WHY RAILWAY BRIDGES ARE MADE UP OF STEEL RATHER THAN CONCRETE ??

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

Bridge can be made up of 2 materials i.e steel or concrete.Concrete is brittle in nature as a result small vibrations may break it.For example you might have seen jack hammer.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. As a result it can absorb high vibrations and sustain.