The erection of railway box girders is crucial in bridge engineering, and it is particularly challenging due to the complex construction site conditions. This article provides detailed information on the preparations, installation process, measurement points, girder placement, support pad placement, and grouting of railway box girder construction. It emphasizes the importance of equipment preparation and plan formulation before construction, as well as measurement and quality control during construction to ensure construction quality and safety.

Preparation for Box Girder Erection

Before installation, it 's crucial to inspect the condition of various construction equipment. For instance, bridge erection machines must undergo moving operations to ensure that all performance indicators are met after obtaining product certification from the technical supervision department. Before girder placement, a dedicated person should develop a design plan and establish safety regulations to establish a complete system for inspecting and maintaining box girders. All essential components for construction should be regularly inspected and maintained to ensure that wheels, tracks, hooks, and other crucial parts meet the construction requirements.

Box Girder Erection

Once all preparations and tests are complete, the formal erection of box girders can begin. The transportation trolley carrying the precast box girders should enter the bridge erection machine with the pre-installed girders. After the lifting and feeding operations are completed, the transport trolley can exit. Once the bridge erection machine is locked and the side guide beam is moved forward, the overhead crane will traverse and place the girders on the pier position, and the bridge erection machine track will be laid.

Girder Erection Construction Measurement

The main data that needs to be measured during box girder erection is the re-measurement of the pier top. First, before erection of the box girder, a special re-measurement operation on the pier top is performed to ensure that the parameters meet the construction requirements and to avoid quality issues during installation. Second, installation measurement. By controlling the longitudinal and transverse axes of the box girder and the cross line of the pier top, deviations can be prevented. When placing the bearings, it's important to control the height difference at the four corners and ensure that the bearings meet the design elevation while achieving the desired placement effect. Third, during the construction period, the maximum error in bridge erection machine girder construction should be within the acceptable range and the girder line should meet the design specifications.

Placing Girders in Position

During the girder placement process, load cells must be used as temporary supports for the girders. It 's crucial to ensure that the average error between the reaction forces of each support point is within 5%. Otherwise, if a single support point is too heavy, it will cause uneven loading on the load cells and seriously impact the quality of girder placement. After the girders are placed on the load cells, grouting should be performed on the bearings. The oil pressure pipelines of load cells for the same girder section should ensure equal loading on the load cells of the same end support to prevent any pipeline failures due to loading issues. The load cells should be placed inside the girder support with a lateral center distance of more than 310cm and a longitudinal center distance between the two ends of 75cm.

Additionally, during the lifting of the precast box girders, they need to be placed on temporary load cells first. The position and elevation should be adjusted using the load cells as construction reference points. It's important to control the speed during the girder placement to prevent damage to the girders from uneven loading.

Support Pad Placement

Before the installation of the box girders, the support pads need to be re-measured. Accurate measurements and alignment are necessary to ensure measurement quality. The longitudinal and transverse centerlines should be aligned during the process of alignment. During the chiseling process of the support pads, the chiseled surface should be the area where the box girder support will be placed. All debris inside the reserved anchor bolt holes should be removed to ensure a clean surface before installing the grouting formwork. The support pads should be wetted with water during this process. Prefabricated wooden boards can be used as grouting formwork. Leak-proof strips should be laid at the bottom plate position, and then the formwork should be fixed to the surface of the support pad using bolts.

Bearings Grouting

Before the formal installation of the bearings, construction personnel should inspect the pier table and anchor bolt holes to ensure that all parameters meet the construction requirements before installation. During the installation of the box girders, grouting should be carried out between the bearings and support pads, as well as inside the anchor bolt holes. It is important to note that the strength of the grouting material must be greater than the design strength of the support pad, and the elastic modulus should be greater than 30 GPa, with a thickness exceeding 10mm. The pressure during grouting should be greater than 1.0 MPa. After the box girder bearings are in place, there should be a gap of 20-30mm between the bottom plate and the bridge pier or support pad to allow smooth grouting of high-strength injection material. Gravity grouting should be carried out from the center position towards the surrounding area, and grouting operations should continue until all gaps around the formwork and bottom plate are filled. To optimize the grouting effect, the volume of the grout should be calculated in advance to avoid insufficient grouting in the middle. Grouting can only be considered complete when the grout is fully compacted and meets the strength requirements. Only then can the girders be placed, with the balance of forces on the bearings be ensured during the girder placement.

Conclusion

The erection of railway box girders is a complex task that requires strict adherence to various preparatory work and safety regulations. Accurate measurement and control must be carried out during the installation process to ensure that the position and elevation of the box girders meet the requirements. The installation and grouting of support pads and bearings must be tightly controlled to ensure their strength and stability. The article's workflow and key points will help facilitate the smooth progress of railway box girder erection.