Structural response of a steel-frame building to horizontal and vertical travelling fires in multiple floors

During previous fire events such as the World Trade Centre Towers (WTC) 1, 2 & 7 in New York (2001), the Windsor Tower in Madrid (2005), and the Plasco building in Iran (2017), flames were observed to travel horizontally across the floor plate and vertically to different floors. Such fires are not considered as part of the traditional prescriptive structural design for fire. Recently, the Travelling Fires Methodology (TFM) has been developed to account for such horizontally travelling nature of fires. A dozen of studies have investigated the structural response of steel, concrete, and composite structures to a single-floor travelling fire. 5 out of 6 of the vertically travelling fire studies have been limited to the structures with a long span composite truss system as in the WTC Towers. The aim of this work is to investigate the response of a substantially different structural system, i.e. a generic multi-storey steel frame, subjected to travelling fires in multiple floors, and varying the number of fire floors, including horizontal and vertical fire spread. A two-dimensional 10-storey 5-bay steel frame is modelled in the finite element software LS-DYNA. The number of multiple fire floors is varied between 1 and 10, and for each of these scenarios, 5 different fire types are investigated. They include four travelling fire scenarios and the standard fire. In total, 51 fire simulations are considered. The development of deflections, axial forces, bending moments and frame utilization are analysed. Results show that the largest stresses develop in the fire floors adjacent to cool floors, and their behaviour is independent of the number of fire floors. Results indicate that both the fire type and the number of fire floors have a significant effect on the failure time (i.e. exceeded element load carrying capacity) and the type of collapse mechanism. In the cases with a low number of fire floors (1–3) failure is dominated by the loss of material strength, while in the cases with larger number of fire floors (5–10) failure is dominated by thermal expansion. Collapse is mainly initiated by the pull-in of external columns (1–3-floor fires; 1–9-floor fires for 2.5% TFM) or swaying of the frame to the side of fire origin (5–10-floor fires). This study has assessed a different structural form compared to previous literature under an extensive range of multiple floor travelling fire scenarios. We find that although vertically travelling fires result in larger beam axial forces and initial deflections, simultaneous travelling fires result in shorter failure times and represent a more onerous scenario for the steel frame investigated

Development of The Viking Speech Scale to Classify the Speech of Children with Cerebral Palsy

Surveillance registers monitor the prevalence of cerebral palsy and the severity of resulting impairments across time and place. The motor disorders of cerebral palsy can affect children’s speech production and limit their intelligibility. We describe the development of a scale to classify children’s speech performance for use in cerebral palsy surveillance registers, and its reliability across raters and across time. Speech and language therapists, other healthcare professionals and parents classified the speech of 139 children with cerebral palsy (85 boys, 54 girls; mean age 6.03 years, SD 1.09) from observation and previous knowledge of the children. Another group of health professionals rated children’s speech from information in their medical notes. With the exception of parents, raters reclassified children’s speech at least four weeks after their initial classification. Raters were asked to rate how easy the scale was to use and how well the scale described the child’s speech production using Likert scales. Inter-rater reliability was moderate to substantial (k > .58 for all comparisons). Test–retest reliability was substantial to almost perfect for all groups (k > .68). Over 74% of raters found the scale easy or very easy to use; 66% of parents and over 70% of health care professionals judged the scale to describe children’s speech well or very well. We conclude that the Viking Speech Scale is a reliable tool to describe the speech performance of children with cerebral palsy, which can be applied through direct observation of children or through case note review

Access to Intrathecal Baclofen Treatment for Children with Cerebral Palsy in European Countries: An SCPE Survey Reveals Important Differences

Aim: The aim is to study access to intrathecal baclofen (ITB) for children with cerebral palsy (CP) in Europe, as an indicator of access to advanced care. Methods: Surveys were sent to CP registers, clinical networks, and pump manufacturers. Enquiries were made about ITB treatment in children born in 1990 to 2005 by sex, CP type, level of gross motor function classification system (GMFCS) and age at the start of treatment. Access to ITB was related to the country's gross domestic product (GDP) and % GDP spent on health. Results: In 2011 population-based data from Sweden, Norway, England, Portugal, Slovenia, and Denmark showed that 114 (3.4%) of 3,398 children with CP were treated with ITB, varying from 0.4 to 4.7% between centers. The majority of the children were at GMFCS levels IV-V and had bilateral spastic CP. In Sweden, dyskinetic CP was the most commonly treated subtype. Boys were more often treated with ITB than girls (p = 0.014). ITB was reported to be available for children with CP in 25 of 43 countries. Access to ITB was associated with a higher GDP and %GDP spent on health (p < 0.01). Updated information from 2019 showed remaining differences between countries in ITB treatment and sex difference in treated children was maintained. Conclusion: There is a significant difference in access to ITB for children with CP across Europe. More boys than girls are treated. Access to ITB for children with CP is associated with GDP and percent of GDP spent on health in the country.info:eu-repo/semantics/publishedVersio

Improved formulation of travelling fires and application to concrete and steel structures

© 2015.Current design codes and consequently most of the understanding of behaviour of structures in fire are based on the often unrealistic assumption of uniform fire within the enclosure. This assumption is especially wrong in the case of large open-plan compartments, where non-uniform travelling fires have been observed instead. An innovative concept called the Travelling Fires Methodology (TFM) has been developed to take into account this non-uniform fire behaviour. In this study, TFM has been improved to account for better fire dynamics. Equations are introduced to reduce the range of possible fire sizes taking into account fire spread rates from real fires. The analytical equations used to represent the far-field temperatures are presented in continuous form. The concept of flame flapping is introduced to account for variation of temperatures in the near-field region due to natural fire oscillations. These updated near-field temperatures cover a range of temperatures between 800 and 1200. °C, depending on fire size and compartment characteristics. These incorporated changes are based on a fire model which can be used flexibly and adjusted to fit experimental data when it becomes available in the near future. Improved TFM (iTFM) is applied to generic concrete and steel compartments to study the effect of non-uniform heating associated with the travelling fires by investigating the location of the peak temperature along the fire path. It is found to be mainly dependent on the fire spread rate and the heat release rate. Location of the peak temperature in the compartment mostly occurs towards the end of the fire path

iTFM Matlab Code for Improved formulation of travelling fires

This is the iTFM code for calculations in Matlab of gas temperature in improved formulation of travelling fires. It is written by Egle Rackauskaite and Guillermo Rein, Imperial College London, UK, and it is based on the journal paper (doi:10.1016/j.istruc.2015.06.001): E Rackauskaite, C Hamel, A Law, G Rein, Improved formulation of travelling fires and application to concrete and steel structures, Structures, 2015. http://dx.doi.org/10.1016/j.istruc.2015.06.001This is the iTFM code for calculations in Matlab of gas temperature in improved formulation of travelling fires. It is written by Egle Rackauskaite and Guillermo Rein, Imperial College London, UK, and it is based on the journal paper (doi:10.1016/j.istruc.2015.06.001): E Rackauskaite, C Hamel, A Law, G Rein, Improved formulation of travelling fires and application to concrete and steel structures, Structures, 2015. http://dx.doi.org/10.1016/j.istruc.2015.06.00

Model parameter sensitivity and benchmarking of the explicit dynamic solver of LS-DYNA for structural analysis in case of fire

Due to the complex nature of structural response in fire, computational tools are often necessary for the safe design of structures under fire conditions. In recent years, use of the finite element code LS-DYNA has grown considerably in research and industry for structural fire analysis, but there is no benchmarking of the code available in the fire science literature for such applications. Moreover, due to the quasi-static nature of structural response in fire, the majority of the computational structural fire studies in the literature are based on the use of static solvers. Thus, this paper aims at benchmarking the explicit dynamic solver of LS-DYNA for structural fire analysis against other static numerical codes and experiments. A parameter sensitivity study is carried out to study the effects of various numerical parameters on the convergence to quasi-static solutions. Four canonical problems that encompass a range of thermal and mechanical behaviours in fire are simulated. In addition, two different modelling approaches of composite action between the concrete slab and the steel beams are investigated. In general, the results confirm that when numerical parameters are carefully considered such as to not induce excessive inertia forces in the system, explicit dynamic analyses using LS-DYNA provide good predictions of the key variables of structural response during fire

Computational analysis of thermal and structural failure criteria of a multi-storey steel frame exposed to fire

Structural fire design, until recently, has only assumed uniform fires inside the compartment, and the assessment of structural failure has been often based on a critical temperature criterion. While this criterion, to some extent, may be able to indicate the temperature at which the structural element is near to failure, it is based on standard fire tests and, therefore, its validity is limited to individual members exposed to uniform temperatures. It is unclear how representative a critical temperature criterion is of structural failure in the case of multi-story structures, particularly in the case of non-uniform fires such as travelling fires. Therefore, the aim of this study is to assess the validity of the critical temperature criterion for structures exposed to non-uniform fires and compare it to uniform fires. A generic 10-storey steel framed building is modelled using the finite element software LS-DYNA. In total, 117 different scenarios are investigated to cover a wide range of conditions of interest for design of modern steel buildings, varying the fire exposure (travelling fires, Eurocode parametric fires, ISO-834 standard fire, and SFPE standard), floor where the fire is burning, beam section size, and applied fire protection to the beams. For the different fire exposures considered, the analysis predicts structural failure at different times, in different locations and floors, and different failure mechanisms. Moreover, it is shown that there is no single worst case fire scenario: different fires can lead to failure in different structural ways. The comparison of the various structural and thermal failure criteria (ultimate strain, utilization, mid-span deflection, and critical temperature) show that there is no consistency between them, revealing a far more complex problem than reported in the literature. Lastly, this work has illustrated that the critical temperature criterion does not predict accurately the structural failure in time, space or failure mode of steel structures subjected to both uniform and non-uniform fires. Structural failure can only be predicted by advanced structural analysis, and, therefore, heat transfer analysis alone is not sufficient for design. Nevertheless, it was shown that the use of the critical temperature leads to conservative results for simple steel structures. For the sake of comprehensive design, a range of different fire scenarios, including both uniform and non-uniform, should be part of the analysis such that all likely structural responses and failure modes can be considered

Structural analysis of multi-story steel frames exposed to travelling fires and tradition design fires

Most of the current understanding of building behaviour in fire is based on the adoption of the standard and parametric temperature-time fire curves. However, these design fires are based on small scale tests and idealize the thermal environment as uniform. Thus, they have important limitations on their applicability to large enclosures. Instead, in large open-plan compartments, travelling fires have been observed. To account for such fires, a design tool called Travelling Fires Methodology (TFM) has been developed and used for design. The aim of the present study is to compare computationally the structural response of a multi-storey steel frame subjected to both uniform design fires (available in current standards) and travelling fires. A two-dimensional 10-storey 5-bay steel frame designed according to ASCE 7-02 is modelled in the general finite element program LS-DYNA. Different fire exposures are investigated. They include travelling fires, Eurocode parametric curves, ISO-834 standard fire and the constant compartment temperature curve from the SFPE standard. These fires are applied to different floors, one at a time, to explore the influence on the structural response, resulting in a total of 80 different scenarios. The development of deflections, axial forces and bending moments is analysed. Uniform fires are found to result in approx. 15–55 kN (3–13%) higher compressive axial forces in beams compared to small travelling fires. However, the results show irregular oscillations in member utilization levels in the range of 2–38% for the smallest travelling fire sizes, which are not observed for any of the uniform fires. Peak beam mid-span deflections are similar for both travelling fires and uniform fires and depend mainly on the fire duration, but the locations in the frame and times when these peak displacements occur are different. The results indicate that travelling fires and uniform fires trigger substantially different structural responses which may be important in the structural design and selection of the critical members

Thermal response of timber slabs exposed to travelling fires and traditional design fires

Engineered timber is an innovative and sustainable construction material, but its uptake has been hindered by concerns about its performance in fire. Current building regulations measure the fire performance of timber using fire resistance tests. In these tests, the charring rate is measured under a series of heat exposures (design fires) and from this the structural performance is deduced. Charring rates are currently only properly understood for the heat exposure of a standard fire, not for other exposures, which restricts the use of performance-based design. This paper studies the charring rates under a range of design fires. We used a multiscale charring model at the microscale (mg-samples), mesoscale (g-samples), and macroscale (kg-samples) for several wood species exposed to different heating regimes and boundary conditions. At the macroscale, the model blindly predicts in-depth temperatures and char depths during standard and parametric fires with an error between 5% and 22%. Comparing simulations of charring under travelling fires, parametric fires, and the standard fire revealed two findings. Firstly, their charring rates significantly differ, with maximum char depths of 42 mm (travelling), 46 mm (parametric), and 59 mm (standard fire), and one (standard fire) to four (travelling fire) charring stages (no charring, slow growth, fast growth, steady-state). Secondly, we observed zero-strength layers (depth between the 200 °C and 300 °C isotherm) of 7 to 12 mm from the exposed surface in travelling fires compared to 5 to 11 mm in parametric fires, and 7 mm in the standard fire. Both traditional design fires and travelling fires, therefore, need to be considered in structural calculations. These results help engineers to move towards performance-based design by allowing the calculation of charring rates for a wide range of design fires. In turn, this will help engineers to build more sustainable and safe structures with timber