Synopsis
This article from the Concrete Bridge Development Group's technical committee examines the prestressing for a concrete bridge. In concrete bridges, for deck spans more than 20-30m, prestressing should generally be used. As described in last month's article, prestressing enhances the capacity of a member that is weak in tension, but strong in compression. It effectively creates a new material that is strong in tension. Prestressing allows a bridge to be more economical, with lighter and more slender members, which improves the appearance. The sections are generally compressed under permanent effects, which give greater durability due to the reduced incidence of cracking. The sections also behave elastically with greater stiffness, allowing deflections to be more easily controlled. A prestressed bridge has much less steel to be handled, which reduces congestion, leading to easier and quicker concrete placing.