Seven state DOTs mark new length records for prestressed concrete bridge girders

Source: CP staff

Advanced precast/prestressed production and hauling techniques, coupled with the prevalence of design-build delivery and value engineering, have led to new length records for single-piece, road-delivered concrete girders. Compared to structures of earlier practice, new precast/prestressed bridges can tend toward a) fewer girders at optimized spacing; b) shallower girders for height-sensitive, new or existing roadway conditions; or, c) longer girders bearing on fewer piers.

A December Concrete Products report tracks delivery of record-length girders—up to 205 ft.—to the sites of six state department of transportation-approved bridges.  The standardization of higher strength concrete (> 8,000 psi) and 0.6-in. diameter prestressing strand, plus state DOTs’ use of more efficient girder cross sections than those of legacy AASHTO designs, have contributed to engineers’ ability to stretch out single-beam spans, according to Dr. Maher Tadros. As Department of Civil Engineering professor, he pioneered the University of Nebraska’s ā€œNUā€ bulb tee girder on which much of the new generation of long-span (> 170 ft.) beams is based.

ā€œThe myth of going to steel specs if you need a shallower depth or longer spanning girder doesn’t hold anymore. If an agency needs a bridge of a given span and width, I can design it with concrete girders of the same or shallower profile than steel girders. I couldn’t make that statement 20 years ago,ā€ affirms Dr. Tadros, now principal of e.construct.USA LLC, Omaha-based structural engineer, and University of Nebraska professor emeritus.

The precast/prestressed producers behind the record-length girder projects in 2010–2011 are:
• Concrete Technology Corp., Tacoma, Wash., Alaska Way Replacement Viaduct, Seattle (205 ft. girders)
• Hanson Structural Precast, Salt Lake City, Interstate 15 & Beck St. (195 ft.)
• Knife River Corp. Northwest, Harrisburg, Ore., Cornelius Pass Bridge, Washington County, Ore. (184 ft.)
• Standard Concrete Products, Tampa, Interstate 275 & S.R. 686, Pinellas County (175 ft.)
• Cretex Concrete Products, Maple Grove, Minn., Highway 61 at Mississippi River, Hastings, Minn. (174 ft.)
• Northeast Prestressed Products, Cressona, Pa., Lehigh River Twin Bridges, Carbon County, Pa. (168 ft.)
• Bexar Concrete Works I Ltd., San Antonio, S.H. 114 & S.H. 121, Irving, Texas (166 ft.)