The Basics In Building A Bridge
When building a bridge, we should consider all the possible types we can make. There are different spans, trusses, and girders we can incorporate into our design, and each has their own strengths and weakness, some more than others. The first step before considering designs, however, should be to identify what the bridge will have to hold, or the use of the bridge, and in what circumstances.
The four principal terms employed when defining a normal bridge are span, material, the position of the roadway regarding the construction of the bridge, and form. Each term has subtopics that leave us many options with the bridge.
The first term is span; there are three main types of spans, and these can be made with many different things. The three things are beams, girders, or trusses. When dealing with an arched bridge, a continuos hinged or simple hinged span will work the best. A span is the distance between the legs of the bridge. Spans are horizontal and when the term span is used, it could also be relating back to the construction of the bridge itself.
The second main part of a bridge is a truss. The truss is the roadway of the bridge. The main types of trusses are deck, pony, and through trusses. A deck truss is used when the bridge is a main street, with traffic and many cars. The pony truss is employed if the builder wants the traffic to travel in the middle of two superstructures. Pony trusses, however, are not crossed like and “X” on the top of the bridge. The last truss is the through truss. With this truss, the traffic would travel underneath the superstructure. Unlike pony trusses, through trusses use cross-bracing.
In a bridge, the girder is the framework made to hold up the weight. What makes horizontal girders so strong is their stiffness. With this they are able to brace the vertical weight on the bridge. A girder is usually very thick, and is sometimes made up of more than one beam.
To strengthen the girder, haunches can be involved in its planning. In a haunched girders are not straight, but rather arched towards the end of the bridge. The constraint of these bridges is their size. On most bridges, smaller beams are used, because they are easier to move around. With this, the smaller pieces have to be joined together, usually by splice plates.
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