Question

WHY ARE THE BRIDGE DECLARED UNSAFE AFTER A LONG USE?

Answer 1

If the bridge is used for a long time, dueto alternate cycles of stress and strain the bridge gradually loses its elastic
property and finally reaches to a condition called elastic fatigue. Hence, at
this stage, the strain produced for a given stress will be very large and
ultimately the bridge may collapse. Hence, bridges are declared unsafe after a
long use.