Development on a CFRP reinforcement method for tmber bearing property loaded perpendicular to the grain

Abstract

In recent years, there is a trend of wooden construction of non-residential building. We are also developing projects with industry-university collaboration, fusing CFRP and timber, and developing to realize better buildings. Timber is an anisotropic material. The grain direction has sufficient mechanical performances as a building structural materials, but the mechanical performances in the direction perpendicular to the grain is never sufficient as a building structural material. In buildings, members of shaft material are combined at right angles to assemble a rectangular parallelepiped structure with a space inside. For this reason, a force flow in the grain perpendicular direction always occurs locally at the joint portion between the members. In non-residential construction, it may be difficult to process the force flow in the direction perpendicular to the grain. How to improve the bearing performance in the direction perpendicular to the grain, which is a weak point of wooden buildings, is considered to be one of the key technologies for wooden non-residential buildings including middle- and high-rise buildings. There are only a few studies on how to prevent snap-in or improve bearing performance, and at the practical design level, processing is carried out by increasing the bearing stress areas. Therefore, in this research, we proposed a method of laminating and bonding carbon fiber reinforced plastic (CFRP) on the bearing pressure surface of wood by adhesive and reported verification experiments of its reinforcing effect. In addition, this reinforcement method is a technology that can be applied directly to AFRW (Advanced Fiber Reinforced Wood) reinforced with high performance fiber reinforced plastic that we are separately developing. We demonstrated the effectiveness of the reinforcement effect by experiments with various parameters set. We can grasp the trend of six conditions of thickness of wood, length of wood, length of pressure plate, thickness of reinforcing CFRP, length of CFRP for reinforcement, adhesion between CFRP for reinforcement and wood, test parameters were set. The following findings were obtained from the experimental results and their examinations. 1) There was a large reinforcement effect on bearing yield strength, about 2 times when the pressure plate length was 100 mm, and about 4 times reinforcement effect when the bearing pressure plate length was 30 mm. 2) When the thickness of the CFRP was 7 mm, there was a reinforcement effect with a bearing stiffness of about 1.2 times and ultimate strength of about 1.5 times. 3) When the bearing pressure area is small, a particularly large reinforcing effect can be expected. 4) By using the concept of effective penetration length, the tendency of wooden bearing performance reinforced with CFRP by the existing AIJs formula was roughly caught. Therefore, as a reinforcement mechanism, CFRP increases apparently effective bearing pressure area, it was thought that it was leading to an improvement.