Long-span prestressed concrete girders are traditionally braced with concrete diaphragms within the span. One of the common problems for prestressed concrete bridges is the deterioration or even the failure of diaphragms. Replacing the existing concrete diaphragms in a major highway bridge presents a real construction challenge as the traffic usually has to remain open at least partially. A good alternative is to use steel diaphragms, which have been shown to be cost effective and functional in several rehabilitated bridge projects. In addition to rapid construction and functionality, steel diaphragms are significantly lighter. As such, the live-load capacity of a bridge can be increased, which is an important issue for most existing bridges. This paper describes in detail the methodology of load and resistance factor design (LRFD) as related to steel diaphragms and their connections and presents an illustrative design example and the economical benefits of using steel diaphragms. Due to their practical and economical advantages, steel diaphragms are recommended for use in all rehabilitation projects involving prestressed concrete bridges. They may also be considered to be utilized in new reinforced or prestressed concrete bridges.