Fire Design Research Articles

Thermo-mechanical behavior of composite beams with corrugated steel webs exposed to localized fire

In this study, a one-way coupling methodology combining fire simulation based computational fluid dynamics (CFD) with finite element (FE) analysis is proposed to investigate the thermo-mechanical behaviors of composite beams with corrugated steel webs (CSWs) under localized fire exposure. Fire Dynamics Simulator (FDS) is used to simulate the local fire environment, and the adiabatic surface temperature (AST) data obtained in FDS are imported into the FE models in ABAQUS by the fds2ascii coupling tool. The validations of FDS models and the CFD-FE coupling method are verified by a localized fire test on a steel beam conducted by the National Institute of Standards and Technology (NIST). Then, the CFD-FE coupling method is applied to analyze the thermo-mechanical behaviors of composite beams with concrete flanges and CSWs exposed to localized fire. As the fire exposure time increases, the composite beam appears significant variation of the temperature gradient at elevated temperature, and induce the dynamic, uneven temperature field in the structural members. Due to the influences of the temperature gradient field, the traditional design assumptions for composite beams with CSWs are not valid when the structures suffered a localized fire. It found that the shear stress on the CSWs is no longer evenly distributed along the depth at elevated temperatures, and the concrete flange resists a considerable part of the sectional shear force, particularly of the fire-affect zone. This study hopes to provide a basis for the fire resistance design of composite girder bridges with CSWs.

Estimation of effective thermophysical properties of firestopping sealants: Methodology and case study

Firestops have been widely applied to protect nonstructural service elements which penetrate fire resistant barriers to maintain the effectiveness of the overall fire separation. While fire stopping applications are well accepted globally, current understanding of actual fire performance is very limited and relies on standard fire test outcomes and extrapolated engineering judgement, without much scrutiny. Above all, a dearth of available thermophysical properties of common firestop materials significantly restrains the development of reliable numerical solutions. The objective of this research is therefore to optimize pseudo thermophysical properties that can be applied to model the temperature response of a typical firestop acrylic sealant. The study adopted an inverse modelling approach. Through iterative adjustment of key thermophysical parameters, a preliminary optimization for a typical firestop acrylic sealant has been attained. The simulated in-depth temperature predictions demonstrate a reasonable consistency with corresponding thermocouple data collected through customized ignition apparatus experiments. The proposed analysis methodology provides an alternative line of thought to obtain the effective thermophysical properties for fire safety designs.

The evolution of flame geometrical characteristics and air entrainment of inclined jet flames

This paper reported the jet fire issuing from different angles, a common hazard in pipeline leakage accidents during the gas storage and transportation process. The flame geometrical profiles including flame projection length in the horizontal direction, vertical height from the nozzle position and flame trajectory length as the essential parameters to evaluate jet fire risk and design safety distance between process equipment were measured experimentally. The result shows that flame projection length in the horizontal direction first increases to a maximum value at the horizontal jet flame condition and then decreases, flame vertical height from the nozzle position increases monotonously and the length of flame trajectory first decreases and then increases with the increasing inclined angle from downward to upward. Then, the normalized flame trajectory and its length for different inclined jet flames were obtained by plotting the flame tip location parameters normalized by a characteristic length representing the interaction between jet flow momentum and buoyant force generated by temperature variation. Finally, the air entrainment coefficients for different inclined jet flames were quantified by an integral model derived from the conservation equations showing a trend of first increase and then decrease with the increasing inclined angle from negative to positive. This work provides a good reference for quantifying the flame size of jet flame in inclined conditions.

A primer and success stories on performance-based fire design of structures

PurposeThe extreme nature of fire makes structural fire engineering unique in that the load actions dictating design are intense and neither geographically nor seasonally bound. Simply, fire can break out anywhere, at any time and for any number of reasons. Despite the apparent need, the fire design of structures still relies on expensive fire tests, complex finite element simulations and outdated procedures with little room for innovation. This paper aims to discuss the aforementioned issues.Design/methodology/approachThis primer highlights the latest state of the art in this area with regard to performance-based design in fire structural engineering. In addition, this short review also presents a series of examples of successful implementation of performance-based fire design of structures from around the world.FindingsA comparison between global efforts clearly shows the advances put forth by European and Oceanian efforts as opposed to the rest of the world. In addition, it can be clearly seen that most performance-based fire designs are related to steel and composite structures.Originality/valueIn one study, this paper presents a concise and global view to performance-based fire design of structures from success stories from around the world.

Distribution of probabilistic design fires for single residential items

When designing scenarios for fire safety in residential buildings, one should consider the natural variability of heat release rate of a single item that can possibly influence fire spread between multiple items. This study intends to represent experimentally measured design fire for single residential items using a combination of t-squared growth method and Ingason exponential decay method. The characterizations required three representative data from experiments including maximum heat release rate, time to reach the maximum heat release rate and total heat released. The methods have established good representations of the experimental design fires with more than 86% similarity. Distribution statistics are considered to characterize the design fires in a probabilistic manner which develop possible design fires from an average curve as well as within a minimum/maximum limit and a 5th/95th percentile limit. Comparisons denote that the probabilistic design fires are reliable to represent the possible heat release rate for single residential items.

Numerical Analysis of Flexural Performances of Composite Steel-Timber Beams under Fire Conditions

Recently, a novel type of composite structure, composite steel-timber (CST) structure, has attracted much attention by combining steel and timber in an effective way to form composite structural components, which unitises the advantages of high strength and excellent ductility of steel and decent sustainability and fire resistance of timber. However, the existing research is lacking, especially in structural fire design and analysis. In this study, based on the sequentially coupled method, the commercial finite element software ABAQUS was used to numerically simulate the dynamic performances in the temperature field and the flexural behaviours in the displacement field for a typical CST beam with a steel element embedded within the Glulam and connected by adhesives and bolts under standard fire for two hours. In the numerical simulations, the temperature distributions within the CST beam were explored, and the flexural performances of the beam in the displacement field were examined. Through the comparative analysis, the temperature distributions in the embedded steel beam and the surrounding Glulam beam under one-hour standard fire verified the advantages of this type of CST beam in structural fire design. Specifically, under a 2-hour standard fire, the surrounding Glulam could still protect the embedded steel beam from sustaining too high temperatures, so as to retain most of its material properties and help maintain the bearing capacity of the whole structure and improve the refractory limit. Parametric studies on the fire resistance of the CST beam were also conducted by adjusting the bolt spacing and the protection thickness of the Glulam. The obtained results indicated that reducing the bolt spacing and the thickness of the Glulam protection layer would have an adverse effect on the temperature distributions in the embedded steel element to a large extent, and would eventually lead to its rapid heating and strength loss and the final failure of the whole CST structure.

Self‐Powered Fire Alarm System with Layer‐by‐layer Graphene Oxide/Chitosan Nanocoating of Flame‐Retardant Nanofilms

This study develops a self‐powered fire alarm system that utilizes a sandwich‐like self‐powered fire sensor (SSFS) with a simple system to prevent room fires. The SSFS is small, flame‐retardant, and can be easily installed on furniture or doors. The SSFS uses a nanogenerator constructed by poly(vinylidenefluoride‐co‐trifluoroethylene) (PVDF‐TrFE) nanofibers and a flexible printed circuit board (FPCB) to produce electrical power by harvesting motion energy. This nanogenerator can fully charge capacitors in a few minutes and produces a maximum voltage output of 6.47 V. The SSFS also features two flame‐retardant melamine foams (MFs) coated with graphene oxide (GO) and a chitosan multilayer nanocoating that is fabricated by layer‐by‐layer technology (LBL technology). While encountering a high‐temperature situation, the electrical state of MFs changes from insulated to conductive, triggering the fire alarm light in about four seconds. The sandwich‐like design allows the SSFS to respond to a variety of fire alarm situations, especially in the case where both the top and bottom of the fire alarm sensor are exposed to flame (bilateral fire burning). It is such an innovative research to decrease the delay time of fire‐warning by using this sandwich‐like design fire sensor. The nanogenerator can keep the warning working for 22 s after the initial trigger, which produces enough time to ensure people stay clear of the fire source. All in all, this study presents a novel approach to reducing the risk of building fires through a lightweight and self‐powered fire alarm system that harvests motion energy using piezoelectric nanogenerators (PENGs).

Modelling carbon monoxide transport and hazard from smouldering for building fire safety design analysis

Smouldering produces massive toxic smoke and carbon monoxide (CO) that is responsible for the majority of fire deaths, but current building fire safety design rarely considers smouldering hazards. This work investigates the transport and hazards of CO from smouldering fire for the building performance-based design practice. The numerical model is firstly validated by reproducing two flat-scale fire experiments, revealing the characteristic surface temperature and CO yield of smouldering sources. The smouldering fire scenario is then designed in an atrium to review the evolution of CO concentration and its associated Available Safe Egress Time (ASET). Results show that a smouldering fire of the same burning rate as a flaming fire not only can provide a similar ASET, but also present a greater threat to occupants and rescue teams by forming a cold layer of lethal CO on the ground. Hence, the smouldering fire scenarios and their CO hazards should be considered in the performance-based design of building fire safety. Simulations also reveal that the smouldering fire can be more dangerous as the atrium height decreases, and ceiling ventilation is particularly effective in extracting CO emissions from smouldering fires.

Fire Performance of Steel-Timber Hybrid Beam Section

Slim-floor-type of steel-timber hybrid floor systems which use steel beams contained within the depth of the cross-laminated timber (CLT) floor slab offer many benefits, but there is still very little research available on the fire resistance performance of these systems. In the study presented in this paper two furnace tests and numerical simulations have been conducted to investigate the thermal profiles of the steel member and CLT slabs and to obtain information on the temperature development and charring of the hybrid beam section when it is exposed to standard fire conditions. Also, the effects of intumescent fire protection on temperatures and charring performance were investigated. Numerical 2D thermal simulations for unprotected and protected cases were conducted using SAFIR software, and the agreement between experiments and numerical-analysis predictions were in general very good. The results show that intumescent protection reduces the temperatures of the steel and CLT components as well as charring depth significantly, and the start of charring at CLT slab support may be delayed if intumescent paint protection thicker than that required for the load bearing steel member is used. The result also showed that CLT temperatures exceed 100°C already in the early stages of the fire which decrease the strength and stiffness properties of CLT much before the start of charring. Therefore, the fire design of the CLT slab support should not only consider the char depth and residual cross-section analysis but also the reduction in strength.

Characterizing the Performance of Adhesive Used in Glued-In Rod Timber Connections at Elevated Temperatures

A glued-in rod, which combines timber, a metal rod, and structural adhesive, is a type of connection whose fire performance is complicated to define since the rod depends on the adhesive’s thermomechanical properties. The objective of this study was to characterize the fire performance of adhesives used in glued-in rods. A total of five structural adhesives were tested: three epoxies and two polyurethanes. The tests performed consisted of applying an axial load to the glued-in rods after heating the connection to a target temperature. Load-slip curves were generated for each sample to determine their behavior at different temperatures. The results show that a reduction of up to 70% can occur in the initial stiffness of the glued-in rod when the temperature at the bond line exceeds the glass transition temperature of the adhesive determined by a dynamic mechanical analysis. This research helps to determine the guidelines for the fire design of glued-in rods and related testing and ultimately leading to a design method for providing fire-resistance to connections made of glued-in rods.

Investigating movement through smoke in virtual reality

Accurately estimating movement through smoke is critical for fire safety design. However, physical laboratory experiments using artificial smoke can be very expensive. Virtual reality (VR) can potentially be an alternative method to cheaply investigate movement through smoke. The primary objective of this study is to determine the relationship between movement speed and visibility in VR. The secondary objective was to compare movement through smoke in VR to existing experimental data. Five scenarios were tested: real-world unimpeded movement, unimpeded movement in VR, and movement in VR with virtual smoke reducing the visibility to 3.5 m, 2.5 m, and 1.5 m. A wireless head mounted display was used to immerse participants in the virtual environment. For the study, 42 participants experienced the smoke scenarios in a random order. The results indicate that movement speed decreased with visibility, but to a lesser extent than in previous physical laboratory experiments with artificial smoke. Unimpeded movement in VR was shown to be significantly slower than real-world unimpeded movement. Prior experience with VR was not shown to have a significant impact on unimpeded VR movement speed. Increasing the realism of the virtual environment could potentially better align results from VR experiments with past physical laboratory experiments.

Experimental Study of the Charring of I-Joists and Recession of Combustible Insulation in Light Timber Frame Assemblies with Comparison to Eurocode 5

Design models are commonly used in fire safety design of light timber frame assemblies. Parameters for use in the models are available for rectangular members with mineral wool, wood fibre or cellulose insulation and for assemblies with I-joists and mineral wool. For assemblies where I-joists and combustible insulations are combined, design parameters are missing. Five fire experiments with two I-joist types and four combustible insulation products have been conducted. The aim was to study charring of I-joist flanges and recession rates of combustible insulations and in addition, to compare their behaviour to the new and existing models of Eurocode 5. Charring rates for the flanges were 0.40–0.76 mm/min and 0.54–1.72 mm/min for the protected and post-protected phase, respectively. Rates decreased with increasing flange size. Charring rates for flanges of solid wood and LVL were comparable. The results show that lateral charring of I-joist flanges can be significant in the protected phase. The tested insulation products showed a lower recession rate than values reported for glass wool insulation, with a more pronounced difference for wood fibre and cellulose insulations. The low recession rates compared to previously reported generic values can possibly be explained by better product-specific properties, negligible shrinking and slightly different test set-up. The insulation stayed well in place after gypsum board fall-off and best-practice for keeping the insulation in place is given. The results, completed with future loaded full-scale tests, can give basis for further development of design models for assemblies with I-joists and combustible insulations.

Numerical simulation of punching shear in RC slabs subjected to elevated temperatures

Studies on the punching shear of reinforced concrete (RC) slabs exposed to fire are very limited. To address this shortcoming, a series of numerical analyses were carried out to study the effects of several parameters on punching shear behaviour of RC slabs under fire conditions. Variables of the study were: (i) gravity load levels before exposure to fire; (ii) presence or absence of shear reinforcement; (iii) duration of fire (at 30 min intervals), (iv) direction of fire (top and bottom face of slab); and (v) thermal conductivity limits. For this purpose, first, the shear response of a slab–column assembly failing in brittle punching shear under ambient temperature, chosen from the literature, was captured and, subsequently, sequential coupled thermomechanical analyses were carried out using the finite-element software ATENA. Results of the study show that the direction of fire significantly affects the deformation pattern and punching resistance of RC slabs; thermal conductivity plays a minimal role in this regard. Exposure to fire causes the reinforcements to yield at load levels well below the failure load. Finally, shear reinforcement has almost no effect on fire resistance of RC slabs. It is concluded that it is acceptable to ignore shear reinforcements in fire design of RC slabs.

Optimising the inherent fire capacity of structures

This paper introduces a structural design optimisation methodology aimed at minimising the consequences of a fire. The methodology considers the trade-off between implementing passive fire protection measures and enhancing a structure’s “inherent fire capacity”, defined as its ability to retain integrity/functionality without additional fire safety measures. The feasibility of the methodology is demonstrated through the fire safety design of a single-span, steel girder bridge. The optimisation process generates multiple Pareto-optimal solutions for minimising the maximum bridge deflection after a given fire exposure time. Passive protection ensures the bridge’s functionality when facing a heavy goods vehicle fire. In the case of exposure to a car fire, solutions requiring fire protection in specific limited girder regions are identified. The decision-making process is further supported by investigating the robustness of the solutions to uncertainties in material properties and the heat flux model.

Causal Network Topology Analysis (CaNeTA) as a tool for risk assessment in fire safety engineering

Risk assessment occupies an integral place in a wide range of areas regarding health and safety, and many risk assessment tools have been applied in the field of Fire Safety Engineering (FSE). However, FSE is facing a lack of diversity of risk methods, and they all have common drawbacks, particularly in those alike methods of generating fire scenarios that are relied upon in the fire safety design process. These drawbacks include the overlook of interdependencies between different fire safety systems, as well as the overreliance on the competence of the risk-analyst. As a result, we applied a novel methodology called the Causal Network Topology Analysis (CaNeTA) to the fire safety strategy for a multi-tenancy retail occupancy. The contributions include: 1) The causal network which interlinks the causalities between the status of individual fire safety systems. 2) The results from network analysis help analysts to observe and engage with overall system performance. 3) The suggestions on the criticality of the status of individual fire safety systems to optimise fire safety strategy. To conclude, the usage of CaNeTA reveals broader insights from the fire safety strategies objectively, to support fire safety design.

Machine learning driven smart fire safety design of false ceiling and emergency response

In modern buildings, false ceilings are widely used for building services systems and aesthetic purposes, but they also pose challenges in terms of fire safety. A fire accident typically results from the failure of multiple safety measures or components. In many fire accidents, fire and smoke reached the false ceiling and kept spreading in the interstitial space without any detection. This study first generates a numerical database of false ceiling fire scenarios by varying the room dimensions, false-ceiling leakage area, fire size and locations. Then, a smart model based on machine learning to predict the fire smoke motion below and above the false ceiling is developed. The trained model is capable to predict the activation time of fire detectors and sprinklers for any given false ceiling design and fire scenario. This methodology enables a designer to generate multiple fire scenarios and determine the available safe egress time (ASET) for performance-based fire engineering designs especially in terms of fire detection time. In case of a real fire, with the data feed from the fire sensor network, the trained machine learning model can further predict the critical building fire events with the false ceiling, such as multi-compartment fires, smoke in the evacuation path, and structural failures. This work proposes a smart framework for improving the building fire safety design of false ceilings and the sensor-driven fire forecast to support firefighting.It enhances the emergency response processes by enabling dynamic risk assessment through prediction of critical events.

Perception of Fire safety evacuation design towards Fire Disaster in core towns of southern region of India

Old south Indian traditional towns are subjected to tremendous morphological changes. In an urban environment, fire is considered a manmade disaster. Urban pressure demands densely constructed built environments with critical fire risk parameters. In spite of various codes, building regulations that are formulated and enforced for the safety of human life and buildings, built environments in traditional areas of south India do not comply with fire safety codes and regulations. This study focuses on the perception of fire safety evacuation design by professionals who design buildings in the urban areas of south India namely “Kumbakonam, Thanjavur and Tiruchirappalli.” The fire safety evacuation parameters related to building characteristics namely number of exits, occupant load, width of exit routes/exit doors, maximum travel distance and corridor widths are considered in the present study. A structured survey has been conducted among 380 architects and engineers, who are directly involved in building designs in the aforementioned cities of south India to understand the perception of fire safety design. Therefore, this study identifies the challenges in complying existing codes and regulations, perception and knowledge in application of fire safety codes in continuous building area (CBA). In continuous building areas, the existing regulations and codes are ineffective for fire safety concern as perceived by architects and engineers. A significant percentage of respondents does not consider maximum travel distance calculation (23.15%), occupancy load (24.21%) and capacity factors calculations (33.95%) in their building design which are important determinant criteria for fire safety evacuation design during a fire disaster.

The collapse mechanism of steel framed structure exposed to parametric design fire and travelling fire scenarios

The structural steel elements exposed to fire is susceptible to collapse owing to the temperature sensitivity of steel sections. The technical advances in the field of fire dynamics have enabled to simulate realistic fire scenarios to determine the performance of structural elements. However, a detailed parametric study is necessary to increase the knowledge on the performance of structural steel elements to various design fires. In this study, the behaviour of three-dimensional steel framed structures subjected to the action of standard fire and parametric fire as well as the travelling fire scenarios are analysed. In this work, the general-purpose finite element software ABAQUS is used to perform the analytical study. The material models calibrated with experiments were adopted for conducting parametric study. The results of the analytical study show, the uniform exposure of temperature to compartment is the most critical scenario as the compartments exposed to uniform fire is causing total collapse of structure. Uniform exposure of parametric fire to compartments is found to be less critical as the cooling phase of fire enabling more resistance against total collapse of the structure. Also, the uniform exposure of standard fire, a small resistance is observed from the unexposed columns. However, the structure exposed to parametric fire was sustained large deflections. The structure exposed to travelling fire is found to receive greater resistance before collapse. However, the structure found to collapse as the fire reaches final compartment.

Experimental and numerical study on the validity of the energy-based time equivalent method for evaluating the fire resistance of timber components exposed to travelling fires

An energy-based time equivalent method that is capable of converting the fire resistance design of timber components exposed to the realistic fire to that of the standard fire was proposed. To verify the effectiveness of the method applied to the improved Travelling Fires Methodology (iTFM) fires, a series of iTFM fires and their corresponding equivalent standard fire tests were implemented on six glued laminated timber columns. The effectiveness of the method was fully confirmed by comparing the fire effects, the temperature distribution of the pyrolysis layer, and the remaining load-bearing capacity after fire for the timber columns under the iTFM fires and their equivalent standard fires. Meanwhile, it was well illustrated that the adhesive layer was almost no effect on the fire resistance of the timber columns by comparing the cross-sectional temperature distribution, charring depth and charring rate in two directions of the timber columns. To simplify the application of the energy equivalence method, the thermal properties relationships applied to the finite element heat transfer analysis of timber were modified. The accuracy of the modified thermal property relationships was demonstrated by comparing the surface temperature, charring depth, and charring rate obtained from finite element simulations with those measured by the experiment. The simplified energy equivalence method based on the finite element was not only easy for designers to apply, but also helped to promote the development of performance-based fire protection design for timber structures.

Structural hazards of smouldering fires in timber buildings

Smouldering, a slow, persistent, and flameless form of combustion has only been observed in few fire experiments of mass timber compartments. Smouldering is a phenomenon well-understood in the wildfire community, but is not yet recognised as a hazard in the fire safety design and fire-fighting of modern timber buildings. This paper presents observations and analysis following the cessation of flaming in CodeRed, a series of three open-plan compartment fire experiments with a mass timber ceiling and columns. The formation of nineteen smouldering hotspots was observed, which developed along the edges of timber elements where heat losses were minimised. Conventional and infrared imaging was used to track the hotspots over the 48 h following the cessation of flaming, observing smouldering hotspot initiation, spread, self-extinguishment, suppression by both hose and rain, and transition to flaming. Structural failures due to smouldering were studied, including the formation of holes in the ceiling and encapsulation, and the collapse of a column. This paper shows that smouldering can be a structural hazard in timber buildings that has not yet been addressed in the literature of timber building fire safety.