Chapter 6: Structural concrete

Previous bridge design specifications and guidelines separated the design of reinforced and prestressed concrete structures. They were based on an outdated view of the different behaviours of the two types of concrete. In the past, the main advantage of prestressed structures was the elimination of tensile stresses and cracks. Over the years, however, it was found that the requirement to reduce cracking in some structures is uneconomical and leads to the design of bridges that are susceptible to side-effects such as deflections of supports and non-uniform temperature changes. Also, it has been found that some structures cannot be designed as fully prestressed. This applies, in particular to structures in which the ratio of the permanent to the live loads is small, or structures subjected to a bending moment of the opposite sign.