Not all bridges will have trusses. A girder is a long slab used as the roadway of the bridge. The girder usually rests on the pier of the bridge. MASS Mass is defined as the amount of matter in an object. Mass and weight are two different things.
Weight is the force of an object due to the earth s gravitational pull.
Weight changes as the elevation gets higher because the object gets farther away from earth. Mass however does not change, no matter where you are, because it measures the amount of matter in an object. Compression is the force that s acts to shorten or compress the object it is acting on. For example when you lay thin slab of wood across two chairs and then add force, the bridge will bend causing it to shorten in length. Tension is the force which lengthens or expands what it s acting on.