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How to protect the structure of bridges with modular multi joint expansion devices

Source：www.jswanbao.com Release date： 2026-10-12

1、 Basic principle of action
Bridges are affected by factors such as temperature changes, vehicle loads, concrete shrinkage and creep, and pier settlement, resulting in displacement of the beam length and position. The modular multi group joint expansion device relies on multiple sets of edge beams, middle beams, displacement control boxes, pressure bearings, and sealed rubber bands to decompose and absorb the large displacement generated at the beam ends, avoiding direct hard contact between adjacent beams and reducing additional stress inside the structure, thus protecting the main structure of the bridge.
2、 Various protective measures for the main structure of the bridge
1. Absorb temperature expansion displacement and release temperature stress
When the ambient temperature increases, the beam elongates, and when the temperature decreases, the beam shrinks. Modular devices can adapt to large expansion and contraction, dispersing the displacement of the beam end into multiple groups of units. If there is no expansion device, the stress generated by the expansion and contraction of the beam will accumulate at the end of the beam and the position of the bridge abutment, causing cracking of the beam and damage to the concrete at the back of the abutment; A modular expansion device that works reasonably can release the deformation caused by such temperature and prevent temperature cracks in concrete.
2. Buffer vehicle load impact and reduce local stress at the beam end
When vehicles pass through the gap at the end of the beam, the wheels will directly act on the steel beams of the expansion device, rather than directly impacting the concrete end of the beam. The pressure bearing and elastic support components inside the device can cushion the impact load brought by the wheels and disperse and concentrate the pressure.
If the gap at the end of the beam is relatively large, repeated impacts from vehicles can cause the concrete at the end of the beam to collapse and corner, and the steel bars to be exposed and corroded; The modular expansion device transfers concentrated loads to the steel beam and support system, reducing the probability of local damage to the concrete at the beam end.
3. Sealed and waterproof to prevent water and impurities from corroding the lower structure of the bridge
The device is equipped with a whole sealed rubber waterstop, which is tightly attached to the groove of the steel section, blocking the downward leakage of rainwater, snowmelt salt water, sediment, and road debris from the road surface.
Once water seeps into the gap at the end of the beam, it will continue to erode the steel bars at the end of the beam, causing them to rust and expand, further cracking the concrete; Corrosion will accelerate in saltwater environments. The accumulation of sediment in the gap between the ends of the beam can also block the beam, limiting its free displacement and generating additional internal forces. Waterstops can prevent such media from entering the beam ends, supports, and cover beam areas, delay the corrosion of steel bars and concrete, and protect the supports from long-term normal operation.
4. Adapt to corner and vertical displacement to avoid secondary stress in the structure
In addition to horizontal expansion and contraction, vehicle loads and uneven settlement can cause vertical corners and a small amount of vertical displacement at the beam ends. The displacement control system of the modular expansion device has a certain adaptability to the pressure bearing, and can be compatible with a small amount of vertical rotation and settlement deformation.
When uneven settlement occurs in the pier and the beam end rotates, the device can adjust with the posture of the beam without forcibly constraining deformation; If the telescopic structure cannot adapt to the turning angle, additional secondary internal forces will be generated at the position of the beam and bridge abutment, inducing structural cracks.
5. Constrain displacement direction to ensure that the beam deforms along the preset path
The device is equipped with a displacement control box and a connecting rod system to control the relative displacement of each center beam, ensuring that the gaps in each group are evenly opened and closed, and avoiding excessive opening or squeezing closure of single gaps.
If the displacement is not controlled, local gaps may become too large, adjacent steel sections may push against each other, causing the beam end to be pushed and generating lateral or longitudinal additional forces; Uniform distribution of displacement can avoid local stress concentration and protect the beam and bridge abutment.
6. Protect the support system and extend the service life of the support
Bridge bearings are responsible for supporting the beam and achieving rotational displacement. If there is water seepage and sediment accumulation at the end of the beam, it will cause corrosion and jamming failure of the support. The waterproof function of the modular expansion device reduces rainwater and debris falling into the support area, allowing the support to rotate and slide normally; The stable working state of the support can continuously bear the load of the beam, indirectly protecting the upper and lower structures of the bridge.
3、 Please note that the protection effect depends on installation and operation
1. The anchoring steel bars of the device need to be reliably connected to the pre embedded components of the beam, and the concrete in the anchoring area should be poured densely; Anchor failure can cause the expansion device to loosen and jump, and instead continue to impact the beam end.
2. Rubber waterstops should be replaced in a timely manner after aging or damage. Once the waterstop cracks, the waterproof function will fail, and the risk of corrosion will rapidly increase.
3. Daily cleaning of accumulated sediment and debris in the gaps to prevent foreign objects from jamming the expansion unit and hindering the normal expansion and contraction of the beam.
4. Regularly inspect the displacement control box and support components. Damaged components can cause uneven expansion and introduce additional stress to the bridge.
4、 Applicable scenario tips
Modular multi joint expansion devices are commonly used in large-span bridges, and single joint expansion devices are difficult to meet large displacement requirements. By coordinating multiple units to share deformation and reduce the deformation pressure of individual components, a systematic protection is formed for the beams, abutments, and supports of large-span bridges.

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