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
T h e V i r g i n i a D e p a r t m e n t o f Transportation (VDOT) was in need of a new bridge to replace the existing 1940s era span in Accomack County, Va. The existing bridge, which carries Route 175 over the Black Narrows and the Chincoteague Channel, was deemed structurally deficient and functionally obsolete. In addition, the maintenance and repairs for the 60-year-old swing span were proving cost prohibitive. The location of the existing bridge also caused adverse impacts on the Town of Chincoteague, m o s t n o t a b l e w a s h e a v y t r a ff i c congestion on Main Street affecting residents, tourists, and emergency- response vehicles. The selected option was an off-line 4035-ft-long trestle Mainline Bridge, including a single leaf bascule, spanning environmentally sensitive wetlands and a navigable channel. A 729-ft-long connector bridge provides the necessary link from the new Route 175 Mainline Bridge to Marsh Island. Superstructure units for the approach spans consist of VDOT bulb-tee precast, prestressed concrete beams with custom variable- depth precast, prestressed concrete fascia beams on curved alignments. The beams support an 8.5-in.-thick reinforced concrete deck slab containing epoxy-coated reinforcing steel. The bridge elements were chosen to minimize the visual clutter and impacts to the scenic vista. Construction commenced in December 2006 and was completed in December 2010. Challenges and Solutions Geometry The determination of the preferred alignment required the collection of considerable information, community perspectives, and significant data from the numerous stakeholders. The selected alignment alleviated the summer congestion, reduced the number of openings at the movable span, and reduced the length of the movable span due to the narrower channel at that location. Commitments were made to minimize the amount of construction impacts to the environmentally sensitive wetlands and oyster beds whose harvests are primary income for many of the inhabitants. Once the bathymetric survey data was received, the design team analyzed the water depths and draft requirements for the construction equipment. It was determined that the alignment be changed to make the best use of the natural channels in this predominantly shallow marshland. This shift increased the length of the connector bridge but significantly reduced the length of temporary trestle needed to perform the construction activities, minimizing impacts to the channel bottom, and considerably reducing the overall cost of the project. profile CHINCOTEAGUE ISLAND BRIDGE REPLACEMENT / CHINCOTEAGUE ISLAND, VIRGINIA BRIDGE DESIGn EnGInEER: Hardesty & Hanover LLC, New york, N.y. CIVIl DESIGn EnGInEER: MMM Design Group, Norfolk, Va. GEoTECHnICAl EnGInEER: Schnabel Engineering, Glen Allen, Va. HYDRAulIC DESIGn EnGInEER: Ayres & Associates, Atlanta, Ga. TRAFFIC DESIGn EnGInEER: JMW Engineering Inc., Fairfax, Va. PRIME ConTRACToR: American Bridge Company, Coraopolis, Pa. CAST-In-PlACE ConCRETE SuPPlIER: Branscome Concrete, Nassawadox, Va. PRECASTER: Bayshore Concrete Products Corp. (subsidiary of Skanska USA Civil), Cape Charles, Va., a PCI-certified producer by Henri Sinson, Hardesty & Hanover LLC CHINCOTEAGUE ISLAND BRIDGE REPLACEMENT Environmentally sensitive asset alleviates seasonal demands Aerial view of the new Chincoteague Island Bridge site. Photo: Patrick J. Hendrickson. 20 | ASPIRE , Summer 2012 P R O J E C T ASPIREBook_Sum12_R02.indb 20 6/29/12 12:38 PM