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/575053
PROJECT SOUTH 200th LINK EXTENSION Connecting communities through segmental bridge design by Heather Yount and Bryant Helvey, PCL Civil Constructors Inc. As the first design-build light rail project for Sound Transit, the South 200th Link Extension lengthens the existing light rail system by 1.6 miles. The project extends the light rail from the Seattle- Tacoma International Airport south to the new Angle Lake Station at South 200th Street. The project comprises 1166 precast concrete segments, each weighing between 35 and 55 tons. The project team used both balanced cantilever and span-by-span erection methods to assemble the units into an elevated guideway. The 10-ft-long segments were assembled into bridge spans with epoxy joints and 0.6-in.- diameter, post-tensioning strands in tendons stressed to 1000 kips. The typical span-by-span unit is 27 ft wide and contains 13 segments, forming one span of guideway wide enough for two trains to pass side by side. The balanced cantilevers are up to 40 segments long (spanning 360 ft) and two segments wide, providing a 54-ft-wide structure that allows trains to switch tracks, and a third storage track between the two running tracks. From Fast-Track to Precast In choosing the design-build procurement method, Sound Transit and the design-build team were able to create efficiency in the design process by providing comprehensive design and construction services through a single point of contact. The design-build approach also allowed Sound Transit to fast-track the project by beginning construction before the total design was complete; thereby, reducing the schedule by nearly 6 months. The term accelerated bridge construction (ABC) applies to a multitude of construction techniques, all used with the intention of reducing impacts to the environment, community, and traffic while positively affecting the project's budget and schedule. The practice of using precast concrete segments as opposed to the more traditional cast-in-place concrete superstructure is one way in which Sound Transit benefited from the use of ABC methods. The use of precast concrete segments enabled the project team to minimize disruptions to vehicular traffic exiting the airport because the segments were manufactured and stored at an off-site casting yard until it was time to erect them. The simultaneous construction of the guideway's substructure PROFILE SOUTH 200TH LINK EXTENSION / SEATTLE AND TACOMA, WASHINGTON SOUND TRANSIT, OWNER BRIDGE DESIGN ENGINEER: HDR Engineering Inc., Bellevue, Wash. BRIDGE DESIGN SUB-CONSULTANT: International Bridge Technologies Inc., San Diego, Calif. PRIME CONTRACTOR AND SEGMENT PRECASTER: PCL Civil Constructors Inc., Seattle, Wash. POST-TENSIONING CONTRACTORS: PCL Civil Constructors Inc., Seattle, Wash., (superstructure) and Schwager-Davis Inc., San Jose, Calif. (substructure) POST-TENSIONING SUPPLIER: Schwager-Davis Inc., San Jose, Calif., and Dywidag Systems International, Long Beach, Calif. OTHER CONSULTANTS: KPFF Consulting Engineers, Seattle, Wash., station structural design OTHER MATERIAL SUPPLIERS: Deal Srl, Italy, precast concrete superstructure formwork and erection gantry; Gerdau Steel, Auburn, Wash., reinforcing steel; D.S. Brown Company, North Baltimore, Ohio, bridge bearings; R.J. Watson Inc., Alden, N.Y., bridge bearings; US Spec, Denver, Colo., posttensioning grout BRIDGE DESCRIPTION: A precast, post-tensioned concrete, segmental box girder bridge with 1.6 miles of double-track light rail, twin-track, and single-track box girders, with span lengths ranging from 99 to 363 ft STRUCTURAL COMPONENTS: 66 cast-in-place concrete columns on drilled shafts; four double-leaf, long-span columns on spread footings; four cast-in-place concrete pier tables; 18 cast-in-place concrete pier caps; 1166 precast, post-tensioned concrete segments; 896 post-tensioning tendons; 1.98 million ft of 0.6-in.-diameter steel strand; 14,500 bags of post-tensioning grout BRIDGE CONSTRUCTION COST: $172.8 million