Steel in the News
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Posted by Jennifer Jernigan on December 17, 2010 at 11:32 AM.
This photo was taken in the San Angelo, Texas, girder shop of AISC Member Hirschfeld Steel Company and shows a newly fabricated 300-ft-long steel plate girder.
In normal practice, a plate girder is thought of as a bending member made up of individual steel plates and their use is very prevalent within bridge design and construction. They are normally the member of choice for situations where the available rolled shapes are not large enough to carry the intended load. Although it is possible to combine steel plates into numerous geometries, plate girders are formed with three plates, one for the web and two for the flanges to form the shape of an “I”. Since the web and flanges of the pate girder are fabricated from individual plates, they may be designed with web and flanges from the same grade of steel or from different grades. Those from different grades of steel are known as hybrid girders.
Railroad bridges have been constructed using plate girders since the late 1800s, made up from plate, angles and rivets to form the familiar shape. In today’s fabrication shops the assembly process of girders is much more efficient but still yields the same versatile product that a traditional wide-flange beam cannot achieve. These plate assemblies have limitless choices when it comes to web or flange thickness and have project-specific custom depths. Automated welding machines and heat curving allow for precise arches to be formed with the steel members. Girders can be used for shorter single-span bridges or longer multi-spans that can make up straight sections or large sweeping curves in a highway interchange.