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/297009
The famous Japanese Shinkansen railway network started operating in 1964 and has been progressively i m p r o v e d w i t h t h e o b j e c t i v e o f operating at a speed of 300 km/h (186 mph) or more. Since the Shinkansen's b e g i n n i n g , m a n y c o u n t r i e s h a v e implemented high-speed rail (HSR) as an easy link between cities. The first section of the French TGV opened to traffic between Paris and Lyon in 1981. The operation of the 345-km-long (214- mile) Taiwanese HSR, which runs most of the time on viaducts at 300 km/h (186 mph), started in 2007. Today, HSR has become a reality in Asia, Europe, and North America, resulting in the construction of large infrastructures that are designed for dense and heavy rail traffic at speeds never before reached. Since its creation in 1981, the French TGV developed throughout France. T h e S o u t h E u ro p e – A t l a n t i c ( S E A ) line is currently under construction between Tour and Bordeaux, with the anticipation of daily operation at 350 km/h (217 mph). As part of this system, many bridges had to be built according to various construction techniques and the latest refinements of the available technology in the field of prestressed concrete bridges. Design of Railroad Bridges The design of railroad bridges has many unique considerations when compared to the design of road bridges: • The loads are sudden and heavy. • The regular distribution of heavy concentrated loads running at v a r i o u s s p e e d s m a y g e n e r a t e substantial dynamic effects, which cannot be ignored. • Horizontal forces generated by the moving loads, due to track curvatures or swaying on the rails (nosing effect, also known as the coning action), as well as acceleration and breaking forces, cannot be neglected. • The bridge design is unavoidably impacted by the rail-structure i n t e r a c t i o n w h e n c o n t i n u o u s welded rails (CWR) are used, which have be evaluated according to the International Union of Railways (UIC) code. This last consideration is of fundamental concern during the design of HSR bridges. The track type, as well as the configuration and mechanical properties of the structure, govern the combined response of the structure and tracks to • deflections and displacements of the superstructure under vertical and horizontal loads, • differential deformations between r a i l s a n d s t r u c t u r e d u e t o temperature and acceleration or breaking forces, • variable horizontal forces generated along the rails, and • stresses in the rails, which cannot impair the track strength and profile. Available Concepts Due to the main design considerations previously mentioned, Taiwanese HSR bridges generally consist of a box cross section about 13 m (43 ft) wide that provides space for two tracks and catenary supports. General design rules for railroad bridges significantly differ from those of road bridges. For example: • Heavy loads and corresponding dynamic effects cause the bridge to be designed for a span length-to- depth ratio of 12 to 14. • The rail-structure interaction favors the design of short spans. Long, continuous spans require rail expansion devices that impact the behavior of the train on the track. This is why Taiwanese HSR viaducts, which are located on flat areas, mainly consist of sections made of simply supported box girders. This means that the Taiwanese HSR viaducts have • short span lengths, and • many piers and many bearing devices, but no rail expansion devices. High-speed trains may also have to cross large and deep valleys. In such cases, pier spacing and span lengths have to be increased. This also requires that the superstructure be continuous and rail expansion devices are unavoidable. For example, the HSR system near Avignon, France, required two unusual HSR bridges made of 100-m-long (328- The Taiwanese high-speed railway running on a long series of viaducts. Photo: VINCI Construction Grands Project- France. by Jacques Combault, Finley Engineering Group Inc. Design and Construction of Segmental Bridges for High-Speed Rail 18 | ASPIRE , Fall 2013 P R O J E C T Book_Fall13ASPIRE.indb 18 9/6/13 12:05 PM