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/297030
A C C E L E R AT E D B R I D G E C O N S T R U C T I O N A c c e l e r a t e d b r i d g e c o n s t r u c t i o n ( A B C ) h a s b e c o m e a watchword for many design teams, as owners look to shorten the design and construction process. Not only does faster construction reduce user costs and enhance community relations, but it increases safety by minimizing the time workers are exposed to hazardous conditions. A variety of methods can accelerate bridge construction based on the types of materials, conditions, and program goals. Bridges that feature precast concrete components have found success using several new techniques. Design-build delivery methods, casting techniques, and design concepts in combination with precast concrete components can shorten construction times. Here are some examples. Eight-Day Schedule With the Mill Street Bridge over the Lamprey River in Epping, the New Hampshire Department of Transportation (NHDOT) officials used precast concrete components to finish erection of the 115-ft-long bridge in only eight days. Seven precast, prestressed adjacent box beams were used, with five abutment and wingwall pieces on one end and six on the other, plus ten footing pieces. The precaster also supplied four precast concrete pilasters to add a decorative touch. This superstructure is supported by an all-precast concrete substructure, composed of full-height cantilevered abutments founded on spread footings. The project was let using an approach somewhere between the traditional design-bid-build and the design-build process. Design control remained with NHDOT engineers but the specific method of bridge assembly was left to the contractor and precaster. They determined where joints within the substructure would be introduced and how the precast concrete bridge elements would be assembled. Horizontal joints in the stems and between the stems and footings feature full moment connections with grouted splice sleeves. The splice sleeves were cast into the front and back faces of the stem elements to accept reinforcement extending from the bottom footing element. The precast concrete components could be cast in advance and delivered for assembly when the site was ready. Savings realized on items such as the reduced rental time for a temporary bridge and elimination of the labor needed to mobilize around available construction windows compensated for the costs associated with the fabrication and delivery of the precast concrete. by Craig A. Shutt Precast Concrete Solutions Mill Street Bridge over the Lamprey River in Epping, N.H. Photo: New Hampshire Department of Transportation. ASPIREBook_Sum12_R02.indb 25 6/29/12 12:39 PM