Z2-8160: Modelling pyrolysis to determine the decomposition of wood in natural fire

Basic info:

Description

The use of timber structures in modern times is rapidly increasing. Concerns for sustainable, ecological, low energy and affordable construction are some of many benefits that speak in favour of timber. In accordance with the Construction act (ZGO-1), to use timber buildings, proof of fire safety is required. However, current prescriptive rules to determine fire safety represent an obstacle for the engineer, since they allow the design of timber buildings only up to four storeys according to Slovenian technical guideline and up to eight storeys according to the most of Europeans guidelines. It is possible to design higher building based on the computational models, which unfortunately at this moment are not precise enough, so that additional measures based on the prescriptive rules are needed to achieve the desired fire safety. However, using mixed approach is not optimal and occasionally also unsafe. Therefore, to design higher structures, a performance based approach is needed, where the influence of natural fire and advanced computational models has to be accounted for. To determine fire safety of timber structures in natural fire, it is necessary to know physical and chemical phenomena that have an influence on the behaviour of timber structures in natural fire. Two processes are dominant. First is heat and moisture transfer, which governs the distribution of temperatures in timber. Second is pyrolysis of wood associated with charring and reduction of mechanical properties of wood at elevated temperatures. The pyrolysis describes the decomposition of the basic chemical constituents of wood (cellulose, hemicellulose, lignin), where the fire growth rate plays a decisive role, because the decomposition of each constituent depends not only on the temperature increase in wood but also on how fast this increase is. Based on the decomposition of constituents, it is possible to determine deterioration and degree of charring of individual wood fibres for a random fire.

This is also the main objective of the proposed project, i.e. development of a new advanced mathematical and numerical model that will couple heat and moisture transfer together with the wood pyrolysis and will be suitable for a random fire load, which will present a step towards a performance based design. New hygro-thermal-pyrolysis model will allow predicting the decomposition of wood fibres, which will be the basis to determine the response and fire safety of timber structures exposed to natural fire. The proposed model will be formed on a precise physical and chemical description of the problem, allowing the design of more secure and economical timber structures. At the same time, new model will represent an innovation in this field. Based on the new knowledge it will be possible to influence on the development of broader scientific community in this field.

Main goals:

• development of a new coupled hygro-thermal-pyrolysis model to determine the decomposition of wood fibres and charring of wood exposed to natural fire,
• the transition to natural fire, which is needed for a performance based design. This will enable to accurately determine the behaviour of timber structure in natural fire, and thus, make it easier to predict the optimal and appropriate measures to ensure the fire safety of multi-storey timber buildings (> G + 3),
• a sensitivity analysis of the new hygro-thermal-pyrolysis model, which will help to identify key parameters that have influence on the model results,
• on the basis of the new coupled hygro-thermal-pyrolysis model it will be possible to contribute to the development of new guidelines for fire design of multi-storey timber structures in Slovenia and Europe (e.g. upgrading of technical guidelines TSG-01-2010 [3] for the use of timber bearing structures for buildings > G + 3),
• three sets of experiments, that will enable model validation and, if necessary, also its calibration.
• based on the sensitivity analysis and newly developed model, it will be possible to propose advanced targeted experiments in the future.

Project work packages:

The project will be divided in 7 work packages:

• WP1: Review of the literature in the field of pyrolysis charring of wood
• WP2: Derivation of governing equations of thermo-hygro-pyrolysis model
• WP3: Derivation of numerical model
• WP4: First set of experimental tests
• WP5: Sensitivity analysis of HMP model
• WP6:  Second and third set of experimental tests
• WP7: Dissemination of the results