Types of rubber materials
Low damped rubber:
Unfilled natural or neoprene rubber are the two most commonly employed rubber materials in our elastomeric bearings. They exhibit great ultimate tensile strength and elongation. The inherent damping of these unfilled rubber materials is typically low, of the order of %2 to %5. Therefore, an isolator device fabricated using these rubber materials must be supplemented with added dampers to mitigate the resonance vibration of the base isolation system.
High damped rubber:
Special fillers and other additives are included in the rubber compound to improve its damping properties. The equivalent viscous damping ratio of our high-damped rubber material increases up to 10% to 15%. As such, unless otherwise dictated by the design calculations, no supplemental dampers are typically required.
Types of internal reinforcement
- Steel plate
- Steel mesh
- Fiber fabric
Types of boundary conditions
The top and bottom layers of elastomer have thick steel end plates bonded to their entire plan area. These end plates are bolted to flanges fixed to the foundation and superstructure.
Partially bonded connection:
The bearing isolator is designed with two thick steel end plates that are partially bonded to the central core of the outer elastomer layers. The top and bottom end plates are attached to the foundation and superstructure through two bolted steel flanges. This partial bonding together with the negligible flexural rigidity of the internal reinforcement layers allows for rollover deformation during shear loads. The rollover deformation provides added lateral flexibility and improves the seismic isolation performance of the isolator. The isolator is capable of resisting uplift forces and preventing relative slip due to the partial bonding at its contact surfaces.
The bearing isolator is placed between the foundation and the superstructure without any mechanical or chemical connection at the contact surfaces. Friction transfers shear forces to the bearing isolator. The bearing can undergo rollover deformation under shear loads, which improves its lateral flexibility and seismic isolation performance. The steel end plates and steel flanges are eliminated, unlike other elastomeric isolator types, resulting in significant cost savings in the seismic isolation system. The unbonded application of isolators is best suited for situations where no uplift forces are applied to the isolator. LBK, Ltd. also offers special mechanical uplift restraining devices that are supplemented with unbonded bearings to resist uplift forces and provide stability against overturning. This system is especially suited for seismic isolation of large and heavy industrial equipment units. Please contact us for more information.
Steel plate reinforced elastomeric isolators: These isolators which are typically employed with fixed boundary conditions are frequently used as ideal isolators for large structures such as hospitals, public buildings, large residential, commercial, and office buildings, bridges, and other similar constructions. LBK Ltd. offers two types of these isolators that can be chosen based on the seismic activity of the region.
Low-damped rubber + supplemental U-shaped metallic dampers: suitable for very-high to high seismic hazard regions.
High-damped rubber isolators:
suitable for high to moderate seismic regions.
Steel mesh reinforced or fiber reinforced elastomeric isolators:
These isolators can be used with partially bonded or unbonded boundary conditions, depending on the project needs. Compared to steel plate reinforced isolators, these isolators are laterally more flexible due to their rollover deformation under shear loads. These isolators are known as pseudo-rolling elastomeric isolators. The improved lateral flexibility makes them ideal for medium to small structures, including police and fire-fighter stations, low-rise residential, commercial, office, and school buildings, as well as bridges. They are also effective for seismic isolation of heavy industrial equipment units like power transformers, boilers, and reactors. Depending on the project, these isolators may include LBK’s supplemental u-shaped metallic dampers.