<Li> spacing at 24x to 36x of slab depth (some specification call for a maximum of 30x) </Li> <Li> special care for inside corners </Li> <P> If a railway track runs over a bridge which has expansion joints that move more than a few millimeters, the track must be able to compensate this longer expansion or contraction . On the other hand, the track must always provide a continuous surface for the wheels travelling over it . These conflicting targets are served by special expansion joints, where two rails glide along each other at a very acute angle during expansion or contraction . They are typically seen near one or both ends of large steel bridges . Such an expansion joint looks somewhat like the tongue of a railroad switch, but it has a completely different purpose and operation . </P> <P> Expansion joints are required in large ducted air systems to allow fixed pieces of piping to be largely free of stress as thermal expansion occurs . Bends in elbows also can accommodate this . Expansion joints also isolate pieces of equipment such as fans from the rigid ductwork thereby reducing vibration to the ductwork as well as allowing the fan to "grow" as it comes up to the operating air system temperature without putting stress on the fan or the fixed portions of ductwork . Example of air or gas ducts can be seen here . Air ducts </P>

In cement concrete road expansion joints are provided at intervals of