Fire Technology最新文献

This study investigates the behavior of super ductile (SD) reinforcing steel bars after exposure to elevated temperatures, highlighting their distinctions and superior performance compared to conventional steel types such as cold-worked, hot-rolled, and thermo-mechanically treated (TMT) bars. The research examines the changes in mechanical properties, including yield strength, ultimate strength, modulus of elasticity, and ductility, through detailed stress–strain analysis and mechanical property evaluation across varying temperature ranges. The findings demonstrate that SD bars exhibit enhanced mechanical properties under high-temperature conditions, retaining higher yield and ultimate strengths, and maintaining a more pronounced strain hardening region compared to other steel types. Specifically, SD bars preserve higher residual strength after exposure to 800°C, significantly outperforming cold-worked and hot-rolled bars. The modulus of elasticity of SD bars shows better stability at moderate temperatures and a less pronounced decrease at higher temperatures, reflecting their superior ability to absorb energy before failure. Parabolic regression models were developed to predict the degradation in yield and ultimate strengths, while polynomial curve fitting methods were used to establish stress–strain models for post-heating scenarios. This research fills a critical gap in the current understanding and provides robust degradation models that are essential for the design and safety assessment of reinforced concrete structures using SD550 steel under thermal stress conditions.

Pressure-sensitive adhesive tapes are used in automotives, railway vehicles and construction, where flame retardancy is of major importance. This is why industrial applicants often buy, and industrial tape manufacturers often produce, flame-retardant adhesive tapes, advertised for their good flammability characteristics. Yet, how flame-retardant tapes influence the fire behavior of bonded materials is a rather open question. To investigate this issue, three different substrates were bonded, using eight double-sided adhesive tapes containing two different carriers and two different flame retardants. The bonded substrates were compared to their monolithic counterparts in terms of flammability, fire behavior and fire stability. The fire behavior of adhesive tape bonded materials differed significantly from the monolithic substrates. The usage of different adhesive tapes let to different burning behavior of the bonded materials mainly due to different carrier systems. In contrast, the implementation of flame retardant into the adhesive had rather minor or no effect on the burning behavior of the bonded substrates despite their positive effect on the flammability of the free-standing tape. The carrier changed the HRR curve in the cone calorimeter and was able to both, reduce and increase fire hazards. Using the carrier with the better fire performance can lower the fire growth rate by 20%, the peak of heat release rate by 27%, and the maximum average rate of heat emission by 30% in cone calorimeter tests. Overall, the fire behavior of bonded materials is a complex interaction between substrate, adhesive, and carrier, and depends on the fire scenario the materials are exposed to.

The existing early-warning methods primarily rely on detecting structural displacements which are often challenging to measure accurately in real fire scenarios. To develop innovative early-warning strategies, this paper experimentally and numerically investigates the fire-induced collapse of an 8 m × 6 m steel portal frame assembly. Detailed thermo-structural responses of the frame were measured and presented, including the displacements and rotations. The results revealed that the vertical mid-span displacement and horizontal displacement at the rafter end are key to developing an effective early-warning system. Structural rotations seem sensitive to structural deformation and emerges as a valuable safety indicator for structural systems. Furthermore, parametric analyses were carried out in order to investigate the effect of load ratio, fire protection and heating curve on key parameters of the structure subjected to fires. It is discovered that the increased load ratio can reduce the peak value of vertical displacement at the mid-span of the rafter. A rotational angle of 6° in the steel beams is optimal for predicting the collapse of steel portal frames in fire conditions. Based on the parametric studies, an innovative early-warning approach using rotational angles is proposed and validated against the test frame, demonstrating significant applicability and reliability. The rotation-based early-warning approach works in two distinct stages, being activated respectively by the maximum and zero rotational angles at the end of rafter. The early-time ratios for the respective warning stages are 0.65 and 0.88. For better precision and practical reliability, it is further recommended to combine the rotation-based and displacement-based approaches for the on-site early-warning of fire-induced collapse of portal frames.

Smoke stratification in a V-shaped tunnel fire is complex due to the coupling effects of the double stack effect induced by the inclined tunnel structure, the fire thermal buoyancy, and the drag force caused by water spray system. This work investigates the influence of water spray flow rate (0 L/min to 600 L/min), atomization angle (0° to 150°) and distance between fire source and grade change point (0 m to 120 m) on smoke stratification in a symmetrical V-shaped tunnel through numerical simulations. The results show that the increase of water spray flow rate causes the increasing drag force which destabilizes smoke layer and contributes to the reduction of smoke layer thickness. While the water spray angle has little effect on smoke layer thickness. Through the dimensionless analysis and simulation results, a correlation for smoke layer thickness considering water spray parameters is proposed. Water spray effects on Fr describing the smoke stratification correspond to these on smoke layer thickness. That is, Fr decreases with the increase of water spray flow rate and is weak dependent on the water spray angle, and the critical Fr for turning point of the dominant effect of thermal buoyancy and drag force is linearly related to fire heat release rate. As the distance between fire source and grade change point increases, Fr changes a little on first double-slope control stage, increases on the left and decreases on the right of fire source, and eventually both levels off on second transition phase stage, thus tends to be stable on third single slope control stage.

Different from objects with clear boundaries in target detection, the fire and smoke generated by fire are variable in shape and hard to be detected by traditional methods. To detect the fire and smoke accurately and timely, a fire identification method based on moving target enhancement and the PRV-YOLO network was proposed in this work. By considering the motion information of smoke and fire in the video data, a PCLAHE-KNN moving target enhancement algorithm is designed to roughly locate the target in the pre-processing stage. In the recognition stage, the PRV-YOLO network is developed for smoke and fire detection. For PRV-YOLO network, CSPResNeXt module is introduced in the backbone position and the VoVGSCSP module is used in the head position, which improves the detection speed and reduces the computation load of the model. Meanwhile, the priority boundary frame loss function PIoU is proposed to improve the regression speed and the accuracy of the detection model. The experimental results have shown that the proposed method has advantages in fire video monitoring, especially in terms of sensitivity to smoke in the early stages of a fire.

Fire incidents in automated vehicle parking (AVP) structures are rare, yet the impact of such incidents on the structural integrity of these systems is crucial for design considerations. Although sprinklers are recognized for their effective fire suppression in various settings, the effectiveness of sprinkler systems in AVP structures fire incidents and their contribution to the post fire conditions of these structures has received scant attention. Consequently, this study performed a comprehensive numerical evaluation of fire performance within these structures, with a primary focus on the evaluation of sprinkler systems. Three distinct fire location scenarios were employed to assess the performance of the sprinkler systems and post fire conditions of the structure. The evaluation process starts with simulation of each scenario using the Fire Dynamics Simulator (FDS). Subsequently, the FDS results were transferred to OpenSees to perform thermo-mechanical analyses. The post-fire conditions of the structure were then evaluated based on structural responses obtained from OpenSees and based on performance-based assessment (PBA) criteria. The findings indicated that the employed sprinkler configuration effectively reduced the vertical progression of fire. Notably, when the fire ignited in proximity to the facade, the sprinkler system had a lower performance compared to the other scenarios. This finding suggests the need for adopting advanced suppression system configurations that are specifically designed to reduce fire risks in these facade-proximate areas. Furthermore, these observations highlight the potential value of considering the use of non-combustible materials in facade design to improve fire safety. The outcome of this study provides insights for enhancing the fire safety measures in car parks with steel structures. Such enhancements are crucial for establishing a robust fire safety framework in these environments.

Subway trains cannot stop immediately to extinguish fires and evacuate passengers if a fire accident occurs. The piston wind generated by train movement coupled with longitudinal ventilation, makes the process of high-temperature smoke spreading upstream and downstream of the fire source more complex and unpredictable. The evacuation process of personnel is affected by high-temperature smoke in tunnels, it is worthwhile to investigate personnel evacuation in interval tunnels under longitudinal ventilation during a train fire. This paper uses a three-dimensional compressible (N - S) equation and a fully buoyant corrected Renormalization-group (RNG) (k - varepsilon) turbulence model to build a fire smoke spread model. Additionally, a cellular automaton model is employed to construct a simulation model for the evacuation of personnel in interval tunnels. We used the models to investigate the influence of longitudinal ventilation speed on smoke spread and the evacuation behavior characteristics of personnel under a moving subway train with fire. Results show that smoke spreads downstream of the fire source, and the temperature of smoke in tunnels decreases as longitudinal ventilation speed increases. A prediction model between longitudinal ventilation and the peak value of smoke temperatures in tunnels was modified based on Li's prediction model. Meanwhile, the total evacuation time decreases as the longitudinal ventilation speed increases. A theoretical prediction model between the peak value of smoke temperatures and total evacuation time is developed. The model parameters are determined using a nonlinear fitting method. The influence of longitudinal ventilation on the average flow rate and arrival time at the exit upstream of the fire source is less. However, it has a significant effect downstream of the fire source. As the longitudinal ventilation speed increases, the average flow rate at the exit downstream of the fire source increases, leading to a decrease in total evacuation time. A notable consideration is that the elderly or minors are significantly affected by smoke in the late stages of evacuation process, leading to an increase in total evacuation time.

This study analyzes socio-economic demographics (including Geomatic conzoom® segmented demographic variables) as well as building and property registration information as risk factors in relation to the prevalence of residential building fires within 100 m × 100 m cells. The logistic regression model achieved a receiver operating curve (ROC) of 0.74 and a precision-recall curve of 0.12 on the testing dataset. The model identifies 19 significant variables related to the risk of residential fire. The top 5 highest performing variables in our model and their odds ratios are the following: number of people (OR 1.25), Multi/family residence-building type (OR 1.20), number of buildings (OR 1.18), conzoom® Type C—Country/Rural Communities (OR 0.85), construction year (OR 0.87). These results indicate that socio-economic factors play a large role in influencing fire vulnerability within residential areas and can help prioritize resource allocation to reduce fire vulnerability in the identified risk factor groups.

The failure of steel connections can lead to the progressive collapse of the entire structure. Accurate modelling of steel connections at elevated temperature allows structural fire engineers to design steel structures that may deal with the severity of a fire. The prEN 1993-1-14 proposes numerical design calculation for the static design check of steel connections. This paper presents a component-based finite element model (CBFEM) to design the T-stubs at elevated temperatures. The generated model is verified and validated against the results from the analytical model and experimental study. The resistance, failure modes and the load-deformation curves are used to validate and verify the CBFEM models for steel connection design at elevated temperatures. The results stated that the CBFEM is a practical design tool to model bolted connections at elevated temperatures and it is possible to apply the recommended 5% plastic limit strain by EN 1993-1-5 for fire design of bolted connections.

Underground pipelines of different burial depths are extensively utilized in the transportation industry for the conveyance of combustible gases. Failure of these pipelines could result in a jet fire in a pit (JFP), potentially endangering nearby pipes, structures, and individuals. The objective of this study is to analyze the flame geometry and temperature distribution of a JFP. A facility, comprising a jet fire apparatus and a rectangular pit, was constructed to experimentally simulate JFPs across three distinct burial depths and nineteen nozzle exit velocities. The JFP can manifest as an impinging jet flame (IJF), a transitional jet flame (TJF) or a jet flame ejected from the pit top (JFEPT), depending on the burial depth and nozzle exit velocity. An increase in burial depth reduces the critical velocities that differentiate these three flame patterns. Empirical correlations for the flame length and width of JFPs are developed, considering different burial depths, exit velocities, and pit dimensions. Additionally, two correlations available in the literature are validated for predicting the temperature distribution of TJF and JFEPT, respectively. These findings can inform the safety design of pipeline burial depths, considering the behavior of JFPs.