Fire Performance Of Structures Research Articles

Experimental study of in-fire and post-fire material response of high-strength aluminium alloys

This paper presents an experimental study on the residual material properties of high-strength aluminium alloys in and after fire. A testing programme was firstly conducted on grade 7075-T6 high-strength aluminium alloy, consisting of 13 in-fire and 24 post-fire coupon tests, to derive the material stress–strain responses at and after exposure to elevated temperatures ranging from 20 oC to 550 oC. The key temperature-dependent material properties including stiffness and strengths were determined from the measured stress–strain curves and normalised by their room-temperature counterparts, resulting in a series of in-fire and post-fire retention factors. These experimentally obtained retention factors were used to analyse the effects of elevated temperatures on the residual stiffness and strengths of high-strength aluminium alloys. The design in-fire retention factors, as given in the European, American and Chinese standards, and the existing predictive models in previous studies for the post-fire retention factors, were also quantitatively and qualitatively assessed based on the test data. They were found to be inapplicable due to less accuracy; especially when used for predicting the in-fire Young’s moduli, a 25% over-prediction can be yielded, leading to unsafe design. To address the shortcoming, a series of predictive models were developed to offer accurate predictions of the in-fire and post-fire residual stiffness and strengths of high-strength aluminium alloys, with the mean test-to-prediction ratios ranging from 0.995 to 1.074 for different in-fire and post-fire material properties and the design accuracy improved by at least 15% than existing design models. The Then, a two-stage Ramberg–Osgood material model that was proposed for describing the room-temperature stress–strain curves of structural aluminium alloys was considered in this study, with its applicability to high-strength aluminium alloys assessed. The considered Ramberg–Osgood model was found to well predict the in-fire and post-fire stress–strain curves of high-strength aluminium alloys. The proposed models for retention factors and stress–strain curves can be further assessed based on more test data on other new high-strength aluminium alloy grades. Future research can focus on developing new coating technologies and optimising existing treatments to improve the fire performance of high-strength aluminium alloy structures.

Influence of continuous elastic lateral restraints on beams and beam-columns of steel-timber hybrid structures in fire

With the climate crisis and pursuit of efforts to reduce embodied carbon impacts in the built environment, steel-timber hybrid structures have emerged as a sustainable form of framed construction which offer numerous benefits over the widely used and well-established steel-concrete hybrid structures. However, there are major concerns about the structural fire performance of such systems among various stakeholders in the construction industry, particularly for the design implications in terms of the lateral-torsional buckling behaviour and the degree of lateral restraint mobilised in the steel-to-timber connections. The screws that connect cross-laminated timber slabs to steel beams may provide a certain degree of restraining action in fire. However, further investigations are required to quantify the slip characteristics of such connections. In this study, it was found from existing literature that at the fire limit state, the continuous elastic lateral stiffness available to restrain the beam varies between approximately 500 kN/m/m and 2000 kN/m/m. Relying entirely on the screws and using this practical range of stiffness, a parametric study using Eurocode 3 design buckling resistance equations on 9 m simply supported span steel beams and beam-columns with span-to-depth ratios of about 10, 15, 20 and 25 was performed. The results indicate that designing such members as fully restrained in fire conditions may lead to unrealistic assumptions and unsafe structures.

The Impact of Various Heating Rates on Real-Time Degree of Hybrid Fire Simulation

AbstractGlobal fire performance of structures in fire is proven to be more advantageous in many cases of engineering practice than the prescriptive fire resistance based on isolated structural member testing. Hybrid fire simulation (HFS) is a novel well-suited method trending in recent years for analysis of global performance of structures in fire. In the principles of this method, the part of a structure which has unknown behavior or is uncertain to be numerically modeled (subjected to fire) would be physically tested, while the rest of the structure is numerically simulated. HFS method enables capturing the beneficial interaction mechanisms evolving between fire-exposed structural members and the adjacent cooler substructure. Due to the continuous temperature increase in a fire test and the existing thermal inertia as well as the rate- and temperature-dependent material behavior of structures exposed to fire, a real-time performance in hybrid fire simulation counts as a necessity. This challenge is more critical for hybrid fire simulations with higher applied heating rates relevant to structural fire engineering. Within scope of this paper, (a) a robust and rigorous approach for real-time HFS is presented; (b) a series of proof-of-concept studies of different hybrid fire simulations with various applied heating rates are carried out for a thermomechanical benchmark problem; (c) the important results of four representative hybrid fire simulations with relevant heating rates to structural fire engineering are discussed; (d) the importance of an appropriate calculation method for stiffness update of the fire-exposed structural member over HFS procedure is highlighted, and e) the precision and accuracy of the applied HFS approach with respect to interface error and real-time degree are evidenced.

Understanding the effect of char oxidation on wood temperature profiles for varying heating and oxygen conditions

The use of mass timber framing as a sustainable material, particularly in high-rise buildings, requires detailed structural fire performance calculations. Thermal models describing only the solid phase are cost-effective alternatives to provide information to structural behavior models. Their accuracy depends on an adequate description of drying, pyrolysis, charring and eventually flaming phenomena. While in recent years there have been considerable contributions to the development of such models, there are still open questions. This work proposes a thermal model which incorporates char oxidation, describing both the kinetic- and diffusion-controlled regimes. The model was used to replicate two sets of experimental results which used standard fire calorimeters to study the ignition of thick wood specimens within a range of incident heat fluxes and oxygen concentrations, respectively. The model yields adequate temperature predictions in the early heating stages, but fails to replicate the behavior at later stages, when the effect of the surface combustion is noticeable. In terms of mass loss rates, a poorer performance is observed. To change from one oxidation regime to another, a Damköhler number is proposed, based on char oxidation reaction rates. It is found that for compartment fire conditions, char oxidation will mostly occur develop under diffusion-controlled conditions.

Performance-based design for structures in fire: Advances, challenges, and perspectives

The Performance-Based Design approach provides a goal-oriented process to support safe, innovative, and resilient structural fire designs. However, adoption of this approach requires both a rigorous framework and appropriate analysis tools to assess the expected performance of structures in fire. The objective of this paper is to provide an overview of the Performance-Based Design approach, including the process and its specific elements, applied to structures in fire. First, the value of the approach is illustrated through a review of case studies. Then, the process is described with identification of the role of the structural fire engineer. Recent research in methods to enable the evaluation of the structural fire performance, conducted within the author's group at Johns Hopkins University, is discussed. Issues addressed include the coupling between the fire and thermal-structural models, the characterization of the material behavior at elevated temperature, numerical modeling of structures subjected to fire, probabilistic risk assessment, and cost-benefit analyses. The paper concludes with a discussion of some challenges and perspectives for the future of performance-based structural fire design.

Numerical Analysis of Restrained Continuous Steel Columns under Standard Fire

The steel column performance in realistic structures during a fire has yet to be fully understood because existing research emphasizes single-story performance, thereby disregarding the influence of continuous steel columns in multi-story configurations devoid of fire. This paper presents a numerical study to comprehend the overall structural fire performance of continuous steel columns, considering the effect of loading ratios, restraint ratios, column continuity, and single-sided lateral moments. An advanced numerical model was initially developed using ABAQUS and validated against experimental tests. The validated numerical model was subsequently employed to investigate the effects of several parameters, including axial restraint ratios (α = 0.05–0.35) and axial load ratios (n = 0.3–0.8). The study findings indicated that the restraint ratios within the designed range have a slightly beneficial impact on the fire resistance of continuous steel columns. The column continuity did not exert a significant impact on the performance of steel columns in fire. Additionally, the comparison showed that the current design approach in EN 1993-1-2 was conservative for predicting the limiting temperature of internal and edge columns.

Structural characterization and fire performance of geopolymer-glass fiber composite panels

With a specific emphasis on understanding the thermal and fire resistance, in this work, sodium- and potassium-type metakaolin geopolymers (with Si:Al > 2) reinforced with glass fiber (GF) fabrics were manufactured. X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy were used to understand the changes in structure and evolution of phases with temperature. The geopolymer matrices have shown stability up to 700 °C, above which a fiber–matrix interaction was detected before they crystallized into different phases at 1000 °C. The fire resistance times of these panels (12–17 mm thick) when a temperature profile similar to ISO 834 fire curve was imposed were 53.6–55.1 min for Na-GF and 53.2–68.7 min for K-GF composites. Further, one-dimensional thermal analysis using cone calorimeter has suggested the initiation of cracking through the matrix during dehydration because of stress relief. This had an influence on the fire resistance timing of the panels. Despite this, both composites still retained ∼25–30% of their initial flexural strength after the furnace test, which was understood as a compromise between the variations of formed phases and morphological features in the exposed and unexposed sides.

Numerical validation of structural fire design for steel framed car park buildings

The installed automatic sprinkler systems in car park buildings can control the fire spread between vehicles, leading to unique localized vehicle fire scenarios. An advanced structural fire design methodology specific to steel-framed car park buildings was proposed by Linus Lim [11] based on the overall performance of structures under localized fire. This paper aims to assess the accuracy and reliability of this design methodology through numerical modelling using ABAQUS. The validated approach of establishing finite element models for steel-framed structures is adopted to simulate an eight-bay car park frame under two different fire scenarios following the design procedure. The overall structural fire performance of simulated structures indicates that even though the structural beams generated plastic deformation in two fire scenarios, none reached failure in the simulation. The comparison of load between simulation and design shows that the structural fire design methodology overestimated the load on the structural components inducing a conservative design result, which can be used for the car park building structural fire design. It should be pointed out that the neighbouring beams at a lower temperature could sustain the additional load from the continuous bending beam right above the fire, resulting in better overall performance of steel beams in localized fire. The assumption of load redistribution between different beams was validated in simulation.

Fire risk assessment of bridges: from state of the art to structural vulnerability mitigation

In recent years, due to the rapid urbanization, the fire risk in transport infrastructures is becoming more critical. These fires, typically caused by highly flammable materials, can significantly compromise the stability of the structure, as well as cause significant economic and social losses. However, in current regulations, no fire design or verification criteria are provided for bridges and the buildings prescriptions are not directly applicable due to the significant differences among the fire conditions. Therefore, starting from a deep literature review, different performance levels for bridges’ structural fire resistance were proposed. These levels were linked to the fire risk classification suggested by Kodur et al., for identifying the most vulnerable bridges to fire. This methodology was applied both to the prescriptive and performance-based approaches, using nominal and natural fire curves derived by advanced zone models of several bridge fire scenarios. To better investigate the structural fire performance of bridges, parametric analyses of a typological bridge were conducted for identifying the most critical structural systems and fire scenarios. One of the most relevant finding is that the use of performance-based approach allows to consider more realistic fire conditions, to satisfy higher performance levels with an optimization of the fire protection design. Therefore, the proposed approach can be useful both for designers and industrial category to assess the bridge performances in fire, not only according to prescriptive approach but also considering the performance-based one.

Review of fire experiments in mass timber compartments: Current understanding, limitations, and research gaps

AbstractThe use of mass timber in buildings instead of non‐combustible materials has benefits in sustainability, aesthetics, construction times, and costs. However, the uptake of mass timber in modern construction for medium and high‐rise buildings is currently hindered by uncertainty regarding safety and structural performance in fire. We attribute this to a lack of data. Insufficient understanding means that for building designs beyond the current range of experiments the fire performance is unknown. To address this uncertainty, we review the available data in the scientific literature from 63 compartment fire experiments with timber, the majority of which use cross‐laminated timber (CLT). We found that most experiments reached temperatures 80–180°C greater than in non‐combustible compartments. Timber ceilings have on average a 16% lower char rate than timber walls. The heat release rate contribution of timber has a positive linear relationship with charring rate, however is susceptible to significant uncertainty and variability. There are limits to the data available, particularly in large open‐plan compartments of floor areas larger than 100 m2 where a wider range of heating conditions occur. Other topics where further understanding is required are compartments with exposed timber areas greater than 75%, compartments with smaller opening areas, and the hazard of smouldering following the flames. Therefore, additional research is needed to design beyond the limits, specifically in compartment size, ventilation, and timber exposure. This paper identifies correlations in the current body of experimental research to improve fire‐safe design of timber buildings.

Structural fire design of square tubed-reinforced-concrete columns with connection to RC beams in composite frames

The tubed-reinforced-concrete (TRC) column is an innovative type of steel-concrete composite column that is gaining increasing engineering usage, and structural fire performance should be an important consideration of its design. As affected by the adjacent members and beam-to-column joints, the fire behaviour of TRC columns integrated into a frame may largely differ from that of isolated columns with idealised end conditions. However, the fire performance of TRC columns in composite frames has not been studied, except for some work done on the fire performance of isolated TRC columns with certain end restraints. This paper presents finite element analysis on single-storey and single-span non-sway frames with square TRC columns, employing the software package ABAQUS. The thermal and deformation behaviour, development of axial stress, axial force and bending moment during heating, working mechanism and failure mode of the frame exposed to fire are numerically investigated. The difference between the fire performance of TRC columns in a frame and those of equivalent isolated columns is quantified. The fire resistance of the framed column is found to lie between those of the columns with rotational end restraints and columns with idealised pinned ends. The complex effects of the connected RC beam on the fire behaviour of TRC columns, e.g. the beneficial restraining effect and the negative effect due to restrained differential thermal expansion, are clarified. Finally, a practical fire resistance design approach is proposed for TRC columns considering the continuity and interactions between structural elements within a composite frame.

Equivalent temperature prediction for concrete-filled cold-formed steel (CF-CFS) built-up column sections (part B)

Innovative concrete-filled cold-formed steel (CF-CFS) built-up column sections subjected to axial compression and elevated temperatures were previously investigated, assessing their structural fire performance. However, the analytical fire resistance methodology presented in the EN1994-1-2 requires advanced heat transfer analysis to compute the temperature evolution of the steel and concrete components of the composite cross-section. This paper presents a set of empirical formulations to predict equivalent temperature for steel and concrete components of CF-CFS built-up column sections. The finite element modeling technique to predict temperature evolution through the CF-CFS built-up column sections was calibrated using a 2-D heat transfer analysis (part A of this study). As a simplification, the concrete infill was divided into two areas, namely inner and outer core areas. The equivalent temperature of the steel section and the steel embedded area were also considered. The results showed good accuracy of the proposed empirical formulas.

Effect of protective coating on axial resistance and residual capacity of self-compacting concrete columns exposed to standard fire

Self-Compacting Concrete (SCC) is a green construction material widely used in the construction industry. While normal weight concrete has notable performance under fire conditions, the open literature continues to lack works examining the structural fire performance of SCC elements. Intending to bridge this knowledge gap, the present study aims to understand the efficiency of different protective coatings on fire response and the residual capacity of SCC short columns. In this experimental investigation, SCC columns were primarily cast from Supplementary Cementitious Materials (SCM) such as Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS) with partial replacement of fine aggregate by utilising the optimum content of Expanded Perlite Aggregate (EPA). Then, a thermal protective coating comprising of Cement Perlite Plaster (CPP) was developed using Ordinary Portland Cement (OPC) and the EPA. The fire performance of SCC elements was examined when protected with the newly developed coating as well as Gypsum Plaster (GP), Basalt Wrapping (BW), and Carbon Wrapping (CW) when exposed to ISO 834 standard fire curve for 60, 90, 120, and 180 min. The experimental results revealed that SCC specimens developed using GGBFS had better resistance to all exposure durations than the FA-SCC specimens. Also, it was noted that the CPP-protected SCC specimens exhibited higher residual strength capacity, followed by GP-protected SCC specimens, compared to the BW and CW-SCC specimens under axial load.

Numerical analysis and structural fire design of protected SHS steel columns with thermally enhanced gypsum-based mortars

Fire protection materials should restrict the temperature increase in steel members to prevent premature steel damage and structural failure in case of fire. The design of fire protection materials must be then precise, efficient, and optimized to make steel structures more competitive in the construction sector, thus reducing the impact of one of the worst disadvantages of steel structures. Therefore, this paper presents a numerical investigation into the performance of gypsum-based mortars enhanced with silica micro and nanoparticles as passive fire protection materials to protect the steel columns against fire. Square hollow section (SHS) steel columns were considered for this investigation. Firstly, finite element models were developed and confronted with observations from experimental tests previously carried out by the authors. Secondly, a parametric study was undertaken to study the role of several parameters on the structural fire performance of such columns when exposed to the ISO 834 standard fire curve, including the fire protection thickness and type (composition), column slenderness and load level. Then numerical and analytical results from current design rules in Eurocodes were compared. And finally, changes to the steel temperature prediction method in current design standards were proposed based on the findings of this study. It was observed that the design predictions excessively underestimated the actual fire resistance of the protected SHS steel tubular columns, especially when fire protection mortars with silica micro and nanoparticles were used. The thermal properties of fire protection mortars as a function of temperature must be considered in the structural steel temperature prediction when subjected to fire conditions. It is then strongly recommended that a new revision should be done in the next generation of Eurocodes on this topic based on the proposed modifications or the presented findings.

Fire Risk Analysis in Large Multi-Compartment Structures Using a Hybrid Multiscale Approach

This paper proposes a hybrid multiscale approach to evaluate the fire performance of large multicompartment structures. A probabilistic network model is at the core of the proposed approach, whose inputs, namely the mean durations of the fire phases and fire transmission through the barriers between compartments (e.g., walls or ventilation ducts), are determined beforehand by a zone model, which is detailed in a companion paper and a one-dimensional computational fluid dynamics code. Next, a proof of concept is developed by applying the hybrid approach to different fire scenarios in a full-scale generic military corvette and a four-story office building. The simulation results highlight the strengths and limitations of the proposed approach. Regarding the latter, a field model is used to evaluate how the hybrid approach performs depending on the interaction between the entire building system and its ventilation and the fire. Finally, a statistical study is carried out to produce fire vulnerability and risk maps, ranking the fire compartments according to their vulnerability or propensity to generate serious fires.

The effect of geologic conditions on the fire behavior of tunnels considering soil-structure interaction

This paper compares the fire performance of bored reinforced concrete tunnel lining sections under four ground conditions, ranging from shallow soft soil to deep rock. The fire performance is analyzed using a verified finite element beam-spring model. The investigated lining sections are adopted from realistic high-profile tunnels. A series of analyses are conducted to evaluate the performance of tunnel sections under a wide range of fire scenarios and ground conditions. First, the fire behavior of the four tunnel sections under the RABT-train fire curve is simulated during heating and cooling, and the results are reported in terms of structural performance and sectional stress–strain response. Second, the time to reach a limit state for the four tunnel sections is quantified under an extended RWS fire curve. Finally, a simplified methodology is proposed to include temperature-dependent soil properties, including the heat induced excess pore pressure and change in subgrade reaction modulus under elevated temperatures. The influence of temperature-dependent soil properties on the structural fire performance of a shallow tunnel section in soft clay is studied. The results show that bored reinforced concrete linings could experience significant irrecoverable damage from exposure to major fires. The moderate-depth tunnel section in soft soil and the deep tunnel section in high lateral pressure rock are the two critical cases, due to the large deformations and high internal forces, respectively. The importance of including temperature-dependent soil properties in tunnel fire analyses is demonstrated.

Finite element analysis of lightweight concrete-filled LSF walls exposed to realistic design fire

PurposeLight-Gauge Steel Frame (LSF) structures are popular in building construction due to their lightweight, easy erecting and constructability characteristics. However, due to steel lipped channel sections negative fire performance, cavity insulation materials are utilized in the LSF configuration to enhance its fire performance. The applicability of lightweight concrete filling as cavity insulation in LSF and its effect on the fire performance of LSF are investigated under realistic design fire exposure, and results are compared with standard fire exposure.Design/methodology/approachA Finite Element model (FEM) was developed to simulate the fire performance of Light Gauge Steel Frame (LSF) walls exposed to realistic design fires. The model was developed utilising Abaqus subroutine to incorporate temperature-dependent properties of the material based on the heating and cooling phases of the realistic design fire temperature. The developed model was validated with the available experimental results and incorporated into a parametric study to evaluate the fire performance of conventional LSF walls compared to LSF walls with lightweight concrete filling under standard and realistic fire exposures.FindingsNovel FEM was developed incorporating temperature and phase (heating and cooling) dependent material properties in simulating the fire performance of structures exposed to realistic design fires. The validated FEM was utilised in the parametric study, and results exhibited that the LSF walls with lightweight concrete have shown better fire performance under insulation and load-bearing criteria in Eurocode parametric fire exposure. Foamed Concrete (FC) of 1,000 kg/m3 density showed best fire performance among lightweight concrete filling, followed by FC of 650 kg/m3 and Autoclaved Aerated Concrete (AAC) 600 kg/m3.Research limitations/implicationsThe developed FEM is capable of investigating the insulation and load-bearing fire ratings of LSF walls. However, with the availability of the elevated temperature mechanical properties of the LSF wall, materials developed model could be further extended to simulate the complete fire behaviour.Practical implicationsLSF structures are popular in building construction due to their lightweight, easy erecting and constructability characteristics. However, due to steel-lipped channel sections negative fire performance, cavity insulation materials are utilised in the LSF configuration to enhance its fire performance. The lightweight concrete filling in LSF is a novel idea that could be practically implemented in the construction, which would enhance both fire performance and the mechanical performance of LSF walls.Originality/valueLimited studies have investigated the fire performance of structural elements exposed to realistic design fires. Numerical models developed in those studies have considered a similar approach as models developed to simulate standard fire exposure. However, due to the heating phase and the cooling phase of the realistic design fires, the numerical model should incorporate both temperature and phase (heating and cooling phase) dependent properties, which was incorporated in this study and validated with the experimental results. Further lightweight concrete filling in LSF is a novel technique in which fire performance was investigated in this study.

Thermo-mechanical analysis of laminated composites shells exposed to fire

This paper describes the research performed within the scope of H2020 project FIBRESHIP in the development and validation of a thermo-mechanical model to assess the fire performance of composite structures. A one-dimensional thermal model with pyrolysis is used to obtain the temperature profile across the thickness, and later, introduced in the thermo-mechanical model with a quadrilateral shell element approach. The composite constitutive model employed is the so-called Serial/Parallel Rule of Mixtures (SPROM) which has been modified to introduce the effect of the thermal deformation. A set of experimental tests are then used to validate the correctness of the numerical method proposed. The experimental data used to validate the thermal model is the classic Henderson experimental test. The thermo-mechanical coupling is validated against an original vertical furnace test of an FRP ship’s bulkhead, following on the 2010 FTP Code standards. These validations demonstrate the correctness and accuracy of the proposed decoupled thermo-mechanical formulation.

Experimental and numerical investigation into the fire performance of glulam bolted beam-to-column connections under coupled moment and shear force

The fire resistance of connection plays a crucial role in the fire performance of timber structures. During the past three decades, massive real-scale fire tests were performed on timber connections to analyse the mechanical behavior of connections under fire situation. Although different loading scenarios was considered in previous timber connection tests, little research focused on the beam-to-column connections loaded with a combination of stress caused by bending moment and shear force. For post and beam structures, when structures undergo large inter-story drift, the interforce at the connection includes not only shear force but also bending moment. In this study, real-scale tests are carried out on bolted beam-to-column connections loaded with coupled bending moment and shear force under normal temperature and ISO fire exposure. Three-dimensional numerical model of the bolted beam-to-column connections are developed and validated by experimental results. The model is capable of simulating the evolution of temperature in the connections as well as their mechanical behavior. The comparison of the rotation-time curve between experimental data and thermo-mechanical model shows comparable tendency. The experiments and numerical models in this study can enrich existed experimental data of glulam connections and can be used to calibrate the design approach for bolted beam-to-column connections under fire exposure.

A Review of the Structural Fire Performance Testing Methods for Beam-to-Column Connections

The structural fire performance tests for beam-to-column connections are critical in determining their fire performance at high temperatures. The current standard fire testing methods provide the procedures for establishing the fire resistance of each construction element exposed to a standard fire. However, these methods cannot verify the fire behaviour of the connections between building elements. Researchers have performed numerous fire tests on beam-to-column connections despite the lack of structural fire performance testing methods. This paper presents a comprehensive literature review of the structural fire performance testing methods for beam-to-column connections. The major areas in this review are travelling fires, development of travelling fires on beam-to-column connections, fire testing considerations, fire testing criteria, recent fire testing, and loading applications. This paper identifies the key issues and challenges of the structural fire performance testing methods for beam-to-column connections. Finally, this paper provides recommendations and discusses the way forward for structural fire performance tests on beam-to-column connections.