Effect Of Deck Cracking On Prestress

Abstract

■ Analysis of the results shows that deck cracking will occur, but approximately 50% of the prestress gain due to differential shrinkage will be retained after the deck cracks. As soon as a prestressing force is applied to a concrete member, loss of that prestressing force begins to occur. The method used for calculating prestress losses in the first edition of the American Association of State Highway and Transportation Officials’ AASHTO LRFD Bridge Design Specifications, was modeled on the 17th edition of the AASHTO Standard Specifications for Highway Bridges and considered losses due to elastic shortening, relaxation of prestressing strands, and creep and shrinkage in the concrete. While the effect of elastic shortening was calculated from mechanics, a simple formula was used to estimate the relaxation, creep, and shrinkage losses. For composite structures, the effects of adding a deck were not considered. These effects include the creep and shrinkage of the girder between the time the girder is fabricated and the time the deck is placed, the dead load of the deck when it is placed, and creep and shrinkage effects in the deck itself.