The Conestogo River Bridge: A Full-Scale Test Specimen Still in Service

The Engineering Research and Development Branch of the Ontario Ministry of Transportation designed the Conestogo River Bridge, which carries Regional Road 85 over the Conestogo River just east of St. Jacobs, ON, as a full-scale test specimen. Research findings of the early 70s indicated that: (1) the familiar AASHTO H20-S44 traffic loading model was no longer representative of Ontario truck traffic; (2) the dynamic effects of the traffic loads were sensitive to the first flexural frequency of the bridge; (3) existing methods to distribute truck load moments laterally to the girders of a multi-girder structure were conservative; (4) steel bolts could be used to replace shear studs to achieve fully composite behaviour of steel–concrete bridge superstructures; and (5) the flexural demands due to wheel loads on reinforced concrete deck slabs were significantly mitigated by compressive membrane action. A series of full-scale tests were conducted in 1975 and 1976 to evaluate the validity of these findings in the field, and the success of these tests supported the inclusion of these research findings in the first edition of the Ontario Highway Bridge Design Code, published in 1979. A landmark paper describing these tests won the CSCE Casimir Gzowski Medal in 1977, and the bridge is now being considered for nomination as a Canadian Society for Civil Engineering National Historic Site.