Question

Why is one end of a steel girder in a bridge kept on rollers instead of fixing it in pillar?

Answer 1

Steel girders are used for constructing bridge.
One end of girder is fixed in concrete, but the other end is not fixed into concrete. It is supported on rollers. This is because when temperature increases in summer, the steel girder in a bridge expands and the rollers slide to allow the expansion otherwise the bridge may break.