Full-scale Fire Tests Research Articles

Estimation and research of the temperature field models of large space spherical mesh shell structures under localized fire

This paper firstly investigated fire dynamics characteristics and the temperature field distributions of large space spherical mesh shell (SMS) structures under localized fire in FDS, and divided the temperature fields into plume region, smoke accumulation region and ceiling jet region. Based on the classical axisymmetric plume model, the predictive models for the steady-state and transient temperature fields in different fire regions for large space SMS structures were proposed in this paper. Thereafter, the proposed temperature models were compared with the simulated results and experimental test results by other scholars, and they were in good agreement. In order to further discover the realistic fire development progress and temperature distribution of large space fire, and validate the proposed temperature field models, this paper designed and conducted three full-scale large space fire tests (Test-1 ∼ Test-3) with different fire source powers in a large space building. Results showed that temperature fields of large space fires could be consisted of near-fire region (Flame region) and far-fire region (Plume region and Ceiling jet region). The steady-state fire source powers were tested for 443 kW, 886 kW, 1090 kW for Test-1, Test-2 and Test-3, respectively, while their maximum temperatures of the roof reached 75 °C, 105 °C and 120 °C. Based on McCaffrey plume model, we further proposed the transient temperature model in flame region for large space structures, and its accuracy was verified by the test results. Moreover, the proposed steady-state and transient temperature fields for large space SMS structures were compared with the tested temperature field data, and the tested and predicted temperature curves were generally in good agreement in plume and ceiling jet regions. Finally, the test results aimed to provide a scientific basis and reference for the fire safety and structural fire-resistant design of large space buildings.

Full-scale car fire tests on FRP reinforced RC columns in piloti structures

Car fire tests were conducted on fiber reinforced polymer (FRP) reinforced columns to evaluate the fire effects on piloti structures. The study involved a mid-size car (1,998 cc) with fuel and tire air pressure removed to reduce the risk of explosion. The objectives were to measure the heat release rate (HRR) and temperature distributions during the fire and to evaluate the fire behavior of the columns in the piloti structure. Results from the car combustion test showed a total heat release of 5,210 MJ, with a maximum temperature of 455.0 °C at 2.5m height above the car ceiling and an internal temperature of 1025.7 °C near the ignition point at the car seat. In the piloti structure fire test, consisting of four reinforced concrete (RC) columns with and without FRP reinforcement and a roof slab, the maximum temperature reached 728.5 °C under the slab. Thicker FRP reinforcement resulted in lower temperatures on the column surface. Fire Dynamics Simulator (FDS) software was used to validate the test results and showed accurate predicted temperatures at 3m (within 10 % error). However, discrepancies were observed at 2.5m (24 % error) and below, although the simulated fire behavior agreed well with the test results for heights of 2.0m and above.

Physical and mechanical response of large-diameter shield tunnel lining structure under non-uniform fire: A full-scale fire test-based study

When a fire occurs in an underground shield tunnel, it can result in substantial property damage and cause permanent harm to the tunnel lining structure. This is especially true for large-diameter shield tunnels that have numerous segments and joints, and are exposed to specific fire conditions in certain areas. This paper constructs a full-scale shield tunnel fire test platform and conducts a non-uniform fire test using the lining system of a three-ring large-diameter shield tunnel with an inner diameter of 10.5 m. Based on the tests, the temperature field distribution, high-temperature bursting, cracking phenomena, and deformation under fire conditions are observed. Furthermore, the post-fire damage forms of tunnel lining structures are obtained through the post-fire ultimate loading test, and the corresponding mechanism is explained. The test results illustrate that the radial and circumferential distribution of internal temperature within the tunnel lining, as well as the radial temperature gradient distribution on the inner surface of the lining, have non-uniform distribution characteristics. As a result, the macroscopic phenomena of lining concrete bursting and crack development during the fire test mainly occur near the fire source, where the temperature rise gradient is the highest. In addition, the lining structure has a deformation characteristic of local outward expansion and cannot recover after the fire load is removed. The ultimate form of damage after the fire is dominated by crush damage from the inside out of the lining joints in the fire-exposed area. The above results serve as a foundation for future tunnel fire safety design and evaluation.

Measuring the fire growth potential of combustible solids using a cone calorimeter

The fire growth rate of interior linings, furnishings, and construction materials is measured in full-scale fire tests such as the ASTM E84 Steiner Tunnel, the ISO 9705 room fire, and a passenger aircraft fuselage as the flame-spread rate, time-to-flashover, or time to incapacitation, respectively. The results are used to indicate the level of passive fire protection afforded by the combustible material or product in the test without providing any insight into the burning process. These large-scale tests require many square meters of product, are very expensive to conduct, and can exhibit poor repeatability–making them unsuitable for product development, quality control, product surveillance, or regulatory compliance. For this reason, smaller (0.01 m2) samples are tested in bench-scale fire calorimeters under controlled conditions, and these one-dimensional burning histories are correlated with the results of the two- and three-dimensional burning histories in full-scale fire tests by a variety of empirical and semi-empirical fire propagation indices, as well as analytic and computer models specific to the full-scale fire test. The approach described here defines the potential of a material to grow a fire in terms of cone calorimeter data obtained under standard conditions. The fire growth potential, λ (m2/J), is the coupled process of surface flame spread and in-depth burning that is defined as the product of ignitability (1/ E ign) and combustibility (Δ Q/Δ E) obtained from a combustion energy diagram measured in a cone calorimeter at an external radiant energy flux [Formula: see text] (W/m2) above the critical flux for burning, [Formula: see text]. However, the potential for fire growth, λ≡ (1/ Ei gn)(Δ Q/Δ E) is only realized as a hazard when the heat of combustion of the product per unit surface area, Hc (J/m2), is sufficient to grow the fire. The dimensionless fire hazard of a combustible product of thickness b is therefore, Π = λ Hc, while the fire hazard of the component materials is an average over the product thickness, π = Π/ b. The measurement of λ, Π, and π from combustion energy diagrams of heat release Q (J/m2) versus incident energy E (J/m2) is described, as well as a physical basis for a fire growth potential that provides simple analytic forms for λ in terms of the parameters reported in cone calorimeter tests. Experimental data from the literature show that rapid fire growth in full-scale fire tests of combustible materials occurs above a value of Π determined by the severity of the fire test.

Full-scale hybrid fire test in real-time with multiple degree of freedom

To experimentally assess the fire resistance of civil structures, testing whole structures is very costly but the standard tests on individual structural elements can sometimes be too simplistic, regarding their boundary conditions. Hybrid fire testing offers a promising solution to these limitations, but performing such tests is technically challenging and few full-scale tests have been conducted. Current approaches rely on high-performance sensors and actuator systems, as well as assumptions about the stiffness of the tested element. This paper presents the detailed methodology and results of a full-scale, real-time test with 3 degrees of freedom on a concrete beam. The use of an adaptive controller allowed for maintaining stability and achieving reasonable precision despite the use of relatively low-precision sensors, regular hydraulic actuators, and no assumptions about the tested element’s stiffness. The comparison with the same element tested using a standard fire resistance test demonstrates the usefulness of this technique in achieving a more accurate representation of the performance of the tested element in realistic conditions.

Improving the fire-retardant performance of industrial reactive coatings for steel building structures

The main aim of this study was to determine key factors that regulate fire-retardant effectiveness of intumescent coatings comprising of ammonium polyphosphate, melamine, pentaerythritol, polymer binder. Fulfillment of the research objectives resulted in the development of a coating with R120 fire resistance. The expected service life of the coating is at least 15 years when applied at Z2 type of environmental conditions (indoor use). It was established that in order to provide fire resistance of around R30 it is advisable to use the styrene-acrylic polymers as binders for both water-based and organic-based intumescent systems. The ratio of target components ammonium polyphosphate/melamine/pentaerythritol in such systems should be close to 2/1/1. The coating thickness is to be 0.4–0.5 mm. To achieve higher fire resistance (R60 or more) the coating should include a vinyl acetate derivative as a binder (copolymers with ethylene or vinylversatate). Target components ratio in this case is to be close to 3.5/1/1.5, while the coating thickness should be kept at 1.6–1.8 mm. If the required class of fire resistance is above R120, coating thickness is usually to be kept above 3.5 mm. In order to achieve higher fire resistance, it is advisable to use nano-clay additives and reinforcing fibers in intumescent compositions.The obtained results were used in the development of intumescent coating, which is produced industrially and provides over R120 fire resistance of steel, which was confirmed in standardized full-scale fire tests.

Numerical analysis of full-scale structural fire tests on composite floor systems

Recent experiments conducted at the NIST examined steel-concrete composite floor systems designed per U.S. practice under standard fire. The first experiment designed per prescriptive provisions for a 2-h fire rating with 60 mm2/m of reinforcement, developed a central breach integrity failure after approximately 1 h of exposure. The second and third experiments, designed with 230 mm2/m of reinforcement, with the third one omitting the fire protection on the central steel beam, showed no failure within 2 h. This paper describes a numerical investigation to gain further insights into the fire behavior of the composite systems tested in these experiments. Nonlinear finite element models were validated against the tests. Simulation of the first test shows concrete damage and rebar fracture in the hogging moment area corresponding with the cracks observed experimentally. Simulation of the third test captures the development of tensile membrane action, confirming the redistribution from the unprotected secondary steel member to the floor reinforcing steel. A sensitivity analysis allows identifying the minimum reinforcement steel for protected and unprotected central beams configurations. The results can support improvements of the fire requirements in the U.S. codes as well as application of performance-based structural fire design for composite structures.

Full-scale experimental study on combustion characteristics and smoke temperature of double-source fires in different tunnels

Through a series of full-scale fire tests conducted in three different tunnels, the common characteristics of combustion and smoke temperature of double pool fires in actual operation tunnel environments are investigated. The evolution process of the coupling effects of shielding entrainment and thermal feedback enhancement is revealed. It is found that the ventilation state and the fire source spacing can alter the dominant relationship between the shielding entrainment effect and the thermal feedback enhancement effect, resulting in different evolution patterns of combustion characteristics and smoke flow patterns of double pool fires in tunnels. The heat release rate increases by 4 times when the double pool fire flames merge under the longitudinal ventilation compared with the double pool fire flames without fusion under the natural ventilation. The flame tilt angles of double pool fires were determined through the image processing method, and the prediction model of the flame inclination angle of downstream fire sources was established, considering fire source spacing. At the same time, the characteristic of temperature measured by Fiber Bragg Grating in double-source fire scenarios was investigated, developing a model to predict the longitudinal temperature rise distribution. It is found that the maximum temperature rise prediction model based on steady-state fire has poor applicability in the weak-plume fire scenario of full-scale tunnels. The analysis of the smoke flow patterns shows that the two-stage ventilation is more suitable for smoke control compared to full longitudinal ventilation in tunnel double-source fire accidents, especially for ensuring the safety of individuals trapped in the area between the two fire sources.

Large-Scale Fire Tests of Battery Electric Vehicle (BEV): Slovak Case Study

Due to the increasing number of battery electric vehicles (BEV) on the roads and the number of BEV accidents with the occurrence of a fire, full-scale fire tests of BEVs were carried out. For initiation, the BEVs were mechanically damaged, forming a gap with a size of 15 cm × 15 cm. The external heat source was a 300 kW propane burner with a maximum power of 54.0 kW and a length of 54 cm. The flame of the propane–butane fuel mixed in air at a temperature of 1970 °C was inserted directly into the battery pack. The increase in the temperature was monitored as a function of time through thermocouples at selected locations of the BEV until the point of initiation. Thermocouples were placed 10, 30, and 50 cm from the place of BEV surface. Accordingly, to obtain the temperature–time curves from the experiment measurement, critical temperatures were subsequently evaluated. The fire tests on BEVs can be described according to the individual phases of the fire. The external heat source started the initiation process at the 25 min time mark. Consequently, the phase of a developed fire with a dynamic course started. A sharp rise in temperature occurred. Within two minutes, the temperature rose to 1056.9 °C. After the initiation source was removed, there was decline in temperature and re-ignition to the stage of a fully developed fire. Thermocouples recorded temperatures in the range of 900 °C. The resulting dynamic process of a BEV fire with a sharp increase in temperature is a problem for the implementation of firefighting works and the liquidation of traffic accidents. Furthermore, foam extinguishing was part of the experiments. In both cases after the foam application, the temperature on the thermocouple T1 (distance was 10 cm from the surface of the BEV) dropped from 486.1 °C to 76 °C after 10 s of application.

Advancing building fire safety through heat resistant and flame retardant hybrid silicone sealant

Rapid urbanization and population growth have led to a significant transformation in the urban landscape, characterized by the proliferation of high-rise buildings. However, this urban development has brought about new challenges, particularly in terms of fire safety. The escalating risk of disasters, especially fires, underscores the critical importance of implementing effective fire safety measures across all building types, necessitating legislative reforms. Despite their crucial role in ensuring structural integrity, sealants have often been overlooked in building safety standards, resulting in a lack of comprehensive regulations. The research addresses these challenges by focusing on the development of fire-resistant silicone sealants designed to enhance the fire resistance of building materials. These sealants were formulated independently, incorporating three fire retardants and four heat-resistant agents. While metal oxide flame retardants generally exhibited excellent performance, excessive mixing led to surface deformation and reduced workability. Optimal combinations of flame retardants and heat-resistant agents were identified, with the FR2 specimen demonstrating promising fire resistance performance. Full-scale fire performance tests conducted on FR2 revealed a maximum temperature difference of 40.6 °C between heated and unheated surfaces over a 2-h period, indicating high thermal insulation performance. These findings validate the efficacy of the proposed method and offer significant enhancements to building safety, thereby mitigating fire damage in urban environments.

Similarity analysis of the fire-resistant behaviour of partially encased composite columns in different scales

As full-scale fire resistance tests commonly involve considerable expense and require specialized experimental apparatus, scale specimens are being employed in many investigations focusing on the performance of structural members under fire exposure. However, since the inherent thermal properties of materials are commonly independent of the geometrical scale factors, it is necessary to analyze the similarity among the thermal responses of scale specimens and their corresponding prototype in advance, in order to generalize the experimental conclusions to practice. In this context, the similarity of the fire-resistant behaviour of partially encased concrete (PEC) columns, a sort of structural member that is widely used in building and industrial structures, in different geometrical scales was studied in this work. A finite element model was developed and verified based on existing experimental results, and then used for the parametric studies. The similarities of the transient temperature fields, deformation states and the fire-resistant durations of the PEC columns with restrained thermal elongation in different scales were analyzed, which indicates that the mathematical relationship between the time-scale factor and the geometric scale factor in the classical similitude theory needs to be improved for such structural members with complex cross-sections. A modified time-scale equation was therefore proposed to ensure the fire endurance prediction accuracy of scale PEC models for the corresponding prototypes under fire, with the proportion of steel in the cross-section (steel ratio) and the aspect ratio well-considered, which could facilitate the temperature-related experiments and analyses of PEC structural members in the future.

Design fire scenarios for hazard assessment of modern battery electric and internal combustion engine passenger vehicles

Full-scale fire testing of battery electric (BEVs) and internal combustion engine (ICEVs) passenger vehicles has historically shown peak heat release rates (HRRs) ranging from 5–10 MW. However, the vehicles tested in these studies are smaller with less energy capacity than vehicles currently on the market. This paper presents a model to extrapolate data from full-scale vehicle fire tests to evaluate the fire hazard associated with larger passenger vehicles. The model is validated on 20 full-scale vehicle experiments in the public literature and is then used to develop conservatively bounding fire scenarios for vehicles representative of the current market environment. No significant difference was observed in the HRRs between the similarly sized ICEVs and BEVs in this work; however, the predicted HRRs for both vehicle types significantly exceeded existing design guidance. While the model may be shown to be overly conservative in future testing, it is validated using the data that currently exists, and points to an alarming trend in the fire protection industry, where the hazard posed by single passenger vehicles may exceed existing design guidance.

Post-earthquake fire resistance of self-centering concrete beam-column joint: An experimental investigation

Fire is an accidental disaster resulting in disastrous consequences for building. Post-earthquake fire is a secondary disaster induced by earthquake, triggering off larger destruction in a higher probability of occurrence. The potential severity of consequences to structures makes fire and post-earthquake fire safety imperative in the design of any new structures. Self-centering concrete joints are introduced as a promoting alternative to traditional reinforced concrete (RC) joints. They always exhibit excellent seismic performance and self-centering capacity, available in high-seismic zone. However, the current lack of experimental data on fire response of self-centering concrete joints means that they remain an open issue in current design codes. In this paper, full-scale quasi-static cyclic test and fire tests were conducted on two self-centering concrete joints connected with bolted angles and posttensioned (PT) tendons. The experiments aimed to explore the performance of self-centering joint in fire situations, and the impact of post-earthquake damages on fire response of self-centering joint. The deformation patterns and thermal responses of self-centering joints including temperature distribution, prestress force of PT tendons, displacements at beam ends and duration were recorded and analyzed. The results show that both self-centering joints exhibited satisfactory fire resistance with endurance over 170 min. Generally, the bolted angles and PT tendons in self-centering concrete joints showed acceptable working performance in fire. The findings unveil the actual response of self-centering concrete joints during the fire and post-earthquake fire conditions, providing experimental data for further numerical simulation and analysis. It can be used to calibrate the design approach for self-centering joints under fire and seismic-induced fire exposure.

Influence of thermal strain on concrete spalling

Understanding the susceptibility to spalling of concrete members in case of fire is important to evaluate the residual load-bearing capacity. The investigations of the spalling phenomenon of a concrete mixture using real scale members are necessary but expensive to carry out. Reducing the specimen size leads to an increase of boundary effects that can result in a reduced spalling or absence of spalling. In this study, fire tests were carried out on unrestrained, single-sided exposed, cuboid shaped specimens (0.6 m ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 0.6 m ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 0.29 m) as well as unrestrained and steel ring restrained cylindrical specimens (Ø = 0.47 m, h = 0.29 m), which induce different boundary conditions. These fire tests were carried out on two ordinary concrete mixtures. The two mixtures differ only in the type of aggregates (quartz gravel and basalt grit) and were used to investigate the influence of the thermal expansion of the aggregate on the spalling behaviour of the concrete. The results show a significant increase of the spalling depth due to the restrained thermal expansion achieved by the applied steel rings. Additionally, the type of aggregate has a direct influence on the spalling behaviour of a concrete mixture. The reduction of the boundary effects by the steel rings recreate the test conditions in the centre of a large concrete member. Thus, this type of specimen is suitable to determine the susceptibility to spalling of a material (screening-tests) as preliminary investigations to full scale fire tests.

Experimental study on the effects of branch tunnel ventilation on the smoke movement and temperature characteristics in bifurcated tunnel fires

A series of fire tests were conducted in a bifurcated tunnel model with branch tunnel ventilation. Three fire locations were considered. The characteristics of smoke movement and temperature profile under various fire source location scenarios were analyzed. The results indicate that when the fire source is not at the intersection, the ventilation airflow in the branch tunnel is diverted at the intersection before it is imposed on the fire source, which results in the actual velocity of ventilation air imposed on the fire source being less than the velocity of ventilation air in the branch tunnel. A new parameter, named the diversion coefficient, was introduced for convenient analysis. By substituting the diversion coefficient values into a classic maximum temperature rise prediction model for the single-line tunnel fires, good prediction results were observed. Moreover, a new dimensionless smoke temperature decay model was developed. The applicability of the model was validated using full-scale fire test data from previous research. The dimensionless temperature decay law of smoke was analyzed based on the newly established model. Results show that when the fire is positioned at the intersection, the decay coefficient of the smoke downstream of the fire decreases linearly as the ventilation rate increases, while decay coefficient of the smoke upstream of the fire decreases slowly at first and then increases with the increase of ventilation rate. When the fire source is not at the intersection, the branch tunnel ventilation conditions could be classified into three categories: sub-critical, critical, and super-critical velocity. Changes in the ventilation velocity within the branch tunnel have little influence on temperature decay process of smoke in the main tunnel under critical and sub-critical velocity conditions. However, under super-critical velocity conditions, the smoke temperature decreases rapidly after reaching the intersection. Furthermore, predictive models for the critical velocity of the branch tunnel under various fire locations were established based on theoretical analysis and experimental data. Within a specific range of heat release rate, the critical velocity is proportional to the cube root of the heat release rate. Compared to when the fire is located at the intersection, the critical velocity is reduced significantly when the fire is not in the intersection.

CONDUCTING A NATURAL FIRE TEST IN THE VERTICAL CABLE TUNNEL OF A NUCLEAR POWER PLANT

The article discusses conducting a full-scale fire test in the vertical cable tunnel of a nuclear power plant (NPP). Vertical cable tunnels in NPPs are used for laying cable lines, wires, safety system lines, connecting the equipment room, and the containment of the nuclear power plant block. The paper analyses research methods and selects options that will be effectively used to determine the temperature regime in the vertical cable tunnel of NPPs with known aerodynamic, technical, and geometric parameters and fire loads. The algorithm for conducting full-scale tests in the vertical cable tunnel of an NPP is described. Based on the research, the maximum temperature in the combustion zone is reached on the fourth minute of the full-scale tests in the vertical cable tunnels of nuclear power plants. By obtaining temperature graphs in the vertical cable tunnel of the NPP, it can be observed that the highest temperature is in plane D (800–900 °C), and it depends on the location of the control point. Thermal energy propagates more intensively in the direction opposite to the filling of the space, which is opposite to the exit of combustion products and ventilation openings. The temperature in plane C is in the range of 500–800 °C. Thermal energy propagates most intensively towards the filling to the exit of combustion products. This temperature significantly deviates from the standard temperature regime, which differs greatly from the full-scale experimental study of fires in the vertical cable tunnels of nuclear power plants. It can be concluded that the standard temperature regime of a fire is not adequate for testing the fire resistance of the structural elements of vertical cable tunnels in nuclear power plants. An important conclusion of these studies is the possibility of determining the fire resistance of building structures of vertical cable tunnels of NPPs with the selection of the most severe temperature regime, according to the conducted field test. It means that research results can be used in practice in designing and evaluating the safety of such objects. Keywords: fire, natural fire tests, nuclear power plant, vertical cable tunnel.

Spatiotemporal state assessment for the underground pipe gallery: Physical model and experimental verification

Understanding the fire safety of underground pipe galleries is attracting more and more attention recently, since it may further trigger heavy economic losses for society. An effective and accurate temperature prediction model for the cable cabin in the underground pipe gallery is critical to describe the temperature evolution and make state assessment. In this study, a spatial–temporal temperature propagation model is established based on the heat conduction equation to reveal the temperature evolution from the perspective of spatial and temporal domains in a concurrent way. To demonstrate the effectiveness of the proposed model, a series of full-scale fire tests are carried out in the largest underground pipe gallery platform in China. The characteristics of fire development can be well captured using the proposed model. The feasibility of the proposed model is demonstrated by analyzing the temperature propagation of spatial and temporal domains. The predictions obtained from the proposed model matched well with the observations measured by sensors, and the temperature spatial–temporal evolution can be depicted precisely. The present work positively provides technical references for state assessment of the underground pipe gallery and making fire protection and intervention strategies, can be applied in other fire scenes with its universality.

A Full-scale Fire Test on Electric Vehiclein an Underground Car Parks

A full-scale test was conducted to evaluate the risk of a modern battery electric vehicle (BEV) fire in an underground car park. A test rig 7,800 × 7,800 × 2,300 mm in size was built to simulate the corner segment of an underground car park. The BEV was positioned in a parking bay at a corner of the structure . The lithium-ion battery pack was heated using an electric heating sheet to activate thermal runaway inside the pack. The temperature distribution in the internal space of the test rig was measured using a thermocouple. The incident heat fluxes on neighboring cars were also estimated using heat flux gauges positioned around the test vehicle. Deflagration venting was observed instantaneously after the initial ignition of the flammable gas accumulated under the ceiling of the test rig. This phenomenon accelerated the growth of the BEV fire, resulting in an average ceiling jet temperature of 1,000 ℃ and a peak heat flux of 225 kW/m<sup>2</sup>.

External precast concrete nib beam-to-column connection under elevated temperatures: Experimental and finite element analysis

The precast concrete nib is one of the most widely used beam-to-column connections to address the architectural drawback of the ordinary precast concrete corbel. However, precast concrete nib beam-to-column connections are not classified as fully rigid or pin but exhibit semirigid properties. Semirigid connections are at risk of deflection at lower loads and cracking during early fire events. In this study, full-scale fire tests were carried out to determine the thermal and structural behaviour of the external monolithic and precast concrete nib beam-to-column connections subjected to 120 min standard cellulose fires. A finite element simulation using ANSYS validated the experimental results based on the internal temperature distributions, load–deflection curves, and stress visualization. Results show that the tension reinforcement of the concrete nib specimen at high temperature was below the critical temperature of 300 °C during the 120 min of heating, compared to the monolithic specimen, which reached the critical temperature of 300 °C at 105 min. The crack patterns and failure modes of monolithic and precast concrete nib specimens at high temperatures were more visible than at ambient temperature. Based on the ductility factor and Monforton’s fixity factor, the concrete nib specimen at high temperatures was categorized as structures with limited ductility and classified in Zone I (pin connection), respectively. This study concluded that external precast concrete nib beam-to-column connections were more vulnerable at high temperatures than monolithic connections.

Full-scale fire resistance tests of lightweight steel framed floor systems

As cold-formed steel profiles are increasingly used for load-bearing structural systems, their fire design requires specific attention due to their thin-walled nature and high slenderness. In some specific applications such as in storage hall floor systems, these structures are used without sheathing or thermal protection on the fire-exposed side. Yet, there is a lack of data from fire resistance tests on full-scale load-bearing thin-walled steel structures, especially with directly exposed steel. This article describes two standard fire resistance tests on full-scale light gauge steel frame floors made of cold-formed steel lipped channel girders and joists topped by chipboard panels. The experimental program was designed to investigate the fire resistance of the unprotected girders. A specificity of this program was that the girders were subjected to a low load level to probe the ability to achieve without passive fire protection a 30-min fire resistance rating typical for storage hall structures in the Czech Republic. The absence of protection resulted in differences in thermal gradients and bracing compared to common fire tests, as well as a very low degree of utilization leading to an expected failure temperature higher than 800 °C. The results showed that the two floors remained stable during the 30 min with limited deflections, but failed the deflection rate criteria after 24 and 22 min, respectively. Comparison is provided with the calculation methods from the Eurocodes. The presented results provide new data on the response of full-scale, unprotected cold-formed steel floor systems subjected to fire, which can be used to calibrate numerical models and fire design methods outside of the range currently covered by the codes.