Fire Safety Design Research Articles

Fracture behavior of high-strength bolted steel connections at elevated temperatures

In fire events, to utilize catenary effect and accommodate large deformation in beams demands a sufficient deformation capacity and ductility in steel bolted connections, which is not well considered in design practice. Therefore, for performance-based fire safety design, it becomes very essential to accurately predict the fracture behavior of steel bolted connections at elevated temperatures. However, experimentally predicting their fracture behavior is very costly at elevated temperatures and limited by the scale of structural components. Therefore, this paper proposes a numerical analysis approach and investigates the fracture behavior of high-strength bolted steel connections at elevated temperatures based on the validated numerical analysis approach. The temperature-dependent material properties including true stress-strain curves and fracture parameters in a three-stage fracture model (describing the pure tension, pure shear, and combined tension and shear fracture behavior) for high-strength ASTM A325 bolt and A572 Grade 50 steel are firstly calibrated from and validated against their tensile and shear test results. They are further validated against the test results on single-bolted and multi-bolted connections at elevated temperatures, which were not used in the calibration of these material properties. The validated material properties and fracture parameters are finally proposed for fracture prediction of different types of bolted connections under various loading conditions at elevated temperatures. This study shows the potential of reasonable prediction of the fracture behavior for the steel bolted connections at elevated temperatures and under complicated loading conditions using a numerical analysis approach. According to the numerical analysis results, the degradation of shear fracture resistance of A325 bolts at elevated temperatures is more significant than that of A572 Grade 50 steel plate, which may lead to a bolt shear failure mode for these connections with a large end distance at high temperatures (>400 °C). It is also found that the fracture failure mode can significantly influence the degradation of the load and deformation capacities of high-strength steel bolted connections at elevated temperatures. With the bolt shear failure mode, the degradation of load and deformation capacities of steel bolted connections are more significant than that with plate tearing-out failure mode.

Effect of initial pressure on the burning behavior of ethanol pool fire in the closed pressure vessel

Fire Hazards associated with pressure vessel seriously threaten the process safety in chemical industries. There are limited literatures about fire characteristics in closed pressure vessels, which are important for fire risk management and safety design. In this study, the effect of initial pressure on the burning behavior of ethanol pool fire in a pressure vessel was investigated. A series of ethanol pool fires with diameters from 4 cm to 10 cm was carried out in a pressure vessel with interior dimensions of 0.6 m (height) ×0.4 m (diameter), and the initial pressures range from 60 kPa to 300 kPa. Results show that the flame structure changes from laminar to turbulent and the flame color changes from yellow to blue as the initial pressure or the burning time increases, which can provide information on the flow and chemical details. Furthermore, considering the effect of initial pressure on the mean burning flux, an empirical formula for predicting the self-extinction time of pool fire in the closed pressure vessel was developed, which showing a good agreement with the experimental data in our study and previous tests. Finally, it was observed that the changes of pressure with time are similar to the change of mass burning rate and could be divided into three representative stages. The relationship for predicting the over pressure peak was introduced and verified by the experimental data.

On simulating the effect of gravity on concurrent flame spread over thin paper through variations in ambient pressure

The environment inside a spacecraft, or a space habitat, can greatly differ from those on earth, affecting the burning behavior of solid fuels. Because in a gravity field there is a flame-induced buoyancy, it is very difficult to reproduce on Earth the environmental conditions of a spacecraft, or a habitat in the Moon or Mars, thus making fire testing and burning predictions harder. A potential alternative approach to overcome this problem is to reduce buoyancy effects by using reduced ambient pressure in normal gravity. The objective of this work is to explore the possibility of simulating the effect of gravity, and in turn buoyancy, through changes in ambient pressure, on upward/concurrent flame spread over a thin combustible solid. Comparisons with available data at different gravity levels are used to determine the extent to which low-pressure can be used to replicate flame spread characteristics at different gravities. Experiments of the upward/concurrent flame spread over thin Kimwipe paper sheets were conducted in normal gravity inside a pressure chamber with ambient pressures ranging between 100 and 30 kPa and a forced flow velocity of 10 cm/s. Results show that reductions of pressure slow down the flame spread over the paper surface, and also reduces flame intensity. Comparison with published partial gravity data shows that as the pressure is reduced, the normal gravity flame spread rate approaches that observed at different gravity levels. The data presented is correlated in terms of a mixed convection non-dimensional number that describes the convective heat transferred from the flame to the solid, and that also describes the primary mechanism controlling the spread of the flame. The correlation provides information about the similitudes of the flame spread process in variable pressure, flow velocity and gravity environments, providing guidance for potential ground-based testing for fire safety design in spacecraft.

Effects of Time to Unactuate Air Conditioning on Fire Growth

Air conditioning systems have become essential equipment in many buildings. However, fire safety design and management in buildings rarely consider whether to turn the system off or keep it on in a fire. This study ignites a stack of wood in a room center or corner to explore the influence of air inlet actions of a fan coil unit (FCU) with the door opened or closed. Simulation results using Fire Dynamics Simulator (FDS) demonstrate that the heat release rate (HRR) and room temperature obviously decrease when the room doorway is closed, regardless of whether the air conditioner is turned on. The air supply for combustion is poor. When the door of the room is opened, turning off the air conditioner can effectively reduce the HRR and the room temperature in the early stages of fire growth. However, along with the fire growth, turning on air conditioning can help decrease the heat radiation feedback and the consequent HRR. Therefore, the conclusion that air conditioning always enhances a fire because it provides oxygen may not always be correct.

Energy‐based time equivalent approach for evaluating the fire resistance of timber components exposed to realistic design fire curves

SummaryAccording to the concept of performance‐based design, the fire safety design of the timber structures should be focused on the actual design fire, which represents the realistic fire situation in a given building. However, the current prescriptive only provides a method for evaluating the fire resistance of timber components under standard fire. This paper proposed an energy‐based time equivalent approach (EBTEA) for evaluating the fire resistance of the timber components in realistic design fire scenarios. As an alternative, this method was based on the principle of energy equivalence so that the fire resistance design of timber components exposed to realistic fires was standardized, which can make fire resistance rating database available under standard fire exposure and promote performance‐based design. The validity of the method was verified by comparing the predicted values of EBTEA with the existing values obtained from the nonlinear finite element analysis. The proposed method was further simplified by analyzing the key factors of energy equivalence and using nonlinear fitting methods to facilitate the use of designers. The simplified EBTEA can predict equivalent fire resistance of timber components under realistic design fire scenarios.

Customising Evacuation Instructions for High-Rise Residential Occupants to Expedite Fire Egress: Results from Agent-Based Simulation

As the possibility of safe escape is one of the most crucial aspects of a building’s fire safety features, understanding of human behaviour under fire conditions is important for a successful evacuation. Although most of today’s buildings are equipped with fire safety systems, a fire can still occur at anytime and anywhere in a building and have devastating consequences. In the last decade, researchers and practitioners have used information technology to assist with fire safety design and emergency management. Building Information Modelling (BIM) is an exemplar process whose underpinning digital technology has been helpful for fire safety design, simulation, and analysis, but there is a lack of research on how BIM-based models combined with agent-based simulations can help improve evacuation via effective navigation and wayfinding in high-rise residential buildings. Customising evacuation instructions based on BIM, simulation results and occupant location, and delivery of these bespoke instructions to occupants’ smartphones during a fire emergency is relatively novel and research is needed to realise the potential of this approach. Therefore, this study investigates how customised evacuation instructions delivered to each occupant in a high-rise residential building could result in a faster evacuation during a fire incident. The research adopted a case study building and used Pathfinder (agent-based evacuation simulation software) to simulate evacuation from this eleven-floor high-rise residential building in Cairo, Egypt. Constraining evacuees (simulated agents in Pathfinder) to take particular exit routes was used as a proxy for delivering customised evacuation instructions to actual evacuees. Simulation results show that, in general, allowing the use of lifts for the benefit of disabled occupants could lead to their misuse by able-bodied occupants; evacuees would attempt to use the first visible point of exit regardless of how crowded it is. With optimally customised instructions, the evacuation time was, on average, 17.6 min (almost 50%) shorter than when the occupant’s choice of egress route was simulated based on standard path planning factors such as route length, nearby crowds and visible hazards. With evacuation instructions sent via smartphones, occupants could exit more rapidly via alternative routes. Such bespoke instructions were shown to reduce the adverse effects of crowdedness and uneven distribution of occupants along vertical and horizontal evacuation routes on evacuation time.

Probabilistic-Based Approach for Evaluating the Thermal Response of Concrete Slabs under Fire Loading

AbstractPerformance-based design for fire safety has been introduced in several international design frameworks. The fire models and simulations include various assumptions and simplifications, and...

Numerical Validation of the Two-Way Fluid-Structure Interaction Method for Non-Linear Structural Analysis under Fire Conditions

Fire accidents on ships and offshore structures lead to complex non-linear material and geometric behavior, which can cause structural collapse. This not only results in significant casualties, but also environmental catastrophes such as oil spills. Thus, for the fire safety design of structures, precise prediction of the structural response to fire using numerical and/or experimental methods is essential. This study aimed to validate the two-way fluid-structure interaction (FSI) method for predicting the non-linear structural response of H-beams to a propane burner fire by comparison with experimental results. To determine the interaction between a fire simulation and structural analysis, the Fire-Thermomechanical Interface model was introduced. The Fire Dynamics Simulator and ANSYS Parametric Design Language were used for computational fluid dynamics and the finite element method, respectively. This study validated the two-way FSI method for precisely predicting the non-linear structural response of H-beams to a propane burner fire and proposed the proper time increment for two-way FSI analysis.

Mechanical behaviours of heat-damaged grouted sleeve connections

An experimental study with 72 specimens was conducted to determine the effects of various factors on the mechanical behaviours of grouted sleeve connections, including an increase in temperature from 20 °C to 600 °C, the loading regime (uniaxial tensile loading or cyclic loading), and the grout compressive strength (83.1–91.1 MPa). After the specimens were exposed to elevated temperatures of up to 600 °C and then uniaxial tensile loading or cyclic loadings, the experimental results indicated that the sleeve was still elastic and the grout had a compressive strength of more than 83.1 MPa, which was beneficial for maintaining the mechanical behaviours of the specimens. In this study, the sleeve region was equal to the gauge length, which consisted of the length of the sleeve and three times the diameter of the rebar from each end of the sleeve. Moreover, a bilinear model was formulated to calculate the yield and ultimate loads of the heat-damaged grouted sleeve connections after different loading regimes. Finally, the constitutive relationship of the heat-damaged grouted sleeve connection was investigated. These findings will be helpful in the fire safety design of precast concrete structures.

Influence of Wind Speed and Direction on the Combustion Parameters of the Exposed XPS Insulation Wall

Most of the fire accidents of exterior insulation in recent years started with the ignition of unprotected and exposed insulation materials. The fire spread on the thermal insulation layer will be affected by outdoor wind. In this paper, the influence of wind direction and wind speed on wall fire propagation characteristics was studied by carrying out medium sized experiments. The temperatures on the wall surface, radiation heat flux nearby, the infrared image and flame image were recorded during the tests with variation of wind direction and wind speed. It is found that with the increase of the angle between the wind direction and the wall, the surface temperature of the material, the radiation heat flux released decreases.This study results can provide valuable references for optimizing the fire safety design of exterior insulation layer.

Cavern fire safety – overview of requirements and pragmatic solutions in Hong Kong

Hong Kong’s steep hilly terrain limits the growth of surface urban areas. In response to the society’s needs for land to support social and economic developments, the Government of Hong Kong Special Administrative Region is actively exploring the use of caverns as one of the innovative measures to supplement Hong Kong’s land resources. The development of cavern space is an attractive option to meet the land demand not only for “not-in-my-backyard” (nimby) type public utilities but also for a wide spectrum of uses including commercial, industrial and community type facilities. The development of cavern fire safety design in Hong Kong evolved from the first cavern project in around 1980s. The design guideline “Guide to Fire Safety Design for Caverns” was jointly established by Building Authority and Fire Services Department in 1994, by referring to overseas and local experience consolidated in the Study of the Potential Use of Underground Space (SPUN) in 1990. This guideline however was developed with a focus on caverns for use by low population public utilities such as sewage treatment works and water service reservoirs where the fire load is generally localised, closely controlled and relatively low. Whereas, other prescriptive fire safety guidelines commonly adopted in the Code of Practice for Fire Safety in Buildings 2011 (FS Code) and the Codes of Practice for Minimum Fire Service Installations and Equipment and Inspection, Testing and Maintenance of Installations and Equipment (FSI Code) were developed for typical surface buildings only. The existing fire design guidelines are found to be not fully compatible with the recent expanding spectrum of cavern usage in Hong Kong. Each cavern development type has its unique site setting and fire safety characteristics under the proposed usage (e.g. government facilities, industrial and commercial facilities like concrete batching/rock processing/asphalt production plants, data centres, logistics/warehouse facilities, etc.). Strictly following the prescriptive fire safety requirements and the design guidelines for typical buildings to these usages in cavern will pose immense technical issues/challenges to cavern projects and could also lead to unwarranted impacts on their functional operations. A more coherent fire safety design approach for new cavern projects is therefore needed to facilitate project proponents to plan cavern projects in the future. This paper provides an overview of fire safety issues for cavern development, and also discusses the practical solutions in formulating the associated fire safety strategies which have been adopted in the latest cavern projects in Hong Kong, covering the technical issues on fire resisting construction, means of escape, means of access for firefighting and smoke management.

Preliminary Study of Fire Damage on Pervious Concrete with Silica Fume and Steel Fiber

Pervious concrete pavement is a porous urban surface. It could reduce runoff capacity, decrease a storm-water detention, reduce the amount of requiring rain drainage pipes, and let rainwater filter into ground and allow groundwater resources to renew in time. Fire damage, could be one of important factors since European countries have been used pervious concrete in buildings construction. This study was conducted to assess the fire damage on pervious concrete with silica fume and steel fiber. The test results find that pervious concrete with 10% silica fume and 2% steel fibers showed the maximum increase in compressive and flexural strengths by 60% and 23% respectively over the control mix while maintaining adequate permeability. It also shows that the flexural strength of pervious concrete with 10% silica fume and 2% steel fiber could reach 45 kg/cm2strength specification. The high temperature exposure results find that pervious concrete could hardly be detected any crack at the temperature of 700 °Cor 800°C and fire duration of 2 hours. There is some damage on strength after the fire-attack test, the ratio of the residual strength can range from about 20%~60% and it depends on temperature, steel fiber, and silica fume content. By this study of pervious concrete will be valuable for fire safety design and construction of practice.

Fire safety of alcoholic beverages in retail stores

SummaryA fire test series to study pool fires of ethanol‐water mixtures in the small, intermediate and large scale has been performed. Additionally, demonstration tests of piles of PET plastic 0.5‐L liquor bottles (39 vol%) in retail store arrays were carried out to illustrate their burning behaviour. On the basis of the test results, the burning of pool fires of different alcoholic beverages and the fire load due to alcohol can be evaluated for the purpose of performance‐based fire safety design. The fire tests of retail store arrays showed that these fires grow slowly, and their heat release rate maxima are relatively low taking into account the mass of the fire load. The estimated heat release rate maxima of four‐layer retail store arrays were ca. 1.5 MW and their growth times were over 600 seconds. Design fires generally used for the fire safety design of shopping centres are typically much more severe than the fire test results of retail store arrays of alcoholic beverages in this study.

Behaviour of austenitic stainless steel bolts at elevated temperatures

Stainless steel bolts have an underlying use in bolted connections, as they possess more significant material properties and resistance than high-strength bolts under fire and/or corrosion conditions. Appropriate estimation for fire safety design of these connections depends largely on the ability to accurately predict the fundamental material response at elevated temperatures. Currently, although residual properties of different stainless steels have been excessively investigated using experimental and analytical methods at elevated temperatures, the mechanical behaviour of stainless steel bolts exposed to fire is much less attentively scrutinized than that of high-strength steel bolts. Thus an elevated temperature experimental investigation was conducted to exhibit discrete reduction factors and continuous stress–strain response for A2-70 stainless steel bolts. Test results indicated that the currently available reduction factors or equations of A2-70 base materials (EN1.4301 equivalent to SUS304) are incapable of providing a more accurate representation of residual properties for A2-70 stainless steel bolts subjected to the cold-forging effect. Hence, for A2-70 residual properties of Young’s modulus, yield strength, ultimate strength, ultimate strain and strain-hardening exponent, their regression-based reduction equations were developed to accommodate test data, respectively. Hereafter, in conjunction with five proposed reduction equations, the full-range measured stress–strain curves of A2-70 stainless steel bolts were evaluated using five ambient temperature mechanical parameters based on a modified material model with a necking stage at elevated temperatures, thus the predicted stress–strain curve up to the ultimate stress can correlate well with stress–strain curves of replicate tests at a given temperature, while the necking segment can be predicted approximately and quantitatively after the peak stress.

Application of building information modelling for fire hazard management in high-rise buildings: an investigation in Sri Lanka

ABSTRACT This paper aims to explore the challenges of fire hazard management in high-rise buildings by extending the application of BIM as a collaborative and automated tool covering deficiencies of fire hazard management. To achieve this purpose, a semi-structured interview approach was adopted to collect a rich dataset from ten selected experts in a fire hazard and BIM. The collected data was analysed using content analysis and coding techniques. The study findings reveal that the Sri Lankan construction sector is lagging in utilising BIM for operating fire hazard management and confirms that the current practice relies on human-centric approaches as some other developing countries. The findings show the suitability of BIM for fire hazard management in high-rise buildings in Sri Lanka during fire safety design, building fire regulation checking, firefighter training, designing building layout, location tracking and distance guidance, evacuation path analysis, prior identification of spreading fire and safety equipment maintenance and record-keeping. Furthermore, the major challenges of BIM adoption were identified in the Sri Lankan fire hazard management. The findings of the study could be utilised by stakeholders involved in firehazard management to overcome the current challenges related to fire hazard through the effective use of BIM technology.

Constitutive model of high-performance bolts at elevated temperatures

Mechanical properties of steel at elevated temperatures are critical to the fire-resistant analysis and the fire safety design of steel structures. Thus, one solution for improving the fire resistance is use of high-performance (HP) steel, such as fire-resistant (FR) steel. However, practical use of the FR steel in steel structures implies requirements of sufficient fire resistance for the high-strength (HS) bolts as well, so that the loading capacities of bolted connections commonly used in steel structures can be guaranteed in case of fire. In this paper, material properties of grade 10.9 HP bolts recently developed in China, possessing both fire resistance and corrosion resistance, are tested at various elevated temperatures. Their stress-strain curves, modulus of elasticity, yield strength, ultimate tensile strength (UTS), and elongation percentage after fracture are obtained. These results are compared with that of conventional HS bolts and with reduction factors given in national standards. Constitutive models and prediction equations of the HP bolts at elevated temperatures are proposed. Besides, the relationship between degradation in macro mechanical properties and change in microstructure is clarified. The research outcomes may provide essential bases for the fire response analysis of steel structures applying the FR steel and the HP bolts.

Behaviour of ultra-high strength concrete encased steel columns subject to ISO-834 fire

Ultra-high strength concrete (UHSC) encased steel columns are receiving growing interest in high-rise buildings owing to their economic and architectural advantages. However, UHSC encased steel columns are not covered by the modern fire safety design code. A total of 14 fire tests are conducted on UHSC (120 MPa) encased steel columns under constant axial loads and exposed to ISO-834 standard fire. The effect of load ratio, slenderness, stirrup spacing, cross-section size and concrete cover to core steel on the fire resistance and failure mode of the specimens are investigated. The applicability of the tabulated method in EC4 (EN 1994-1-2-2005) and regression formula in Chinese code (DBJ/T 15-81-2011) to fire resistance of UHSC encased steel columns are checked. Generally, the test results reveal that the vertical displacement-heating time curves can be divided into two phases, i.e. thermal expansion and shortening to failure. It is found that the fire resistance of column specimens increases with the increase of the cross-section size and concrete cover to core steel, but decreases with the increase of the load ratio and slenderness. The EC4 method overestimates the fire resistance up to 186% (220 min), while the Chinese code underestimates it down to 49%. The Chinese code has a better agreement than EC4 with the test results since the former considers the effect of the load ratio, slenderness, cross section size directly in its empirical formula. To estimate the fire resistance precisely can improve the economy of structural fire design of ultra-high strength concrete encased steel columns.

Experimental and numerical analysis of residual load-carrying capacity of cross-laminated timber walls after fire

Cross-laminated timber (CLT) panels are widely used as structural members applied in a range of modern timber buildings. Changes in the load-carrying capacity of CLT walls after exposure to fire need to be discussed and summarized, but few studies have considered this due to a lack of available measurements and the prohibitive cost of performing the relevant experiments. To investigate the residual load-carrying capacity of CLT walls after fire, the multiple tests including axial compression tests under the ambient condition, standard fire tests and residual load-carrying capacity tests after fire were performed, and a numerical approach was developed in this study. The appropriate constitutive relationship and mechanical properties of timber affected by temperature were adopted, and the corresponding user-defined material subroutine was coded in ABAQUS and verified by typical examples. It was shown that the numerical models could reproduce adequately the failure process and mechanical behavior of the CLT specimens tested. The validated numerical method was used to carry out a parametric prediction that revealed the influence of the number of layers and the combustion time on the residual load-carrying capacity after fire. Moreover, the presented results could serve as a reference for the structural fire safety design of CLT structures.

Deflection of a Concrete T-beam with Prestressed and Non-prestressed Fiber Reinforcement Polymers at Elevated Temperatures

Prestressed concrete members have gained popularity as an efficient and effective way of designing a structural member with the best engineering and material properties. The method of prestressing a structural concrete member has the capability of controlling increased service loads with less depth over longer spans. However, deflections from over-loading or loading over time give a disadvantage to the common steel reinforced concrete members by the effect of corrosion as the structural concrete develop cracks. To prevent corrosion of a structural concrete member, exchanging of steel reinforcement with Fiber Reinforcing Polymers (FRP) has sparked engineering interest in recent years. Both prestressed and non-prestressed FRP reinforcement can reduce tension in concrete. However, the performance of such structural members under elevated temperatures is currently unknown. The knowledge and application of this may lead to a cost effective, and practical consideration in fire safety design. In this article, an analytical model is developed using flexural rigidity of a concrete T-beam with both prestressed and non-prestressed FRP reinforcement to study the deflection behavior at practical elevated temperatures. The model is compared with the finite element model (FEM) of a T-beam with both prestressed and non-prestressed reinforcement subjected to practical elevated temperatures. In addition, comparison is also made with an indirect reference to the real behavior of the material. The results of the analytical model correlated reasonably with the FEM and the real behavior, and were within the accepted range of the American Concrete Institute (ACI) specifications.

Thermodynamic and Kinetic Characteristics of Combustion of Discrete Polymethyl Methacrylate Plates with Different Spacings in Concave Building Facades.

Polymethyl methacrylate plates are widely applied to buildings, producing significant fire hazards. It lacks a theoretical basis for the fire risk assessment of polymethyl methacrylate in concave building facades. Therefore, experimental methods are used to investigate combustion characteristics of discrete polymethyl methacrylate plates in a concave building facade. Influences of fuel coverage and structure factor are investigated, which is scant in previous works. When structure factor is invariable, average flame height increases first and then decreases as fuel coverage increases, and the turning point is between 0.64 and 0.76. In total, three different patterns of pyrolysis front propagation are first observed for different fuel coverages. Flame spread rate first increases and then decreases as fuel coverage rises, and the turning point is also between 0.64 and 0.76. When fuel coverage is invariable, the flame spread rate first increases and then decreases with increasing structure factor, and the turning point is 1.2. A model for predicting the flame spread rate of discrete polymethyl methacrylate is also developed. The predicted values are consistent with experimental results. Fuel spread rate of discrete polymethyl methacrylate rises as the fuel coverage increases. The above results are beneficial for thermal hazard evaluation and fire safety design of polymethyl methacrylate used in buildings.