Why Does Bridge Bearing Voiding Occur?

Clients have always been puzzled by bridge bearing voiding. So, why does bridge bearing voiding occur? Let's explore this issue!

I. Design Factors

1.Improper Selection of Bearings: Failure to accurately calculate the load distribution of the beam body leads to insufficient bearing capacity of the bearings. After being stressed, local compression and settlement occur, resulting in voiding.

2.Oversights in Structural Design: Mismatch between the size or shape of the bearing pad and the bearing. For example, if the area of the bearing pad is too small, it will cause stress concentration at the edge of the bearing and local lifting, thereby leading to voiding.

II. Construction Factors

1.Non-Standard Construction of Bearing Pads: If the surface flatness of the bearing pad exceeds the standard or the concrete strength is insufficient, it will cause local suspension of the bearing after installation; excessive deviation in the elevation of the bearing pad will lead to uneven stress on the bearing after installation, which may further cause voiding.

2.Problems in Beam Prefabrication and Installation: Uneven triangular wedge blocks at the beam ends during beam prefabrication—especially for skew slab beams, which are difficult to control—will result in gaps after bearing installation; inaccurate hoisting and positioning of the beam body cause misalignment between the bearing center and the bearing pad center, leading to eccentric stress and edge lifting with subsequent voiding.

3.Improper Prestressing Construction: In prestressed beam bodies, especially skew beam bodies, inaccurate control of tension force during prestressing construction (e.g., uneven tension force on both sides) will cause beam torsion, resulting in voiding at the obtuse corners.

4.Inadequate Grouting: Inadequate grouting—such as failure of high-strength mortar to fill the gap between the bearing and the bearing pad, or gaps formed after the shrinkage of grouting materials—prevents effective force transmission between the bearing and the bearing pad, thus causing voiding.

III. Material and Component Defects

1.Dimensional Errors: Insufficient thickness of the steel basin base plate or excessive compression deformation rate of the rubber block leads to overall settlement under stress, resulting in edge voiding.

2.Rubber Aging and Deformation: After long-term use, the elasticity of rubber decreases, and it hardens and shrinks. This causes separation from the inner wall of the steel basin, forming gaps and leading to bearing voiding.

IV. Influences of Operating Environment

1.Excessive Beam Displacement: Under temperature changes or live loads, if the horizontal displacement of the beam body exceeds the design allowable value of the bearing, it will cause partial separation of the bearing from the bearing pad.

2.Uneven Settlement: Settlement or displacement of the pier foundation changes the stress state of the bearing, leading to excessive local stress or suspension, and further causing bearing voiding.

3.Impact Loads: Under the action of frequent passage of overloaded vehicles or earthquakes, the instantaneous impact force on the beam body exceeds the bearing capacity limit of the bearing, which may cause local voiding.

V. Inadequate Maintenance and Management

Failure to timely clean up debris or accumulated water around the bearing will cause long-term erosion and damage to the bearing pad, leading to indirect voiding of the bearing. Delayed detection of bearing voiding defects and failure to promptly adopt jacking and repair measures will cause the defects to gradually expand.