Mechanical properties of bamboo-concrete composite structures with dowel-type connections

Bamboo is a novel engineering structural material, and it can be effectively applied in some specific structures of low-rise, multi-storey buildings and landscape bridges. Bamboo structures have a lot of advantages such as environmental protection, ecology, low caron, and so on. Existing studies have shown that the ordinary bamboo structures have insufficient load bearing capacity, low section stiffness and limited spanning capability as flexural members. In this paper, concrete and bamboo materials were composited to form a novel bamboo-concrete composite structure, in which the bamboo and the concrete materials were located in the lower and upper cross-section respectively, and the 2 types of materials worked together, connected by the dowel type connections. To investigate the mechanical properties of bamboo-concrete composite structures with dowel type connections, the mechanical test and theoretical analysis of bamboo-concrete composite connections and beams were carried out. Three dowel-type shear connections with identical parameters were designed and prepared for the push-out shear test. The test results showed that the dowel-type shear connections exhibited an excellent slip deformation capacity under the loading and the failure mode was the ductile failure. The load-slip curves of 3 connection specimens were quite homogeneous and consisted with 3 stages of elasticity, elasticity-plasticity and full plasticity. Based on the test results, the load-slip models that could describe the obvious features in the 3 stages of the load-slip curves were provided for the dowel-type shear connections, which could be used in the fine numerical analysis of the load-displacement curve for the dowel-type bamboo-concrete composite structures. One dowel-type bamboo-concrete composite beam and one bamboo beam were investigated by four-point bending test. The failure mode of bamboo-concrete composite beam was the bamboo fiber fracture on the bottom of the beam and no concrete crushing was found in the upper compression zone. At the later loading stage, there was a strain jump in the interface of 2 kinds of materials, and the interface slip increased from the mid-span to the both ends of the beam. The phenomena showed the characteristics of partial composite structures. Ultimate load enhanced by 89% and the load corresponding to the limiting value of deflections for beams prescribed in Chinese timber structures code of the bamboo-concrete composite beam increased by 274% compared to values for the bamboo control beam, respectively. Due to the composite effect generated by the 2 kinds of materials, the load-carrying capacity and the section stiffness of the bamboo-concrete composite beam were greatly improved. According to the test results, the equivalent stiffness method was suggested, in which slip stiffness of shear connections was considered to predict the displacement of the bamboo-concrete composite beam, and when the reduction factor of 0.8 was used for the equivalent sectional stiffness, the predicted load-displacement curves were in good agreement with the experimental curves. This study demonstrates that the bamboo-concrete composite structures have excellent flexural performance, and can be used for the flexural members in some potential landscape bridge or building structures. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.