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Bridge Lifting In Construction May 03, 2018

Lifting construction feasibility requirements

Bridge lifting strand jacks construction is the transformation of existing bridges, so there are many constraints, and some of the better solutions that have been used in the construction projects are not implemented in actual bridge jacking. lifting strand jacks often need to be set in a narrow space on the abutment caps, and sometimes even cannot be directly installed at all, and special design brackets are needed as a support platform.

The layout design of lifting strand jacks and auxiliary supports is one of the most important aspects of construction organization design. Only the construction personnel with rich practical experience can flexibly cope with various complex restrictions on the site.

The lifting scheme must have good operability. In view of the structure and structural characteristics of shiplock bridges, the operability-restricted factors are the size of the jack, the location of the installation, the space for construction operations, and whether there is a need to interrupt traffic.

For jack size, placement and construction operation space, the type of lifting strand jacks and its support location can be flexibly selected based on the size of the site components and the location of the space.

Under the action of the load, a reaction time is required when the hydraulic pressure of lifting strand jacks reaches a predetermined value, and the impact load will cause damage to the jack cylinder. Therefore, taking into account the safety in the lifting process and the requirement for the normal operation of the lifting equipment, this time During the entire process of replacing the bearings, it is recommended to limit the speed of the bridge vehicles to 40 Km/h under the condition of no interruption and no closed bridge traffic, combined with the reinforcement design requirements.

Design of Limiting Device in Structure Lifting Shift

Because of the influence of various factors such as the installation of the jack, the synchronization precision of the jacking, and the temporary support and installation after the fall, the horizontal deflection is often generated during the jacking process, which will directly affect the safety of the bridge. Performing structural limits is the main method of controlling deflection. Limits generally include lateral and longitudinal limits. The design of the limiting device is an essential element to ensure the success of the bridge lifting.

Lift limit solution

The bridge is in a floating state when the whole roof is lifted. Due to vertical errors in the installation of hydraulic jacks and other unfavorable factors in the lifting process, slight horizontal displacements may occur during the jacking process, which makes the jacking dangerous. In order to avoid this kind of situation, it is necessary to set a horizontal limiter vertically and horizontally on the upper part of the bridge. Limit devices should have sufficient strength and have sufficient stiffness in the direction of the limit. After the dismantling of bridge expansion joints, the back wall is connected to the height required by the design, and the gap between the back wall and the beam body is filled with wood to serve as the longitudinal support for lifting so as to achieve the purpose of longitudinal restraint. The horizontal limit is achieved through two measures. First, the abutment ear wall is raised to the height required by the design, and the gap between the ear wall and the beam body is filled with wood; secondly, the length of each side of the pier cover beam is 50 cm. Reinforced concrete block is made on the cover beam after extension. These two measures act as lateral support when they are lifted, and they act as a lateral limit, and are used as shock-proof stops after jacking.

Monitoring system setting when lifting

When the bridge rises, appropriate observation devices such as displacement, deformation, and stress shall be set to control the whole movement trajectory, overall attitude, and structural stress change during the bridge lifting, so as to ensure the safety and smoothness of the bridge jacking. Displacement observation: set observation points on both sides of the same section of the beam body, set observation scales on the observation points, and use high-precision leveling instrument to observe the readings of the various scales during the lifting in real time to verify whether the overall posture of the beam body during lifting is Whether the balance and lifting displacement are synchronized provide data in a timely manner. Stress observation: The strain gauges are pasted on the proposed beam section and the strain data of each observation point are collected in time by computer. Cracks were observed using a scale magnifier. Secondly, temporary concrete foundation settlement observation, expansion joint clearance, and hydraulic jack trip observations should be observed. In the jacking system, the temporary concrete foundation is a reinforced concrete structure that is placed on both sides of the original bearing platform. During the lifting process, the carrying capacity of the temporary foundation and the safety of the jacking system are reflected by the settlement observation data of the temporary foundation. Observe the change of the clearance of the girder, observe once during each lifting stage, especially when the top elevation to a certain height may collide, it is necessary to observe and adjust the lifting sequence in time to avoid the collision between the two end plate beams. Longitudinal displacement; Jack's top-level numerical error directly reflects whether all jacks are synchronized, so that adjusting the fuel supply through the manual valve, so that the jack synchronous lifting