Looking for POT bearing vs elastomeric bearing? Look no further because in today’s article we’re going to elaborate this very important topic in bridges and girders.
As a bridge engineer you might know that the bridge girders won’t go directly on the beam seat and instead bearings are provided that act as a resting surface between the girders and the pier or abutment.
So, we can say that bridge bridges are provided so as to allow relative movement between superstructure and substructure.
Did you know? These bearings are not only used in bridges. They’re also used in large infrastructure projects such as heavy building and high rise building so that loads, moment, rotation are transferred to underneath structures without any damage.
Purpose of Bridge Bearings
The bridge bearings serve two purposes as structural devices in bridges. They are meant to transmit heavy imposed loads from the super structure to substructure. They also provide mechanism so as to allow bridge to accommodate relative movements between super and substructure due to vehicular or other environmentally imposed loads.
But before you can understand what type of bearing is good POT or elastomeric, it is very important that you understand the movements that are there on bridge bearings.
Translation: These are lateral or transverse movements in the superstructure and substructure due to shrinkage, temperature, and creep effects.
Rotation: Rotation is the other type of movement on bridge bearings. They are caused either because of settlement in the structure or due to traffic imposed loadings.
Types of bridge bearings
There are two broad classes of bridge bearings i.e. fixed bearings that only allow rotation but restrict any lateral movement. Expansion bearings is the other type that allow both rotation and translation movements.
As per the mechanism of bearings and their structure, there are variety of different types of bearings like sliding bearings, rocker and pin bearings, roller bearings, elastomeric bearings, curved bearings, disk bearing, and pot bearings.
But discussing all these types is actually out of scope of this post. In this post we’ll only discuss about the elastomeric bearings and pot bearings.
These are one of the most common types of bridge bearings used. Elastomeric bearings are made with thin layers of synthetic or natural rubber. In between these layers, steel plates are placed. Both are merged by vulcanization process.
Because of their joint behaviour, they are capable of supporting high vertical loads with very small deformations. Elastomeric bearings, as the name suggests are flexible or soft under lateral loads i.e. they are hard in vertical direction and soft in horizontal direction. In order to enhance the damping capacity of the bridge bearing, lead cores are provided. These lead cores allow energy dissipation so as to deform plastically. This phenomenon is very useful in seismically active areas under earthquake loads.
A pot bearing is another common type of bearings used for bridges and heavy loaded buildings. In pot bearings, a plain elastomeric disk is encased in a shallow steel ring called pot, hence named pot bearing. Vertical loads are transmitted through a steel piston and it sits closely with the pot ring wall.
Above the corner of the elastomeric disk, internal flat sealing rings are provided that contain the disk inside the pot. In such an arrangement, elastomeric pad behaves like a viscous fluid within the pot that allows the bearing to rotate.
In a pure pot bearing, there’s no translational movement allowed and the lateral load is transmitted through the piston that presses against the pot wall. Such a type of pot bearing is fixed pot bearing. To allow rotation in such a transfer, a sliding surface is provided with material of low friction coefficient. Such a guided type is called guided pot bearing.
Elastomeric bearings vs POT bearings
In elastomeric bearings, there’s no confinement as compared with POT and thus they can’t take heavier loads. Such a conventional elastomeric pads will require larger area for the same load and thus the load will not be uniformly distributed.
So, pot bearing is recommended for heavier loads.
Here’s another amazing article for your thirst: Prime Coat thickness & specification