THE CONCRETE BRIDGE MAGAZINE

SUMMER 2018

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/995102

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The U.S. Route 95 (U.S. 95) northwest corridor in Las Vegas is one of the fastest-growing areas in souther n Nevada, and the U.S. 95/Clark County Route 215 (CC 215) Interchange serves as a critical link for regional commuters between the predominately residential areas in northwest Las Vegas and the large employment centers in the area. To meet the growth in the region, the Nevada Department of Transportation (NDOT) is currently u p g r a d i n g t h e U . S . 9 5 / C C 2 1 5 Centennial Bowl Interchange, the third busiest intersection in the state, from an at-grade intersection to a full system-to- system interchange. In 2008, NDOT began design on the i n t e rc h a n g e , w h i c h w a s i n i t i a l l y estimated to cost around $250 million. To work within funding constraints, the project was divided into three projects. In July 2017, the first phase of the interchange—a 2365-ft-long post- tensioned cast-in-place (CIP) concrete box girder carrying westbound CC 215 to southbound U.S. 95 (WS Flyover)— was completed. Type Selection Type selection and preliminary layout for the Centennial Bowl Interchange s t r u c t u re s b e g a n i n 2 0 1 0 . N D O T considered four different superstructure types for the interchange's 15 grade separations: CIP post-tensioned box girders; steel plate girders; precast concrete I-girders; and precast concrete U - g i r d e r s . S t r u c t u r e t y p e s w e r e evaluated based on cost, aesthetics, constructability, and durability. For the three large flyover structures, the selected structure type needed to accommodate spans longer than 200 ft, horizontally and vertically curved alignments (horizontal radii less than 850 ft), and superelevations of 6%. Historically, the CIP post-tensioned box girder is the most cost-efficient bridge type in Nevada, with typical costs under $150 per square foot of deck. At the time of type selection, steel plate girders and precast concrete girders cost $200 per square foot and $220 per square foot, respectively. The geometric constraints of the interchange favored the CIP and plate girder solutions, with CIP ultimately selected based on cost, aesthetics, and durability. The use of CIP post-tensioned box girders for the interchange will result in an estimated 14% total project cost savings, lowering the cost for total structures by $30 million compared with steel plate girders. Design The WS Flyover is a fourth-level ramp, crossing over the major U.S. 95 and CC 215 roadways, six future interchange ramp movements, one existing local road, and a 36-in.-diameter high- p re s s u re g a s l i n e . D u e t o t h e s e horizontal constraints, the layout of the flyover uses three frames with lengths of 858 ft, 862 ft, and 645 ft, for a total length of 2365 ft. The WS Flyover's alignment crosses the southbound lanes of U.S. 95 at a sharp skew, necessitating profile CENTENNIAL BOWL INTERCHANGE (WESTBOUND CLARK COUNTY ROUTE 215 TO SOUTHBOUND U.S. ROUTE 95 FLYOVER BRIDGE) / LAS VEGAS, NEVADA BRIDGE DESIGN ENGINEER: Nevada Department of Transportation, Carson City, Nev. PRIME CONTRACTOR: Las Vegas Paving Corporation, Las Vegas, Nev. POST-TENSIONING CONTRACTOR: DYWIDAG Systems International, Long Beach, Calif. Centennial Bowl Interchange Westbound Clark County Route 215 to Southbound U.S. Route 95 Flyover Bridge by Michael Taylor, Nevada Department of Transportation Overview of Westbound Clark County Route 215 to Southbound U.S. Route 95 Flyover Bridge showing the horizontally and vertically curved alignment. Photo: CA Group. 12 | ASPIRE Summer 2018 P R O J E C T

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