: single-track for reasons of cost, to prevent

:  The key objective of today’s paper is the Extension ofsingle-track lines into double-track in bridges without the demolition ofexisting structures like pier, abutments etc by providing suitable retrofittingmethods as it will be an important part of future rail investments.            Most Indian railway lines are single-track and the steadygrowth in demand for passenger and freight transportation calls for morecapacity, which in turn imposes a need for more double-track sections in thenear future.

                                    Varioustechniques have been suggested in this paper to strengthen the bridge structuredue to doubling of tracks in the railway networks system.1.     INTRODUCTIONThe Indian Railways, the largest rail network in Asia and the world’s secondlargest network operated under a single management. In the earliest days ofrailways most lines were built as single-track for reasons of cost, to preventhead-on collisions on single lines. Indian gauge 1,676 mm (5 ft 6 in) (a broad gauge) is the predominant gauge used by IR with 108,500 km of track length. The Indian Railways is lookingto upgrade its existing rail network “Doubling is probably one of the mostremunerative investments”.

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According to experts, investments in doubling oftracks will lead to favorable economic returns. Hence doubling is important andeventually the entire network has to be double line.   However,construction of new tracks and train-routes has been nominal compared to theincrease in traffic, leading to frequent congestion and over-utilization ofexisting tracks             Today one of the biggest challengesthat railways faces is freight share going down because of the constraint ininfrastructure and the line capacity and as the Railways generate three-fifthsof its revenue from freight volumes Projects such as doubling of lines are necessaryto improve the overall freight share of the railways. Now, IR’s Research Design and Standards Organisation (RDSO), undertakes research, designs andstandardisation. IR has undertaken several initiatives to upgrade its ageinginfrastructure and enhance its quality of service. The Indian government plansto invest ?9.05 trillion (US$140 billion)to upgrade the railways by 2020.

To fast-track creation of a robustinfrastructure, the government has sanctioned plans for doubling and triplingof 16,500 km of railway tracks in few years as against only 22,000 km in last 70 years.Definitions:Retrofitting refers to the additionof new technology or features to older systems. Power plant retrofit,improving power plant efficiency / increasing output / reducing emissions.

Homeenergy retrofit, the improving of existing buildings with energyefficiency equipment. Similarly, Bridge Retrofit improves the strength of theexisting structure.              Theprocess of expanding a single track to double track is called duplication or doubling. 2. RETROFITTING METHODS            Some of the retrofitting methods are beingsuggested as follows and the best method can be adopted depending upon the sitecondition and the available materials. External prestressing method.

The prestressed wires are stretched in the angle sections which are attached to the girder. The prestressed wires results in the hogging action which counteracts the deflection produced due to the bridge, making it stable. Increasing the number of supports. When the number of abutments is to be increased, the need for the construction of Foundation, Abutments, Bed Block and Bearings arises which becomes a tedious process both in the design and construction stage. By increasing number of girders. When the girders are being increased the I value of the girder increases simultaneously.

It is considered as one of the costly solutions since the number of girders used will increase. Insertion of Brackets at the abutments. The angle brackets which are Corrosion resistant, highly durable which connects the abutments and the deck slab to improve the strength off the strength and reduces the deflection. Skilled personnel’s are required for selecting the suitable bracket and deciding its spaces. Introduction of End Plates in the Structure. The end plates are usually placed near the piers where steel rods are inserted and prestressed from both the ends to reduce excessive deflection.

This method has been adopted across a bridge in Yamuna River, India.3.METHODOLOGY·        Initially,the site has to be investigated.·        Theexisting structure must be analyzed.·        Analysisshould be carried out both manually and by using software’s like SAP2000,Staad.

Pro, SolidWorks.·        Due  to the double tracking of the bridge thedeflections produced exceeds the permissible values causing the structure tofail.·        Hence,Suitable retrofitting methods should suggested depending upon the results ofthe analysis.  4. ADVANTAGES·        The requirementfor the construction of a new structure is not necessary.·        Cost for the construction of a new structurebecomes negligible.

·        Increases thespeed of trains.·        Ease thecongestion. ·        Increase trafficon the railways network. ·        Increasing itsfreight and passenger revenue.   5.DISADVANTAGES ·        Constantmaintenance is required after Retrofitting to avoid failure.

·        Skilled personnelis required and care should be taken for carrying out the process·        Thetraffic in the particular area has to be temporarily stopped in order to do theretrofitting methods6. CONCLUSION       Hence the conversion of a single track network to double track can bedone by adopting suitable retrofitting methods without the need for thedemolition of the existing structure and the construction of a new bridgeparallel to the existing structure for doubling. The cost is being saved inthis process. The revenue of the railways is being increased as the number ofpassengers and frights increases. Since insertion of girders and abutments isconsidered as a costly solution even though it reduces the deflection to acertain extent. External prestressing method is considered to be the bestmethod as it counteracts maximum deflection and less amount of maintenance isenough. 

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