ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/306186
A E S T H E T I C S C O M M E N T A R Y by Frederick Gottemoeller Curvilinear rail and cantilever slab frame an overlook and view of the Great Miami River. Founded at the confuence of four rivers, Dayton, Ohio, needs many bridges. The bridges, taken as a group, provide much of the civic char- acter of Dayton. In the past, the typical Dayton bridge consisted of multiple earth-flled concrete arches. As these bridges are replaced, the challenge is to create new civic assets of equal quality within the resources of local budgets. Dayton's rivers are mostly wide but not deep, allowing fairly short spans, well within the range of standard precast concrete girders. These have such overwhelming cost advantages that they are the default choice for new superstructures. Adding visual character to precast girder bridges without breaking the budget requires creative thinking about the other parts of the bridge: the piers, parapets, and railings. Most recent replacement bridges in Dayton include details aimed at making a precast girder bridge look a bit like an arch. At Stewart Street, the city decided instead on a new approach. The bridge is adjacent to the University of Dayton's new research campus, so the city decided to create a bridge with a contemporary appearance but with the rhythm and scale of the traditional arch bridges. A Y-shaped pier provides a repeated, standardized, easy-to-build element that economically meets this goal. The triangular openings in the cross wall lighten the visual weight of the piers and make them more transparent. A precast concrete fascia covers and unites the edge girder and the barrier and recalls the monumentality of the traditional concrete arches. Its upper facet catches the light, creating a striking horizontal band sweeping from bank to bank, interrupted just briefy at the piers. Even the lighting poles pick up the angular theme. With the new Stewart Street Bridge, Dayton has found a way to bring its tradition of monumental civic bridges into the twenty-frst century. deck. At the contractor's suggestion, these beams were changed to precast concrete of the same design to accelerate construction. They were attached with 1-in.-diameter dowels grouted into the transfer girder. They act as composite tee-beams after the deck is cast and cured. Given the aesthetic goals, budget constraints, and a shortened construction window that necessitated higher costs, the bridge team made every attempt to keep the design simple and attractive to local bridge contractors. As a result, the cast-in-place transverse box beam and precast concrete beam elements were used in lieu of a post-tensioning solution. Most of the substructure elements were supported by 16-in.-diameter, cast-in- place pipe piles below a 3-ft-thick by 12.5-ft-wide by 80-ft-long cast-in-place concrete pile cap. Pier 1 required six, 6-ft-diameter drilled shafts, 52 ft deep. This pier is between two existing utilities: a 36-in.-diameter water main and a 7-ft 9-in. by 5-ft 4-in. sanitary box sewer. By using shafts, encroachment was minimized and vibration from pile driving was eliminated. Construction began June 1, 2008, and was completed in only 18 months. On November 30, 2009, dedication was held to celebrate the re-opening. Public appreciation of the bridge continues to grow ever since. __________ Mike Avellano is vice president at Woolpert Inc., in Dayton, Ohio. For additional photographs or information on this or other projects, visit www.aspirebridge.org and open Current Issue. ASPIRE , Summer 2011 | 17 Book_Sum11.indb 17 7/1/11 9:59 AM