Fire analysis of load-bearing bamboo structures

Abstract

The remarkable high strength-to-weight ratio of bamboo and the recent innovations and development of laminated bamboo products has enabled the potential for new larger and taller structural bamboo applications. However, there is little understanding of the behaviour and performance of bamboo structures during and after a fire. To date, bamboo has been used widely in low-rise constructions where structural integrity during and after a fire does not pose a risk to the life safety of occupants, fire service intervention, and significant impact to property protection or business continuity. Nevertheless, a comprehensive understanding of the structural fire performance is crucial if bamboo is to be widely used in the construction of mid- and high-rise load-bearing structures.An extensive literature review on the fire performance of bamboo structures shown herein identifies that novel fire testing methods were needed to investigate the mechanical response of bamboo, primarily to study the reduction in the strength and stiffness at elevated temperatures. Past research outcomes have evidenced the need for constitutive stress-strain models to describe the mechanical behaviour of bamboo at elevated temperatures, as well as numerical models to predict the response of the bamboo load-bearing members during and after a fire.Several small and bench-scale experimental studies were conducted to understand the reduction in the mechanical properties of bamboo at elevated temperatures. Compressive tests were performed for round and laminated bamboo for test samples at temperatures between ambient and 250oC. Another set of experiments was performed in laminated bamboo samples to see the response in compression after heating and cooling. Round bamboo strips were tested in tension to understand the reduction in the tensile strength at elevated temperatures. The modulus of elasticity was obtained for all bench-scale experiments to quantify the reduction in stiffness due to high temperature. A dynamic mechanical analysis of bamboo strips was carried out to investigate the decrease in the modulus of elasticity at elevated temperatures, and to compare this against the results of bench-scale tests to analyse the effect of a different test set-up and heat transfer scenario.With the experimental results of the reduction of the compressive and tensile strength of bamboo, as well as the modulus of elasticity, constitutive stress-strain models were proposed to correlate the stress-and strain relationship at elevated temperatures. Equations for the reduction factors of strength and modulus of elasticity were presented, as well as stress-strain curves. The linear elastic behaviour of bamboo under tension and compression, and the elastoplastic behaviour under compression were analysed to quantify the effects of elevated temperatures.Another series of experiments were conducted to investigate the performance of laminated bamboo beams exposed to fire. The bamboo beams were loaded at different stress-levels whilst exposed to a constant indecent heat flux. The beams were fully instrumented to measure the loss of cross-section, the strain profiles, and the deflections at the mid-span during the heating exposure. Detailed results of the experimental tests showing the effects of simultaneous loading and heating in laminated bamboo beams are presented in this document.Finally, a numerical model combining the thermal performance, and the mechanical behaviour of bamboo at elevated temperatures was developed to predict the stress-strain profiles, the deflection, and the bending capacity of bamboo beams during a fire. The results of the numerical model were compared against the results obtained from the experimental tests, and the model showed a good agreement with the experimental results. The proposed framework shows that structural analysis can be carried out if heat transfer analysis and constitutive stress-strain models are available to predict the thermo-mechanical response of laminated bamboo beams.Findings from this work provide a good understanding of the reduction on the strength and elasticity of bamboo at elevated temperatures. These results will enable predictions to be made for the bending capacity of bamboo beams during a fire, and they will constitute the basis for designing fire-safe bamboo structures.