Fire performance assessment for the design of safe laminated bamboo structures

Abstract

The threat of global warming and the need to make the construction industry accountable for their polluting emissions and waste management has played an important role in research and development of innovative products. Recently, bamboo has gained acceptance as a valuable construction material due to its aesthetic and mechanical similarities with timber, fast growth rate, high strength to weight ratio and, noticeably, its environmentally sustainable characteristics. Bamboo products are predominantly made in Asian countries, where architects have incorporated it as an essential component in the design of modern multi-story buildings. However, existing design codes around the world prescribe bamboo structures to be a maximum of two stories high or disallow its use as main structural component altogether.Limited knowledge of the fire behaviour of bamboo is one of the main reasons that explains why the construction of bamboo mid-rise and high-rise buildings is stalled. To date, there are no methodologies that allow for performance-based fire design of laminated bamboo facilities, leaving insulation and encapsulation as the only alternatives available in codes in order to obtain acceptance by the reviewing authorities. Given this scenario, bamboo products developers need to confidently demonstrate the material’s fire properties, which is only possible by means of adequate research and testing.This research project proposes a methodology that uses a holistic approach to understand the fire behaviour of engineered bamboo products of the species Phyllostachys pubescens (Moso). A model of study was developed using the principles of performance-based design, where the evolution of a compartment fire over time is expressed as a function of the energy released. The phases of the fire (growth, fully-developed and decay) were correlated to the processes of flammability, thermal evolution (heat transfer) and self-extinguishment, which were assessed and quantified by means of laboratory testing. Samples with different bonding adhesive, density and orientation were tested to evaluate variations in their fire behaviour. Specimens were exposed to heat fluxes from 10 to 80 kW/m2 in the Cone Calorimeter to study the thermal decomposition, flammability parameters, thermal evolution and self-extinguishment of laminated bamboo. The experiments allowed to measure variables such as thermal conductivity, critical heat flux for ignition and thermal inertia, which are key to describe the evolution of a compartment fire within a laminated bamboo structure.The experimental tests included variation in sample configuration, which was used to assess the impact of lamellae orientation upon the relevant fire parameters. Experimentation yielded mixed observations. For instance, while results of critical heat flux for spread proved to be non-conclusive from a quantitative standpoint, charring rates values showed to be similar between perpendicular and parallel configurations. Results were obtained for the average of one-hour test, quasi-steady state and peak values.In addition, different types of adhesive were analysed to determine how they can have an incidence on the rate of heat release and upon the occurrence of self-extinguishment. It was noticed that samples with urea-formaldehyde as bonding adhesive showed debonding and fall-off, which prevented self-extinguishment. On the contrary, samples that used phenol-formaldehyde did not show debonding and self-extinguishment occurred at heat fluxes of40 kW/m2 or lower. This phenomenon was not identified for any kind of sample tested over that magnitude. When tested at 40 kW/m2, mass loss rate for self-extinguishment of laminated bamboo proved to be very similar to that of timber.Furthermore, the analysis of the bench-scale testing results presented in this work was compared with outcomes from large-scale compartment tests in order to contextualise the behaviour of laminated bamboo under fire conditions. Different fire scenarios were studied to assess to what extent the presence of laminated bamboo can alter the fire dynamics of a non-combustible compartment. This exercised allowed to conclude that, as laminated bamboo is a composite material fabricated by joining together narrow strips using a bonding agent, lamellae fall-off is a critical failure mode that directly affects the time-energy released curve of a compartment fire.In summary, the main objective of this research project is to detail the fundamental principles that describe the fire behaviour of laminated bamboo. This is done by framing the study in four areas: general thermal characterisation (provides the basic material fire properties), flammability parameters (determines ignition and growth), thermal evolution (describes size and duration) and self-extinguishment (establishes the conditions for decay). As a consequence, this work provides unprecedented data that creates the groundwork towards developing full understanding of the fire behaviour of laminated bamboo, which can eventually lead to the definition of a relevant design fire that can be adapted into design codes. Further, this thesis constitutes a methodological tool that facilitates developing performance-based design of structures made from laminated bamboo under fire conditions, which can be used as a benchmark for the study of other kinds of engineered bamboo products.