The cantilever construction technology of prestressed cast-in-situ box girder with form traveler is a method that determines the positions of the support system and the form traveler based on the dimensions of the box girder. Through the anchoring system, suspension system, and traveling system, a large-scale "form traveler" (or hanging basket) is assembled, in which concrete is poured to complete subsequent bridge segments. During actual construction, the form traveler can move freely, allowing its position to be adjusted according to construction requirements. Therefore, compared with other construction methods, this technology offers high construction efficiency and strong stability, effectively improving the quality of the bridge. Moreover, the cantilever construction method with form traveler can effectively avoid the problem of repetitive erection and dismantling commonly seen in traditional municipal bridge construction, as the form traveler only needs to be dismantled once, which is a significant means of improving construction efficiency. In addition, this technology has strong compatibility and can be integrated with BIM and other digital technologies to optimize construction processes while also enhancing construction accuracy.

Application of Cantilever Construction Technology of Prestressed Cast-in-situ Box Girder with Form Traveler

1.Construction Preparation Phase

The construction sequences of the prestressed cast-in-situ box girder cantilever construction with form traveler are closely interrelated. Prior to the commencement of municipal bridge construction, the contractor needs to carry out thorough preparatory work, clarifying key construction points and precautions, so as to reduce the probability of construction issues. For instance, the contractor should proactively communicate with the design institute and conduct technical briefings using BIM models and other tools. This approach enables the contractor to quickly understand construction requirements and identify potential problems in advance, serving as an important means of front-end problem resolution.

2.Construction of Segment Pier Table

Although the construction of the pier table is not part of the form traveler cantilever construction process per se, it serves as the starting point of the entire project and provides the foundation for the form traveler cantilever construction. It is the basis for the subsequent construction of the 1#, 2#, and 3# blocks, and its quality is directly related to the overall quality of the municipal bridge construction. During the construction of the pier table, in order to improve its bearing capacity and ensure the stability of subsequent construction, triangular brackets (or corbels) need to be embedded on the pier shaft. The prestressing system of the pier table includes three types: longitudinal prestressing system, transverse prestressing system, and vertical prestressing system. Together, these three systems effectively ensure the stability of the pier table.

3.Construction Process of Form Traveler Cantilever Technology

3.1 Fabrication and Installation of Form Traveler

The fabrication of the form traveler is the fundamental step of the cantilever casting construction. Before fabrication, the contractor should carefully review the design drawings to clarify the various parameters, dimensions, and technical requirements of the form traveler.

The installation of the form traveler shall be carried out strictly in accordance with the following steps:

Track Laying: Survey and setting-out shall be performed on the top surface of the pier table to determine the track position. The tracks are made of structural steel sections. Through anchoring techniques, the upper clamping beams on the tracks, front supports, and counter-rotation roller sets are installed to ensure tight connection with the pier table. After laying, leveling treatment shall be carried out to ensure the flatness of the tracks.

Main Truss Installation: The main truss shall be installed using a prefabricated assembly method. After the main truss is assembled, it shall be hoisted as a whole onto the tracks, with the front end of the main truss extending 20 cm beyond the end of the box girder. After installation, the main truss shall be secured using the rear anchor clamping beams, and the rear anchor horizontal bracings and cross-bracings (or diagonal bracings) shall be installed to connect the main truss as a stable integral structure.

Bottom Formwork and Bottom Cross Beams Installation: The bottom cross beams shall be connected via suspension rods. The front bottom cross beam and the rear bottom cross beam shall be installed separately, forming two supporting points to provide conditions for the installation of the bottom longitudinal beams.

 Side Formwork and Ancillary Installation: The outer sliding beams and outer guide beams shall be installed and connected to the front cross beam by means of suspension rods. Subsequently, the bottom formwork shall be installed and casting preparations shall be made, thereby completing the assembly of the form traveler.

Symmetric Construction: Because the subsequent casting loads are relatively large, in order to avoid unbalanced loading and instability of the pier table, identical form travelers shall be installed at symmetric positions on both sides of the pier table and construction shall be carried out simultaneously to ensure structural stability.

3. 2 Preloading

During municipal bridge construction, the form traveler is subjected to significant loads, and deformation of the form traveler may affect the quality of the construction. Therefore, after the installation of the form traveler, preloading treatment is required. Preloading, in simple terms, involves applying pressure to the form traveler structure through prestressing tendons, external devices, etc. Through this preloading treatment in advance, the form traveler structure can adapt to the subsequent construction loads in advance, ensuring the overall stability and safety of the project. Generally speaking, to ensure smooth construction, the bearing capacity of the form traveler should reach 1.5 times the weight of the segment to be cast. Therefore, during construction, the construction personnel should develop a comprehensive treatment plan, taking into account the conditions of the cross beams and other structural components, to ensure the rationality of the test.

3.3 Traveling (Forward Movement)

After casting and curing are completed, the form traveler can be moved forward to carry out the construction of the next segment. The forward movement of the form traveler requires the use of jacks, oil pumps, and other equipment, while the advancement of the internal formwork is accomplished by means of suspension rods and internal sliding beams. During the traveling process of the form traveler, the construction personnel need to control the traveling speed and deviation to avoid excessive deviation that may affect the construction quality. During traveling, the traveling distances of the two sets of form travelers must remain consistent, and the traveling distance for each step should be controlled within 40 cm.

Conclusion

In summary, the application of cantilever construction technology of prestressed cast-in-situ box girder with form traveler in municipal bridge construction plays a significant role in improving the construction quality and efficiency of municipal bridge projects, and is an important means of promoting the development of the bridge engineering industry. Therefore, relevant entities should also clearly recognize the value of this technology. Based on the cantilever construction technology of prestressed cast-in-situ box girder with form traveler, it is necessary to conduct thorough analysis of construction steps, optimize and supervise construction processes, improve the quality of municipal bridge construction, and thereby contribute to the sustainable development of the enterprise.