1.1 Maximizing the Use of Small Timber and Upcycling Low-Grade Timber
Glulam is formed by longitudinally joining or transversely splicing and gluing short timber pieces together in the length, width and thickness directions. Thus, it can be fabricated into components with custom large cross-sections and arbitrary lengths, realizing the full utilization of small-sized timber.The reticulated wood structure of the Recreation Water Park in the Asian Games Village of Beijing was constructed with Glulam components made by finger-jointed gluing of 4cm-thick wood boards, with beams measuring 30m in length, 2m in height and 4m in width. A Glulam arch bridge completed in Ehime Prefecture, Japan in 1994 has a load capacity of 20t, a total length of 2636m, a width of 8m and a span of 23m.
Before gluing, wood defects such as knots, wormholes and decay, as well as growth defects like warping and hollow cores, are removed from the raw materials, enabling the production of defect-free Glulam. Even if there are minor defects in the timber, they can be dispersed during board matching, achieving the upcycling of low-grade timber.
1.2 Easy Drying and Multifunctionality
Glulam is mainly made from short timber pieces, which allows for sufficient and uniform drying. The finished long, large-cross-section components feature consistent moisture content across all parts, and are far less prone to cracking and deformation compared with large sawn timber products.
Prior to gluing, the timber boards can be pre-treated with special processes such as anti-corrosion, fire retardant, insect and termite prevention. Compared with large-cross-section sawn timber, Glulam has a deeper and more effective penetration of chemical treatment agents, endowing the finished products with excellent anti-corrosion, flame retardant and insect-resistant properties.In addition, Glulam has low thermal conductivity, good thermal insulation, strong sound absorption, excellent acoustic performance, and moisture-regulating capacity, boasting multiple functional advantages.
1.3 High Strength and High Timber Utilization Rate
During the Glulam production process, the straightness of the wood fibers in the blank can be controlled, reducing the impact of oblique grain, disordered knot grain and other defects on the strength of wood components. The lamination of boards can follow the principle of strength-based configuration: high-grade timber species are used for the outer layers, and low-grade ones for the inner layers.Tests have proven that such a configuration makes Glulam 1.5 times stronger than solid wood. This not only improves the product strength but also fully utilizes low-grade timber, thereby increasing the overall timber utilization rate.
Glulam can be a combination of different timber species, or a mix of sawn timber graded by appearance and by mechanical properties. Both combination methods greatly enhance the production flexibility of Glulam. However, for axial load components mainly bearing axial tensile and compressive stresses, the laminates of the components are preferably made of sawn timber of the same grade.
1.4 Mechanical Performance Characteristics
Although the free lamination of Glulam can arbitrarily disperse the strength-impairing defects of sawn timber, the neutral axis of structural Glulam under bending load is not fixed (unlike solid wood beams). Instead, it changes with the increase of load: the compressed part may even extend below the central line, and the stress on each section of the tensile part is not completely the same.
Therefore, tensile strength—the primary evaluation index for the strength of structural Glulam components—requires special consideration. The outermost 10% tensile zone on the tensile side of structural Glulam bending components can be divided into two parts: the outer 5% tensile zone and the inner 5% tensile zone.For components with different thicknesses, the requirements for strength-influencing factors (such as disordered grain, knots, oblique grain, density, annual ring width, and the proportion of pith and compression wood) in the outer 5% and inner 5% tensile zones are also different.
1.5 High Design Flexibility for Product Shapes
Generally, Glulam is made by gluing 2~4cm thick small timber pieces, and can be fabricated into wood components meeting various special shape requirements, such as chord frames, arch frames, upper chord components, and curved keels and frames.The bending radius of curved Glulam can reach 150 times its thickness, providing great creative space for the design and construction of wood structure buildings.A typical example is the pagoda-shaped Nichimanri Building in Kamigyo Ward, Kyoto, Japan, which is an all-Glulam structure with 4 underground floors, 72 above-ground floors, a height of 339m and a total floor area of 5027 square meters. Its simple and elegant appearance is a design effect that is difficult to achieve with other wood product structures.
1.6 Feasibility of Continuous Mass Production
In Europe, North America, Japan and other countries, Glulam production has realized industrial continuous manufacturing, which greatly improves the production speed of various special-shaped wood components and the assembly speed of buildings.
1.7 Disadvantages
Glulam production requires specialized production equipment, advanced technology, a sound quality control system, and professional product inspectors or institutions.Compared with solid wood products, Glulam production consumes more energy in sawing, planning, gluing and other processes, resulting in a relatively higher production cost.
