Bearing Pads In General:
Bridge bearing pads in pakistan contribute to the flexibility as they absorb the load of the structure itself and are also caused due to traffic. Bridge bearing pads bears different types of loads i.e.
- Dead Load is permanent load (self-load of structure)
- Live Load is temporary load (Wind load, Precipitation, or traffic load
- Dynamic load similar to live but changes its direction and magnitudes
The Neoprene rubber is stronger than natural rubber since it resists ozone and heat. Natural rubber, on the other hand, softens under extreme exposure to the sun, whereas Neoprene does not.
Bridges normally carry heavy loads. Unmonitored loads and monitored loads. Excessive load can cause the bridge bearing pads to collapse. The bearing pad absorbs this load and releases it slowly to the substructure. And thus not only the bearing pad prevents the bridge from collapsing but also increases the life of the bridge by preventing wear and tear on bridge materials.
Types of bearing pads used in Pakistan?
In Pakistan, the decision to use which type of bearing pads lies purely with the designers and consultants of the project. It is sometimes difficult for designs to understand the distinction between local and European bearing pads. To minimize costs locally manufactured bearing pads one allowed and used in bridge projects in Pakistan. But with the passing time, the consultants witness issues in locally manufactured bearing pads. Locally manufactured bearing pads are being replaced by European manufactured bearing pads. There are many clients who insist on European bearing pads such as NHA, KDA, etc.
- Number of girders
- Distribution Loads on girders & pier thickness of bearing pad
- Thickness of upper and bottom layer elastomer
- of steel plates and thickness of steel plates
- Thickness of elastomer
- The membrane between steel plates and no. of elastomer membrane between steel plates
Normally these are recommended by the structure engineer while compiling the total load of the bridge. Generally, the following three types of bearing pads are installed in Pakistan.
Engineer while compiling
- Elastomeric Bearing Pad. (Generally, all major road bridges include Neoprene elastomeric bearing pads)
- Pot Bearings. Bridges where the maximum load is constantly shifting from horizontal to vertical direction.
How do determine the quality and life of bearing pads in a bridge?
In an earthquake, excessive jerks on the bridge can indicate poor quality or outdated bearing pads. Some European vendors claim to give 20 years warranty by using top-grade material (quality of rubber & steel plates). Bearing pads exceed the stipulated life it no longer serves its purpose of resisting
What is bulging/deformation on a bearing pad?
Through countless surveys we have conducted on countless public sector projects, we observed bulging/deformation of bearing pads in Pakistani bridges today
There may be in mere micro or nanometers a difference in leveling of the concrete seat. Other reasons may include design problems, bearing pad size, and local/poor quality bearing pads.
Bearing pad suppliers and manufacturers in Pakistan?
There are several manufacturers of bearing pads in Pakistan. One can understand from the example that the requirement of bearing pads to be manufactured under ideal ASTM & AASHTO standards is to be made at a controlled and variable temperature.
Supabizz is a commercial importer of bridge-bearing pads and Expansion Joints. SupaBizz completed the requirement by importing bearing pads from DSL Korea.
Why consultants prefer Imported bridge bearing pads?
Consultants in Pakistan prefer imported bridge-bearings pads. Designed with the latest technology, imported Bridge bearing pads are the favorites of consultants and clients. Steel plates used in imported bridge bearing pads are equally gapped and have accurate gauged thickness. NHA, ATSTM, AASHTO, and British Standards all recommend the use of natural neoprene rubber in imported bearing pads. Due to the good quality of rubber, it makes a strong bond with steel plates due to which imported bearing pads effectively release all loads on the bridge without getting bulged.
What is the difference between European-origin bearing pads and other-origin bearing pads?
The question arises in most people’s minds that “why do designers and consultants specify the use of European bearing pads for their bridges?” other origins are not specified as often European origin or even USA origin
European-origin bearing pads
An export license is different from operating and manufacturing bearing pads in a factory. To export and even manufacture their products internationally, manufacturers must adhere to certain by-laws and standards. There is a feeling that restrictions and quality standards are not perceived in such a manner by other manufacturers originating from other countries.
Quality of those bearing pads
This doesn’t mean that manufacturers operating outside of Europe are not complying with all quality standards. The consultant and designers will need to visit other origin factories to verify their quality standards. By determining the quality of bearing pads manufactured by other origins, they can better guarantee their quality.
The cheapness of local bearing pads comes from old techniques that lack accuracy. Local bearing pads have gaps that aren’t equal, and the rubber material is inadequate. Rubber and steel plates have uneven gaps.
Bridge bearing pads are manufactured under different standards and codes of several organizations like BRITISH STANDARD, AASHTO, and EUROPEAN NORMS.
In Pakistan, the NHA has given a different set of standards according to those bearing pads that have been tested. These standards are as follows
- Tensile strength: D 412
- Elongation at Break: D 412
- Compression set 22hrs at: 67oC D 395 (Method B)
- Tear Strength: D 624 (Die C)
- Hardness: (Shore A)D 2240
- Low-temperature brittleness: D 736
- Low-temperature stiffness: D 797
- Ozone resistance 20% strain: D 1149
- 100 hours at: 38o C.
SupaBizz is the sole importer of all types of mentioned bridge bearing pads.