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Different types of base isolation techniques are developed one after the other, each prepared for specific seismic conditions and structures. Some of the important base isolation systems used in buildings are elastomeric bearings and friction pendulum bearings. These are explained briefly in the article.

Also Read: What is Base Isolation?

1. Elastomeric Bearing

Elastomeric bearing is the most widely used base isolator. This isolation system consists of a layer either made of natural or synthetic rubber sandwiched between the mild steel plates. This together acts as a single unit.

The steel plates help the rubber layer to prevent bulging during the earthquake action. It is the component that provides vertical load capacity and stiffness to the unit. When the unit is subjected to movements that result in vertical deformation, it is granted as horizontal movements by the bearings. The shearing deformability of the rubber sheets provides horizontal flexibility. This movement is not restrained by the steel plates.

The top and bottom units of the system has thick mounting steel plates that allow to firmly connect to the superstructure above and the foundation below.

Elastomeric bearings have a wide application in buildings and large-span bridges. The elastomeric bearings can be of three types:

  1. Natural Rubber Bearing (NRB)
  2. Synthetic Rubber Bearings
  3. Lead Rubber Bearing (LRB)
Fig.1. Types of Elastomeric Bearing; (a) Natural Rubber Bearing (NRB) (b) Elastomeric Bearing Device (d) Lead Rubber Bearing (LRB)
Fig.1. Types of Elastomeric Bearing; (a) Natural Rubber Bearing (NRB) (b) Elastomeric Bearing Device (d) Lead Rubber Bearing (LRB)

2. Friction Pendulum Bearings

A friction pendulum bearing is the most extensively used kinematic systems in base isolation. As shown in figure-2 below, the pendulum system has a globe that is placed in two steel concave curved surfaces. Instead of a globe, a cylinder member with a global contact surface can also be used. This type of isolation system make use of special metals.

Cross-Section of a Friction Pendulum Bearing
Fig.2. Cross-Section of a Friction Pendulum Bearing
Technical Details of a Friction Pendulum Bearing
Fig.3. Technical Details of a Friction Pendulum Bearing

This isolation system have all advantages of a rubber bearing with sliding property on a global concave surface. This system by assuming a position elevates the building during the seismic lateral motion. This hence reduces the effect of an earthquake on the building a lot.

The friction pendulum system is widely used in heavy roof systems with large spans, in buildings. As these systems use special metals, it can be employed in building construction in cold regions were a high danger of freezing is expected.

Based on the sliding surface geometry, there are two types of sliding bearings, namely:

  1. Flat Slider Bearings
  2. Curved Slider Bearing
Flat Friction Pendulum Sliding Bearings
Fig.4. Flat Friction Pendulum Sliding Bearings
Curved Friction Pendulum Sliding Bearing
Fig.5. Curved Friction Pendulum Sliding Bearing

Also Read: What is Base Isolation?

About Neenu ArjunVerified

Neenu is a Civil and Structural Engineer and has experience in Design of Concrete and Steel Structures. She is an Author, Editor and Partner at theconstructor.org.