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Fire in hollow spaces: Short circuit as ignition sources and the role of ventilation
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In Germany, there are currently no standard regulations suitable for designing load-bearing steel structures within hollow spaces in fire situation in a cost-efficient method. Therefore this national research project is funded by AiF e.V., German Federation of Industrial Research Associations (project no. 18894N) and FOSTA e.V., Research Association for Steel Application (project no. P1139) to determine a natural fire scenario for hollow spaces and investigate the effect of this natural fire on unprotected steel elements and composite dowels in composite slab structures.
The natural fire model is to be developed with the help of CFD (Computational Fluid Dynamic) programs, such as Fire Dynamics Simulator (FDS) by performing a parametric study on governing boundary conditions, which are the construction form of space-enclosing elements such as composite or raised floors, the combustible electric cables and wirings (main fire loads), ventilation’s conditions, required openings as well as any unplanned and planned leakages.
To validate the results from the numerical simulations, small-scale fire tests are conducted to investigate the effect of the parameters on the initiation and propagation of cable-induced fires. As the project is ongoing, this paper deals only with the parametric study using numerical simulations and subsequent validation with real small fire tests.
In later phase of the project, which is not part of this paper, the results of the validated small-scale tests are going to be used to develop advanced numerical simulations on real scale models. After that, real-scale fire tests are to be performed for fire in hollow spaces, above and below the hollow spaces. The fire tests are then used as a basic for developing simplified design methods, which ideally will enable an economical design of floor constructions, due to the omission of additional fire protection measurements in Germany.
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... The regulatory fire resistance is one of the main problems in the metal frame design of buildings and structures [11][12][13][14]. The high thermal conductivity of steel and the small value of the reduced thickness can lead to a sharp increase in the temperature of the supporting structures during a fire and, as a consequence, the deterioration of the mechanical characteristics [15][16][17][18][19][20]. In the European regulatory document EN1993-1.2 ...
There is a fire resistance investigation of the light steel thin-walled wall system with foam concrete filling (low density of 200 kg/m³) in a fixed formwork of glass-magnesite sheets. The wall fragment model in the PC SOFiSTiK presents dependence temperature gradient in the section from fire duration. According to the results of the calculation and modelling, the wall system has the fire resistance limit more than 120 min in standard fire conditions. The standard fire tests of natural wall samples confirmed the correctness of the design model. The samples did not reach a critical state. This result correlates with the simulation model. In the article, we designed the standard bearing wall solution for buildings of the second degree of fire resistance (REI 90). It is recommended to repeat the tests before reaching the limit state due to the theoretical validity of the actual fire resistance of REI 120.
... Nowadays, modeling of thermophysical processes in building structures is commonly carried out in software packages Ansys (USA) and Abaqus (USA), which are considered as the most appropriate programs for solving the problems of fluid and gas mechanics, heat transfer and heat exchange, including fire resistance [10][11][12][13][14][15][16]. We consider the possibility of using the SOFiSTiK software package (Germany) for analyzing the distribution of temperature fields for various building structures [17,18]. ...
There is a temperature gradient investigation of the steel hollow circular column. This dependence was carried out from simulated section in the PC SOFiSTiK and experimental data from the manual. The comparison of the modelling and manual results gives excellent convergence for both unprotected section and with fire protection of cement-sand plaster. The average relative deviation for most of the values does not exceed 5%. Modeling of the temperature gradient in steel structures can be considered validated. Software complex SOFiSTiK can be used to pre-assess the heating of sections of building structures.
Die brandschutztechnischen Regelungen fordern zusätzlich zum üblichen Feuerwiderstand an ein Deckensystem in Verbundbauweise für die stählerne Tragkonstruktion der Fußbodentragschicht im Deckenhohlraum die Feuerwiderstandsklasse R30. Um diese Feuerwiderstandsklasse zu erreichen, sind bisher Brandschutzmaßnahmen für die Stahlquerschnitte erforderlich. Solche Brandschutzmaßnahmen erschweren die Wettbewerbsfähigkeit von Deckensystemen in Verbundbauweise. Fraglich ist, ob die vorhandenen Brandlasten im Deckenhohlraum und die Ventilationsverhältnisse überhaupt ein Brandszenario ermöglichen, das mit der Temperaturentwicklung der Einheits‐Temperaturzeitkurve vergleichbar ist. Diese Frage war ein zentrales Thema des Forschungsprojekts P1139. Im Ergebnis wurde ein Naturbrandszenario für den Hohlraum von Deckensystemen entwickelt, welches auf realen Brandlasten und Ventilationsbedingungen basiert. Unter Verwendung dieses Naturbrandszenarios wurden zwei Großbrandversuche mit einem innovativen vorgespannten Verbunddeckensystem durchgeführt, um den Einfluss auf das Tragverhalten bei einer Brandbeanspruchung im Hohlraum des Deckensystems beurteilen zu können.
In diesem Beitrag werden die experimentellen und numerischen Untersuchungen zum Erwärmungs‐ und Tragverhalten des Deckensystems infolge des Naturbrandszenarios für den Hohlraum beschrieben. Zusätzlich zu den experimentellen Untersuchungen wird ein numerisches 3‐D‐Modell in Abaqus erstellt, das mit den Versuchsdaten validiert wird und mit dessen Hilfe die Systemtragwirkung des Deckensystems vertiefend untersucht wird.
In Germany, there are currently no standard regulations suitable for designing load-bearing structures within hollow spaces in a cost-efficient method. The current codes for fire design have many restrictions such as limiting the fire sections to be below 400 m², heights of hollow spaces to be either less than 20 cm or 50 cm depending on their usage or the maximum allowed fire loads to be lower than 7 kWh/m² [6] [7] [8]. Once any of these limitations is exceeded, certain fire resistance ratings are applied, which means that the inner load-bearing steel structures must be designed using standard temperature-time curve [9] or passive fire protection measures are needed. Therefore this national research project is funded by AiF e.V., German Federation of Industrial Research Associations (project no. 18894N) and FOSTA e.V., Research Association for Steel Application (project no. P1139) to determine a natural fire scenario for the design of hollow spaces and investigate the effect of this natural fire on composite dowels in composite slab structures.
Interview for determination of fire loads
- H Scherer
Scherer, H. (2016). Interview for determination of fire loads. 05 August 2016.
Department of Commerce (2015): FDS and Smokeview
- Nist Technology
The National Institute of Standards and Technology, NIST, U.S. Department of Commerce (2015): FDS
and Smokeview. http://www.nist.gov/el/fire_research/fds_smokeview.cfm (23.03.2016)
Simulation Software for Science and Engineering. Manage Geometry, Specify Parameters, Deliver Results Sheathed Building Wire NYM-J/-O. Data sheet
- Thunderhead Engineering Consultants
- Inc
Thunderhead Engineering Consultants, Inc. (2015): Simulation Software for Science and Engineering.
Manage Geometry, Specify Parameters, Deliver Results. http://www.thunderheadeng.com (09.08.2016)
[9] Faber
Kabel
(2016):
Sheathed
Building
Wire
NYM-J/-O.
Data
sheet.
http://www.faberkabel.de/en/produkte/typgruppe/6092/nym-j-o.html (18.10.2016)
DIN EN 1991-1-2. Eurocode 1: Einwirkungen auf Tragwerke -Teil 1-2: Allgemeine Einwirkungen -Brandeinwirkungen auf Tragwerke
- Normenausschuß Bauwesen
Normenausschuß Bauwesen (NABau) im DIN Deutsches Institut für Normung e.V. (Dezember 2010):
DIN EN 1991-1-2. Eurocode 1: Einwirkungen auf Tragwerke -Teil 1-2: Allgemeine Einwirkungen -Brandeinwirkungen auf Tragwerke.