Linear Rubber Bearing Protects Bridges from Earthquakes

Linear rubber bearing is a specialized seismic protection device that allows bridges and buildings to move horizontally while supporting heavy vertical loads. Unlike traditional fixed bearings that resist all movement, a linear rubber bearing permits controlled sliding or deformation during earthquakes and temperature changes, reducing stress on the structure.

The basic design of a linear rubber bearing consists of layers of natural rubber bonded between thin steel plates. This laminated construction creates a block that is flexible in the horizontal direction but stiff in the vertical direction. When the ground moves during an earthquake, the bearing allows the bridge deck or building floor to shift sideways, absorbing seismic energy. After the shaking stops, the rubber’s elasticity returns the structure to its original position.

The linear motion capability of this bearing comes from its low horizontal stiffness. Under normal conditions, the bearing supports the weight of the structure without noticeable movement. When temperature changes cause the bridge to expand or contract, the bearing accommodates this slow movement without building up stress. During an earthquake, the bearing allows larger, faster movements while dissipating energy through the rubber’s internal friction. This combination of functions makes the linear rubber bearing effective for many seismic applications.

The steel shims inside a linear rubber bearing serve an important purpose. Rubber alone would bulge sideways under heavy weight, much like a thick eraser squeezed between fingers. The thin steel plates restrict this bulging, allowing the bearing to support vertical loads many times greater than rubber alone could handle. The steel also increases the bearing’s resistance to overturning forces during strong shaking. The number and thickness of the rubber layers and steel shims are selected based on the required vertical load capacity and horizontal flexibility.

The lead rubber bearing is a common variation of the linear rubber bearing. A lead plug inserted through the center of the rubber-steel assembly provides additional energy absorption. When the bearing moves horizontally during an earthquake, the lead plug deforms plastically, converting seismic energy into heat. This added damping reduces the movement of the structure, providing extra protection. Lead rubber bearings are often used in medium to high seismic regions where greater energy dissipation is needed.

The installation of a linear rubber bearing occurs during construction or retrofitting. For new bridges, bearings are placed at the top of each pier before the bridge deck is poured. For existing structures, retrofitting involves lifting the structure slightly, removing old bearings, and inserting linear rubber bearings in their place. This process requires careful planning and specialized equipment but can be completed without demolishing the structure. The bearings must be installed level and plumb to function correctly.

For regions prone to earthquakes, the linear rubber bearing offers a practical method for protecting infrastructure. It requires no external power, no moving parts that need lubrication, and small maintenance. When the ground shakes, the bearing does its job silently, absorbing energy that would otherwise damage columns, beams, and connections. From highway bridges to hospital buildings, linear rubber bearings save lives and reduce repair costs after seismic events.