Why do they put flexible connections in the road on a bridge? put it into five complete sentences

Flexible connections are used because bridges sway. If there were steel or non flexible connections, the road would crumble. Another reason is steel would expand or contract in the heat or cold. If the steel expanded or contracted, then the road would be weak. And since the people on the road don't want it to crumble, the architect put flexible connections instead of hard ones.

B. a graduated substance