The live load fraction carried by a beam (girder) in a bridge superstructure is usually determined using the simplified equations from current AASHTO standards. Many of these formulas are known to be conservative. In 1993, the AASHTO Subcommittee on Bridges approved a substantial change in the way future bridges will be designed. The subcommittee adopted the LRFD Specification, which drastically affects the loading and procedures with which live loads are distributed to various beams. The new specification offers two valid approaches: the simplified method and a variety of approved refined procedures. This paper examines the impact of the LRFD Specification on the design of prestressed concrete /-beams and spread-box beams in rectangular bridge superstructures. Significant reductions in the distribution factor for interior beams are found in both the simplified and refined procedures.
