Why there is a gap between the railway tracks or in the bridge segments?
If there is no gap → When the material (railway track, concrete, steel, etc.) is heated it expands and when it is cooled it contracts. So the railway track or the bridge in summer season will be heated and so it tries to expand. So the track or the bridge will try to bend in different directions if there is no gap. But the track or the bridge in winter season will be cooled and so it tries to contracts. So the track or the bridge will try to straighten or separate themselves apart by cracking. If there is gap → When the railway track or the bridge tries to expand the gap is filled. When the railway track or the bridge tries to contract the gap is increased some more. Thus the railway track or the bridge stays in their original direction.
When a material is heated it expands and when it is cooled it contracts. When it is summer season the railway track or bridge is heated and so it expands. So the length of the railway track or bridge increases. When it is winter season the railway track or the bridge is cooled and so it contracts. So the length of the railway track or bridge decreases. See the figure below.
Can you imagine if a long railway track is expanded and contracted for a long length on summer and winter seasons alternatively what will happen? See below.
When there is no gap in the Railway Track
From the figure we can understand that if the railway track tries to expand or contract the track’s width will not be even. The railway track will try to change its position in different directions. So the train’s wheel will slip from the track and so the derailing of the train will occur.
If you consider the bridge, the complete bridge will try to change its direction and so the bridge may be cracked or knocked down.
To avoid these dangerous results, the railway track or the bridge is separated into segments and they are joined by allowing little gaps between them.
Bridge Gap
Railway Track gap
If there are little gaps between them then if the length is increased the gap closed and if the length is decreased the gap is increased a little. Thus it compensates the heating and cooling of the seasons. See the figure below.
When there is gap in the Railway Track
Summary:
If there is no gap →
When the material (railway track, concrete, steel, etc.) is heated it expands and when it is cooled it contracts. So the railway track or the bridge in summer season will be heated and so it tries to expand. So the track or the bridge will try to bend in different directions. But the track or the bridge in winter season will be cooled and so it tries to contracts. So the track or the bridge will try to straighten or separate themselves apart by cracking.
If there is gap →
When the railway track or the bridge tries to expand the gap is filled. When the railway track or the bridge tries to contract the gap is increased some more. Thus the railway track or the bridge stays in their original position without changing it's own way or direction.
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