A Detailed Study of the Dynamic Response of Elastomeric vs. POT PTFE Bearings on Railway Bridges for Indian Infrastructure Development (10m-50m Span Range)

A Detailed Study of the Dynamic Response of Elastomeric vs. POT PTFE Bearings on Railway Bridges for Indian Infrastructure Development (10m-50m Span Range)

Kanhaiya Lal Pandey, Prof Dr. Rakesh Varma

Department of Civil Engineering, COE, Shri Ram Swaroop Memorial University, Lucknow

Abstract: The railway system is the most important part of India’s transportation system. When it comes to ensuring that the structure is safe and sound, bridge bearings are of utmost importance. Within the scope of this comprehensive investigation, the response of elastomeric bearings and POT PTFE (Polytetrafluoroethylene) bearings to dynamic forces is investigated. The present study focuses on railway bridges with spans of 10 to 50 meters and compares their performance to Indian Roads Congress (IRC) standards and Indian Railway specifications.

Keywords: Bridge, Bearing, Elastomeric, POT-PTFE, Dynamic, Seismic

1. INTRODUCTION:

Bridge bearings are used to carry loads from the superstructure to the foundation and also allow for thermal movements, vibrations from traffic, and seismic pressures. Selection of the right bearing systems for the fast growing Indian railway network has a big effect on both the cost of developing it and the expenses of keeping it up over time. India has a wide range of seismic zones, from Zone II to Zone V. Therefore, selection of the right bearings becomes even more important for making sure structures are safe and work well.Indian Railways bridge bearing technology has come a long way from the days of traditional rocker and roller bearings. Nowadays elastomeric and POT PTFE systems has gained enormous attention. Until the 1980s, steel bearings were the most common type used in building railway bridges. But elastomeric bearings have drawn attention for the role for medium-span bridges as they don’t need any maintenance and are cheaper. Recent comparative studies have revealed that elastomeric and POT PTFE bearings behave significantly differently under dynamic loading conditions. These differences are significant enough to drawn comparison. POT PTFE bearings are becoming increasingly popular for spans that are longer than 30 meters, particularly when they are required to handle a significant amount of weight, according to studies conducted on various Indian railway projects. It was demonstrated that POT PTFE bearings are capable of supporting substantial railway loads by the Third Godavari Bridge in Rajahmundry, which was constructed with bow-string arch girders measuring 90 meters. An extensive number of legislation and standards govern the design of bearings for railway bridges in India. A minimum polychloroprene concentration of sixty percent and compliance with UIC 772-R rules are two of the extensive specifications that are outlined in IRC:83 Part II (2018) for elastomeric bearings. The specifications of BS-3784 are outlined in IRC:83 Part III, which is applicable to POT PTFE bearings and mandates the utilization of PTFE Grade A. IRS Bridge Rules for railway loads and IS:1893 Part III for seismic design standards are the two types of bearings that must be adhered to.

2.0 TECHNICAL SPECIFICATIONS AND DESIGN PARAMETERS AS PER INDIAN ROAD CONGRESS

For the purpose of constructing a single structural component, layers of steel reinforcing plates and chloroprene rubber are stacked on top of one another, and then the layer is vulcanised under controlled heat and pressure. A minimum of sixty percent polychloroprene, a low crystallisation rate, and a long shelf life are all requirements that the IRC:83 Part II regulations stipulate for the elastomer. To ensure that the load is distributed evenly and that rubber does not bulge when it is squeezed, steel laminates must conform to the standards established by IS:2062/IS:1079.

Standard configurations enable a vertical load capacity of up to 2,200 kN. The maximum amount of horizontal movement that can be accommodated with elastic deformation of 60 mm. Additionally, the maximum rotational capability is 0.025 radians. Under typical working conditions, the service life is between twenty and twenty-five years. Inspections are performed every three to five years with only minor intervention being necessary.

2.1 Configuration of POT PTFE Bearing

POT PTFE bearings use a steel cylinder (POT) with a restricted elastomeric disc inside it. A close-fitting piston loads the disc, which makes hydrostatic pressure conditions. When combined with stainless steel surfaces, the PTFE sliding surface, made to BS- 3784 Grade A requirements, has a very low friction coefficient (usually between 0.03 and 0.05).

Technical specifications for POT PTFE bearings include;

1. Vertical load capacity: Up to 17,800 kN for heavy-duty applications;
2. Horizontal movement: Unlimited through PTFE sliding interface;
3. Rotational accommodation: 0.04 radians through elastomer deformation;
4. Design life: 50-60 years with proper maintenance; and Maintenance interval: 10-15 years for comprehensive inspection and seal replacement.

1. 1. RESULT AND DISCUSSION
   2. Analysis for Dynamic Response
      1. Comparison of Seismic Performance

         The seismic response characteristics of both bearing systems differ significantly throughout India’s seismic zones. An analysis of bridges spanning from 10m to 50m reveals distinct performance characteristics for each bearing type when exposed to seismic stress conditions. Elastomeric bearings perform better for base isolation in lower seismic zones (Zone II and III), reducing base shear by 65% and 62%, respectively. Figure 1 shows the relationship between the seismic base shear reduction performance of Elastomeric and POT PTFE Bearings.

         Seismic Performance: Bearing Comparision

         Base Shear Reduction % – Elastomeric Base Shear Reduction % – POT PTFE

         Zone II Zone III Zone IV Zone V

         Figure 1: Seismic Base Shear Reduction Performance: Elastomeric vs POT PTFE Bearings across Indian Seismic Zones

      2. Dynamic Behavior (Span-Specific)

For both bearing systems, the dynamic response testing conducted throughout the span range of 10 meters to 50 meters reveals significant performance limitations. If the span is up to thirty meters, elastomeric bearings perform well.Figure 2 shows the dynamic shear force response comparison with elastomeric and POT PTFE Bearings for Railway Bridges (10m-50m Spans). This variation is considerable when comparing spans of the same length. When a high-speed train is loaded, this difference has a direct impact on the likelihood that resonance will occur in the train. Whereas,figure 3 shows application compatibility matrix of elastomeric vs POT PTFE bearings for different railway purposes.

Railway Bridge Bearing Response

Shear Force (KN)

Shear Force – Elastomeric (kN) Shear Force – POT PTFE (kN)

Bridge Span (m)

Figure 2: Dynamic Shear Force Response Comparison: Elastomeric vs POT PTFE Bearings for Railway Bridges (10m-50m Spans)

Seismic Zone V Med Spd Pass Heavy Freight

POT PTFE Suitability

Score

Elastomeric Suitability Score

High Spd Rail

Urban Metro

0 5 10

Figure 3: Application Compatibility Matrix: Elastomeric Vs POT PTFE Bearings for Different Railway Applications

3.1.3 Mechanisms of Load Transfer

The two bearing systems have quite different patterns for transmitting shear force. POT PTFE bearings show higher shear force transmission rates. For example, at a 10m span, the rate goes from 150 kN to 1,320 kN at a 50 m span, which is a 780% increase. Elastomeric bearings show more moderate increases, going from 120 kN to 820 kN over the same range, which is a 583% increase.

1. 1. 1. Cost and Economy Analysis (Life Cycle)

         It has been shown via study on costs that the initial investment requirements of various bearing systems are very different from

         one another. For each bearing, the price range for elastomeric bearings is between 15,000 and 50,000, while the price range for

         POT PTFE bearings is between 60,000 and 150,000.This means that the initial cost of POT PTFE bearings is three to four times greater.

         Span Range (m)

         LCC – Elastomeric 20yr (Lakhs Rs) LCC – POT PTFE 20yr (Lakhs Rs)

         LCC – Elastomeric 50yr (Lakhs Rs) LCC – POT PTFE 50yr (Lakhs Rs)

         Figure 3: Life Cycle Cost Analysis: Elastomeric vs POT PTFE Bearings for Railway Bridges

      2. Maintenance Cost Inference

There are a variety of bearings, each of which requires a certain form of care. Elastomeric bearings do not need a great deal of maintenance; in most cases, they just need to be inspected once every three to five years. The cost required to maintain each bearing is between 2,000 and 5,000 on an annual basis. Some kinds of bearings, such as POT PTFE bearings, need more maintenance than others.This includes checking the seals, assessing the quality of the PTFE surface, and replacing worn parts on a regular basis. This costs 5,00015,000 per bearing each year.

1. 1. SELECTION CRITERIA AND PERFORMANCE OPTIMIZATION
   2. Selection Matrix (Span Based)

      When sselecting bearings, span-based criteria from scientific and economic research must be considered. This will lead to the best performance and the greatest value for money. Elastomeric bearings work well and are cheap, therefore they may be used for spans of 10 to 25 meters. The transition zone was obtained at 2535-meter transition zone in this case loading conditions is needed to be addresses in order for maintenance and long-term costs.For spans longer than 35 meters, POT PTFE bearings are utilised. At 4050 meters, the higher initial cost of POT PTFE bearings can also be considered because of the technical advantages.

   3. Considerations for Environmental Effect

The climate has a significant impact on both the performance of bearings and the selection of bearings. POT PTFE bearings are superior for use in environments with extreme temperature fluctuations as they are able to absorb it in any direction. Bearings made of elastomeric material may have their lifespan shortened in coastal regions that are subjected to high levels of salt and humidity. On the other hand, POT PTFE systems are better when it comes to their ability to resist corrosion. While taking into consideration the seismic environment, it is essential to consider the dynamic qualities of both kinds of bearings. In areas with moderate seismic activity, elastomeric bearings are superior in terms of their ability to isolate the base. POT PTFE bearings perform better than other types of bearings in high seismic conditions as they make use of controlled friction mechanisms.

5. CONCLUSION AND FUTURE SCOPE:

In the present work detailed study of the differences between elastomeric and POT PTFE bearings for use in Indian railway bridges based on the various performance characteristics and application areas of each type was performed. Elastomeric bearings (Neoprene) are more economical and evidence of excellent performance during dynamic loading and earthquake for spans up to 30 meters, particularly in urban environments and low seismic zones. POT PTFE bearings are good for high seismic zones,

substantial loading conditions, and extended spans (30m and more), where accurate movement regulation and enhanced load capacity are critical. On the basis of the results obtained selection rules that are suggested for the building of railway bridges in India, based on an extensive financial and technical analysis are given below;

The Indian Railways should consider developing standardized selection matrices that take into consideration span length, loading conditions, seismic zone, and economic elements in order to make the most efficient use of bearing selection techniques when it comes to bearing selection. The specific requirements and characteristics of each bearing system should be the primary focus of training programs for design engineers and maintenance professionals.

Long-term performance studies of existing installations should be conducted to validate theoretical predictions and enhance selection criteria. Climate change impacts bearing performance, particularly under extreme temperatures and increasing seismic activity. Further research is required to ensure that structures remain secure and function well.The comparative investigation indicates that elastomeric and POT PTFE bearings possess distinct relevance in the development of Indian railway infrastructure.

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