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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            Most Indian railway lines are single-track and the steady
growth in demand for passenger and freight transportation calls for more
capacity, which in turn imposes a need for more double-track sections in the
near future.

                                    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 Indian Railways, the largest rail network in Asia and the world’s second
largest network operated under a single management. In the earliest days of
railways most lines were built as single-track for reasons of cost, to prevent
head-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 looking
to upgrade its existing rail network “Doubling is probably one of the most
remunerative investments”. According to experts, investments in doubling of
tracks will lead to favorable economic returns. Hence doubling is important and
eventually the entire network has to be double line.

 

 However,
construction of new tracks and train-routes has been nominal compared to the
increase in traffic, leading to frequent congestion and over-utilization of
existing tracks

            Today one of the biggest challenges
that railways faces is freight share going down because of the constraint in
infrastructure and the line capacity and as the Railways generate three-fifths
of its revenue from freight volumes Projects such as doubling of lines are necessary
to improve the overall freight share of the railways.

 

Now, IR’s Research Design and Standards Organisation (RDSO), undertakes research, designs and
standardisation. IR has undertaken several initiatives to upgrade its ageing
infrastructure and enhance its quality of service. The Indian government plans
to invest ?9.05 trillion (US$140 billion)
to upgrade the railways by 2020. To fast-track creation of a robust
infrastructure, the government has sanctioned plans for doubling and tripling
of 16,500 km of railway tracks in few years as
against only 22,000 km in last 70 years.

Definitions:

Retrofitting refers to the addition
of new technology or features to older systems. Power plant retrofit,
improving power plant efficiency / increasing output / reducing emissions. Home
energy retrofit, the improving of existing buildings with energy
efficiency equipment. Similarly, Bridge Retrofit improves the strength of the
existing structure. 

            The
process of expanding a single track to double track is called duplication or doubling.

 

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.

·        
Increases the
speed of trains.

·        
Ease the
congestion.

·        
Increase traffic
on the railways network.

·        
Increasing its
freight and passenger revenue.

 

 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.