of a comparable slab with normal reinforcement. This phenomenal performance can only be explained by the presence of huge in-plane or membrane forces produced by lateral confinement. Tests performed while the author was employed by the Ontario Ministry of Transportation indicated that the influencing factors on the load-carrying capacity of the deck slabs are: level or degree of confinement, ratio of slab span to thickness, and amount of reinforcing steel.
Fatigue tests conducted by the State of New York with a single mat of isotropic reinforcement indicated that a moment component does exist and has to be resisted by steel placed at a certain distance from the neutral axis. A prefabricated, four-layer isotropic reinforcing mat consisting of bars or wires supported by chairs attached to welding is illustrated in this article. The Ontario Ministry of Transportation estimates that more than $1 million per year in steel costs has been saved by isotropic deck design method. In addition, the automated production process and the elimination of ties can be expected to speed construction and further increase economy.