Bio-inspired cross-laminated timber for protective structural applications

Abstract

Major blast events have occurred annually in several regions around the world. Accordingly, building codes, design standards and structural design recommendations are of paramount importance to protect occupants and property against unpredictable blast events. Cross-laminated timber (CLT) has recently emerged as a sustainable and lightweight engineered wood product. CLT offers several advantages as a construction material, in terms of both mechanical properties and environmental protection, including a high stiffness-to-weight ratio, a high two-way stiffness, and a low embodied carbon footprint. The increasing use of CLT in structural members combined with emerging threats highlight the importance of improving its resilience to blast loads. The study on the performance of CLT under blast loadings is significant to protect important structural elements and improve their resilience to blast loads. CLT possesses a lamellar structure, similar to that of marine seashells such as conch shells. A conch shell is primarily composed of brittle minerals (over 99% aragonite) but boasts a high fracture toughness due to its unique lamellar structure. By taking inspiration from the striking resemblance between the lamellar structure of the conch shell and CLT, this research aims to develop an innovative bioinspired CLT structure with superior resilience to blast loadings. Specifically, three main research areas are reviewed, namely blast loading, bio-inspired armour systems and cross-laminated timber. A comprehensive review is conducted on these topics to highlight the significance of protective structures against blast loading, the toughening mechanisms of biological armour systems, and the need for enhancing the performance of CLT under blast loadings. The review emphasises the lack of studies on the behaviour of CLT under blast loadings to improve its toughness and resilience in an explosion. Moreover, a striking resemblance between CLT and biological structures such as conch shell offers innovative solutions for increasing the toughness of CLT through bio-mimicking techniques. With this knowledge, the feasibility of mimicking the micro architecture of the conch shell on a larger scale to enhance the toughness of conch-like CLT is investigated. Programable 3D printing instructions were used to manipulate the 3D printer to develop tough conch-like prototypes. The prototypes were tested under single-edge notched tension to investigate their fracture behaviour. Then, a numerical model was developed and validated using these experimental data and an analytical solution. The model employed to examine the toughening mechanisms in the innovative proof of concept conch-like structure. A parametric study was also conducted to investigate the effect of different parameters on the toughening behaviour of the conch-like prototypes. A finite element (FE) model was proposed to simulate the behaviour of CLT under both quasi-static and dynamic loadings. The FE model was validated using experimental results and subsequently employed to simulate the bio-inspired CLT panel under both quasi-static and blast loads. An analytical solution was also proposed to capture the behaviour of CLT panels under blast loadings to validate the FE model. This validated FE model was used to conduct a numerical study on the performance of bio-inspired CLT under blast loading. In this study, the lamellar arrangement in the conch shell structure was mimicked to improve the toughness of a conch inspired CLT panel subjected to blast loadings. Several key parameters from the conch shell were also mimicked to enhance the toughness of CLT panels, namely the lamellar arrangement and the interlocking mechanisms. These bioinspired CLT panels were investigated by conducting numerical simulations of four-point bending tests. As such, several design recommendations were provided to enhance the performance of the conch-inspired CLT including changing the cross-section of timber planks in the middle layer of a CLT panel, introducing carbon fibre composite layers for ductility improvement, using pins to enhance interlocking mechanisms and adjusting the mechanical properties of the bonding adhesive. The bioinspired CLT panel was shown to exhibit several performance benefits over its benchmark counterpart, namely increased stiffness, strength and toughness. Finally, the conclusions of this research project and directions for future work are also provided.