Standards for Single Span Prefabricated Bridges - ST-811

Standards for Single Span Prefabricated Bridges were developed by HDR for the Iowa Department of Transportation in 2016 for the use on the county road system. These standards incorporated single span precast or precast/pretensioned concrete box beams with span lengths ranging from 30-feet to 70-feet, clear roadway widths of 24-feet and 30-feet, and skews of 0, 15 and 30 degrees. Additionally, the standards provided both cast-in-place and precast abutment design options founded on steel H-piles. The standards were developed utilizing the MicroStation V8i software. After the development of the standards, the Iowa Department of Transportation developed a procurement package under a federal grant for up to 14 bridge sites throughout the state using the single span prefabricated bridge standards. The purpose of the procurement package was to encourage the use of the standards amongst contractors and precast fabricators operating in Iowa. This initial procurement of bridges generated a request from the precast fabricator supplying the concrete box beams to eliminate fully tensioned prestressing strands from the tops of the box beams because the precast fabricator’s tensioning beds and formwork could not accommodate the forces from the top strands. To address the precast fabricator’s request and based on updated calculations for the 50-foot span, the precast fabricator was allowed to add mild reinforcing steel in the top flange and reduce the pretensioning in the top strands to a nominal 5000-pounds each (one located in each top corner). As a result of the modifications during the initial procurement project, the Iowa Highway Research Board requested an update to the standards to provide an option to eliminate fully tensioned prestressing strands in the top flange for all span lengths and substitute these strands with mild reinforcing steel. An additional update to the standards was also requested to update the CADD files from the MicroStation V8i platform to the MicroStation CONNECT platform