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/295658
In recent years, more than 35,000 spans of high-speed railway (HSR) bridges have been built in China and large investments in HSR infrastructure have been made in Europe, Japan, Korea, and Taiwan. Long prestressed concrete (PC) bridges are the typical solution for HSR infrastructure on poor soil. The combination of long bridges and short spans results in a large number of modular spans. This allows for investments in large precasting facilities and special means for beam transportation and erection. L i g h t - r a i l t r a n s i t ( L R T ) p r o j e c t s also include miles of PC elevated guideways. Many HSR bridges and the first new-generation LRT bridges have been built with precast concrete b e a m s . P r e c a s t i n g o f f e r s r a p i d construction and repetitive casting processes in factory-like conditions. The beams can be erected all year round in almost any weather conditions. This article illustrates the application, transportation, and erection of full- span precast concrete beams for LRT and HSR bridges. U-beams for LRT Bridges Dual-track precast concrete segmental box girders have been used intensively for LRT bridges. Single-track, precast concrete U-beams, however, are being used more frequently because of their higher quality and faster erection rate. Single-track U-beams include two edge girders and a bottom slab that supports the track via ballast or direct fixation. The edge girders keep the train on the bridge in case of derailment, and the top flanges are used as walkways for passenger evacuation. Precast concrete beams offer simple casting operations, r a p i d a n d i n e x p e n s i v e e r e c t i o n with ground-based cranes, optimal integration with the urban environment, built-in sound barrier and system functions, and the possibility of lowering the vertical profile by 5 to 6½ ft. 1 A single-track U-beam is 15 to 18 ft w i d e , w e i g h s f ro m 3 4 0 k i p s f o r 82-ft-long spans to 500 kips for 115-ft-long spans, and is typically transported on the ground with trucks and rear steering trolleys. Different proportions of pre- and post-tensioning are possible. Pretensioning simplifies forming and diminishes the cost of prestressing, but requires anchor bulkheads and reaction beams designed for the prestressing force of many strands. The fabrication process is consistent with the speed of erection. Storage for completion of curing is necessary only when the beams are delivered on the completed deck. Ground transportation and crane erection require two to three days of curing, and the beams can complete curing on the piers. A small storage area may be needed to provide some flexibility in case of delivery delays or defective beams. In typical conditions, the beams are picked up from the Span stacking on support frames. Photo: Systra. Precasting offers rapid construction and repetitive casting processes in factory-like conditions. by Marco Rosignoli, HDR Inc. FULL-SPAN PRECASTING OF RAILWAY BRIDGES 16 | ASPIRE, Spring 2014 AspireBook_Spr14.indb 16 3/21/14 2:20 PM