1 Preparation for Box Girder Erection

Before erection, strict attention should be paid to the actual conditions of various construction equipment. For example, after the bridge girder erection machine obtains product certification from the technical supervision department, it is necessary to perform machine-moving operations to ensure that all performance indicators of the machine meet requirements. Prior to girder erection, special personnel should formulate design plans and safety regulations, and then establish a complete box girder inspection and maintenance system through careful implementation. Various key components required during construction should be inspected and maintained regularly to ensure that all important parts such as wheels, tracks, and hooks can meet construction requirements during formal construction.

2 Box Girder Erection

After completing all preparation and test work, the formal box girder erection can be carried out. At this time, the girder transport trolley, carrying the prefabricated box girder that has been pre-erected, moves into the bridge girder erection machine. The girder transport trolley can exit only after the girder lifting and feeding operations are completed. After the bridge girder erection machine is locked and the side guide beam is moved forward, the crane trolley will traverse and lower the girder to the pier position, and then the tracks of the bridge girder erection machine will be laid.

3 Measurement in Girder Erection Construction

The main data to be measured during box girder erection are as follows:

• First, pier top re-measurement. Before the formal erection of the box girder, special re-measurement of the pier top is required to ensure that all parameters of the pier top after completion meet the construction requirements and avoid quality problems during erection.

• Second, erection measurement. The longitudinal and transverse axes of the box girder and the cross centerline of the pier top are controlled to prevent deviations. When placing the bearings, attention should be paid to controlling the height difference of the four corners to ensure that the bearings meet the design elevation while ensuring the placement effect.

• Third, during construction, it is necessary to ensure that the maximum error during the girder erection by the bridge girder erection machine is controlled within the allowable error range, and the alignment of the completed bridge meets the design specifications.

4 Girder Lowering and Positioning

During the girder lowering process, a load-measuring jack should be used as a temporary support. It is necessary to ensure that the reaction force error of each support relative to the average value of other supports is within 5%; otherwise, excessive stress on a single support will cause serious impacts on the quality of girder lowering. After the girder is lowered onto the jacks, grouting operations for the bearings are carried out. For jacks in the same girder segment, their oil pressure pipelines should be arranged to ensure equal stress on the bearings at the same end, preventing pipeline failures due to uneven stress. The jacks should be installed inside the bearings at the beam ends, with a lateral center distance of more than 310 cm and a longitudinal center distance of 75 cm from both ends.
In addition, during the hoisting of prefabricated box girders, the box girders should first be placed on temporary load-measuring jacks, which are used as construction benchmarks to adjust the position and elevation. It should be noted that the speed of girder lowering must be controlled to avoid damage to the box girder due to uneven stress.

5 Bearing Pad Stone

Before the formal erection of the box girder, the bearing pad stones should be re-measured. Accurate measurement and setting-out are required to ensure measurement quality, and the longitudinal and transverse centerlines should be set out simultaneously during setting-out. During the chiseling of the bearing pad stones, the main chiseling area is the surface of the box girder bearing placement area. All debris in the reserved anchor bolt holes must be removed, and the grouting formwork can be installed only after ensuring the holes are clean. At this time, the bearing pad stones should be wetted with water. The grouting formwork can be made of prefabricated wooden boards; a leak-proof strip is laid on the bottom plate, and then the formwork is fixed to the surface of the bearing pad stone with bolts.

6 Bearing Grouting

Before the formal installation of the bearings, construction personnel should specially inspect the piers, abutments, and anchor bolt holes to ensure that all parameters meet the construction requirements before proceeding with installation. During the box girder erection, after the girder is lowered onto the jacks, pressure grouting is carried out between the bearings and the bearing pad stones, as well as inside the anchor bolt holes. It should be noted that the strength of the pressure grouting material must be greater than the design strength of the bearing pad stones, with an elastic modulus greater than 30 GPa and a thickness exceeding 10 mm. The grouting pressure must be greater than 1.0 MPa.
After the box girder bearings are positioned, a gap of 20-30 mm should be reserved between the bottom plate of the bearings and the top surface of the piers or bearing pad stones. This gap is mainly to facilitate the smooth implementation of the pouring operation of high-strength grouting materials. For gravity grouting, grouting should be carried out from the center to the surrounding area, and the operation should continue until all gaps between the formwork and the bottom plate are filled. To avoid slurry deficiency in the middle, the volume of the slurry should be calculated in advance before grouting to optimize the grouting effect. The girder can be lowered only after the slurry is completely filled and meets the strength requirements, and the bearing stress must be balanced during the lowering process.

Conclusion

In summary, railway box girder erection is a crucial project. Since the normal operation of the railway must be considered during erection, it is necessary to ensure the quality of erection while maximizing the construction speed, and also ensure construction safety. It is believed that with more attention paid to railway box girder erection construction, the girder erection technology will be further improved.