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.

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The I-84–Ten Mile Road Interchange project in Meridian, Idaho, will add much needed interstate access for a growing community. The interchange improves connectivity along I-84 and replaces an existing overpass. Five interchange types were considered. The standard single-point urban interchange (SPUI) was selected based on several factors, including construction cost, right-of-way impacts, anticipated year 2030 level of service, and environmental i s s u e s . T h e p ro j e c t a l s o f e a t u re s widening of both Ten Mile Road and I-84, mechanically stabilized earth (MSE) walls, and a culvert. SPUIs are becoming popular in urban areas throughout the United States due to their compact layout and efficient t r a ff i c m a n a g e m e n t . T h e t y p i c a l hourglass shape of SPUI structures, however, results in a geometrically complex bridge with complicated structural behavior. This SPUI is an innovative solution for this region; the first designed in the state of Idaho and only the second SPUI constructed there. Evaluation of Alternatives G i v e n t h e u n i q u e s h a p e o f S P U I bridges, framing configurations need to be carefully considered to minimize unused deck area and account for multi-directional load paths. Several alternatives were investigated. For each of the superstructure types evaluated, the design team developed conceptual d e s i g n s a n d c o s t e s t i m a t e s . A n important benefit of the project was the opportunity to replace the existing five-span structure with a single-span b r i d g e t h a t w o u l d a c c o m m o d a t e widening of I-84 under the bridge. A single-span bridge would improve motorist safety by increasing visibility and eliminating a potential collision hazard. It also would reduce material requirements, construction duration, and impacts to median construction operations. The additional structure depth required by the single-span bridge was accommodated by modifying the vertical profile of both the I-84 and Ten Mile Road approaches in the early stages of design. Based on conceptual evaluations, the design team recommended a single- span, cast-in-place, post-tensioned concrete box-girder bridge with a splayed framing plan. In addition t o l o w e r c o n s t r u c t i o n c o s t , t h e recommended structure type reduced the tunnel effect caused by alternatives featuring larger bridge widths. It also provided future flexibility for median- re l a t e d c o n s t r u c t i o n a c t i v i t i e s b y eliminating the center pier. The stiffness and redistribution characteristics of the bridge offered excellent structural performance. Since there was no unused deck area, the bridge did not require additional safety railings and resulted in a more aesthetically pleasing profile TEN MILE ROAD INTERCHANGE OVER I-84 / MERIDIAN, IDAHO BRIDGE DESIGN E NGINEER : HDR Engineering Inc., Boise, Idaho FALSEwoRK DESIGN ENGINEER: vAK Construction Engineering Services, Beaverton, Ore. RoADwAy DESIGN ENGINEER: H.W. Lochner, Meridian, Idaho PRIME C oNTRACToR: Idaho Sand and Gravel Company, Nampa, Idaho BRIDGE CoNTRACToR: Concrete Placing Company, Boise, Idaho PoST-TENSIoNING CoNTRACToR: DyWIDAG Systems International-USA Inc., Long Beach, Calif. CoNCRETE SuPPLIER: Idaho Concrete Company, Nampa, Idaho by Ted Bush, HDR Engineering Inc. Ten Mile Road Interchange SPuI Bridge Ideal Fit over I-84 in Idaho The I-84–Ten Mile Road Interchange Bridge in Meridian, Idaho, features an hourglass-shaped, cast-in-place concrete box girder with 10 curved webs. Photo: Idaho Airships. 18 | ASPIRE , Summer 2011 Book_Sum11.indb 18 7/1/11 9:59 AM

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