Wood Structural Elements

structural elements made of wood that are used in construction. Wood structural elements in the form of rod systems may have metal, usually extended elements (bottom chord, braces, tie beams in arches). Wood structural elements may be supporting or protecting, depending on their use. They are distinguished by type, namely, beams, trusses, arches, frames, vaults, and shells and by the means used to join the elements, such as nails, pegs, keys, buttressing, and glue.

Wood structural elements are one of the oldest types of structural elements used in construction. The main advantages of wood structural elements are the possibility of using local materials, small dimensions, and transportability. In modern construction there are two basic types of wood structural elements: those constructed without glue, with parts made of bars and boards and having pliable joints with pegs or nails (for example, metal and wood triangular segmented trusses and compound beams) and bonded structural elements composed of glued wood elements manufactured at plants. The most efficient wood structural elements are the bonded ones, which have several important advantages. They make it possible to obtain monolithic elements of virtually any size and with any form of cross section that have a high carrying capacity, durability, and refractoriness. Another advantage is that the material, which consists of various kinds of small-size lumber, can be used very efficiently. Bonded wood structural elements are best used as roofing and coating for production, agricultural, and public buildings (sports, exhibition) and for some industrial buildings and installations (including those with a chemically corrosive environment). They are also used in the construction of cooling towers, shaft installations, bridges, trestles, and buildings and installations in the Far North and in remote and heavily forested regions, as well as in earthquake-proof construction.

The plant method of production ensures the high quality of the bonded parts and reduces their cost. Bonded structural elements are made mainly from the lumber of coniferous trees, sometimes using construction plywood (bonded with water-resistant glue, such as phenol-formaldehyde glue). Plywood supporting wood structural elements are made in the form of beams with a plywood wall, of frames and arches with a box transverse cross section, or of protective structural elements—panels with a plywood sheathing and wooden supporting longitudinal ribs or a middle layer made of foam plastic. The dimensions of the panels are usually 1.2-1.6 x 6 m. To increase their rigidity, bonded wood structural elements may be reinforced; the reinforcement is glued to longitudinal canals previously made in the wood. The parts of wood structural elements that are designed for external use (the span structures of bridges, cooling towers, masts, towers) are treated with protective antiseptics. The finished wood structural elements used in covering buildings are treated with waterproof or fireproof paint and varnish. In the USSR, the main type of enterprise producing bonded wood structural elements is the specialized shop of a woodworking combine; the annual production capacity of a shop ranges from 6,000 to 15,000 cu m of finished structural components (1970). The five-year plan for the development of the national economy of the USSR for 1971-75 calls for more extensive use of bonded wood structural elements in construction.