Fire Technology最新文献

Exploring fire resistance of high strength steel end-plate connections is one of the key technical bases for fire resistance design and fire safety assessment of high strength steel structures. Numerical simulation and parameter analyses of high strength Q690 steel flush end-plates will contribute to a reasonable design of high strength flush end-plate connections. In this paper, a finite element model of high strength steel flush end-plate connection considering thermal creep effect was established and validated by experimental results. The thermal creep finite element model can simulate accurately heat performance, failure modes and deformations of high strength flush end-plate connections at elevated temperatures. The increase of axial compression ratio has little effect on rotation, deflection, failure time, critical temperature, and critical rotation with elevated temperatures. The increase of bending moment ratio has little effect on the development trend of rotation and deflection. Proper increase of thickness of the end-plate can improve failure time and critical rotation, and the increase range is within 7% and 36% respectively. Proper increase of diameter of bolt can improve failure time, critical temperature, and critical rotation to a certain extent, and the increase range is within 10%, 6% and 27% respectively. Proper increases of thickness of the end-plate and diameter of bolt will improve the fire resistance of flush end-plate connection.

Model-scale experimental tests and numerical simulations were conducted to investigate the characteristics of the smoke overflow at the lateral carriage doors and the smoke temperature below the tunnel ceiling of a carriage fire in a longitudinally ventilated tunnel. Results indicates that the smoke overflows from the carriage into the tunnel through the lateral doors downstream of the fire source under the impact of longitudinal ventilation. Depending on the fire location, the amount of the overflow smoke exhibited either an inverted V-shaped variation or a monotonical increase with the door position. Multiple peaks in the smoke temperature below the tunnel ceiling is attributed to the uneven distribution of the overflow smoke. A dimensional analysis revealed a quantifiable relationship between the heat flow of the overflow smoke and the peak temperatures below the tunnel ceiling. Consequently, an empirical model was developed to predict the maximum smoke temperature below the tunnel ceiling under different heat release rates and longitudinal ventilation velocities. These findings are excepted to enhance the understanding of carriage fires and provide a theoretical guidance for future ventilation and safety designs in subway systems.

This paper is aimed at studying the down-reaching flame behaviors of tank fires with large ullage heights. Experiments were first conducted using a gas burner in a transparent quartz glass cylinder to simulate the large ullage and the experimental data was used to validate the computational fluid dynamics (CFD) model. Subsequently the effects of ullage height, fuel velocity and burner diameter on the flame behaviors were examined systematically. Both experimental and numerical results showed that, for lower fuel velocities, the down-reaching flame height (h_down) is restricted by the ullage height. As the fuel velocity continues to increase exceeding a critical value, independent of the ullage height, h_down starts to decrease. For a given fuel velocity, h_down increases with an increase of the burner diameter owing to enhanced air entrainment. A detailed analysis of the flow field and oxygen concentration inside the tank at the steady burning stage was also carried out. Based on the numerical results and dimensionless analysis, a piecewise function was proposed to predict the down-reaching flame height and validated against the experimental data.

The post-fire assessment of concrete structures is a complex task that requires the integration of multiple measurements from different techniques. The current approach to integrate information from different sources relies mainly on expert judgement, meaning that no explicit consideration is given to the precision of different techniques. This paper presents a Bayesian updating methodology that integrates information from different sources about the maximum temperature the concrete experienced during fire exposure at a certain depth, such as discoloration and rebound hammer measurements, by considering the uncertainties and errors associated with measurements. The data is then used to update the prior information on the uncertain parameters of interest, here the fire load density and opening factor. These updated distributions provide a better estimate of the fire exposure, thermal and damage gradient and the residual condition of the structure. The proof-of-concept and effectiveness of the proposed methodology are demonstrated through a case study. The results show that the proposed methodology is able to effectively incorporate the uncertainties and errors associated with the assessment techniques, producing more reliable estimates of the fire severity. This method has the potential to improve the post-fire assessment process and provide more accurate information for the rehabilitation of concrete structures.

One environment that hinders the performance of reinforced concrete is fire. In most cases, this results in the affected part or the entire structure being rendered useless or completely collapsing. When fire mishaps happen in structures, this is the case. This study reviews green structural retrofitting materials for reinforced concrete buildings in an effort to repair damaged structures in an environmentally friendly manner. The information gathered from earlier laboratory test results is assembled to comprehend the impact of room temperature strength properties and varied concrete mix material composition on the residual mechanical properties of concrete. The performance of various fibers, synthetic and natural, as laminate materials for concrete were evaluated, and the study showed that to a significant extent, distressed structural elements could be repaired with retrofits. However, provision of appropriate guidelines for using natural fibre laminates for retrofitting has not been overly explored. This review has highlighted areas that require further study in order to fully understand the residual strength characteristics of concrete exposed to high temperatures, particularly damaged concrete that have been retrofitted with fibers. Overall, the review's findings will be helpful to academics, professionals in the field of civil engineering, and those engaged in construction.

For more than a century, smoke explosions have been documented in the fire research literature. Yet even with this long history, smoke explosions have received very little attention in the fire research community. The few review articles on unexplained explosions (overpressure events) have adopted the conventional names of smoke explosions, backdraft, smoke gas explosions or rapid fire progression. Anecdotal evidence from firefighters have shown a number of overpressure events that cannot be explained as a gas leak or flammable liquids ignition. In this study, experiments were conducted in a plywood lined compartment with a timber crib as a sustained fire source and the ignition source. The compartment had a single vent that was open for the entire time. After an extended period of burning, the flames detached from the crib, traveled around the compartment, and finally self-extinguished. Sometime after the flames self-extinguished, the compartment erupted in flames culminating in a large horizontal flame projecting more than 2 m from the vent opening. In this study, a consistent cycle that leads to an overpressure event has been identified. A total of 29 overpressure events were created in 13 experiments with many experiments experiencing multiple overpressure events. Gas species, compartment temperatures, vent velocities, and compartment pressure were all recorded during the experiments. Conditions in the compartment immediately prior to the overpressure event are reported. Having demonstrated that an overpressure event within a combustible compartment can be reproduced, future research is recommended to better quantify the conditions leading to an overpressure event.

The main objective of this paper is to use the residual strength theory to study the probability of a domino effect accident occurring following the explosion of a spherical tank. We build a novel domino effect accident probability model, using Monte Carlo methods to simulate the ejection of debris. At the same time, the velocity and velocity distribution of fragments ejecting from the upper and lower parts of the explosive spherical tank are obtained. Finally, the relationship between the volume of the exploding spherical tank and the target, the crater Angle (ψ₀ and ϕ₀) of debris impacting the target, the probability of target destruction and the risk of domino effect accidents are considered. The results show that the maximum speed of debris from the lower part of a spherical tank exceeds that from its upper part, and the hazard associated with the debris from the lower part cannot be ignored. With the same target volume and spacing, the probability of a domino effect accident caused by projectile debris from the upper half of an exploding spherical tank is higher than that from the lower half. As theψ₀ value increases, the probability of target failure gradually decreases, and as the ϕ₀ value decreases, the probability of target failure also gradually decreases. Moreover, with changes in ψ₀ and ϕ₀, the probabilities of destruction and the occurrence of a domino effect accident significantly change. The results of this paper can provide guidance for the risk assessment of oil and gas storage tanks.

The knowledge of the fire safety distance of the multiple pool fires is essential to model, manage, and mitigate the fire hazardous scenarios to safeguard the surrounding people, buildings and equipment. In this work, experiments are performed on 0.1 m gasoline double pool fires to calculate the fire safety distances using an infrared imaging technique. The distance (S/D) between the two pool is varied from 0 to 1. The irradiance from the two pools is calculated using the two-dimensional temperature field obtained by an IR camera. The calculated irradiance along the flame axial direction and on the ground is presented in a contour format. The safety distances are also represented as a function of their respective flame lengths. Two threshold heat fluxes: (I) 1.4 kW/m² and (II) 4.7 kW/m² which are required for human safety are emphasised in the contour plots for all the configurations.

Nowadays, significant research effort is being dedicated to explore environmentally friendly block materials with high strength and high-temperature resistance. Ground-granulated blast-furnace slag (GGBFS) is produced during the iron smelting waste process and can be activated to form the environment friendly alkali-activated slag cementitious material (AASCM) when mixed with alkaline activator. The aggregate consists of particles of different sizes, which are crushed and are screened using the paste of AASCM. In this study, the compressive strengths of 234 block specimens during and after high-temperature treatment were investigated. The test results showed that the compressive strength of the blocks gradually decreased slowly when the temperature was lower than 600°C, and decreased rapidly when the temperature was above 600°C. The reduction coefficient of compressive strength of the blocks during and after 900°C exposure were 14.2% ~ 28.1% and 15.3% ~ 28.7% of the ambient temperature strength, respectively. The steel fibre reduced the compressive strength loss of the blocks during and after the high-temperature exposure. With the increase of temperature, the steel fibre lost its effect gradually. Moreover, the compressive strength of the block after the high-temperature treatment was higher than that during the treatment when the strength level and temperature remained constant, the ratio was between 0.99 and 1.14. The high-temperature strength loss of the alkali-activated slag crushed aggregate concrete block was lower than that of the alkali-activated slag ceramsite concrete block. The fitted equations for calculating the compressive strength during and after the high-temperature treatment provided a basis for evaluating the fire resistance of this new type of block. The microstructure and composition of the block were analysed through scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results provide theoretical basis and data support for the application of AASCM in masonry blocks in high-temperature environments.