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A girder is a structural support which is designed to carry transverse loads, and to transfer those loads to vertical supports such as columns. Girders are utilized in the construction of buildings, bridges, and some types of heavy equipment, and they come in a range of styles. They are usually designed by engineers who also determine their placement, aiming for maximum structural stability and efficiency. wiseGEEK readers who frequently pass by or over a bridge have probably seen girders in action, since girder bridges are the most common type of bridge design.
If all of the weight of a structure was carried vertically, the structure would be at great risk of collapsing or warping. Girders are designed to help distribute weight evenly. They reduce the development of hot spots and pressure points when they are installed properly, while adding crosswise reinforcement which makes structures safer and more stable. Girders can connect with columns, rafters, and beams in a structure.
The simplest girder is simply a block of timber or concrete to which other structural supports can be bolted. Girders can also be made from metal which has been molded or forged, with I, H, and Z shapes being utilized in various kinds of construction along with tubular or box girders, which have a hollow core. An engineer can also opt to make a girder by welding several pieces together to create a truss in which large horizontal pieces are joined by smaller vertical ones which create a series of triangles to distribute weight and pressure.
Girder design can get very tricky, especially with custom or complex structures. Basic buildings and bridges may be made with girders which have already been manufactured, saving costs, but for big projects, it is often necessary to fabricate girders. The fabrication process must be carefully monitored to ensure that the girders adhere to building standards, for safety and structural integrity, and the girders are usually inspected after installation to confirm that they were installed properly and to check for signs of safety issues.
The layout of girders can sometimes create use limitations for a structure. Because the integrity of a structure is paramount, girders take priority over internal walls and spaces, and sometimes compromises must be made to accommodate girders. Some designers specialize in developing innovative and creative layouts in which the girders do not hamper the utility of the space, or in which girders are used as decorative elements in addition to structural ones.
@letshearit - I agree that the big metal girders in skyscrapers are what most people think of, but they can found in more places than just a tall building. Girder usage is common in bridges as the article noted - you might not work in a tall building, but chances are good that you drive over girders every day!
Something interesting that you might have learned in science class is that metals expand and contract by a particularly large amount in hot and cold weather, so engineers have to construct bridges in a way that gives the girders room to change size without buckling.
There are a number of new skyscrapers going up around the industrial area of the city that I work in, and you can often see a girder being lifted up into place by a crane. Girder style seems to be pretty consistent among those big commercial buildings, those long metal reddish-colored ones are what most people usually think of when a girder is mentioned to them.
For myself, I think of a famous old Depression-era photo of construction workers sitting on a girder eating lunch, even though it's something I've never actually seen workers do in person. I imagine safety standards and construction techniques have changed since that time, does anyone know?
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