Wood the building material
The oldest building material, timber has not lost its popularity over years. There are two basic types of wood distinguished – hard (oak, maple, nut tree. etc.) and soft wood (pine, fur, cypress, sequoia, etc.) The former species lends itself to joinery and interior finish, while the latter type is typically employed in building construction. For both indoor and outdoor work, it has become increasingly popular to use glued laminated timber, since its load-bearing strength and dimensional stability is substantially higher than those of sawn wood. Lamination thickness may range from several centimeters to 3 mm. Popular in contemporary architecture, glued laminated timber is used to manufacture elements of various shape – be it straight-line or curvilinear.
Strength of timber is determined by its layering. Compression strength is maximal when parallel to the grain, whereas shear strength is the highest when perpendicular to the grain. For oak, the limiting crushing strength parallel to the grain is 52 Mpa, while its limiting shear strength parallel to the grain is 14 Mpa. Seeking to determine the allowable stress, the above-mentioned values are multiplied by the coefficient accounting for the humidity level, size, defects, duration of the load, slope of grain etc. For laminated beams the longitudinal shear strength is most important, because shear strength parallel to the grain is not high. Tensile strength is almost three times as high as the compression strength.
To ensure high durability of timber, it must be protected from rot and timber-worms. To avoid these problems, antiseptic impregnation is necessary. It can be provided either by the processing company or applied right at the building site. Industrial impregnation is of a higher quality, since in this case high pressure can be applied, which is hardly possible if impregnating the wood at the building site. To protect wood from timber worms, it is treaded by special chemicals called insecticides.
Since dry wood is highly combustive, special measures should be taken to prevent its ignition. Specialists recommend tocover wooden structures with fireproofing materials.