The paper presents the use of computationally coupled thermo-pyrolysis model to determine the charring of timber elements exposed to natural fire and standard (ISO) fire. The natural fire curves are modelled with the software Ozone. Thermal model is based on the Fourier partial differential equation, while the pyrolysis model is based on the Broido-Shafizadeh kinetic scheme, where the decomposition of wood at elevated temperatures is followed by the formation of char, tar and pyrolysis gases. Case studies of wood specimen exposed to natural fire curves and standard (ISO) fire curve were carried out. Based on the decomposition of wood and formation of char, the criterion to determine charring of wood as well as the temperatures when charring starts (char front temperature) is proposed. As discovered, for the specimen exposed to natural fire curve with faster heating rate than the ISO curve, the char front temperature is higher than the one calculated for ISO curve. On the other hand, the char front temperature for the specimen subjected to natural fire with slower heating rate is lower compared to the char front temperature for the specimen exposed to ISO curve. Therefore, considering the same char front temperature for natural fires as determined for ISO fire is not appropriate.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 8921441The presented study shows the use of the Broido-Shafizadeh pyrolysis model in combination with the heat transfer model for determining the charring of timber structural elements exposed to a natural fire. In the pyrolysis model, the decomposition of wood at elevated temperatures is followed by the formation of char, tar and pyrolysis gases. These governing phenomena are described by a system of ordinary differential equations and reaction rates following Arrhenius law. Case studies showed that the heating rate of fire has a significant impact on the development of the charring depth as well as on the temperature when charring starts (char front temperature). For standard fire exposure char front temperature is close to 300 °C. The presented two-phase method has the potential to make a transition to desired performance-based approach, and thus the more realistic behaviour of timber structures in fire.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 8839265The main purpose of the paper is to determine charring and char front temperature in wood exposed to elevated temperatures, where Broido-Shafizadeh pyrolysis model is used. Two studies of charring for different temperature developments in wood are conducted. In the first study the development of temperature in wood is based on the empirical model calibrated on standard fire exposure, where it is discovered that BS model accurately estimates charring depth. The second study analyses several simple temperature developments in wood, which are linearly dependent on time. The study shows that slower development of temperatures leads to lower char front temperature and vice versa.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 8612193This publication is the result of work carried out within COST Action FP1404 Fire Safe Use of Bio Based Building Products, supported by COST (European Cooperation in Science and Technology). COST is a funding agency for research and innovation networks. The Actions help connect research initiatives across Europe and enable scientists to grow their ideas by sharing them with their peers. This boosts their research career and innovation. More information available at http://www.cost.eu. Updates and corrections: http://www.costfp1404.ethz.ch/publications. This publication was created in WG2 and can be considered as state of the art document regarding the timber-concrete composite structures exposed to fire. The information in the book was carefully selected by experts from general technical knowledge, standards, most recent research results and building practice.
F.31 Development of standards
COBISS.SI-ID: 8719713