Study on laminated bamboo lumber-wood I shaped joist with web opening reinforced by oriented stand board plates plates

Abstract: Bamboo is considered as one of fastest-growing plants in the world, widely distributed in South America and Southeast Asia. Especially in southern China, the planting area and output of bamboo ranks first in the world. For decades, raw bamboo has been successfully used in civil construction, often in the form of beams, columns, rafters and so on. However, several problems arise in practical applications and need to be solved, such as thin-walled hollow, irregular shape, easy to crack when exposure to moisture alternation frequently. Laminated bamboo lumber (LBL) is considered as a promising green engineering material in modern bamboo construction, due to higher strength/weight ratio and more rapid renewability than common wood. Oriented strand board (OSB) is mainly made from thin wood flakes sliced from small-diameter, fast-growing trees. Due to good cost-efficiency ratio, the OSB panel has been used as webs of wood I-joist, floor sheathing, roof sheathing, and so on. An OSB webbed laminated bamboo lumber I shaped joist is introduced, which consists of four LBL flanges and OSB web. The LBL is attached to the OSB by adhesive and nails spaced at 150 mm in center. To study the capacity, deformation performance and failure mechanism of the OSB webbed bamboo I-joists with circular web opening, 42 joints with/without web opening are tested. Among them, 12 joists with web opening without strengthened, 27 joists with web opening are retrofitted by collar oriented strand board (C-OSB), two U shaped oriented strand board (TU-OSB) or U shaped oriented strand board (U-OSB) and 3 joists without opening for comparison. Results show that the effect of joists with hole diameter to web height less than 25% are negligible, no repairs are required. With the increase of ratio of the hole size to web height (d/hw), the peak load capacity and stiffness of the joists with big opening (d/hw≥50%) decrease significantly, and the joists failed in web shear failure around the opening, mainly in compression and tension failure. The cracking loads strengthened by OSB plates increases by 52.9%, the loads at allowable deflection increase by 12.1% on average, and the ultimate loads increase by 28.2%, respectively. The increase of carrying capacity is closely related to the types of OSB plates, and the C-OSB plate is the biggest. Also, the OSB plates can improve the initial stiffness, increased only by 11.5% on average. The improvement of C-OSB on mechanical performance of composite joists is most effective, TU-OSB less and U-OSB least. It is evident that the C-OSB has the greatest enhancement effectiveness on joist with opening, however, the selection of OSB plates for reinforcement should be considered comprehensively in practical applications. The C-OSB is suitable to retrofit joist with opening prior to the installation of the service pipes, while the TU-OSB and U-OSB can be used to reinforce the joist with the opening diameter less than 75% without removing the pipeline facilities. The results indicate that the OSB webbed LBL I joist has excellent mechanical performance which can be used for the bending members in bamboo structures and wood structure.