according to the connection mode and cross-sectional shape, wood structures can be divided into log or square wood structures connected by teeth, plate structures connected by split rings, toothed plates or nails, and glued wood structures.
the structure of log or square wood structure with teeth connection is mainly made by hand. Simple processing, the earliest development and the widest application. This structure is also the most widely used in China. In the process of drying, logs or square timber with pith core often crack along the grain. When the cracks coincide with the shear surface of the lower chord connection of the truss, the safety of the wood structure will be reduced, and even damage will be caused. Therefore, when using logs or square timber structures, reliable measures should be taken to minimize the adverse effects of cracks on the structure. Logs and squares have large cross sections, and drying is time-consuming. Therefore, only semi-dry wood with an average moisture content of not more than 25% inside and outside the cross section can be used for production. When the semi-dry wood is gradually dried to balance with the relative humidity in the air after installation, it will produce horizontal grain shrinkage, and the horizontal grain or twill produced at the joint will be deformed under pressure, and then due to the deviation of manual operation of tooth connection, the log or square wood structure will be deformed greatly. In addition to cracking, the lower chord of logs or square wood trusses is often difficult to choose wood that meets the material standards of tensile members because of the low quality of the wood supplied. In order to ensure the safety and reliability of logs or timber structures, steel wood truss with steel as bottom chord and tie rod is widely used in China. To ensure the safety and reliability of the structure, and to some extent, improve the stiffness of the structure and reduce the deformation.
The plate structure connected by split ring, toothed plate or nail is composed of wooden plates with a thickness of less than 1cm. The thickness of the board is small, which can be dried in a short time, and the deformation of the structure is small, and the board has no complete annual rings. The warping caused by the inconsistency of tangential and radial shrinkage rates during drying can be controlled by pressurizing. The internal stress caused by uneven drying is very small, even if cracks occur, the safety of the structure will not be affected because of the slight degree of cracking.
The split ring of plate structure connected by split ring can transfer large internal force, which can be used for joint connection as well as joint connection; The cracked ring can be produced in a standardized way, and the ring groove can be dug by machines, which can make the production of wood structure enter industrial production. The split ring is supported by the ring groove and connected by wood shear, and its safety is controlled by the shear strength of brittle wood. The split ring is hidden after installation, so it is not easy to check. Therefore, it is gradually replaced by the toothed plate.
The toothed plate punched from the plate structure connected with toothed plate is directly pressed into the wood by an oil press, which is simple to manufacture. Compared with the split ring connection, it has higher tightness, reduces the deformation of the structure and is convenient to check. The toothed plate disperses the load and transmits force through a large number of teeth, which has good toughness and is more reliable than the split ring connection. In foreign countries, toothed plates are often used to connect truss joints and joints.
The plate structures connected by nails are mostly manufactured in the construction site. Due to the convenience of processing, they can be made into reasonable structural forms such as arc trusses, which are widely used in the Soviet Union. China has been used for large-span roof structures such as gymnasiums and warehouses. Because of the large deformation of nail connection in the later stage, its application is limited to some extent.
Glued wood structure includes laminated glued structure and plywood structure. Glued wood structure can make better use of the advantages of wood and overcome its disadvantages, making the application of wood in the structure more reasonable, so it has been greatly developed in some technologically developed countries and has become the main form of wood structure. Mostly used in long-span houses. Glued wood domes with diameters of 153 meters, 162 meters and 28 meters have been built in the United States. In addition, the wood is cut into 3-1 mm thick veneers, and the wood grains are laminated in parallel and hot-pressed to form 3-5 mm thick plates, which can be used to make various components or structures. The advent of dense-layer glued wood makes the application of glued wood structure reach a new height. For example, the 122-meter-span dense-layer glued wooden tube arch built in 1976 is used for the roof of the football field of Idaho State University in the United States. The upper and lower flanges are made of dense-layer glued wood with a thickness of 45 mm glued by 16 layers of veneers. The picture shows the cylinder arch being hoisted.
the wood structure connected by bolt-ball joints is a new type of wood structure proposed in 21. It is characterized by hybridizing wood structure with steel structure, using wood as the main material and steel structure with bolt-ball joints as the connection, and forming a spatial hinged bar system through hinging, thus expanding the application field of wood structure from traditional houses to long-span spatial structures. This connection technology of wood structure with bolted ball joints was put forward by civil aviation university of china, and was granted the invention patent by the Patent Office of China Intellectual Property Office in 212 (authorization number ZL21157461.X), which is the latest achievement in the field of wood structure research.
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