Innovative Technology for 500-meter Scale Concrete-Filled Steel Tubular Arch Bridge Construction

A concrete-filled steel tubular (CFST) arch bridge refers to an arch bridge with a CFST arch or a truss arch with CFST chords. The web member of the truss arch can be section steel or steel tube with or without in-filled concrete. Longitudinally-welded rolled steel tubes with strength grades of Q235, Q345, and Q390 specified by Chinese standard for design of steel structures are generally adopted for the steel tubes (Ministry of Housing and Urban–Rural Development of the People’s Republic of China, Inspection and Quarantine of the People’s Republic of China. Standard for Design of Steel Structures: GB50017-2017. China Architecture & Building Press, Beijing, 2017 (in Chinese)), and the in-tube concrete generally utilizes concrete with strength grades of C40 ~ C80 specified by Chinese code for highway reinforced concrete and prestressed concrete bridges and culverts (Ministry of Transport of the People’s Republic of China, in Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts: JTG 3362–2018. China Communication Press, Beijing, 2018 (in Chinese)).

There are three 500-m scale CFST arch bridges around the world, including the Bosideng Bridge which was opened to traffic in 2013, the Hejiang Yangtze River Highway Bridge, and the Pingnan Third Bridge which is under construction. All three bridges are designed by Sichuan Highway Planning, Survey, Design and Research Institute Ltd. The design includes bridge location and bridge type selection, key structural studies, and strength and stiffness calculations.

It is inevitable that the occur of different errors for the construction of CFST arch bridges, in which the error of the arch rib between the actual bridge line and the design bridge line is called as the arch shaft error. As the increase in the span of the CFST arch bridge.

The cable-stayed buckle method is the most commonly used construction method for large-span arch bridges, and it is often combined with other construction methods such as arch rotation.

CFST arch bridges have been rapidly developing and widely used in China owing to many advantages, including their economy, aesthetics, convenient construction and good durability. As of January 2015, more than 400 CFST arch bridges have been built, and their construction spans as well as the arch ring segment numbers have continuously created new records. Particularly, the effective span of the Wushan Yangtze River Bridge and the Bosideng Bridge hit 460 m and 530 m, respectively. Meanwhile, the number of arch ring segments reached 22 and 18, respectively. Besides, the number of arch ring segments of Matan Hongshui River Bridge during the construction stage was 24, which had a higher requirement for the control of structural alignment and cable force uniformity during construction. So far, the calculation method used for determining the CFST arch bridge cantilever assembly construction cable force mainly includes analytical and numerical methods. The analytical method is based on the principle of moment balance, which is also known as the “zero moment method”. The numerical method mainly includes the positive assembly analysis method, the inverted disassembly analysis method, the fixed length buckling method, etc. Currently, the analytical method is primarily applicable to rib structures with small spans alongside a small number of arch ring segments, which challenges and limits its application in analyzing the center of gravity location and effective length of large-span truss CFST arch under complex force conditions. However, the numerical method, particularly the finite element method, effectively addresses the abovementioned drawbacks of the analytical method. It also has been widely utilized in engineering practice through various finite element software. Nevertheless, the traditional fixed-length buckling method employed in the numerical approach relies on a "controlled process and optimal result" methodology that often imposes multiple state variables as constraints, including the arch rib stress, buckling tension and displacement. This leads to numerous constraints and poor uniformity of cable force during the construction. Therefore, further research is needed to develop a more precise method for optimizing diagonal buckling suspension construction. In response to issues of excessive constraints, uneven cable forces, and the challenge of alignment control when applying the traditional fixed-length buckling method during the construction of CFST arch bridges, this chapter introduces a one-time tensioning method based on an "optimal process and controllable results" for the first time. This method has been successfully utilized to analyze a CFST arch bridge with a span of 265 m, i.e. the Matan Hongshui River Bridge, and another arch bridge with a span of 575 m, i.e. the Pingnan Third Bridge (the largest span arch bridge under construction). It is confirmed that such a method offers a couple of advantages including the less constraint condition, uniform cable force distribution, high calculation efficiency and precise construction alignment.

The design and production of the in-tube concrete is the key technology for building CFST arch bridges. The grouting of CFST is recognized as one of the most important processes in the construction of CFST arch bridges, as it directly affects the quality and safety of the built CFST arch bridge. During the sustained development of CFST arch bridges, the debonding issue of arch ribs has constantly existed and is difficult to solve. As the span of CFST arch bridges increases, the above issue endangers structural safety seriously and restricts the development of span. In order to solve the debonding problem, this chapter introduces the construction technique of vacuum-assisted grouting, the preparation method of in-tube concrete and the associated new materials alongside technologies.

The installation technology of arch ribs is one of the foundations of arch bridge development. From construction with supports to that with fewer or even no support, each method has been gradually developed through long-term practice. Construction with supports is a traditional method which is constrained by the bridge site, terrain, and geology. Moreover, with the increase in bridge span, construction costs and risks also rise. At present, the most commonly used method for the arch rib construction of the large-span arch bridge is support-free constructions, including cable-stayed fastening-hanging cantilever assembly, suspended-basket grouting, rotation construction, and integral lifting construction. Among them, the first one is most commonly used in the construction of CFST arch bridges with a span exceeding 200 m. The method of cable hoisting and cable-stayed fastening-hanging cantilever assembly is to lift arch rib segments with a cable crane and secure them in place with equipments such as buckle cable and hawser cable for arch rib installation. Typically, the arch rib segments are symmetrically lifted in a proper order, and butted to create two cantilevered arch sections. Finally, the closure segment is installed between the two sections, and the buckle cables are loosened to form the complete arch ring.

CFST arch bridges can save material because the steel and concrete of the cross section can play a full role due to the small eccentricity of the arch ring. However, the installation cost is high (about 20% of the total price). Suspension lifting and cable-stayed fastening-hanging system are the main methods for construction of arch bridges without scaffold system. Note that the suspension lifting system requires suspension towers, while the buckle system requires buckle tower. The suspension tower and buckle tower account for about 50% of the cost of the suspension lifting and cable-stayed fastening-hanging systems.

The steel reinforced concrete (SRC) arch bridge was invented by Austrian engineer Josef Melan in 1898 and is also known as the Milan arch. China’s engineers adopted the CFST as the stiff skeleton of SRC arch bridge, and they also developed an ingenious load-regulating technique to improve its cost-effectiveness and reduce the construction risks, which has increased the span length of the SRC arch bridge from 260 to 445 m.