During the construction of urban roads, bridges, housing buildings and other projects, environmental pollution and noise problems are prone to occur. Although such construction meets the needs of urban construction and development, it is not in line with people's pursuit of quality of life. Segmental precast assembly structures, however, have the advantages of low pollution, low noise and high safety, showing great advantages in urban bridge construction. They have received attention from the construction industry and the government, with a promising application and development prospect. As an important work in viaduct engineering construction, the application of segmental assembled girders occupies a crucial position. Analyzing the construction of viaduct segments will better enhance the analysis and control of segmental assembled girders, and thus further optimize the final overall effect of viaduct engineering construction through reasonable measures and approaches.

1. Overview of Segmental Girders

A segmental girder refers to a construction process in which a full-span bridge is divided into multiple segments. These segments are precast in a prefabrication yard, then transported to the bridge construction site. A special bridge erecting machine is used for hoisting, adjustment, glue application for splicing, tensioning, and installation of the full-span girder. This construction technology is relatively mature in regions such as Hong Kong, China, Europe, America, and Southeast Asia. After years of promotion and application in China, some achievements and construction experience have been gained. However, there are still few design and construction projects of segmental girder construction technology in China, with immature design and construction experience, and no guiding and systematic design specifications and acceptance standards have been formed. Therefore, research efforts should be intensified.

2. Advantages of Segmental Assembly Technology

(1) Using this technology in bridge construction can reduce the impact on traffic and the surrounding environment, with good environmental protection;
(2) The segments are lighter in weight and smaller in size, making transportation more convenient and construction assembly faster, which is conducive to shortening the construction period. Factory-made concrete is easy to control the construction quality;
(3) It can effectively reduce the shrinkage of concrete after installation and bridge formation. The segmental assembly technology is suitable for external prestressing, so the cross-sectional size of the girder can be reduced during construction, improving the efficiency of material use;
(4) It is beneficial to properly control the geometric shape and ensure the aesthetics of the concrete structure in bridge construction.

3. Construction Technology of Segmental Girders for Viaducts

Segmental Girder Prefabrication

Due to the consistent cross-sectional and shape characteristics of bridges constructed with precast segmental assembly technology, short-line method is more suitable for segmental girder prefabrication. That is, instead of prefabricating all segments of each girder at one time on a full-length pedestal, only one type of segment is prefabricated for each set of pedestals. Advanced equipment is used for standardized and modular construction to ensure the production of precast segments with high quality and standards, and batch replication is carried out to improve the utilization rate of equipment and tools and reduce costs.
In addition to the necessary infrastructure, the most critical part of the short-line method construction for precasting segmental girders is the model system. In addition to using fixed steel formwork, a three-dimensional control system and positioning trolley should also be configured. The starting segment is prefabricated first, and then adjacent segments are prefabricated with the end face of the starting segment as the matching face. That is, the formed end face of the segment is used as the formwork for the adjacent segment, and a release agent is applied to the matching face to prefabricate the next segment. This process is repeated until the last segment is prefabricated, effectively eliminating the cumulative error of the full-span girder caused by errors, properly solving the problem of segment assembly and connection, and thus effectively ensuring the consistency between the assembled segments.

4. Application of Segmental Girder Bridge Erecting Machines for Viaducts

The segmental girder bridge erecting machine is the most important basic equipment for erecting segmental girders. During the design and manufacturing of the segmental assembly bridge erecting machine, it should meet the technical index requirements and construction process requirements for erecting segmental girders according to the structure of the segmental girders, such as single-segment hoisting, full-span girder bearing, segment moving and adjustment, and accurate positioning of the full-span bridge. According to the structural characteristics and walking mode of the bridge erecting machine, it can be divided into upper-type and lower-type bridge erecting machines, which have different applicability, advantages and disadvantages. The upper-type bridge erecting machine can not only carry out rear girder feeding but also lower girder feeding. During the process of crossing rivers and roads, a cross-bridge gantry crane is used to lift the segmental girders to the bridge deck, and then a girder transport vehicle is used to transport them longitudinally to the erection position, and then rear girder feeding technology is used for erection.

5. Assembly and Erection of Segmental Girders for Viaducts

After transporting the segmental girders from the prefabrication yard to the bridge site, they are assembled using a bridge erecting machine. For any type of bridge erecting machine, except for processes affected by its structure such as girder feeding, girder lifting and girder lowering, the rest of the processes are basically the same.
For the assembly and erection of each span of the bridge, starting from the front or rear end of the bridge erecting machine's construction direction, the first segment is positioned first, and then adjacent segments are assembled. The process is carried out in the order of applying splicing glue, adjusting and aligning, and temporary tensioning until the assembly of all segments of the full-span girder is completed. Prestressing tendons can be threaded and tensioned for the temporarily assembled full-span bridge, and finally the full-span girder is installed on the bridge bearings.

6. Conclusion

In bridge construction, the application of precast segmental assembly technology can reduce pollution, lower energy consumption, and ensure bridge safety. In this regard, it is necessary to strengthen the research and grasp of the precast segmental assembly technology, continuously improve the construction technology and construction control, and improve the level and quality of bridge design and construction in China.