Although prestressed concrete has not been used as long in the United States as it has been in Europe, there have been a few mistakes in design, details and specifications which should not be repeated. Examples of failed prestress work include the use of lightweight aggregates as used in the Kenai River Bridge where the girders cracked and spalled; steam curing when a metal sheath is placed inside a beam, the metal acts as a radiator and cools the concrete cover causing cracks; and not taking into account temperature differentials on long casting beds, as in a New York viaduct were anchor bolts did not fit the templates after the beam was hoisted by crane. Most failures are the result of inadequate attention to small details. Joints must allow for differential thermal, creep and shrinkage in the connected members. These are all time dependent changes. Bearing resistance may be reduced by axial forces, with serious bracket stresses and often splitting of the concrete seat on the beam. Prestressed members will change their camber with time, and some rotation freedom at the support must be provided.