why we place steel girders over railway track in bridge rather than rcc beams?

Sanjeev Sagar

Junior Member
Sep 27, 2017
20
6
Bareilly
Sir, when we construct a bridge over highway and railway track then why we place steel girders over railway track in bridge rather than rcc beams.
Sir please tell me.
 

ARN

Newbie
Sep 15, 2017
5
18
pune
Sir please reply me
Generally bridge is constructed to connect two ends of valley or river or sea to access the train, buses and other vehicles.

And another term is called flyover (it is also type of bridge) is constructed on highway to regulate the vehicles traffic on particular rout without disturbing the underneath traffic crossing and some time across & over the railway line.

Now a days RCC as well as Steel both type of girders are used. But steel girders are preferred due following reasons :

a) It withstands more for vibrations than RCC. ( when train moves it create lot of vibrations)
b) The design of this particular span (which crossing over Indian railway territory) in accordance with Indian railways and they might have belief and safe experience with steel bridges or preferring as per their guidelines.
c) To do the faster & safe work without disturbing and diverting underneath railway movement.

if you want to know in more elaborate then pls. take the feedback from expertise specially in Indian Railway bridge domain.

Thanks
ARN
 

Dnyan Deshmukh

Eternal Member
Staff member
Sep 7, 2017
2,235
3,855
Pune
Also from maintenance point of view, steel beams are good.

As replacing it is easier and faster.
If it RCC beam, it requires lot of work to demolish and recast.

Also we need to wait for almost a month for rcc beam to gain strength and after that we can have traffic on it.

Steel wont waste time on maintenance.
 

hary1973

Newbie
Jun 12, 2019
7
3
Mumbai
As far as I know, girders are used because the span length of the beams under the bridges are very long. We cannot cast such a long RCC beam. Therefore, girders are used.
 

sonukhode

Newbie
Jun 8, 2018
7
4
Pune
Dear Team,

Trains are pretty long and heavy and they generate high frequency vibrations when moving through the bridge.

Now a bridge can be made of steel or concrete. But the only drawback of concrete is its low ductility and resistance against vibrations.

Have you seen a jack hammer?
1567681847461.png

How does it break concrete on which it is used? Does it generate very large force? No. It vibrates very quickly and splits up concrete into smaller chunks. This is because of brittle nature of concrete and low fatigue value.

But steel is not brittle, it is ductile. It can sustain such oscillations and has higher fatigue strength. I am not saying that when train passes through the bridge, it generates very high forces, no..!! Concept of fatigue is completely different then the concept of non-linearity.

Take a steel wire and repetitively bend it back and forth you will notice that the application of force applied by your hand is reduced drastically after certain cycles. This is called fatigue. It is”Stamina" of material as how long can it survive in this endurance. Steel can take many more cyclic loading as compared to concrete.

When a train passes over a bridge deck, then the deck vibrates up and down. This vibration demands endurance. Thus steel is preferred over concrete in case of railway bridges.

Thanks in Advance.
HARSHAL S KHODE
TECHNICAL