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A structural beam is a component used in construction to add strength to any structure or design. Manufactured of steel, concrete or wood, the structural beam is typically used to span an open element of a structure, as well as to give support underneath a very heavy component of a structure. In iron work, the steel I beam is the most common type of beam used, while wooden beams are typically used in home construction. Concrete structural beam manufacture often involves a steel I beam being encased in concrete for use in building bridges, buildings and other concrete structures. Other beam styles are made up of C channel, angle iron and round steel pipe.
The use of a structural beam is typically applied to large, open expanses, such as over large doorways and windows or openings from one room to another in a family home. It is also common to use a structural beam to divide the floor above a basement or crawl space. The use of the beam provides a solid structural component on which to place the inner end of the floor joists to prevent bouncing or sagging of the finished floor. This type of structural beam is typically manufactured of steel I beam, however, manufactured wooden beams are becoming more popular.
The basic I shape is commonly used not only in the manufacture of the steel I beam, it is also the common shape of the manufactured wooden beam. The I shape provides superior strength against bending when used in horizontal applications. The I beam is also used in vertical applications, such as pillars or pilings. The typical structural beam is installed in a flat and level position, however, some beams used in the building of bridges as well as reinforcing inside of concrete road supports are typically installed pre-arched or pre-stressed.
A pre-stressed beam will allow the beam to provide increased support for heavier loads. Depending on design, a round, steel pipe will provide greater strength than a similarly-sized angle iron or C channel, but an I beam properly placed will provide superior strength when placed under a similar load. The I type structural beam is preferred in applications where only a vertical force is pushing down on the beam, however, in applications that might include not only downward forces but back and forth forces as well, the I type structural beam could allow shifting of the materials in the building.
@umbra21 - Unfortunately that's somewhat of a myth. While that particular building that you're thinking of does have structural beams of oak wood supporting the roof, they were simply cut from an ordinary forest, grown for the purpose of providing wood, but not specifically for that particular hall.
Apparently the best way of growing a forest for wood in England is to have a mixed bag of different trees which come of age at different times, including oaks. While the others might be cut and replaced, the oaks are left until they come of age at about 150 years.
Oxford happened to have such trees around when they needed to replace the ceiling, but they are just there for general purposes, not for that particular roof, unfortunately.
It's still a good example of looking ahead though.
I once read this amazing story about the structural beams they used in a particular hall at Oxford University.
Apparently these particular beams were beginning to look a bit run down and were close to needing to be replaced. The caretaker in charge of that particular building went to ask permission to start looking for some kind of wood that would do. It would be difficult to find it, just because the originals were huge, oak beams.
And when he asked about it, he was directed to a forest of oak trees that were planted not far from the building. These, he was told, were planted years ago, specifically so that they could be harvested one day to become the new structural wood beams.
Isn't that amazing?