ABSTRACT:  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.

            Thereis a steady growth of passengers and freight transportation in the upcomingyears and since the Indian railway networks are single-track it increases thedesideratum for its capacity. The possible solution against this problem isquoted to be the doubling of track.                                    Varioustechniques have been suggested in this paper to strengthen the bridge structuredue to doubling of tracks in the railway networks system.1.     INTRODUCTION      The world’s second largest network and the Asia’s largest rail networkis TheIndian Railways.  Themain reasons to opt for single track were due to costs and to prevent head-on collisions on single linesin the earlier days. Indian 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 existing rail network is seekingfor its up gradation to doubling as it is  probably one of the most advantageous andgainful investments. Hence the investments in this sector will increase theeconomic returns of the nation and eventually the network has to be entirelydouble lined.  Even though thereis recurring congestion and the existing tracks have been over-utilized, theconstruction of the new tracks is being nominal when related with the risingtraffic though the decades.            Dueto the lack of the line capacity and the infrastructure, the huge challengethat the railways is facing in today’s circumstances is that the freight shareis decreasing gradually and might hit the rocks bottom if not properly takencare off. As this freight share contributes about three-fifth of the nation’srevenue, in order to improve the overall freight share of the railway theprojects based on the doubling of tracks can be undertaken.        In recent times, the Indian Research Design and Standards Organization havebeen undertaking various researches, standardizations and designing works. Inorder to enhance the quality of service and the ageing ofinfrastructure the Indian Research has taken several initiatives to upgrade itssystem by implementing the necessary changes.

The Indian government has plannedto invest about 9.05 trillion for the up gradation of railways by 2020. To speed up the process of the planswhich has been sanctioned for the doubling, the government has set its targetto 16,500km of railway tracks in the next few years.    Definitions:            Theaddition of new technologyor features to older systems is referred to as Retrofitting. BridgeRetrofit improves the strength of the existing structure.

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              Doublingor duplication is the process of expanding a singletrack to double track. 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.·        The speed of thetrain increases.·        Ease thecongestion. ·        The railwaysnetwork traffic gets increased. ·        The passenger andthe freight revenue increases.

  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.