Performance of CFRP-bolted timber joints with slotted-in corrugated steel plates

There are various shaped sections of slotted-in steel plates and timber grooves among the bolted timber joints with slotted-in steel plates to satisfy the design and assembly criteria in practical engineering. The different shapes affect the performance but have not been widely researched. To visualize the effect of shaped sections on the joints and provide some experience for targeting improving the ductility, we performed monotonic loading tests parallel to the grain on 16 sets of the proposed end U-shaped carbon fiber reinforced plastics (CFRP)-bolted timber joints with slotted-in corrugated steel plates. The effects of the wavelength, wave height, wave angle, timber thickness, number of CFRP layers, and interaction between the parameters were mainly considered. The results showed that the joints were susceptible to failure as a result of a number of manifestations, including shear damage, pressure damage, opening-mode cleavage in the grain direction (TL cleavage), CFRP cleavage, etc. Similarly, the joints had multiple combinations of yielding deformation modes of bolts, which included IS, IS & IIIS, IIIS, IIIS & IV, and V. The load-displacement curve showed that the joints mainly undergo the elastic stage, the fracture failure transition stage, and the fracture failure stage without an obvious yield stage. According to the experimental results, an orthogonal parametric analysis of the mechanical properties was conducted and the degree and pattern of each parameter were obtained. Among them, each parameter affected the elastic stiffness relatively less; wave height and wave angle had relatively significant influences on the ultimate strength and ductility, and the ultimate strength fluctuated with the increasing wave height, but negatively correlated with wave angle, while the ductility was negatively correlated with both. Additionally, a strength formula was derived by theoretical analysis, and a good agreement was indicated by the average ratio of 1.03 between the theoretical and experimental results. This study contributes to the understanding of the effect of shaped slotted-in steel plates on the mechanical behavior of bolted timber joints with slotted-in steel plates and provides some theoretical and experience basis for the reinforcement. However, this study is mainly focused on spruce and slotted-in corrugated steel plates, which still need to be adequately investigated for other tree species and cross-sectional forms, especially the fracture characteristics. In addition, the group effect of bolted timber joints is more significant, which needs to be specifically studied for the design in engineering applications.