Performance Evaluation of Artificial Neural Networks (ANN) Predicting Heat Transfer through Masonry Walls Exposed to Fire

The multiple benefits Artificial Neural Networks (ANNs) bring in terms of time expediency and reduction in required resources establish them as an extremely useful tool for engineering researchers and field practitioners. However, the blind acceptance of their predicted results needs to be avoided, and a thorough review and assessment of the output are necessary prior to adopting them in further research or field operations. This study explores the use of ANNs on a heat transfer application. It features masonry wall assemblies exposed to elevated temperatures on one side, as generated by the standard fire curve proposed by Eurocode EN1991-1-2. A juxtaposition with previously published ANN development processes and protocols is attempted, while the end results of the developed algorithms are evaluated in terms of accuracy and reliability. The significance of the careful consideration of the density and quality of input data offered to the model, in conjunction with an appropriate algorithm architecture, is highlighted. The risk of misleading metric results is also brought to attention, while useful steps for mitigating such risks are discussed. Finally, proposals for the further integration of ANNs in heat transfer research and applications are made.

Thermoplastic Intumescent Coatings Modified with Pentaerythritol-Occluded Carbon Nanotubes

A thermoplastic intumescent coating system (IC) based on poly(vinyl acetate) was modified by two forms of multiwalled carbon nanotubes (CNTs), i.e., by a nanofiller powder and its solid dispersions in pentaerythritol (PER-CNTs). It was revealed that only the PER-CNTs modifier allows us to obtain solvent-borne ICs with a relatively high CNTs concentration (1–3 wt. parts of CNTs/100 wt. parts of paint solids) and acceptable application viscosity. Thermal insulation time (TIT) and intumescent factor (IF) of the ICs on a steel substrate (a fire test according to a cellulosic fire curve), as well as morphology, chemical structure (by the FT-IR technique) and mechanical strength of the charred systems, were investigated. It was found that the CNTs powder decreases TIT and IF values while PER-occluded CNTs improve these parameters (e.g., +4.6 min and +102% vs. an unmodified sample, respectively). Compressive strength of the charred ICs was improved by the PER-CNTs modifier as well.

Analytical Equations Applied to the Study of Steel Profiles under Fire According to Different Nominal Temperature-Time Curves

Some analytical methods are available for temperature evaluation in solid bodies. These methods can be used due to their simplicity and good results. The main goal of this work is to present the temperature calculation in different cross-sections of structural hot-rolled steel profiles (IPE, HEM, L, and UAP) using the lumped capacitance method and the simplified equation from Eurocode 3. The basis of the lumped capacitance method is that the temperature of the solid body is uniform at any given time instant during a heat transient process. The profiles were studied, subjected to the fire action according to the nominal temperature–time curves (standard temperature-time curve ISO 834, external fire curve, and hydrocarbon fire curve). The obtained results allow verifying the agreement between the two methodologies and the influence in the temperature field due to the use of different nominal fire curves. This finding enables us to conclude that the lumped capacitance method is accurate and could be easily applied.

Fire resistance of concrete lining in road tunnels

Fire is an incidental load on structures. Experience has shown that in the event of a fire, extremely high temperatures are developed, as a result of which very often a colapse of the tunnel bearing structure happens, usually caused by spalling of concrete. Road tunnel fires are usually caused by vehicles using the tunnel, but can also be caused by exidants, technical breakdowns in tunnel equipment or improper tunnel maintenance. The intensity and frequency of fires in the tunnels are function of several factors such as: length and geometry of the tunnel, density and type of traffic, vehicle speed, slope, availability of ventilation equipment and so on. All of these factors define the fire risk. Based on the defined fire risk, known fire load and location of the fire, it is possible to define the fire curve that defines the temperature in the tunnel versus time. Several fire curves, usually used in EU countries, will be described in this paper, the fire curves characteristics will be defined and the most proper fire curve for typical tunnel, as case study, will be recomended. In the framework of this paper, a methodology for fire resistance analysis of road tunnels, based on the performance, is elaborated. A numerical procedure for defining the behavior of the tunnel lining in case of nominal fire curve (standard fire) is described and applied on one case study. The impact of the fire on the stress-strain state of the concrete structure of a tunnel is analyzed and measures for proper tunnel design in terms of increasing the fire resistance is proposed.

Investigation on the performance of fiber reinforced concrete subjected to standard fire exposure

Purpose Aim of this research work is to examine the stress–strain behavior and modulus of elasticity of fiber-reinforced concrete (FRC) exposed to elevated temperature. The purpose of this paper is to study the effect of standard fire exposure on the mechanical and microstructure characteristics of concrete specimens with different strength grade. Design/methodology/approach An electrical bogie hearth furnace was developed to simulate the ISO 834 standard fire curve. Specimens were exposed to high temperatures of 821°C, 925°C and 986°C for the duration of 30, 60 and 90 min, respectively, as per standard fire curve. Peak stress, peak strain, modulus of elasticity and damage level of heated concrete specimens were evaluated by experimental investigation. SEM-based microstructure investigation has been carried out to analyze the microstructure characteristics of heated concrete specimens. Findings The results revealed that carbon fiber reinforced concrete was found to be better than the FRC made with other fibers on improving the modulus of elasticity of concrete. An empirical relationship has been established to predict the modulus of elasticity of temperature exposed specimens with different type of fiber and grade of concrete. In comparison with low melting point fibers, high melting point fibers exhibited higher modulus of elasticity under all tested conditions. Surface damage and porosity level of concrete with carbon and basalt fibers were found to be lower than other FRC. Originality/value Empirical relationship was developed to determine the modulus of elasticity of concrete exposed to elevate temperature, and this will be useful for concrete design applications. This research work may be useful for finding the residual compressive strength of concrete exposed to elevate temperature. So that it will be helpful to identify the suitable repair/retrofitting technique for reinforced concrete elements.

Fire behaviour of large scale loaded tunnel segment tests for project Rotterdamsebaan, The Netherlands

<p>Assessing the performance of tunnels in fire is becoming increasingly crucial for the overall usability and durability of the structure. One of the most reliable methods for evaluating the presentation of the concrete during fire in tunnels is by testing. In this work, the fire tests performed on the Victory Boogie Woogietunnel, project Rotterdamsebaan (The Hague, the Netherlands) are discussed. The study aims to assess the fire performance of the cut and cover concrete section when subjected to a tunnel fire curve. A series of 6 fire tests were performed on concrete slabs of the size 5,0 m x 2,4 m x 0,4 m when exposed to Rijkswaterstaat (RWS) fire curve for 120 minutes. Based on the work, one of the main conclusions drawn were that it is necessary to test a large-scale specimen to judge the performance of a protection system accurately. Another important conclusion is that the test specimen should have the concrete mixture which accurately represents the tunnel concrete to avoid uncertainty in the fire induced spalling behaviour of concrete.</p>

Evaluation of unprotected steel beam temperature during fire using CFD simulation

Fire resistance of building construction is essential part of the design process. Thermal loading of loadbearing elements can be obtained by using simplified standard fire curve or advanced numerical fire model. The paper shows the process of numerical fire modelling in unprotected steel structure carpark using the Computational Fluid Dynamics (CFD) method. In Fire Dynamics Simulator (FDS) software, three scenarios are created to represent open, semi-open and closed carpark building. The resultant HEB500 beam temperatures are compared with standard evaluated temperatures.

Spalling Resistance of Fiber-Reinforced Ultra-High-Strength Concrete Subjected to the ISO-834 Standard Fire Curve: Effects of Thermal Strain and Water Vapor Pressure

The prevention and mitigation of spalling in high-strength concrete (HSC) rely on mixing polypropylene (PP) as an additive reinforcement. The dense internal structures of ultra-high-strength concrete (UHSC) result in risks associated with a high thermal stress and high water vapor pressure. Herein, the effects of pore formation and thermal strain on spalling are examined by subjecting fiber-laden UHSC to conditions similar to those under which the ISO-834 standard fire curve was obtained. Evaluation of the initial melting properties of the fibers based on thermogravimetric analysis (TGA) and differential thermal analysis (DTA) demon strated that although nylon fibers exhibit a higher melting point than polypropylene and polyethylene fibers, weight loss occurs below 200 °C. Nylon fibers were effective at reducing spalling in UHSC compared to polypropylene and polyethylene fibers as they rapidly melt, leading to pore formation. We anticipate that these results will serve as references for future studies on the prevention of spalling in fiber-reinforced UHSC.

Evaluation of Design Fire Curves for Single Combustibles in a Cinema Complex

An actual fire test was performed on single combustibles placed in a local cinema complex, and quantitative differences in the maximum heat release rate (HRR) and fire growth rate were investigated based on the design fire curve methods (i.e., the general and 2-stage methods). In terms of combustible use and fire load, a total of 12 combustibles were selected, classified into cinema lounge and movie theater. It was found that the maximum HRR and fire growth rate determined using the two-stage method were quantitatively different from those of the general method. The application of the two-stage method, which can be used to determine the fire growth rate of the initial fire stage more precisely, could be useful in accurately predicting the activation time of fire detectors and fire-extinguishing facilities, as well as the available safe egress time (ASET) and required safe egress time (RSET).