Development of bamboo-timber composite beams

The construction industry is among the top sectors that contribute a significant amount of greenhouse gases globally. Among all the contributing aspects, building materials play a critical role in shaping the sector's carbon footprint. In contrast to traditional materials with high energy consumption and pollution, bio-based materials, relying on their low carbon emissions and strong carbon sequestration capacity, have emerged as a highly promising sustainable alternative. Additionally, their outstanding material and mechanical properties, such as a high strength-to-weight ratio and customisable processing flexibility have enabled them to be widely used in various areas of the building industry, including beams, columns, and floors. Among these, beams made from single-species bio-based materials have undergone massive exploration and research, and their advantages in structural performance and sustainability have been thoroughly validated and extensively acknowledged. Building upon these achievements, multi-species bio-based composites provide a new route for designing more economical, stronger, and more architecturally appealing members. Considering that the stress intensity within a structural member is not uniform, designing a composite cross-section based on the material property not only leverages the complementary strengths of different components but also effectively mitigates the risk of early fracture in the weaker components, thereby improving material utilisation, enhancing structural efficiency, and reducing overall costs. Specifically, by optimising the layout of different bio-based materials, based on their mechanical properties, such as placing materials with higher strength in higher stress zones and lower strength materials in lower stress zones, the composite structural elements can achieve higher performance at a very economical cost. Moreover, under the concept of multi-species adoption, the creation of the multi-species composite not only enhances biodiversity in resourcing construction materials but also offers a unique architectural effect with combined natural textures. Furthermore, the composite cross-section also provides an opportunity for implementing the novel prestressing technology with pure bio-based materials, to further enhance the structural strength and enable their applications in large-span and high-rise buildings. The key concept of this prestressing technology is to force laminating components with different materials and geometrical shapes together to form a straight beam, and the prestress stresses were then activated during the press release stage. To explore the feasibility of these bio-based composite concepts in real-world engineering applications, this study conducted in-depth studies on bio-based composite beams from experimental and analytical perspectives. As the first part of the study, a comprehensive investigation was conducted on the flexural performance of bio-based and bio-based composite beams through theoretical and experimental studies. Since classical Euler–Bernoulli beam theory cannot model the effect of shifting neutral axes in partially yielded regions on the deflection behaviour of the beam, an enhanced theory by incorporating piecewise constitutive relationships for bio-based and bio-based composite materials was developed to model the inelastic flexural behaviour of bio-based composite beams. Building on this foundation, an innovative pure bio-based prestress technology was developed to produce prestressed bio-based composite beams with low-cost, high-performance, efficient material utilisation, and in-situ flexibility. The feasibility, effectiveness, and industrial scalability of the proposed technology were validated through both experimental testing and theoretical analysis. Furthermore, fundamental research on bio-based material properties and their constitutive models is essential for understanding their mechanical and structural properties, as inaccurate measurement methods and inappropriate data analysis techniques can compromise the reliability of theoretical frameworks. As a result, this study investigated essential parameters that could affect the effectiveness of the proposed analytical models and the accuracy of experimental validations, including the test result-based constitutive model specifications and current test standards. Identified mistakes and shortages were corrected and supplemented through experimental and theoretical validation. In summary, these efforts lay a solid foundation for advancing future research and practical applications of multi-species bio-based composite structural systems in structural engineering.