What are bearings in a metro viaduct. Explain the types of bearings and analyses the types with respect to their advantages and disadvantages

Bearings in a metro viaduct are mechanical components that support and reduce the friction between moving parts. They are crucial in the construction of metro viaducts as they allow for the necessary movements of the structures due to various factors such as temperature changes, traffic loads, and wind forces, while also ensuring the overall stability of the structure.

There are several types of bearings used in metro viaducts:

1. Elastomeric Bearings: These are the most common type of bearings used in bridge structures. They are made of rubber and are designed to deform under load to accommodate movements and rotations.

   Advantages: They are simple, reliable, and require little to no maintenance. They are also relatively cheap and easy to install.

   Disadvantages: They have limited capacity for rotational movement and are not suitable for structures with high vertical loads or large horizontal movements.

2. Pot Bearings: These bearings consist of a confined elastomer disc, steel piston, and a pot. The elastomer disc allows for rotational movement while the pot and piston carry the vertical load.

   Advantages: They can accommodate larger rotations and are suitable for structures with high vertical loads.

   Disadvantages: They are more complex and expensive than elastomeric bearings. They also require regular maintenance and inspection.

3. Spherical Bearings: These bearings consist of a convex surface (calotte) and a matching concave surface (slide plate) that allow for rotational movement in any direction.

   Advantages: They can accommodate large rotations in any direction and are suitable for structures with complex load and movement conditions.

   Disadvantages: They are the most complex and expensive type of bearings. They require regular maintenance and inspection, and their installation requires high precision.

4. Sliding Bearings: These bearings allow for horizontal movement by sliding of one surface over another.

   Advantages: They can accommodate large horizontal movements.

   Disadvantages: They have limited capacity for rotational movement and are not suitable for structures with high vertical loads.

In conclusion, the choice of bearing type depends on the specific requirements of the metro viaduct, including the expected loads, movements, and rotations, as well as considerations of cost, maintenance, and durability.