Numerical Investigation of Thermal Responses of a Composite Structure in Horizontally Travelling fires Using OpenSees (original) (raw)
Related papers
Modelling the Thermal Effects on Structural Components of Composite Slabs under Fire Conditions
Computation
This paper presents a finite-element-based computational model to evaluate the thermal behaviour of composite slabs with a steel deck submitted to standard fire exposure. This computational model is used to estimate the temperatures in the slab components that contribute to the fire resistance according to the load-bearing criterion defined in the standards. The numerical results are validated with experimental results, and a parametric study of the effect of the thickness of the concrete on the temperatures of the slab components is presented. Composite slabs with normal or lightweight concrete and different steel deck geometries (trapezoidal and re-entrant) were considered in the simulations. In addition, the numerical temperatures are compared with those obtained using the simplified method provided by the standards. The results of the simulations show that the temperatures predicted by the simplified method led, in most cases, to an unsafe design of the composite slab. Based on ...
Mechanical behaviour of structures subjected to travelling fire
2014
Observations of accidental fires and real-scale experiments have shown that large and even middle size compartments do not burn simultaneously but flames tend to travel, burning a specific area at a certain time. During these observations, difference of temperature up to 400°C has been measured inside the compartment while traditional methods of design use the approach of homogenous temperature in the entire compartment at the same time. Therefore studies regarding travelling fire express high interest as they tend to give results closer to the real situations. To study the effect of the spreading flames on the structural behaviour of a building, a simple 3D structure has been conceived and modelled in the software Vulcan. Traditional methods described in design codes and several travelling fire scenarios with different direction of the flames have been applied to the structure. All models of travelling fire have their root on shifted parametrical fire curves which are based on the rate of heat release, the so-called iBMB fire curves. Mechanical behaviour of the structure has been evaluated in the terms of deflection and axial force obtained in the beams. Results of the analysis have been showed for each thermal load case and also comparisons have been done among the fire scenarios. Comparison of the results has provided important conclusions. Travelling fire models gives the most severe cases for fire resistance requested for long period of time. On the contrary, traditional methods provide worse results for short requested period of fire resistance. All travelling fire scenarios should be taken into account to determine the most severe fire conditions.
Modelling of Steel-Concrete Composite Structures in Fire Using OpenSees
Advances in Structural Engineering, 2014
This paper presents the extension of the structural analysis software framework OpenSees for modeling steel framed composite structures subjected to fire including the development of a geometrically nonlinear shell element. The new shell element is formed by a combination of membrane elements and Mindlin plate bending elements using a general total Lagrangian formulation. The MITC technique (Mixed Interpolation of Tensorial Components) is applied to alleviate shear locking problems and the addition of drilling degrees of freedom is included. A new thermal load class was created to define the temperature distribution through the thickness of the shell section. The two-dimensional OpenSees material, DruckerPrager, was modified to model the concrete in the composite deck slab at elevated temperature with temperature-dependent material properties according to the Eurocode 2. A three-dimensional finite element model of a composite structure was built in OpenSees, consisting of a flat rei...
Applied Sciences
The term “travelling fire” is used to label fires which burn locally and move across the floor over a period of time in large compartments. Through experimental and numerical campaigns and while observing the tragic travelling fire events, it became clear that such fires imply a transient heating of the surrounding structure. The necessity to better characterize the thermal impact generated on the structure by a travelling fire motivated the development of an analytical model allowing to capture, in a simple manner, the multidimensional transient heating of a structure considering the effect of the ventilation. This paper first presents the basic assumptions of a new analytical model which is based on the virtual solid flame concept; a comparison of the steel temperatures measured during a travelling fire test in a steel-framed building with the ones obtained analytically is then presented. The limitations inherent to the analyticity of the model are also discussed. This paper sugge...
A Review of Models for Heat Transfer in Steel and Concrete Members During Fire
Journal of Research of the National Institute of Standards and Technology, 2021
Structural design for fire is conceptually similar to structural design conducted under ambient temperature conditions. Such design requires an establishment of clear objectives and determination of the severity of the design fire. In the commonly used prescriptive design method for fire, fire resistance (expressed in hours) is the primary qualification metric. This is an artifact of the standard fire tests that are used to determine this quantity. When conducting a performance-based approach for structural design for fire, it is important to determine structural member temperatures accurately when the members are exposed to a real fire. In order to evaluate the fire resistance of structural members such as structural steels and concrete, both the temporal and spatial variation of temperatures must be accurately determined. The transient temperature profiles in structural members during exposure to a fire can be determined from a heat transfer analysis. There are several models/appr...
Sequentially coupled thermal-stress analysis of a new steel-concrete composite slab under fire
The paper describes the numerical simulations required to estimate the performance of a composite slab using a re-entrant profiled steel sheet, prior to conducting a loaded fire test to verify the performance predicted by the simulations and obtain a fire rating according to accepted international standards. The purpose of the simulations was to optimize the design of the composite slab, by eliminating unnecessary reinforcement bars. Heat transfer analysis involving convection, conduction and boundary radiation was undertaken on a detailed solid modelled slab as part of a new steel-concrete slab product development. The simulation accounted for the thermal contact resistance at the cold-formed steel-concrete interface. The novelties of the model to incorporate the temperature dependent formulation of the interface thermal conductance provided a realistic prediction of the cross-sectional temperature field, which matched the fire test measurements. The slab top surface temperatures were assessed according to EN 1363-1:2012 to enable comparisons to be made with the insulation performance criteria. Following the uncoupled heat transfer analysis, the temperatures calculated through the thickness were used as an input into a sequentially coupled thermal-stress analysis of an equivalent shell modelled slab. This was necessary due to the excessive computing time required for the detailed solid modelled concrete slab that was used for the heat transfer analysis. Nevertheless, the calibrated shell that represented the composite slab model accounted for the dissimilar temperature-time (T-t) curves through the slab depth, since the bottom surface, close to the fire source, heats up at a much higher rate than the top surface. From the explicit-quasi static simulation, the load bearing capacity was calculated, which is expressed by the limiting largest deflection and deflection rate for flexural loaded structural members as given in EN 1363-1:2012. From these analyses, it was found that the overall fire resistance was limited by the load bearing capacity criteria. The predicted insulation and load bearing capacity compared very favourably with the fire test measurements, which are also presented in this paper, and provides confidence in the methodology used in this study.
Journal of Advances and Scholarly Researches in Allied Education
For understanding of building behaviour in fire, most of the time standard and parametric temperature time fire curves are adopted. However, the disadvantages of design fires on the standard parametric curves are based on small scale tests and also idealize the thermal environment as uniform. Thus, they have important disadvantage on their applicability to large enclosures. But in large open-plan compartments, travelling fires have been observed. To analyse such fires, a design tool called Travelling Fires Methodology (TFM) has been developed & used for design. In this paper, the review of study on analysis of multi-storey steel frame in traditional fires & travelling fires studied. The comparison between traditional method through parametric curves & travelling fires studied.
Fire Safety Journal, 2000
Modelling the full-scale Fire Tests at Cardington has led to new understanding of the behaviour of structures under "re conditions. Much of this understanding has come from parametric explorations using models veri"ed against the tests. The structural phenomena observed in highly redundant, composite structures, during a compartment "re are dominated by restrained thermal expansion. The large de#ections experienced in the structural elements in the region of the "re are almost entirely attributable to thermally induced strains. The mechanisms responsible for producing these large de#ections are restrained thermal expansion and thermal bowing. Material degradation and loading are secondary in#uences. A clear understanding of the response of the structure to an average temperature increase and through depth temperature gradients is essential. This paper discusses the structural response when subjected to di!erent heating regimes obtained by changing the mean temperature and temperature gradient applied in the concrete slab of the composite #oor slab system to a computer model of the British Steel restrained beam test.
Analysis of Composite Steel-concrete Beams Exposed to Fire using OpenSees
Journal of Structural Fire Engineering, 2015
OpenSees is an open-source object-oriented software framework developed at UC Berekeley. The OpenSees framework has been recently extended to deal with structural behaviour under fire conditions. This paper summaries the key work done for this extension and focuses on the validation and application of the developed OpenSees to study the behaviour of composite steel-concrete beams under fire conditions. The performance of the developed OpenSees are verified by four mechanical tests and two fire tests on simply supported composite beams. A parametric study is carried out using OpenSees to study the influence of boundary condition as well as composite effect of slab on the behavior of composite beams exposed to fire. The stress and strain along the beam section is output and compared with yield stress limit at elevated temperature to explain these influences in detail. The results show that the stress distribution in the web of the steel beam is more complex due to the support effects.
Engineering Structures
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 10storey 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.