One of the major factors affecting the economy of highway bridges with a concrete deck on stringers or longitudinal girders is spacing of the main members. Older bridges typically had spacing of 8 ft or less. Now, however, longer concrete-deck spans (up to 15 ft) are practicable through use of such devices as stay-in-place metal or precast-concrete forms. This makes possible fewer girders. (To eliminate the potential for fracture criticality when I-shape girders are used, there should be at least three.) Although the steel weight per square foot of bridge may be higher with fewer girders, the reduced costs of fabrication, handling, transportation, erecting, and painting, if required, usually provides substantial overall savings.
Stringer or Girder Spacing