THE CONCRETE BRIDGE MAGAZINE

SPRING 2012

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-405 Renton, Wash., Stage 2 design- build project provides improvements to accommodate high occupancy vehicles and new freeway connections to local arterials of the city of Renton. As part of this project, the existing 1970s vintage Benson Road Bridge over I-405 was replaced with a new, wider, longer bridge that enabled widening of the freeway below. The project was part of the Washington State Department of Transportation's (WSDOT's) I-405 Corridor Improvements Program. Superstructure Description The replacement bridge provides for two traffic lanes, two bicycle lanes, and one sidewalk for a curb-to-curb width of 40 ft. The bridge consists of a three-span structure with spans of 132, 207, and 182 ft. The bridge was constructed with spliced precast, post- tensioned concrete girder technology. Span 1 used single segment precast girders and Spans 2 and 3 used two- segment precast girders. Four girder lines were used, with t h e m u l t i - s e g m e n t s p a n s e re c t e d on temporary falsework bents. The f i e l d - c a s t g i rd e r a n d p i e r c l o s u re p l a c e m e n t s w e r e c o n s t r u c t e d m o n o l i t h i c a l l y w i t h t h e b r i d g e d e c k p l a c e m e n t . T h e b r i d g e w a s t h e n p o s t - t e n s i o n e d , f o l l o w e d b y p l a c e m e n t o f t h e a b u t m e n t e n d diaphragms. The girders were then jacked up at the abutments to re-set the elastomeric bearings to relieve s h o r t - t e r m d e f o r m a t i o n s c a u s e d by post-tensioning. The final result was a highly efficient, cost-effective, durable, fully composite structure. The bridge construction was completed ahead of schedule and was opened to traffic in July, 2010. options Considered The replacement for the existing Benson Road Bridge was conceptualized as a five-span curved steel plate girder bridge in the original request for proposal (RFP) documents. At 845 ft long, the RFP design represented a significant portion of the total project construction cost. The long lead time for the procurement of steel also posed a significant scheduling risk to the overall project. D u r i n g t h e p r o p o s a l s t a g e , t h e design-build team considered various alter natives. Most significant was changing the overcrossing alignment and the use of different structure types and materials. The final solution selected was a three-span alternative that would significantly shorten the overall bridge length to approximately 521 ft. The revised alignment also allowed the bridge structure to be profile BENSON ROAD BRIDGE / RENTON, WASHINGTON BRIDGE DESIGN ENGINEER: CH2M HILL, bellevue, Wash. PRIME CoNTRACToR: I-405 Corridor Design builders (a joint venture between CH2M HILL and Gary Merlino Construction Co.), Renton, Wash. BRIDGE SPECIALITy CoNTRACToR: Mowat Construction Company, Woodinville, Wash. PRECASTER: Concrete Technology Corporation, Tacoma, Wash., a PCI-certified producer PoST-TENSIoNING CoNTRACToR: VSL, Wheat Ridge, Colo. by Paul Guenther, Ben C. Gerwick Inc. and Hong Guan, CH2M HILL THE BENSoN RoAD BRIDGE oVER I-405 Extending Precast Concrte Spans with Wasington State's "Supr Girder" The Benson Road Bridge over I-405 in Renton, Wash., has spans of 132, 207, and 182 ft and at a 45-degree skew. All photos: CH2M HILL. 24 | ASPIRE , Spring 2012 Book_Spr12.indb 24 4/3/12 9:18 AM

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