Bridge jack straight down bend

Bridge jacking involves carefully lifting or lowering a bridge superstructure using hydraulic or mechanical jacks to correct deflections, bends, or misalignments while ensuring structural safety.

Overview of Bridge Jacking

Bridge jacking is a controlled process used to adjust, repair, or replace components of a bridge superstructure. It can be applied to correct bends, sagging, or misalignment in steel or concrete bridges. The process requires precise calculation of loads, lift points, and jack capacities to prevent structural damage or collapse ( ).

Equipment and Systems

Common jacking systems include:

• Hydraulic jacks: Provide precise lifting and lowering control, often with pressure gauges and control valves for each jack ( ).
• Strandjacks: Utilize hydraulic cylinders and steel wires, suitable for heavy loads in confined spaces, with capacities from 15 to 1,130 tons ( ).
• Jack supports and bracing: Ensure stability and prevent unwanted movement during lifting or lowering ( ).
• Shims and buildup blocks: Used to adjust height and distribute loads evenly ( ). Modern systems, such as the SCJ Cube Jack, incorporate self-aligning metal cribbing blocks to reduce manual intervention and enhance safety ( ).

Procedure for Straight Down Jacking

1. Load Calculation: Determine the weight of the bridge and the load at each lift point. For continuous spans, all beams may need to be lifted simultaneously to maintain uniform stress ( ).
2. Placement of Jacks: Position jacks at designated lift points, often at the bottom of girders or diaphragms. Temporary bents may be used mid-span to relieve dead load effects ( ).
3. Controlled Lowering: Lower the bridge gradually to correct bends or deflections. The system should allow synchronous movement to prevent differential stresses ( ).
4. Monitoring: Use gauges and sensors to track load distribution and stroke movement. Abrupt changes in elevation should be avoided to maintain structural integrity and safe riding surfaces if traffic is present ( ).

Safety Considerations

• Ensure adequate foundation for jacks to prevent tipping or uneven settlement ( ).
• Follow differential beam lift tolerances, which depend on span length and bridge type ( ).
• Consult heavy lifting equipment manufacturers for jack selection and capacity verification ( ).
• Maintain restraining systems to prevent lateral movement during jacking ( ).

Applications

Bridge jacking is used for:

• Correcting bends or sagging in existing bridges.
• Bearing replacement or deck leveling.
• Load transfer during strengthening or retrofitting.
• Situations where conventional phasing is impractical ( ). By following these guidelines, engineers can safely perform straight-down jacking to correct bends while minimizing risk to the structure and personnel.