Research Record, RR-102

Since the 1950’s, prestressed concrete beams have become a factor in almost one third of all new bridge construction in the United States. In Michigan, prestressed concrete was introduced in 1954 and the first prestressed concrete side-by-side box-beam bridge was built in 1955. Pontis data indicates 2,054 side-by-side prestressed concrete box-beam bridges in Michigan; 236 are part of the National Highway System (NHS) and under the responsibility of MDOT. The remaining 1,818 bridges are under local agency control. A side-by-side box-beam bridge under MDOT jurisdiction is constructed by placing precast prestressed box-beams adjacent to each other, grouting full depth shear-keys, applying transverse posttensioning, and casting a six-inch thick reinforced concrete deck (see Figure 1). The side-by-side prestressed concrete box-beam bridge design is generally used for short (30-60 feet) or medium (60-110 feet) bridge spans. This bridge type is popular with local agencies for single span and multi span bridges because the low depth-tospan ratio maximizes clearance under the bridge. In fact, this is the bridge of choice in Michigan for spans less than 110 feet. Side-by-side box-beam bridges are popular because of four key advantages: (1) simple designs; Box-Beam Concerns Found under the Bridge Expanding Inspector Handbook Promises Timely Bridge Care