The weight of the bridge is a dead load
In the picture above both the weight and momentum of the train represent a live load.
Click on the above picture to
learn more about the collapse of this bridge.
Forces are always pushing or pulling on structures. Five types of stress on structures are:
i.e. Garbage Truck
Compression is pushing
i.e. A sling shot.
The weight of the water jug is causing tension on the rope supporting it. It is a pulling force.
Shear strength is the ability of a material to resist being fractured by opposing forces acting of a straight line but not in the same plane, or the ability of a metal to resist being fractured by opposing forces not acting in a straight line. Think of scissors, which is easier to cut, Paper? Cardboard? Metal? Which of those would have more shear strength? The thicker the material the more shear strength it has.
Bending occurs when a load is placed on or near the center of a horizontal beam. When bending occurs, the top of the beam is in compression and the bottom in tension.
Trusses are beams (top and bottom chord) that are made of two horizontal pieces joined in the middle by a series of triangles. The shape and design of the triangles can vary. Trusses are lighter, stronger, and more cost effective than a solid beam of the same dimensions.