The seventies will be recorded by engineering historians as the decade in which prestressed concrete segmental bridge construction came of age in North America. Segmental box girder bridges have attracted the attention and captured the imagination of bridge engineers and designers across the continent. Because of practical limitations of handling and shipping, the precast prestressed I-girder type of bridge construction is limited to an approximate range of 120 to 150-ft (37 to 46 m) spans. Beyond this range of span, post-tensioned cast-in-place box girders on falsework are more attractive. However, in certain instances the extensive use of falsework can prove to be an economic disadvantage. Where deep ravines or navigable waterways must be crossed, extensive formwork may be impractical.
