Structural analysis of multi-storey steel frames exposed to travelling fires and traditional design fires

Rackauskaite, Egle; Kotsovinos, Panagiotis; Jeffers, Ann E.; Rein, Guillermo

doi:10.1016/j.engstruct.2017.06.055

Cited by 45 publications

(19 citation statements)

References 28 publications

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“…More realistic fire scenarios must be used for the analysis of bigger structures or in case of employing a three-dimensional frame, that because a real fire is not uniform throughout a storey neither throughout the building height. A real fire walks through the building, following the more inflammable materials and with that forming a highly non-uniform temperature field [6,20]. It is hoped that this work inspires other authors to follow the path started here, as the global analysis of concrete buildings in fire situation is of great importance to the research sequence of the structures in this area.…”

Section: Discussionmentioning

confidence: 65%

On the use of parameter γ z in fire situation

Naccache

Pierin

Silva

2019

Rev. IBRACON Estrut. Mater.

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Section: Discussionmentioning

confidence: 65%

On the use of parameter γ z in fire situation

Naccache

Pierin

Silva

2019

Rev. IBRACON Estrut. Mater.

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“…We explore the range of design fires that were developed for a generic open plan compartment studied by Rackauskaite et al [28]. These authors used a thermomechanical model to investigate the response of steel frames subjected to uniform and non-uniform fires.…”

Section: Choice Of Design Firesmentioning

confidence: 99%

Thermal Response of Timber Slabs Exposed to Travelling Fires and Traditional Design Fires

et al. 2020

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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.

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“…The TFM is not predictive and is intended to be used as a complementary tool by designers when undertaking structural fire engineering analyses for robustness purposes in addition to traditional design fires. [4][5][6][7] As the fire travels throughout the compartment, the structural elements at the ceiling level experience the thermal exposure from the far field and near field regions. 2,3 TFM considers the near field and far field regions of a fire.…”

Section: Introductionmentioning

confidence: 99%

“…Thermal conditions from the family of fires allow selecting the most challenging scenario for structural design. The TFM is not predictive and is intended to be used as a complementary tool by designers when undertaking structural fire engineering analyses for robustness purposes in addition to traditional design fires . As the fire travels throughout the compartment, the structural elements at the ceiling level experience the thermal exposure from the far field and near field regions .…”

Section: Introductionmentioning

confidence: 99%

Flame extension and the near field under the ceiling for travelling fires inside large compartments

2019

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Summary Structures need to be designed to maintain their stability in the event of a fire. The travelling fire methodology (TFM) defines the thermal boundary condition for structural design of large compartments of fires that do not flashover, considering near field and far field regions. TFM assumes a near field temperature of 1200°C, where the flame is impinging on the ceiling without any extension and gives the temperature of the hot gases in the far field from Alpert correlations. This paper revisits the near field assumptions of the TFM and, for the first time, includes horizontal flame extension under the ceiling, which affects the heating exposure of the structural members thus their load‐bearing capacity. It also formulates the thermal boundary condition in terms of heat flux rather than in terms of temperature as it is used in TFM, which allows for a more formal treatment of heat transfer. The Hasemi, Wakamatsu, and Lattimer models of heat flux from flame are investigated for the near field. The methodology is applied to an open‐plan generic office compartment with a floor area of 960 m2 and 3.60 m high with concrete and with protected and unprotected steel structural members. The near field length with flame extension (fTFM) is found to be between 1.5 and 6.5 times longer than without flame extension. The duration of the exposure to peak heat flux depends on the flame length, which is 53 min for fTFM compared with 17 min for TFM, in the case of a slow 5% floor area fire. The peak heat flux is from 112 to 236 kW/m2 for the majority of fire sizes using the Wakamatsu model and from 80 to 120 kW/m2 for the Hasemi and Lattimer models, compared with 215 to 228 kW/m2 for TFM. The results show that for all cases, TFM results in higher structural temperatures compared with different fTFM models (600°C for concrete rebar and 800°C for protected steel beam), except for the Wakamatsu model that for small fires, leads to approximately 20% higher temperatures than TFM. These findings mitigate the uncertainty around the TFM near field model and confirm that it is conservative for calculation of the thermal load on structures. This study contributes to the creation of design tools for better structural fire engineering.

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Structural analysis of multi-storey steel frames exposed to travelling fires and traditional design fires

Cited by 45 publications

References 28 publications

On the use of parameter γ z in fire situation

On the use of parameter γ z in fire situation

Thermal Response of Timber Slabs Exposed to Travelling Fires and Traditional Design Fires

Flame extension and the near field under the ceiling for travelling fires inside large compartments

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