written by: Aggeliki K.
• edited by: Lamar Stonecypher
• updated: 2/3/2014
Simple beam bridges may use wood beams, but modern beam bridges use light and strong materials. Construction of a multi-beam bridge involves the use of a bridge crane, beam clamp for holding, and other tools. Bridge load rating is done to determine the loads that can be safely carried.
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What is a Bridge?
A bridge is essentially a construction that is built to cover a road, valley, water body, or other natural obstacles to provide a route over the barrier. Several bridge designs are used that depend upon their function and the soil conditions of the site for bridge construction. A bridge is described normally by its form of construction, like beam, truss, arch, etc. A bridge may also be characterized by the construction materials used, like concrete, stone, and metal. A bridge may have different types of spans that include simple, cantilever, continuous etc.
Beam bridges can be simple and made of wood beams. Heavy beams are carried by a bridge crane using a beam clamp to hold the beams. Bridge load rating is executed to establish the loads that can be safely carried by the beam bridges. It is essential to calculate the bending moments in a beam to establish a safe design of the beam bridges.
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Characteristics of Beam Bridges - Types of Beam Bridges
Beam bridges basically consist of beam that is laid across the piers or supports. The beam should possess the strength to bear the loads that are expected to be placed on it. These loads are borne by the bridge piers. The loads cause the beam top edge to be compressed, while the lower edge is being stretched and is under tension.
Existing beam bridges are formed by girders, normally box girders, trusses or I-beams, that are supported on strong piers.
Box girders are stretched, box shaped elements that are more suitable to bear the twisting loads.
Trusses consist of one or more triangular units connected at joints or nodes.
I-beams are economical and simple to fabricate. They are simply beams with an I-shaped or H-shaped cross-section. The horizontal elements of the "I" design are flanges and the vertical is the web of the construction.
Other beam bridges may be fabricated from concrete beams that are pre-stressed. These materials possess the steel characteristics to endure loads in tension, and concrete strength to bear the compressive loads.
The beam bridge's strength is largely influenced by the distance between the piers. Therefore, the beam bridges are normally not suitable for longer length, unless several such bridges are connected with each other.
The beam bridge's span is dependent upon the beam weight and the materials strength. As the bridge material thickens, its capacity to hold the loads increases. Therefore, the span could also be increased. However, a sturdy beam may become too heavy, and sag. The beam bridges can be supported by the utilization of trusses.
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Beam Bridges Materials
With the advancement in technology, materials science has also advanced considerably. Beam bridges materials being used are strong, light, and durable. The advanced materials for bridge construction have good operational characteristics.
Such materials include reformulated concrete, composite materials that are reinforced with fiber, steel, and pre-stressed materials. Pre-stressed concrete is well suited for beam bridge construction since it can endure excessive compressive stresses. Steel rods are fixed in the concrete that can bear the tensile loads. Furthermore, pre-stressed concrete is cheaper.
The current techniques include use of finite element analysis to improve the design of beam bridges. Distribution of stresses on different bridge elements is analyzed to ensure strong beam bridges that can endure the bridge loads. The beams should be held by piers at the ends to increase the bridge load bearing capacity. Concrete, steel, or stones are normally used for the construction of piers. Since stones and non-reinforced concrete are weak in tension, they are normally used for beam bridges that are designed for lighter loads.