CENTRAL BEAMS AND FOUNDATIONS
The building structure is generally based on a foundation and on central support beams. The number of support beams will vary from one or more depending on the width of the building. The central beams support the weight of the floors, up to the building’s roof, while the foundation walls support the weight on the periphery of the building and the exterior cladding. Several forces are added to the weight of the building, including snow, wind, rain and usage. The bearing capacity of the foundations and the central beams must take into consideration of all of these forces.
A central beam can be made out of wood or steel depending on the construction year and according to the specifications in the building plans. The wooden girder may consist of a single piece of solid wood or composed of an assembly of several boards of structural timber. Each beam must be supported by one or more load bearing posts, according to length of the building. The number of posts is proportional to the size of the building and they are generally spaced eight feet apart. These posts can be made of concrete, wood, stone and / or steel, and must be based on a rigid surface such as a concrete footing.
CENTRAL BEAM PROBLEMS
Several problems can alter the load capacity of the central beam, such as lack of support poles, soil compaction and degradation, including rot, nicks, insects and cracking.
Insufficient support post weight bearing capacity
The collapse of a central beam can be caused by different factors. Insufficient weight bearing capacity of the posts is one of those causes. This may be due to a lack of support posts in proportion to the length of the beam and the building, or the low bearing capacity of each post from the building’s weight. The posts can also be inadequately placed to properly support the central beam. The central beam must sometimes be made up of several solid wood parts assembled one after the other, according to length of the building. Sometimes the posts are poorly positioned and do not adequately support the extremity of a piece of wood.
The collapse of a central beam can also be caused by the subsidence of the soil under the support posts. In most of these cases, the foundation sags and the central beam tends to twist. These settlements are common in clay soils. This type of soil tends to dry up during hot dry summers or profit trees growing near the building. Once drained, clay shrinks and definitely loses some of its volume. Subsidence can also result from the soil’s low weight bearing capacity.
A central wooden beam is prone to deteriorate after a certain time. Several elements can contribute to the degradation of wood. Water and air humidity help proliferate mold and wood decay. Some insects can also damage the wood beams. The cracking of the central beam is frequent due to temperature variations and the age of the wood. Finally, human activity, such scores in the beam can greatly affect the bearing capacity of the beam. The National Building Code forbidden forbids scoring and boring openings in the central beam. Steel beams may also deteriorate due to rust. It is therefore recommended to paint the metal and maintain it regularly to preserve the beam.