What forces act on a bridge?
A bridge looks pretty placid and static from a distance, but if you stand on it, you may feel the movements as the traffic passes. In time of flood you may feel vibration from the water flow. Many kinds of forces act on bridges. A bridge is often at its most vulnerable when it is incomplete. During construction, some parts may not be connected in the same way as in the complete structure, and they may exert greater forces than in the final design. Parts may be free to swing in the wind.
