Lec-1 Introduction-I. The Dam Site. A typical dam is a wall of solid material built across a river to block the flow of the river thus storing water in the lake that will form upstream of the dam as water continues to flow from the river upstream of the dam. The main purpose of most dams is to create a permanent reservoir of water for use at a later time. The dam must be watertight (ie impermeable or impervious to water) so that water does not leak out of the dam and escape downstream. An essential part of a dam is therefore the "impermeable membrane", ie the watertight part of the dam that prevents water leaking out. As we shall see later, it is not necessary that the entire dam wall be watertight. The natural earth or rock on which the dam is built (ie the dam foundation) must also be watertight as must the river valley in which the storage reservoir forms.
If these natural areas (dam foundation and storage area) are not watertight then water could leak out of the reservoir even if the dam itself is watertight. Bridge Basics - A Spotter's Guide to Bridge Design. Bridge Basics Because of the wide range of structural possibilities, this Spotter's Guide shows only the most common fixed (non-movable) bridge types. Other types are listed in the Bridge Terminology page. The drawings are not to scale. Additional related info is found on the other Terminology pages which are linked to the left. The four main factors are used in describing a bridge. Span (simple, continuous, cantilever), material (stone, concrete, metal, etc.), placement of the travel surface in relation to the structure (deck, pony, through), form (beam, arch, truss, etc.).
The three basic types of spans are shown below. Examples of the three common travel surface configurations are shown in the Truss type drawings below. Beam and Girder types Simple deck beam bridges are usually metal or reinforced concrete. One method of increasing a girder's load capacity while minimizing its web depth is to add haunches at the supported ends. Arch types There are several ways to classify arch bridges.