Fire Load Research Articles

Quantitative analysis on post–fire–resistant performance of high–strength steel plate girders using LSTM

After a fire, the exposure temperature and cooling method have lasting effects on the mechanical performance of structural steels, which have an influence on the bearing performance of steel members. To evaluate the residual service capacity of steel structures after a fire, it is meaningful to perform a quantitative analysis of the effects of differences in the stress–strain properties on the bearing performance of steel members. To address this issue, a long short–term memory (LSTM) network was constructed to accurately predict the post–fire load–displacement curves to facilitate the behavioural study of numerous samples of the Q690 high–strength steel (HSS) plater girder under shear. Then, the complex effects of the exposure temperature and cooling method on the bearing capacity of the HSS plater girder were quantified using four performance indexes extracted from the load–displacement curves for three different limit states. The LSTM model was trained and tested on the comprehensively validated finite–element analysis results. For better prediction accuracy of the load–displacement curves, Bayesian optimisation was employed for hyperparameter tuning, followed by ten–fold cross–validation. The developed LSTM model was proven to be accurate and efficient in reproducing the load–displacement curves of plate girders.

CFD-Based Fire Risk Assessment and Control at the Historic Dong Wind and Rain Bridges in the Western Hunan Region: The Case of Huilong Bridge

The Dong wind and rain bridges in western Hunan are among the most extraordinary historical buildings that express the unique culture of the Dong people, and are an unparalleled display of history, culture, aesthetics and architectural skills, but they are exposed to various disasters. However, fire poses a serious challenge to historical wind and rain bridges. This study investigated the fire risk of wind and rain bridges in terms of building materials, structural forms, fire habits, and fire loads. Fire dynamics simulator software and SketchUp modeling software were used to visualize and numerically simulate fire conditions. The survey results indicated that the fire load of the Huilong bridge was 1,794,561 MJ. After a fire, the central pavilion underwent a flashover at 200 s. By 600 s, the maximum temperature of the bridge was 1200 °C, and the entire bridge was in flashover condition. Furthermore, targeted fire-mitigation strategies were proposed according to the architectural characteristics and cultural environment of the wind and rain bridges in terms of the following four components: automatic fire-extinguishing equipment, fireproof coatings, suspended ceiling, and skylights. The effectiveness of the fire-resistance performance of the strategies was also evaluated. The fireproof coating measures were the most effective, and the bridge sections delayed reaching the flashover state by 40–80 s. The reported results can help reduce the fire-related risks of wind and rain bridges and protect our historical heritage more effectively and efficiently. Furthermore, this study can serve as a reference for other historic wooden structures to develop appropriate mitigation strategies.

Performance of Composite Plate Shear Walls/Concrete Filled (C-PSW/CF) Under Fire Loading: A Numerical Investigation

Concrete-Filled Composite Plate Shear Walls (C-PSW/CF), also known as SpeedCore walls, are being increasingly used in commercial buildings due to the benefits of modularization and expedited construction schedules. This paper numerically investigates the behavior of C-PSW/CF subjected to combined gravity and fire loading. 3D non-linear inelastic finite element models of C-PSW/CF were developed and benchmarked to existing experimental data. The benchmarked models were used to understand the thermal and structural behavior of the walls under uniform fire loading, and to evaluate the effect of different parameters on the response of C-PSW/CF to combined gravity and fire loading. The parameters considered in the study were boundary conditions, wall slenderness ratio, wall thickness, axial load ratio, concrete strength, steel plate slenderness, steel reinforcement ratio, and tie bar spacing. Fire loading led to high surface (steel plate) temperatures, the evolution of non-linear thermal gradients through the cross-section, and progressive degradation of the material properties. The walls expanded longitudinally due to the thermal loads. The degradation in material properties resulted in local buckling of the steel plates between the tie bars. Continued fire exposure led to crushing/global instability failure of walls under gravity loads. The time to failure of the walls reduced considerably with a reduction in rotational fixity at the boundary conditions, reduction in wall thickness, and an increase in the wall slenderness. The steel plate slenderness of the walls should be limited to 1.2√Es/Fy to improve the time to failure of the walls. The results from this study will form a basis for the development of recommendations to estimate the fire-resistance rating and the compressive strength of the walls at elevated temperatures.

Comparative study on the dynamic mechanical properties of steel fiber reinforced concrete at high temperatures and after high temperature cooling

The mechanical behaviors of structure concrete can degrade significantly at high temperatures from fire. The mechanical performance of structure concrete may recover to some extent during the subsequent cooling process after fire. A comparative study on the dynamic performance of concrete between at high temperature and after cooling down is necessary to predict dynamic response of structures subjected to fire or blast loads more precisely. In this paper, the dynamic characteristics of Steel Fiber Reinforced Concrete (SFRC) after high temperature cooling were examined with the use of Split Hopkinson Pressure Bar (SHPB) and compared with the test results at high temperature. The dynamic compressive strength, dynamic increase factor (DIF) of stress and peak strain of SFRC with different fiber volume (0%,1%,2%) after natural cooling from different target temperatures (200 ℃, 400 ℃, 600 ℃) to ambient temperature were obtained and compared. Experimental results show that the dynamic compressive strength and peak strain of the specimen first increases and then decreases with the increase of the strain rate cause the high temperature cooling process made the specimens prone to local failure at high strain rates. The mechanical properties of SFRC such as strength can be well recovered during the natural cooling process after high temperature. The deformation capacity and energy dissipation capacity of different types of concrete after high temperature cooling are greatly improved compared with that under high temperatures.

Experimental study on the effectiveness and safety of cement powder on extinguishing metal magnesium fires based on pneumatic conveying technology

A pneumatic conveying powder device was carried out to investigate the fire-extinguishing performance of cement powder against metal magnesium fire. The fire suppression test shows that pneumatic conveying can effectively transport cement powder to the combustion area for suppressing metal magnesium fire, and the fire-extinguishing time increases with the fire load of metal magnesium. The fire suppression effect of cement powder in metal magnesium fire is ascribed to the formation of a thermally insulation layer as physical barrier concomitant with heat absorption during pyrolysis process that effectively weaken the heat transfer and reduces the combustion intensity, as supported by the morphology and DSC analysis. The results of explosion suppression test reveal that cement powder has a significant inhibitory effect on reducing the explosion max-pressure and max-pressure rise rate of methane explosion, exhibiting a high-level security in the fire-extinguishing process. This work provides an effective and safe strategy for extinguishing metal magnesium fires. • A pneumatic conveying device was designed to transport cement powder in fire extinguishing field. • Pneumatic conveying cement has excellent extinguishing effect in metal magnesium fires. • Inhibition effect of cement powder on methane explosion verifies the safety in extinguishing process. • The fire suppression mechanism of cement powder in metal magnesium fires is proposed.

Analysis on the Dynamic Responses of Steel Beam under the Condition of Heat and Blast Loads

Numerical simulation and analysis on the responses of steel beam under fire thermal load and blast load are performed using ABAQUS general finite element program. In this study, two cases with different order of applying the fire thermal load and blast load in a different order are considered: 1) when the steel beam is heated by fire first and then is impacted by blast load, the influence of the temperature on the pulse amplitude–impulse (P-I) diagrams is discussed and the saturated impulse and the minimum impulse related to temperature are analyzed. 2) when steel beam is impacted by blast loading first and then is attacked by fire, the influences of the initial static load and the pulse amplitude on the critical temperature-impulse (Tcr-I) diagrams are analyzed. The analysis results show that the higher the temperature is, the lower the impact resistance capability of steel beam is. The saturated impulse and the minimum impulse can be used to measure the impact resistance capability of steel beam. The impulse I(ηD) can be used to measure the fire resistance performance of steel beam. The blast load can obviously reduce the fire resistance capability of steel beam.

A Latent‐Fire‐Detecting Olfactory System Enabled by Ultra‐Fast and Sub‐ppm Ammonia‐Responsive Ti3C2Tx MXene/MoS2 Sensors

AbstractExplosive developments in modern society bring huge fire loads. Previous fire detections at early stages are basically enabled by recognizing abnormal high‐temperatures, smoke particles, and flame light signals. However, the identification of these characteristic signals is generally accompanied by an open flame or smoke, which makes it difficult to prevent further serious damage. Herein, a latent‐fire‐detecting strategy of trace ammonia (NH3) analysis based on nanohybrid Ti3C2Tx MXene/MoS2 is proposed. Benefiting from nanoscale high‐density Schottky heterojunctions between MoS2 and Ti3C2Tx MXene, ultrafast (3 s @100 ppm), sub‐ppm (200 ppb minimum), and high‐sensitivity (81.7% @100 ppm and 10.2% @200 ppb) detection of NH3 are enabled. An assembled latent‐fire‐detecting olfactory system (LFOS) based on MXene/MoS2 and interdigital electrodes can monitor trace NH3 releases from different materials (wool, leather, foam, and nylon) during thermal decomposition at latent stages. Notably, the LFOS can detect fire threats at least 84 s earlier than commercialized smoke detectors, providing more fire dealing time and an escape period; this offers a promising latent‐fire‐warning approach for eliminating fire treats at an early stage.

Prediction of air quality in Sydney, Australia as a function of forest fire load and weather using Bayesian statistics.

Smoke from Hazard Reduction Burns (HRBs) and wildfires contains pollutants that are harmful to human health. This includes particulate matter less than 2.5 μm in diameter (PM2.5), which affects human cardiovascular and respiratory systems and can lead to increased hospitalisations and premature deaths. Better models are needed to predict PM2.5 levels associated with HRBs so that agencies can properly assess smoke pollution risk and balance smoke risk with the wildfire mitigation benefits of HRBs. Given this need, our aim was to develop a probabilistic model of daily PM2.5 using Bayesian regression. We focused on the region around Sydney, Australia, which regularly has hazard reduction burning, wildfires and associated smoke. We developed two regional models (mean daily and maximum daily) from observed PM2.5, weather reanalysis and satellite fire hotspot data. The models predict that the worst PM2.5 in Sydney occurs when PM2.5 was high the previous day, there is low ventilation index (i.e. the product of wind speed and planetary boundary layer height), low temperature, west to northwest winds in the Blue Mountains, an afternoon sea breeze and large areas of HRBs are being conducted, particularly to the west and north of Sydney. A major benefit of our approach is that models are fast to run, require simple inputs and Bayesian predictions convey both predicted PM2.5 and associated prediction uncertainty. Future research could include the application of similar methods to other regions, collecting more data to improve model precision and developing Bayesian PM2.5 models for wildfires.

Cost-optimization based target reliability for fire design of insulated steel columns

Adequacy of a structural fire design can in theory be demonstrated through a probabilistic risk assessment (PRA) where the compliance with tolerability limits and the ALARP requirement are explicitly ascertained. However, explicit assessment of ALARP requirement is challenging and impractical for day-to-day designs, due to the burden of estimating uncertain future costs and current safety investment costs. For normal design conditions, the use of target reliability indices has been recommended instead. These target reliability indices however have not been defined for structural design under fire events. To address this gap, the current study demonstrates a method to derive target reliability indices for a fire-exposed structure. As a case study, an insulated steel column (with varying levels of ISO fire rating) exposed to parametric natural fires is considered. The target reliability indices are derived for the steel column for varying fire exposure scenarios, considering different fire load densities and opening factor, relating to the building occupancies. This study thus investigates the important issue of adopting target reliability indices in fire design that are cost-optimized from quantitative analyses considering natural fire exposures, which has significant implications for fire safety and rational use of resources in the construction industry.

Experimental study on behavior of restrained high strength Q690 steel beams exposed to fire

In comparison to the isolated steel beam, the restrained steel beam is able to sustain fire loads using the effect of the surrounding restraints. However, Q690 steel has lower resistance to high temperatures than other types of carbon steel. To address this gap, a series of experimental tests on restrained high-strength Q690 steel beams subjected to fire are reported in this paper. Four full-scale restrained high-strength Q690 steel beams were investigated under several fire scenarios, and one was tested at room temperature. In this study, three transient tests and one steady-state test were chosen to fully comprehend the behavior of the restrained high-strength Q690 steel beams exposed to fire. Under the two test conditions, the impact of the steady-state and transient conditions on the fire response of the restrained Q690 steel beams are compared, and the variation of axial peak force, bearing capacity, and deflection were analyzed. The results showed that the critical temperature of the steady-state test is close to the critical temperature of the transient test, and the maximum axial force of the steady-state test is comparable to the one of the transient test. Due to the combined action of load and axial forces, the restrained Q690 steel beam generally develops flexural-torsional buckling failure after reaching the critical temperature in transient tests. In comparison, the steady-state test exhibits early flexural-torsional buckling behavior before reaching the critical temperature.

An overview of the impacts of autonomous vehicles on fire safety in parking buildings

Several fire safety benefits are realised when considering autonomous vehicles (AVs) using parking buildings. Hazards posed by the increasing number of alternatively powered vehicles on the road, such as electric vehicles (EVs), may be mitigated. Parking AVs in designated zones would allow for the installation of fire-suppression systems other than those that are water-based, permit alternative ventilation requirements and allow for the reconfiguration of the building structure. Connected AVs could communicate with other vehicles, the parking building and the emergency services, resulting in a more effective response to a developing fire incident. However, AVs may increase fire safety hazards when considering alternative parking arrangements that promote more extensive fire spread, increase the median fire load energy density by at least 13% and inhibit firefighting. This may impact on the operational capability of the emergency services and the expectations of the structural fire safety design of the building. In this paper, options are presented that would influence the design and use of parking buildings where AVs and EVs are present. Presently, it is unclear whether the introduction of AVs will increase or decrease the fire safety risk to life and property, and further research is suggested to better understand such matters.

3D numerical investigation on response of shield tunnel under combined effects of fire and structural loading

As a significant infrastructure hazard, fires in tunnels have brought about a great deal of economic and social losses each year. From a holistic tunneling design perspective, it is essential to predict accurately the displacements and internal forces of the lining under coupled effects of elevated temperatures and various loading conditions. To this end, an elaborate three-dimensional (3D) numerical model, which incorporated the concrete segments, reinforcing rebars and connecting bolts, was established to investigate the deformation and failure mechanism of the segmental ring in shield tunnels under coupled effects of fire and structural loading. The validation based on the experimental results of segment lining and joints shows that the established model can be employed to analyze the entire tunnel ring structures. Two types of numerical models, i.e., single-ring and three-ring models, were established and the thermo-mechanical coupled performance were examined. Based on the verified model, the general temperature field and deformation distribution were described and elaborated. With respect to the significant insights on mechanical behaviors of shield tunnel rings in fire, the results of inner force redistribution, the joint opening elaboration and the failure mechanism of the shield tunnel structure under fire effects and initial loadings were further discussed. The results of this study can provide valuable guidance for the fire resistance design in the tunnel.

Theoretical Prerequisites for Creating a Fire-Extinguishing Solution Based on Water-Absorbing Polymer Ecoflocf-07 for Extinguishing Fires in Ecosystems

Extinguishing fires in ecosystems has features compared to extinguishing fires in residential and industrial buildings, due to the composition and structure of combustible materials, which can form many foci of smoldering and have the ability to re-ignite, have a relatively low fire load compared to man-made ones. All this leads to high costs of water for extinguishing, carrying out operations for additional extinguishing of fires that occur after the main extinguishing and sets special requirements for aqueous extinguishing agents for their extinguishing.The paper analyzes the current state of the availability and trends of development in the world and domestic practice of effective water extinguishing agents and technologies for their use. Possible ways to improve recipes and increase the efficiency of fire extinguishing substances are outlined, taking into account, first of all, the criteria of efficiency, economy and environmental friendliness.It is noted that the main direction of increasing the fire extinguishing capacity of water is to create combined fire extinguishing solutions that can combine several methods of extinguishing in one technological operation: cooling, isolation and inhibition, which, other things being equal, reduces fire extinguishing consumption and extinguishing efficiency. An integrated direction of increasing the fire-extinguishing capacity of water can be considered to increase the coefficient of active use of water by reducing the surface tension of the fire-extinguishing solution, increasing the wettability and viscosity of water by introducing appropriate additives, obtaining optimal droplet dispersion.

Numerical model for tracing the response of Ultra‐High performance concrete beams exposed to fire

AbstractThis paper presents a numerical procedure for evaluating the thermo‐mechanical response of Ultra‐High Performance Concrete (UHPC) beams exposed to fire. The numerical model is based on a macroscopic finite element formulation and utilizes sectional moment‐curvature relations to trace the response of UHPC beams from the linear elastic stage to collapse under combined effects of fire and structural loading. Fire‐induced spalling, temperature‐dependent properties of concrete and steel reinforcement, and realistic failure criteria are incorporated into the analysis. Specifically, an advanced analysis approach for evaluating spalling is incorporated in the model by considering the stresses arising from the combined effects of thermal gradients, structural loading, and pore pressure generated in the concrete section. Comparisons of the predictions from the model with data from fire resistance experiments show a good correlation, indicating the proposed model can reliably predict the thermo‐mechanical response, including the extent of spalling in UHPC beams subjected to fire exposure. The applicability of the model for undertaking advanced analysis is shown by conducting a case study to illustrate the influence of load level and fire scenario on the fire response of the UHPC beams.

Performance Evaluation of Reinforced Concrete Columns under Simultaneously Combined Fire and Cyclic Loads

Reinforced concrete (RC) structures could suffer from the combined action of fires, earthquakes, and other loads during their life cycle; more importantly, coupled disasters lead to further deterioration and damage to structural performance. This paper investigated the multiple performances and distinguished the safe working conditions of the RC column subjected to simultaneously combined fire and cyclic loads. The numerical model considered the degradation of the mechanical properties of steel and concrete and the bond-slip performance between steel and concrete at high temperatures. The results show that the performance of RC columns with different section sizes, longitudinal reinforcement ratios, cover thicknesses, axial load ratios, and cyclic loads differs greatly under simultaneously combined fire-cyclic loads. In specific, when the cyclic load application time is less than 2 h, the cyclic load has little effect on the response of the RC column. According to the different characteristics of RC columns when subjected to combined fire-cyclic loads, the firing process of RC columns is divided into four stages. To avoid the excessive performance degradation of RC columns, the minimum designed fire resistance time of RC columns is recommended to be 2.5 times the fire resistance time of the RC column under static loads.

Determining the effect of fire from external air conditioning units on buildings' facades

This paper considers the issue of assessing the possible impact of fire in external air conditioning units on the evolution of façade fires using the example of a typical façade of the building. Current methods for assessing the effectiveness of limiting the spread of façade fires do not take into account the possibility of external fire load. Existing methods of studying the effects of combustible components in façade systems are intended only to investigate the reaction to the fire of façade systems. At the same time, it should be understood that modern façade systems include additional components that not only have a significant fire load but can be the cause of a fire. Taking that into consideration, a study was conducted on the impact of a possible fire of external air conditioning units on the development of its evolution by vertical structures in buildings. During the FDS modeling, the possibility of facing materials from a low combustibility group, which are typical for modern façade systems, is taken into account. Analysis of the fire load of the components included in the design of air conditioning units has made it possible to recreate the model of the combustion reaction of the main components and determine the value of its maximum intensity. The data on the thermal distributions on the surface of the façade made it possible to make assumptions about the necessary structural parameters that should be observed when determining the places of installation of baskets for air conditioners. The established dependences are a prerequisite for revising the criteria for assessing the potential fire danger of façade systems, which may include additional engineering systems. The derived dependences will make it possible to revise approaches to existing field procedures for assessing the fire danger of façade systems. The practical result of the implementation of these data may be amendments to building codes to increase the level of fire protection of façade systems and buildings in general

Study of the evolution mechanism of multi-window carriage fire under longitudinal ventilation in a metro tunnel

The fire evolution and ejected flame characteristics of a metro train under longitudinal wind were investigated by numerical simulation and scale-model experiment. The combustion heat release rate (HRR), geometric characteristics of the external flame, and temperature distribution beneath the tunnel ceiling were studied under a total of 159 working conditions. The results show the influence of longitudinal ventilation in the metro tunnel on the airflow of upstream and downstream windows. The airflow enters the carriage from downstream windows and exits through upstream windows. The flow rate of windows is positively correlated with ventilation velocity. Parameters such as fire load, ventilation factor and longitudinal ventilation determine the heat release rate of fire combustion in the enclosed space. When the fire load is less than 1500 times the ventilation factor, longitudinal ventilation will reduce the combustion heat release rate; otherwise, the longitudinal ventilation will promote combustion reaction. Longitudinal ventilation affects the external flame size by changing the window airflow and air entrainment. In addition, the longitudinal inertial force increases the flame deflection angle and horizontal length. The temperature beneath the tunnel ceiling decreases significantly under longitudinal ventilation. Therefore, in a metro tunnel with longitudinal ventilation, passengers should be protected from high temperature when passing by the fire carriage during evacuation.

A Quantitative Analysis of the Fire Hazard Generated from Hydrogen Fuel Cell Electric Vehicles

There is a lack of information on (i) the potential fire load of new green-technology vehicles, (ii) flame spread behavior, (iii) thermal impacts on high-pressure hydrogen storage vessels (HSVs) and lithium-ion batteries (LIBs) during fuel cell electric vehicles fires (FCEVs), and (iv) thermal damage to adjacent vehicles and upper structural members during FCEV fires occurring in civil structures, such as underground spaces, multi-story parks, and tunnels. In view of this, a full-scale fire test was conducted in this study to quantitatively assess the fire risk of hydrogen FCEVs. Large-scale cone calorimetry was used to quantify the thermal intensity released from the FCEV fire. The flame spreading behavior through an FCEV with HSVs and LIBs was observed using the thermocouples installed. Changes in the temperature and irradiance around the FCEV fire were also measured using an instrumented test rig. The peak heat release rate, total heat released, and fire growth rate were observed to be 5.99 MW, 11.8 GJ, and 0.0055 kW/s², respectively. The temporal point of hydrogen gas release from the HSVs' thermal pressure relief device (TPRD) was estimated to be 16.2-26.2 min. The initiation of thermal runaway of LIBs was deduced from the temperature-time profiles of the LIB modules and their metal housing approximately 22.2 min after HCEV ignition. Moreover, FCEV fires could thermally impair adjacent upper structural members by 800 ℃ combustion gas for at least 13 min and emit a median heat flux of 27.2 kW/m² (peak heat flux of 76.5 kW/m²) to adjacent vehicles. The measurements and findings obtained from this study can contribute to the evaluation of and further studies on newly emerging fire hazards.

Effect of Shape on the Temperature of an Opening Jet Plume at the Bottom of a Horizontal Member

In this study, combustion tests, in which the opening condition of a fire source was changed using a large-scale compartment and horizontal member, were conducted. The inner temperature, temperature distribution under the horizontal member, external flame shape, and neutral zone height of the compartment were measured under various opening conditions. The results were analyzed using the temperature prediction equation for the opening jet plume at the bottom of a horizontal member, proposed by the Architectural Institute of Japan (Building fire load and design fire property guideline (draft)), and a review was deemed necessary.

Mechanical Performance Analysis of Steel Beam-Column Joints in Fabricated Multirise Steel Structures after Fire

This study aims to analyze the mechanical properties of fabricated multistory and high-rise steel structures and steel beam-column joints after fire. Considering that the steel structure building has the characteristics of good seismic resistance, flexible structural layout, short construction period, and good safety, first, the thermal and mechanical properties of steel are analyzed. They are thermal conductivity, the thermal expansion coefficient of steel, yield strength, and elastic modulus of ordinary steel. Next, the thermal conduction principle of steel under fire environment is analyzed, including thermal conduction, thermal convection, and thermal radiation. Then, the three-story and three-span reinforced concrete is selected as the experimental object. The local frame calculation model is established through the finite element software Abaqus. It is found that when the axial compression ratio is 1.0 and the fire time of the steel body is 180 min, the vertical deformation speed of the middle column and side column of the frame will increase rapidly. Besides, the bending moment at the bottom of the side column of the frame will increase inversely. The change is not obvious when the axial compression ratio is other values. The axial deformation of the universal beam is obvious under the condition of different fire load ratios. When the load ratio increases, the maximum fire resistance of the universal beam will decrease rapidly. Meanwhile, when the steel body is subjected to the same load ratio, different bearing capacity β has little effect on the fire resistance limit of the steel body. This thesis focuses on a series of changes in the steel of fabricated multistory and high-rise steel buildings after the fire, hoping to provide a reference for the relevant teams of steel construction and make the future housing construction safer.