Two different girder bridges. The top is a, while the bottom is a concrete girder bridge.

Ancestor Related,, Descendant, Carries,,,, Span range Short, Medium Material,, Movable No Design effort low required No A girder bridge is a that uses as the means of supporting its. The two most common types of modern steel girder bridge are plate and box. [ ] The term 'girder' is often used interchangeably with 'beam' in reference to bridge design. However, some authors define slightly differently from girder bridges. A girder may be made of concrete or steel.

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Many shorter bridges, especially in rural areas where they may be exposed to water overtopping and corrosion, utilize concrete box girder. The term 'girder' is typically used to refer to a steel beam.

In a beam or girder bridge, the beams themselves are the primary support for the deck, and are responsible for transferring the load down to the foundation. Material type, shape, and weight all affect how much weight a beam can hold. Due to the properties of inertia, the height of a girder is the most significant factor to affect its load capacity. Longer spans, more traffic, or wider spacing of the beams will all directly result in a deeper beam.

In and -style bridges, the girders are still the main support for the deck, but the load is transferred through the truss or arch to the foundation. These designs allow bridges to span larger distances without requiring the depth of the beam to increase beyond what is practical. However, with the inclusion of a truss or arch the bridge is no longer a true girder bridge. Contents • • • • • • History [ ] Girder bridges have existed for millennia in a variety of forms depending on resources available. The oldest types of bridges are the, and bridges, and they are still built today. These types of bridges have been built by human beings since ancient times, with the initial design being much simpler than what we enjoy today. As technology advanced the methods were improved and were based on the utilization and manipulation of rock, stone, mortar and other materials that would serve to be stronger and longer.

In, the techniques for building bridges included the driving of wooden poles to serve as the bridge columns and then filling the column space with various construction materials. The bridges constructed by Romans were at the time basic but very dependable and strong while serving a very important purpose in social life.

As the came and went, new materials with improved physical properties were utilized; and was replaced with due to steel's greater strength and larger application potential. Design [ ] All bridges consist of two main parts: the substructure, and the superstructure. The superstructure is everything from the bearing pads, up - it is what supports the loads and is the most visible part of the bridge. The substructure is the foundation, transfers loads from the superstructure to the ground. Both must work together to create a strong, long-lasting bridge. The superstructure consists of several parts: • The deck is the roadway or walkway surface. In roadway applications it is usually a poured slab, but can also be steel grid or wood plank.

The deck includes any road lanes, medians, sidewalks, or railings, and miscellaneous items like drainage and lighting. • The supporting structure consists of the steel or concrete system supporting the deck. This includes the girders themselves, diaphragms or cross-braces, and (if applicable) the truss or arch system. In a girder bridge this would include only the girders and the bracing system. The girders are the primary load support, while the bracing system both allows the girders to act together as a unit, and prevents the beams from toppling. • The job of the bearing pads is to allow the superstructure to move somewhat independently of the substructure. All materials naturally expand and contract with temperature - if a bridge were completely rigid, this would cause unnecessary stress on the structure and could lead to failure or damage.