Fire Curve Research Articles

Performance of RC beams strengthened using NSM FRP and cement based adhesives after exposure to elevated temperatures

A popular method for strengthening of reinforced concrete (RC) structures is the use of carbon fiber reinforced polymers (CFRP) bonded to the structural elements using the near surface mounted (NSM) techniques. While this method possesses many advantages, poor fire resistance as a result of the low glass transition temperatures (TG) of organic resins remains a significant drawback. Replacement of organic resins with cement based adhesives (CBA) could potentially improve the fire performance of NSM FRP systems and reduce the amount of insulation required to achieve the required fire endurance period. This paper presents an experimental program consisting of fifteen RC beams strengthened in flexure using NSM FRP bonded using CBA and subjected to the standard fire time temperature curve up to a target temperature of 600 °C. Twelve of the beams were strengthened using NSM-FRP laminates and bars including both smooth and rough FRP laminates and the remaining three specimens acted as control beams. Further, the use of plasterboard was explored as fire protection to further increase the residual strength of the specimens after heating. Results showed that the reinforced concrete beams strengthened with NSM CFRP retained 82 % to 61 % of their unheated strengthened ultimate load after heat exposure. This was a result of the superior performance of the cement-based adhesive at high temperature and the fire protection provided to the CFRP through embedment in the grooves. Moreover, the use of plasterboard as fire protection decreased the CFRP temperature by 42–24 %. The insulated beams behaved similarly to strengthened beams prior to fire exposure.

Performance-based analysis on fire behavior of shield tunnel joint with DDCI connector

In recent years, there has been significant advancement in large-diameter shield tunnel technology, with the continuous emergence of new joint types. To meet the different requirement of application, numerous studies have been done on the mechanical behavior of the various new joints. In this paper, a new DDCI connector for the shield tunnel joint was proposed. Simultaneously, a thermo-mechanical performance analysis was conducted on the new longitudinal joint combining inclined bolts and the DDCI connector. A refined finite element model of the new joint was established and various working conditions were designed to obtain a full understanding of the thermo-mechanical performance of the structure. This evaluation included the presence of initial loads and exposure to different fire curves, specifically the RABT and RWS fire curves. The validity of the numerical model and the indirect coupling analysis method were verified by physical experiments and previous research, respectively. The temperature distribution, joint opening and internal force of the connectors were analyzed in the study. According to the results, different fire curves and thermo-mechanical sequences both have a great impact on the mechanical response of the new joint under elevated temperature. Moreover, due to the involvement of the DDCI connector, the new joint shows clear advantages in strength and stiffness over the conventional joint. The results contribute to the fire-resistant design of the large-diameter shield tunnels adopting the scheme of the new joint with a DDCI connector.

Investigations on the effects of rebar diameter on the post-fire bond capacity of RC flexural members and development of a novel post-fire bond model

This study is part of a comprehensive research effort focused on examining the impact of various parameters on the post-fire bond behaviour of RC flexural members. Precisely, the impact of the rebar diameter is thoroughly discussed. Beam-end specimens, which realistically simulate the boundary conditions of a full-scale beam while maintaining a relatively compact size, were subjected to ISO 834 fire curve. To investigate the behaviour of lap-splice in a slab and beam, two different fire exposure scenarios, where one side (slab) and three sides (beam) of the specimens were exposed to fire, were considered. It is evident that although the initial and residual load-carrying capacities increase with larger rebar diameters in absolute terms, the differences in residual bond capacities remain relatively insignificant across nearly all examined fire-exposure durations. Based on the evaluation of the test results, a model for local bond stress-slip curve of bond affected by fire is proposed.

Thermal Analysis of Composite Slabs Based on Experiment and Numerical Simulations

AbstractThis paper presents an experimental and numerical investigation on the thermal response of composite slabs under fire condition, considering various slab geometries. Fire tests were conducted on six composite slabs to obtain the temperature distributions exposed to the ISO 834 standard fire curve for a duration of 210 min. The results indicated that the depth of the concrete significantly affects the temperature of the unexposed surface, while the height of the steel deck has minimal impact. During heating, water vapor and condensation occurred on all tested slabs, causing a delay in the early temperature development of the concrete. The temperature distribution across slab cross-sections was subsequently calculated using numerical simulations. The numerical models were then validated using experimental data. The challenge of precisely simulating the interface between steel deck and concrete was resolved in this numerical model.

Influence of fire severity and concrete properties on the thermo‐hygral behavior of concrete during fire exposure

AbstractSince the world is transitioning toward performance based design, the study of thermo‐hygral behavior of concrete when subjected to real fire becomes crucial. Fire accidents have revealed that nominal fire curves cannot be applied because of varying severity of real fire. In 2008, traveling fire concept was developed in which severity is dependent on heat release rate and fire size. This study explores the effect of fire severity and other concrete properties like strength, aggregate type, and relative humidity. The proposed model has been developed by combining the principles of mechanics and thermodynamics and upon validation with the experimental results, a reasonable agreement has been observed. It can be concluded that severity of fire is directly related to thermo‐hygral behavior of concrete. On the other hand, this study also highlights the influence of type of aggregate and moisture content in addition to the traditional variables like volume fraction of solid and permeability. On studying the influence of type of aggregate, it can be concluded that recycled aggregate concrete performed better than conventional concrete. The integration of proposed model in the performance based design is a leap toward development of resilient structure subjected to dynamic fire conditions.

Experimental and numerical investigations of post-fire behaviour of circular steel tube confined steel-reinforced concrete columns under eccentric loading

Experimental and numerical analysis were conducted to investigate the post-fire behaviour of circular steel tube confined steel reinforced concrete (STCSRC) columns. A total of fifteen circular STCSRC columns, including five stub specimens and ten slender specimens, were tested under eccentric loading after heating following the ISO-834 standard fire curve. The test findings, such as cross-sectional temperature, failure modes, column deformation, residual load-bearing capacity, strains of steel tubes, etc., were all discussed in detail. A sequential thermal-stress coupling finite element (FE) model, including a heat transfer FE model and a mechanical FE model, was then developed using ABAQUS software and verified using the test results. To obtain further numerical data over a wide range of parameters, a parametric analysis was carried out using the established FE models. A simplified calculation method was presented to estimate the residual load-bearing capability of circular STCSRC columns subjected to eccentrical compression after ISO-834 fire exposure.

Modeling, optimization and control of a ceramic tunnel kiln for consistent product quality under changing production demands

This study presents a detailed physics-based model focusing on an industrial tunnel kiln under feedback control. Initially, an empirical sintering model is integrated into the kiln model to accurately predict the product outlet density, a quality-defining parameter reflecting firing process efficacy. Afterwards, the initial steady-state burner valve positions are determined using industrial temperature data. Subsequently, the interactions between gas temperatures and burner valve positions are quantified through the investigation of the Relative Gain Array. A systematic derivation of optimal set-points for different production rates is then carried out, aiming at minimizing energy consumption while meeting end-product quality specifications. The PID controllers are tuned using a dynamic optimization approach, which involves the minimization of integral criteria. Finally, a case study is conducted to evaluate the efficacy of the optimal set-points under varying production rates. The results demonstrate exceptional system response, thus indicating that firing curves should adapt to production rates for consistently producing quality products.

Fire performance of aged and corroded reinforced concrete columns

The existing guidelines for determining the fire ratings of reinforced concrete (RC) columns only take into account undamaged components, without considering any deterioration caused by age or corrosion. An experimental study was conducted to examine the effect of corrosion on the fire performance of RC columns. In this study, six full-scale RC column specimens were cast, corroded, and tested in fire conditions, consisting of two made of normal strength concrete (NSC) and four made of high-strength concrete (HSC). Out of these six, three RC columns (1-NSC and 2-HSC) were corroded using a specifically designed accelerated corrosion setup for a target mass loss of 30 %. After the completion of the accelerated corrosion exposure time, these three corroded column specimens, along with three other non-corroded control column specimens, were tested in a fire furnace, simulating the ISO-834 fire curve. It was found that due to corrosion exposure, the steel reinforcement underwent significant mass loss, and severe corrosion cracks were observed. These cracks were discovered to serve as convenient channels for heat transfer. This facilitated the earlier and more severe spalling of the concrete cover, ultimately leading to premature deterioration in the strength of the corroded RC columns during the fire. Consequently, this contributed to the catastrophic failure of the corroded RC columns, with a significant reduction in fire ratings- 44 % for NSC columns and 40.49 % for HSC columns. This paper also addresses the spalling characteristics of the corroded columns and their structural responses, including axial deformations, lateral deformations, and load variations.

NUMERICAL ANALYSIS OF TEMPERATURE DISTRIBUTIONS IN GLULAM BEAMS EXPOSED TO FIRE AND REINFORCED WITH ARAMID COMPOSITE

Currently, strengthening timber elements with the use of various materials has become popular.Reinforcements are used to repair existing elements or improve the static operating characteristicsof new elements. Fibre composites are being increasingly used as reinforcement. Investigationshave shown that the use of fibre composites influences the nature of static work. However, anunder-researched issue is the determination of the influence of composite reinforcement ontemperature distributions and, consequently, the depth and shape of charring in the cross-sectionduring fire. The article presents a numerical thermal analysis of cross-sections of glulam beamsreinforced with aramid materials in various forms. Fire action was assumed in accordance with theISO fire curve and the fire load on three of the four edges of the beams was modelled. Temperaturedistributions are presented for all analysed cases, which shows the beneficial effect of the use ofaramid reinforcement on the temperature distribution in the cross-section during a fire.

Theoretical model of the three - Stage parameter fire curve considering the contribution of combustible materials

Fire resistance is a critical factor constraining structural safety performance, specifically for Cross Laminated Timber (CLT) structures. Due to wood being a combustible material, the exposed wood will participate in combustion, increasing the fire load density and char rates, thereby causing more severe fire risks. In order to investigate the effect of exposed wood on fire temperature, this paper summarized 32 char rate data from 11 CLT room fire tests and fitted the relationship between wood exposure area and char rate, establishes a theoretical formula for the proportion of fire load burned outside the room to the total fire load, and it also establishes a theoretical formula for the three-stage parameter fire curve, which considers the contribution of combustible materials to fire load and char rate, as well as the transition from ventilation controlled to fuel controlled during the cooling stage of the fire. The accuracy of the three-stage parameter fire curve was verified through comparison with test results. Sensitivity analysis was conducted on the main parameters that affect the three-stage parameter fire curve. The results showed that the degree of influence of each factor on the maximum temperature of the fire and the time to reach the maximum temperature was as follows: fire load density > vent height > vent width > wood exposure area.

Oil and Gas Structures: Forecasting the Fire Resistance of Steel Structures with Fire Protection under Hydrocarbon Fire Conditions

The hydrocarbon temperature–time curve is widely used instead of the standard curve to describe the temperature in the environment of structural surfaces exposed to fire in oil and gas chemical facilities and tunnels. This paper presents calculations of the ratio of time to reach critical temperatures at different nominal fire curves for steel structures such as bulkheads and columns with different types of fireproofing. The thermophysical properties of the fireproofing materials were obtained by solving the inverse heat conduction problem using computer simulation. It was found that the time interval for reaching critical temperatures in structures with different types of fireproofing in a hydrocarbon fire decreased, on average, by a factor of 1.2–1.7 compared to the results of standard fire tests. For example, for decks and bulkheads with mineral wool fireproofing, the K-factor of the ratio of the time for reaching the critical temperature of steel under the standard curve to the hydrocarbon curve was 1.30–1.62; for plaster, it was 1.56; for cement boards, it was 1.34; for non-combustible coatings, it was 1.38–2.0; and, for epoxy paints, it was 1.71. The recommended values of the K-factor for fire resistance up to 180 min (incl.) were 1.7 and, after 180 min, 1.2. The obtained dependencies would allow fireproofing manufacturers to predict the insulation thickness for expensive hydrocarbon fire experiments if the results of fire tests under standard (cellulosic) conditions are known.

Analytical and Experimental Behaviour of GFRP-Reinforced Concrete Columns under Fire Loading

Fire engineering endeavours to mitigate injury or the loss of life in the event of a fire. This is achieved primarily through fire prevention, containment, and extinguishment measures. Should prevention fail, the structural integrity of buildings, coupled with effective evacuation strategies, becomes paramount. While glass fibre-reinforced polymer (GFRP) materials have demonstrated efficacy in reinforcing concrete elements, their performance under fire conditions, notably in comparison to steel, necessitates a deeper understanding for structural applications. This study experimentally and numerically investigates the fire performance of GFRP-reinforced concrete (RC) columns subjected to only fire load without additional external loads. The research aims to ascertain the fire resistance based on the thickness of the concrete coating and the ultimate tensile strength of GFRP rebars after 90 min of fire exposure. Four GFRP-RC columns were subjected to a standardized fire curve on all sides in the experimental program. In the analytical program, a theoretical model was developed using the heat transfer module of the COMSOL software. The results of both analyses were very close, indicating the reliability of the procedure used. Based on the findings, recommendations regarding the fire resistance of GFRP-RC columns were formulated for structural applications. Results from this research provide the civil engineering community with data that will help them continue using FRP materials as internal reinforcement for concrete.

Effect of ductility of flush end-plate connections on the behaviour of MRFs under fire conditions: An experimental study

The performance of beam-to-column connections is a key factor in the behaviour of moment-resisting frames (MRFs) under fire conditions. In this work, the behaviour and failure mechanisms of a half-scale 3D frame, composed of single-bay, single-storey MRFs and Braced Frames, in two perpendicular planes, equipped with 6 mm thick flush end-plate connections, under fire conditions was studied. A ‘scaled’ ISO 834 standard fire curve was followed during fire loading of the frame. The maximum reached temperature was 1100 °C. The temperatures of the elements of frames were measured at 2-minute time intervals. The rotations of the connections and the deflections of the MRFs’ beams at these time points were worked out using an image processing technique. Furthermore, the effect of the ductility of connections was investigated by comparing the results of this study with those of a previous one in which less ductile connections were used. The results showed that the connections used in this study could sustain large rotations of up to 0.7 radian and endure 65 min under fire. Moreover, it was found that using flexible connections (connections with thinner end-plates) enhances the ‘robustness’ of moment frames in fire.

Bovine hydroxyapatite/3Y-TZP bioceramic: Aligning 3Y-TZP content with sintering parameters

This study aimed to produces and characterize bovine hydroxyapatite (HA) bioceramic with 3Y-TZP addition and analyze different sintering curves. HA was extracted from bovine bones and nanoparticulated. HA discs (0, 1, 5 and 10 wt% 3Y-TZP) were subjected to uniaxial and isostatic pressing. Dilatometry analysis was performed and the groups were sintered using 3 different firing curves (conventional, 1300 °C; 2-step, 1292 °C; 2-step, 1420 °C). The samples were analyzed by X-ray diffraction (XRD), biaxial flexural strength (BFS), Vickers microhardness (VH) and Field emission scanning electron microscopy (FE-SEM). The dilatometry results signaled the need for sintering optimization in groups added with 3Y-TZP. XRD demonstrated the characteristic crystallographic peaks of HA in the pure groups and with 1% 3Y-TZP, and decomposition of HA into β-TCP and formation of calcium zirconate in the groups with 5 and 10% 3Y-TZP. Considering each composition, the groups of pure HA (131.3 ± 13.5 MPa; 401 ± 12.7 GPa) sintered by the conventional curve and HA+1%3Y-TZP (145 ± 8.6 MPa; 507 ± 47.9 GPa), HA+5%3Y-TZP (68.1 ± 14.2 MPa; 183 ± 9.8 GPa) and HA+10%3Y-TZP (55.6 ± 5.1 MPa; 96.1 ± 7.64 GPa) sintered by the 2-step curve at 1420 °C, combined the best BFS and VH results. The addition of 1 wt% 3Y-TZP and optimization in the sintering process improved the mechanical and microstructural properties of HA bioceramics and maintenance of its crystalline characteristics. Refinement in material processing is necessary for the future use of this bioceramic in dentistry.

ANN based fire resistance prediction of FRP-strengthened RC slabs with fireproof panel including air layer

In this study, an Artificial Neural Network (ANN) model to predict the fire resistance of Fiber Reinforced Plastic (FRP) strengthened Reinforced Concrete (RC) slabs with fireproof panel including air layer exposed to fire is developed. FRP-strengthened RC slabs with fireproof panel including air layer has a structure that improves structural performance and fire resistance by placing FRP and a fireproof panel including air at the bottom of the RC slab. First, fire test is performed using the air layer as a variable, and the validity of the software ABAQUS heat transfer analysis is verified by comparing it with the fire test results. Through this heat transfer analysis, the temperature distribution of the slab is determined, and 1521 data sets are obtained by calculating the strength reduction coefficient and elastic coefficient reduction coefficient of each material. The data consist of eight input parameters: the type of fire curve, fire exposure time, insulation thickness, air layer thickness, concrete covering thickness, and FRP thickness. The output parameter is the value of the strength and elastic modulus reduction coefficient for each material. The average values of MSE, RMSE, R, and SSE for all output parameters, which are performance indicators of the ANN model, are 0.00202, 0.03978, 0.98235, and 1.10445, respectively, and the developed ANN model has high computational accuracy and high generalization ability. Therefore, the ANN model developed here can determine the mechanical properties of each material in FRP-strengthened RC slabs with fireproof panel including air layer exposed to fire and evaluate the fire resistant without complex calculations. Through contribution and sensitivity analysis, the effect of input data on output data is confirmed.

Probabilistic model for predicting fire casualties in an urban traffic tunnel

Fire accidents could result in severe casualties in an urban traffic tunnel due to the concentration of users and narrow space. However, fire casualties could not be easily predicted due to the complicated evacuation environment and uncertainty in personnel distribution. This paper proposes a probabilistic model to predict the fire casualties in an urban traffic tunnel with only natural ventilation, considering the effects of the thermal and carbon monoxide distribution, in addition to the arrangement of various vehicles. First, the general framework of the probabilistic model was put forward and the methods to analyze the fire scenario, evacuation process, casualty criteria, and probability curve were introduced in details. Then, a case study based on a three-lane traffic tunnel was conducted, and the effects of maximum heat release rate on probabilistic curve of fire casualties were discussed. The results showed that the fire casualty increased with the maximum heat release rate. Besides this, when the distance between fire source and evacuation exit was reduced to 150 m, the impact of maximum heat release rate would decrease significantly. This study made notable contributions toward evaluating the personnel loss in tunnel fire and laid a foundation for assessing and improving the resilience of tunnel.

Numerical analysis of fire-exposed reinforced concrete sections for assessing post-heating axial and flexural capacity

PurposeThis study investigates the impact of the fire decay phase on structural damage using the sectional analysis method. The primary objective of this work is to forecast the non-dimensional capacity parameters for the axial and flexural load-carrying capacity of reinforced concrete (RC) sections for heating and the subsequent post-heating phase (decay phase) of the fire.Design/methodology/approachThe sectional analysis method is used to determine the moment and axial capacities. The findings of sectional analysis and heat transfer for the heating stage are initially validated, and the analysis subsequently proceeds to determine the load capacity during the fire’s heating and decay phases by appropriately incorporating non-dimensional sectional and material parameters. The numerical analysis includes four fire curves with different cooling rates and steel percentages.FindingsThe study’s findings indicate that the rate at which the cooling process occurs after undergoing heating substantially impacts the axial and flexural capacity. The maximum degradation in axial and flexural capacity occurred in the range of 15–20% for cooling rates of 3 °C/min and 5 °C/min as compared to the capacity obtained at 120 min of heating for all steel percentages. As the fire cooling rate reduced to 1 °C/min, the highest deterioration in axial and flexural capacity reached 48–50% and 42–46%, respectively, in the post-heating stage.Research limitations/implicationsThe established non-dimensional parameters for axial and flexural capacity are limited to the analysed section in the study owing to the thermal profile, however, this can be modified depending on the section geometry and fire scenario.Practical implicationsThe study primarily focusses on the degradation of axial and flexural capacity at various time intervals during the entire fire exposure, including heating and cooling. The findings obtained showed that following the completion of the fire’s heating phase, the structural capacity continued to decrease over the subsequent post-heating period. It is recommended that structural members' fire resistance designs encompass both the heating and cooling phases of a fire. Since the capacity degradation varies with fire duration, the conventional method is inadequate to design the load capacity for appropriate fire safety. Therefore, it is essential to adopt a performance-based approach while designing structural elements' capacity for the desired fire resistance rating. The proposed technique of using non-dimensional parameters will effectively support predicting the load capacity for required fire resistance.Originality/valueThe fire-resistant requirements for reinforced concrete structures are generally established based on standard fire exposure conditions, which account for the fire growth phase. However, it is important to note that concrete structures can experience internal damage over time during the decay phase of fires, which can be quantitatively determined using the proposed non-dimensional parameter approach.

Effect of uniaxial loading on the spalling of concrete panels for Melbourne's Metro Tunnel Project

AbstractThe Metro Tunnel is a Victorian Government funded infrastructure project which will create a new end‐to‐end rail line from Sunbury in the west to Cranbourne/Pakenham in the south east, with bigger and better trains, next generation signaling technology and five new underground stations. This article provides a detailed summary of the structural fire testing requirements for the platform tunnel side wall and arch lining in the Metro Tunnel's State Library and Town Hall stations. Contrasted to building fires, tunnel fires are more significant within a few minutes due to the confined space which can cause concrete spalling and jeopardize the bearing capacity of the tunnel, which is a significant concern to designers. The catastrophic European tunnel fire events in 1999 and 2001 led to the development of innovative regulations and recommendations, including guidelines endorsed by the European Federation of National (EFNARC 132F r3:2006) and Efectis R0695:2020. This paper explains the methodology taken to design the fire rated concrete test for the platform tunnel side wall and arch lining in the State Library and Town Hall stations of Melbourne's Metro Tunnel Project for structural stability for the period of a serious fire event. For the first time, uniaxial loading (500T) was applied to five large‐scale flat concrete panels (1800 × 1800 × 400 mm) which are normally unloaded during fire exposure and exposed to the RABT ZTV (rail) fire curve. The first testing program investigated the influence of polypropylene dosage in the concrete mix design and its effect on the magnitude and severity of concrete spalling. The results indicated that the recommended 2.0 kg/m3 polypropylene dosage requirement as specified by Eurocode is conservative. Concrete mix designs with a stable aggregate and the correct curing regime can mitigate spalling at significantly lower polypropylene dosage rates. The water pooling effect was evident during the fire testing and the surface cracking that developed was vertical to the surface, allowing for the release of the pore water pressure build‐up.

A critical analysis of the influence of architecture on the temperature field of RC structures subjected to fire using CFD and FEA models

The temperature–time-heating curve describes the dynamics of a fire in a room. A variety of factors related to the architecture and the thermal properties of the furniture influence the temperatures. The reinforced concrete (RC) structures of the buildings are designed for the case of fire with standardized curves that ignore the real fire temperatures. In this study, a group of individual rooms were solved numerically to understand the thermal cross-sectional field in RC structures based on real fire curves. The fire dynamics of the room were defined by a computational fluid dynamics (CFD) model solved with the Fire Dynamics Simulator (FDS) software. A finite element analysis (FEA) model was created for the RC structures and solved using Abaqus software. A typical RC ribbed slab on the roof of the room was considered. The structure was heated according to the real and standardized fire curves. The real fire temperatures were up to 70 % lower than those predicted by the standard. The results show how safe the buildings are from fire-induced collapse.

Investigation on Residual Mechanical Properties of Galvanized Iron Cold-Formed Steel Sections Exposed to Elevated Temperatures

Cold-formed steel (CFS) sections are used to construct medium and low-rise structures designed to carry small-scale loads. CFS sections are manufactured without the application of heat. Therefore, it is crucial to comprehend the properties of CFS sections which are exposed to fire or elevated temperatures. To simulate the real- time fire exposure, an ISO Standard fire curve was used to heat the CFS sections. The objective of the study is to assess the residual mechanical strength of exposed sections after the elevated temperature test. The study aims to compile data for forecasting the degeneration of elements and to ascertain whether the structural components can be reused or replaced. The CFS sections were subjected to different temperatures, and after heating, two cooling methods were used to bring down to room temperature. The characteristics of the retrieved specimens, taken from exposed CFS sections were assessed using a tensile coupon test. The residual properties such as ultimate strength, yield strength, and elastic modulus were examined and reported. The influence of heating and cooling is more pronounced from the test results. A reduction in the yield and ultimate strength was noticed, and it was found to decrease as the heating intensity increases for air and water cooling respectively. In the case of yield and ultimate strength, the strength reduction is critical beyond 60 minutes. The elastic modulus was also found to be reducing with a similar trend. Based on the test results, reduction factors are proposed for ultimate strength, yield strength and elastic modulus. Reduction factors obtained for yield strength under 60 minutes of heating for air and water cooling is 0.575 and 0.557 respectively. In 120 minutes, the values are 0.400 and 0.329. Reduction factors obtained for ultimate strength under 60 minutes of heating for air and water cooling is 0.586 and 0.566 respectively. For 120 minutes, the values are 0.331 and 0.313.