Replacement of bridge bearings and lifting construction

During the use of bridges or building structures, bearings may need to be replaced due to aging, deformation, or design adjustments. One of the key steps in replacing bearings is lifting construction, which involves using external force to partially lift the structure and create operational space for bearing replacement. This process requires rigorous technical solutions and standardized operations, which will be explained from multiple aspects below.

1. Basic principles of jacking construction

Lifting is achieved by using hydraulic jacks and other equipment to apply controllable lifting force at the point of structural stress, causing the beam or upper structure to briefly detach from its original support. Its core goal is to maintain structural balance and avoid local stress concentration. Before construction, it is necessary to calculate the lifting height (usually 5-20 millimeters) and the number of lifting points to ensure synchronization error is less than 1 millimeter and prevent structural cracking.

Common question: Will lifting damage the structure?

If the operation is standardized, the structure will not be damaged. The key is to predict stress changes through finite element analysis and monitor displacement and strain data in real-time during lifting. For example, the lifting speed of concrete bridges needs to be controlled within 1 millimeter per minute, while steel box girders can be appropriately increased.

2. Preparation work before construction

(1) On site investigation and design review

Check the original support type (such as plate rubber support, pot support), degree of damage (cracking, crushing, etc.), and verify the structural drawings to confirm the position of the lifting point. If hidden diseases (such as bolt corrosion) are found, the plan needs to be adjusted.

(2) Equipment selection and debugging

The tonnage of the hydraulic jack should be 1.2-1.5 times the design load and equipped with a synchronous control system. At the same time, prepare temporary support steel pads with a strength higher than the original structural concrete grade.

(3) Safety Plan

This includes emergency support for sudden power outages, emergency pressure relief measures for asynchronous lifting, and isolation warnings for work areas.

3. Decomposition of lifting construction steps

Step 1: Test lifting

Apply 10% of the design lift force first and observe whether the structure is evenly detached from the support. If abnormal noise or uneven displacement is found, immediately stop and investigate the cause (such as foundation settlement or equipment failure).

Step 2: Gradual lifting

The lifting height of each level shall not exceed 2 millimeters, and the data shall be checked by staying for 5 minutes. Focus on monitoring the displacement difference between adjacent piers and abutments to avoid the generation of secondary internal forces.

Step 3: Temporary locking

After reaching the target height, wedge the beam with steel pads to ensure that the load is completely transferred to the temporary support before removing the old support.

Common problem: What should I do if the lifting height is insufficient?

It may be due to limited stroke of the jack or structural weight calculation deviation. Construction needs to be suspended and resolved by adding lifting points or replacing equipment. Forced lifting is strictly prohibited.

4. Support replacement and reset

(1) New support installation

Clean the surface of the bearing pad stone and level it with epoxy mortar to an error of less than 0.5 millimeters. During installation, it is necessary to ensure that the deviation between the centerline of the support and the design position is ≤ 2 millimeters.

(2) Structural reset

Unload temporary supports in stages and slowly lower the jacks synchronously. After resetting, it is necessary to check whether the new support is tightly attached to the bottom of the beam, and if necessary, use thin steel plates to pad it firmly.

5. Quality Control and Acceptance

-Material inspection: A mechanical performance test report is required for new bearings, and the aging index of chloroprene rubber needs to be checked for rubber bearings.

-Process records: including top lift curve, displacement sensor data, weather conditions (temperature changes may affect steel beam expansion and contraction).

-Acceptance criteria: After resetting, the structural elevation error is ≤± 3 millimeters, and the support has no hollowing or tilting.

6. Safety precautions

-It is strictly prohibited to carry out construction in wind speeds greater than level 6 or rainy days to avoid the hydraulic system from being affected by moisture and becoming ineffective.

-Operators need to stay away from the lifting area and adjust parameters through a remote monitoring system.

When dismantling old supports, accumulated stress may be released, and explosion-proof tools need to be used.

7. Economy and construction period

Taking a simply supported beam bridge with a span of 30 meters as an example, replacing a single span bearing takes about 3-5 days and costs about 50000-80000 RMB (including equipment rental and labor). If multiple consecutive operations are carried out, the marginal cost can be reduced.

From the above process, it can be seen that replacing the support and lifting construction is a technical work that relies on refined management. Only scientific planning and standardized operation can ensure the unity of structural safety and engineering efficiency.