ABSTRACT: 

The key objective of today’s paper is the Extension of
single-track lines into double-track in bridges without the demolition of
existing structures like pier, abutments etc by providing suitable retrofitting
methods as it will be an important part of future rail investments.

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            There
is a steady growth of passengers and freight transportation in the upcoming
years and since the Indian railway networks are single-track it increases the
desideratum for its capacity. The possible solution against this problem is
quoted to be the doubling of track.

                                    Various
techniques have been suggested in this paper to strengthen the bridge structure
due to doubling of tracks in the railway networks system.

1.     
INTRODUCTION

      The world’s second largest network and the Asia’s largest rail network
is The
Indian Railways.  The
main reasons to opt for single track were due to costs and to prevent head-on collisions on single lines
in 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 seeking
for its up gradation to doubling as it is  probably one of the most advantageous and
gainful investments. Hence the investments in this sector will increase the
economic returns of the nation and eventually the network has to be entirely
double lined.

 

 Even though there
is recurring congestion and the existing tracks have been over-utilized, the
construction of the new tracks is being nominal when related with the rising
traffic though the decades.

            Due
to the lack of the line capacity and the infrastructure, the huge challenge
that the railways is facing in today’s circumstances is that the freight share
is decreasing gradually and might hit the rocks bottom if not properly taken
care off. As this freight share contributes about three-fifth of the nation’s
revenue, in order to improve the overall freight share of the railway the
projects based on the doubling of tracks can be undertaken.  

 

    In recent times, the Indian Research Design and Standards Organization have
been undertaking various researches, standardizations and designing works. In
order to enhance the quality of service and the ageing of
infrastructure the Indian Research has taken several initiatives to upgrade its
system by implementing the necessary changes. The Indian government has planned
to invest about 9.05 trillion for the up gradation of railways by 2020. To speed up the process of the plans
which has been sanctioned for the doubling, the government has set its target
to 16,500km of railway tracks in the next few years.

   

Definitions:

            The
addition of new technology
or features to older systems is referred to as Retrofitting. Bridge
Retrofit improves the strength of the existing structure. 

            Doubling
or duplication is the process of expanding a single
track to double track.

 

2. RETROFITTING METHODS

            Some of the retrofitting methods are being
suggested as follows and the best method can be adopted depending upon the site
condition 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.

·        
The
existing structure must be analyzed.

·        
Analysis
should be carried out both manually and by using software’s like SAP2000,
Staad.Pro, SolidWorks.

·        
Due  to the double tracking of the bridge the
deflections produced exceeds the permissible values causing the structure to
fail.

·        
Hence,
Suitable retrofitting methods should suggested depending upon the results of
the analysis.

  4. ADVANTAGES

·        
The requirement
for the construction of a new structure is not necessary.

·        
Cost for the construction of a new structure
becomes negligible.

·        
The speed of the
train increases.

·        
Ease the
congestion.

·        
The railways
network traffic gets increased.

·        
The passenger and
the freight revenue increases.

 

 5.
DISADVANTAGES

 

·        
Constant
maintenance is required after Retrofitting to avoid failure.

·        
Skilled personnel
is required and care should be taken for carrying out the process

·        
The
traffic in the particular area has to be temporarily stopped in order to do the
retrofitting methods

6. CONCLUSION

      
Hence the conversion of a single track network to double track can be
done by adopting suitable retrofitting methods without the need for the
demolition of the existing structure and the construction of a new bridge
parallel to the existing structure for doubling. The cost is being saved in
this process. The revenue of the railways is being increased as the number of
passengers and frights increases. Since insertion of girders and abutments is
considered as a costly solution even though it reduces the deflection to a
certain extent. External prestressing method is considered to be the best
method as it counteracts maximum deflection and less amount of maintenance is
enough. 

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