Papers by Keyword: Fire

Abstract: Recently, several lives were lost because of the collapse of structures under fire. Steel members are mainly used in the columns and beams of buildings for improving construction efficiency. The fire resistance of steel structure is very important because when it don’t have fire resistive covering, it rapidly changes with high temperature. In fire resistance design of steel, steel structure must have fire resistive covering. But many facilities as temporary facilities, parking lot don’t have it. The buckling behavior of steel structures under fire is also significant because it can cause local buckling failure through the reduction in structural material properties by temperature. In this study, the elastic buckling behavior of a circular steel tube under fire was investigated using finite element analysis. The parameters for this analysis used were, diameter–thickness ratio, fire exposure area, and fire scenarios. The elastic buckling strength of circular steel tube rapidly decreased when subjected to the fire curve. Local buckling occurred and this can lead to global failure. When fire resistance design of circular steel tube was performed, buckling behavior must be considered.

Abstract: This study aims at a better understanding of the behaviour of very high performance concretes (VHPC) subjected to high temperatures. The temperature increase within the concrete originating from the hydratation exothermic reaction of cement is emphasized by the mass effect of the structures and can lead to thermal variations of around 50°C between the heart and the structures walls. These thermal considerations are not without consequence on durability and the physical and mechanical properties of very high performance concrete, such as the compressive strength. This work is an experimental research that shows the effects of temperature on the mechanical properties of very high performance concrete (VHPC) and compares them with those of conventional concrete and HPC. Test specimens in usual concrete, HPC and VHPC are made, preserved till maturity of the concrete, and then subjected to a heating-cooling cycle from room temperature to 500°C at heating rate 0.1°C/min. Mechanical tests on the hot concrete and cooling (air and water) were realized. The results show that the mechanical characteristics of VHPC (density, compressive strength, tensile strength and elastic modulus) decrease with increasing temperature, but their strength remains higher than that of conventional concrete.

Abstract: Abstract. In this study, controlled qualitative comparative experiments regarding the behavior of several insulation materials such as autoclaved aerated concrete, ignifugated wood panels, decorative insulation panel, expanded polystyrene and plasterboard to fire exposure have been assessed. Strong deformation has been observed after 5-20s of fire exposure, followed by advanced charring of the exposed area. In the case of polystyrene and ignifugated wood, intense and irritant aerosols occurred.

Abstract: Mathematical models which can sufficiently describe processes proceeding in concrete during fire play an important role when assessing a load bearing capacity of concrete structures. In this paper a coupled heat and mass transport model based on principles of conservation of mass and energy is presented. A 2D computational solver using FEM was created to find three unknowns – a temperature, an amount of free water and a magnitude of pore pressure in concrete cross section during rapid heating. These variables, mutually connected through state equation, are necessary not only for determination the load bearing capacity of concrete element but also for prediction of concrete spalling. A parametric study of numerical results influenced by material properties of concrete (e.g. permeability, thermal conductivity) and initial conditions (e.g. relative humidity, temperature) is introduced and discussed in the end.

Abstract: The design procedure recently proposed by the same authors and based on a simplified FE model for underground tunnels subjected to internal explosion is extended in this work taking into account different possible positions of the explosive source inside the tunnel. The situation in which the internal explosion is preceded by fire accidents is also analyzed. The reference situation is represented by the explosive source located at the center of the tunnel cross–section. The tunnel geometry considered is that of the metro line in Brescia, Italy. It has an internal diameter of about 8.15 m and is located about 23.1 m below the surface. Six segments and a smaller key segment (6+1) make up the tunnel. The ring has an average width of about 1.5 m. Dynamic analyses were carried out in order to reproduce the blast scenario. The aim of this work is to evaluate the influence of the position of the explosive source on the tunnel dynamic response. An ultimate limit state criterion based on the eccentric ultimate flexural capacity and capable of including fire–blast interaction is adopted. An innovative layered precast tunnel segment solution made of different fiber–reinforced cementitious composites is considered.

Abstract: The present work deals with numerical simulations concerning the international benchmark “Vulcain tests on 3 Walls” regarding fire tests conducted in CSTB in Paris, France. To this aim, sequentially-coupled thermo-mechanical analyses have been performed on three reinforced concrete walls, characterized by different load levels and boundary conditions. The numerical results show that the imposed compressive load and boundary conditions significantly influence the magnitude of the displacements. In the case of simply supported walls, the wall with the lower load level exhibited a gradual and monotonic increase of the displacements at mid-height (both in the tests and in the numerical analyses), while the wall with the higher load level exhibited a displacement reversal due to second-order effects after approximately 60 minutes of fire exposure. This reversal, which was obtained in the analyses, was not observed in the test. Load bearing capacity of all the three specimen walls was maintained in such a way that the collapse did not take place during two hours of fire exposure.

Abstract: The use of high strength concrete (HSC) in multi-story buildings has become increasingly popular. Selection of HSC over normal strength concrete (NSC) allows for reducing the dimensions of the columns sections. However, this reduction has consequences on the structural performance in case of fire, as smaller cross sections lead to faster temperature increase in the section core. Besides, HSC experiences higher rates of strength loss with temperature and a higher susceptibility to spalling than NSC. The fire performance of a column can thus be affected by selecting HSC over NSC. This research performs a comparison of the fire performance of HSC and NSC columns, based on numerical simulations by finite element method. The thermal and structural analyses of the columns are conducted with the software SAFIR^®. The variation of concrete strength with temperature for the different concrete classes is adopted from Eurocode. Different configurations are compared, including columns with the same load bearing capacity and columns with the same cross section. The relative loss of load bearing capacity during the fire is found to be more pronounced for HSC columns than for NSC columns. The impact on fire resistance rating is discussed. These results suggest that consideration of fire loading limits the opportunities for use of HSC, especially when the objective is to reduce the dimensions of the columns sections.

Abstract: Concrete structures exposed to fire suffer from damage, but can remain a certain degree of residual strength. International research has shown that the compressive strength of concrete decreases not only with temperature, but also by the way of cooling and the storage conditions after fire. Fast cooling introduces a thermal shock which, based on experiments by the authors, could result in a 30% additional strength loss with respect to the loss during heating. When storing the concrete after the fire in air or under water, additional strength losses of about 20-30 % are found within 14 days after the fire. In this paper it is investigated for a high performance concrete what the combined effect is of heating, cooling and storage. One of the conclusions – but with respect to the specific test conditions (e.g. slow heating, 550°C max, pre-dried samples) – is that superposing both expected strength losses of about 30% in case a fast cooling is followed by a period of post-cooling storage results in too conservative strength estimations. It is deemed that the cracks resulting from fast cooling, will act as expansion chambers for the newly produced portlandite, thus strongly reducing additional stresses, which results in expected lesser damage.

Abstract: As the general public begin to attach greater importance to the firefighting capacities of large public infrastructures, it is high time for an overhaul of the medical, leisure and teaching infrastructures and so on concerning their firefighting capacities. In response to the especially drastic increase in the demands for medical resources, armed forces hospitals are being opened to the public for medical and teaching purposes. In order to meet the daily needs and maintain their operations in a sustainable manner, these hospitals have gone through many spatial and furnishing alterations, hence the changes in their original constructional and fire protection design. These changes, however, might lead to an increase in the risk factors. With Taoyuan Armed Forced General Hospital, which is fairly large in size, as the fireground for the simulation, and the previous cases of fire in the hospital as the basis for the numerical simulation analysis, this study is set out mainly to investigate and validate the impacts of the firefighting facilities (which are consistent with the fire codes and regulations) on the efforts of the people inside the hospital to escape from a fire under such a variety of circumstances as when the space is closed, open, or as the fire sources change in nature and position. Compartmentalization and precautions are used in the process to minimize fire losses. The main objective of this study is to develop some fire safety education materials for such public places as government organizations and schools.

Abstract: Modification of combustible materials, against easy ignition and combustion is an effort of many researchers. Modification of traditional materials, wood and textiles from natural mate-does it for their natural character quite complicated. Despite this complexity, it is one of the ways within the fire prevention.