Full-Span Precasting of High-Speed Railway Bridges

Full-span precasting of high-speed railway bridges

Numerous major viaducts have been built in recent years for High-Speed Railway (HSR) projects. The 113km Beijing-Tianjin route in China includes 100km (88%) of bridges, the 1318km Beijing-Shanghai route includes 1140km (86%) of bridges, the 904km Haerbin-Dalian route includes 663km (73%) of bridges, and the 995km Wuhan-Guangzhou route includes 402km (41%) of bridges. More than 35.000 spans for HSR bridges have been built in China, and large investments in HSR infrastructure have also been made in Europe, Japan, Korea and Taiwan.

Embankments and bridges for HSR infrastructure are both expensive. Most HSR embankments require expensive transition wedges at abutments and box culverts for progressive increase and reduction of the track stiffness, long embankments may require many overpasses for ground mobility and hydraulic reasons, and long-term track stability requires specific solutions for embankment consolidation. HSR embankments, in other words, are more expensive than conventional highway embankments, which suggests the use of shallow embankments in HSR projects.

When the HSR infrastructure is supported on soil with poor mechanical properties, the HSR embankments are often replaced with prestressed-concrete (PC) bridges on deep foundations. Replacing a shallow embankment with a PC bridge lifts the track profile, and design restrictions on longitudinal gradient and vertical transitions in the track profile often result in long bridges. Project economy and control of deflections and train-induced span resonance under high-speed railway traffic often suggest the use of short PC spans, the combination of long bridges and short spans results in hundreds of spans, and a large number of equal spans allows the investment needed to set up large precasting facilities and to provide special transportation and placement means.

For all of these reasons, many HSR bridges have been built with precast spans transported into place and positioned with specialized equipment. Full-span precasting of HSR bridges accelerates construction, enhances quality, facilitates quality control, minimizes the labor demand, and further increases the competitiveness of PC bridges over HSR embankments. Single-cell box spans are well suited for single- and dual-track bridges, while single-track U-spans offer advantages of noise reduction, train containment in case of derailment, optimum integration with the environment, lower vertical profile of the track, and easier handling due to the lighter weight.

Full-span precasting offers rapid construction and repetitive high-quality casting processes in factory-like conditions. The spans are cast, transported and erected all year long in almost any weather conditions. The maximum span length depends on the load capacity of the erection equipment, even if in the large-scale projects where this construction method is used, it is common to design and fabricate custom equipment for the length and weight of the spans to be handled.

Full-Span Precasting of High-Speed Railway Bridges explores the organization of large-scale precasting facilities designed for just-in-time delivery of precast spans. It explains how to optimize the productivity of casting cells and rebar jigs, the pros and cons of span post-tensioning vs. pre-tensioning and hybrid prestressing systems, and the organization of the stockyard in relation to the span curing time at delivery.

The eManual explores the use of portal carriers with underbridge and span launchers fed by tire trolleys for transportation and placement of precast spans. It compares loads, kinematics, performance, productivity, structure-equipment interactions and span curing time at delivery of the two solutions and explains how to choose the most appropriate span delivery method in relation to the length and weight of the precast units, the length and number of bridges to erect, the presence of tunnels and crossover embankments along the delivery routes, and the area available for the span stockyard.

The eManual is an essential tool for bridge owners, designers and constructors interested in the planning, design, design-build bidding and construction of large-scale railway bridge projects.

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