Experiments and design of concrete-filled steel tubes with timber chips under axial compression

This study includes experimental and analytical sections, which discuss the structural response of concrete-filled steel tubes (CFST). In the experimental section, the authors investigate the CFST columns with different proportions of recycled redwood timber chips embedded inside the concrete. An analytical investigation was also carried out in this paper, which puts together equations proposed by four design codes of Eurocode-4, AISC-LRFD, the Chinese code of DL/T, and ACI to predict the axial capacity. The idea of embedment of timber inside aggregates was inspired due to the significant compression strength of timber compared to concrete. In addition, environmental and sustainability concerns advocate substituting conventional aggregates with recycled natural material. In this study, 18 stub columns (in two groups with different steel tubes) were tested under pure axial compression with various compositions of the aggregates. The failure, capacity, weight, and energy absorption of the specimens were studied to evaluate the effect of the weight reduction as a result of timber embedment into the concrete. The results showed that embedding waste timber inside concrete is promising in upcycling wood residue into a commercially viable product. An equation is developed in this paper that takes into account the effect of confinement based on the assumptions that have been made in the literature. 100 test samples were extracted from the literature with a relatively wide range of geometry and material features, and then the capacity of these columns was calculated by the four standards and the proposed equation in this study. The results of the comparisons were analysed and it was found that the proposed equation predicts the capacity accurately.