Elastic buckling analysis and optimization of thin-walled bamboo-like pipe beam subjected to pure bending

In this paper, a stiffening design imitating the bamboo node is proposed for weight reduction of the long composite pipe beam subjected to bending load. The distribution of bamboo nodes can efficiently suppress the ovalization of the section, thus significantly improving the bending resistance of the bamboo. Based on this principle, ring stiffeners are proposed to be fixed to the pipe beam, making the long beam equivalent to the combination of a series of short pipes that suffered less section ovalization. A database of the optimal laminate orientations for different normalized lengths is obtained through optimizations, where the discreteness of the ply count is considered. Based on this database, weight optimizations are conducted, and the optimal designs of beams with and without stiffeners are obtained and compared. The comparison results show that the proposed bamboo-like stiffened beam not only regains a near-linear load–displacement relationship, but also reduces the weight by up to 16% under the same buckling load. In addition, it is found that for the pipe beams with radius-to-thickness ratios of more than 18, increasing the radius leads to a decrease in elastic buckling resistance when the weight remains a constant, which is opposite to the design for strength and stiffness. The model and database developed in this paper can provide a reference for weight reduction design and weight estimation for composite pipe beams.