SP fire technology is increasing the capabilities for numerical modelling for fire resistance and fire dynamics.
In particular, we are promoting our work in areas of heat transfer, structural mechanics and fire modelling. Using a range of software, we are using modelling more and more as part of our daily work for research projects, development and for assessments. Looking to the future we can only imagine that this use will increase. At the moment we are focusing our efforts on three software packages, Comsol multiphysiscs, Abaqus and NISTS FDS.
Heat transfer
Heat transfer is one of the principal problems of fire resistance – since a lot of fire resistance testing boils down to questions of insulation for separating elements. It is also a critical factor in the load bearing capacity of a building element. There are three mechanisms for heat transfer: conduction, convection and radiation.
Conduction is the mechanism whereby temperature changes are ‘felt’ through a solid. It is dependent upon the material properties which may not be constant with temperature! Convection is the mechanism for transfer of temperature between a gas to a solid – this is not only dependent upon the gas and the solid temperature but also on the speed of the flow of gas over the surface of the solid. Finally radiation is the mechanism for transfer of heat in the form of electromagnetic waves from a solid without needing a physical medium.
All of these must be taken account of in our calculations. Often these are done in conjunction with our experimental work – e.g. measuring material properties including temperature dependent material properties and using these in our models.
Structural mechanics
The use of Finite Element Analysis (FEA) codes for structural calculations allows us to estimate the mechanical response of building elements in fire. One significant advantage of this type of approach is that preliminary studies can be carried out to give a pre estimate of the expected fire resistance of building elements. This type of analysis is also commonly employed in industry when carrying out a full fire engineering design of a building since it is possible to model more complex geometry, longer spans and structural interactions by changing the boundary conditions in the model.
In research, we are also able to study the expected failure mechanisms of building elements and gain a better understanding of structural response to fire.
Fire modelling
Understanding fire behaviour and the impact of fires on structures through simulations is a very challenging topic. We have used the CFD (Computational Fluid Dynamics) software FDS (Fire Dynamics Simulator) for simulations of fire-driven fluid flows. FDS is a versatile software that predicts the fire evolution from a given fire source. The software was first developed by NIST and currently has a large community of users in fire engineering, consultancy and research.
Recent work at SP Fire Technology includes investigations of the fire dynamics in e.g. a façade test rig, a room-corner test and objects exposed to pool fires. The simulations give detailed information of the flow field, temperatures and general heat transfer properties in the different scenarios. We are looking into the response of prestressed elements and hollow core slabs as well as connections, structural detailing and models for studying extended application.
As a large testing laboratory, we have an extensive range of test results upon which to benchmark our models and this can give us better confidence that what our modelling represents the actual behaviour of building elements when subject to fire testing. In the future we are aiming at a larger predictive capability in order to take part in earlier stages of testing and design.
