•Experimental results of full-scale timber connections exposed to fire.•Numerical model to predict the thermo-mechanical behavior of timber connections.•Simplified formula easy to use by ...engineers.•Significant improvement of existing formulas.
A large experimental and numerical program based on fire tests of timber connections under various mechanical loadings was performed in France since 1999. Numerical models, simulating the thermomechanical behavior of these tested connections were developed and validated on the basis of experimental results. The developed model is sufficiently relevant to realize parametrical studies on timber connections. Then, considering the four main parameters influencing the fire resistance of the connections (type and diameter of fasteners, thickness of timber members and load ratio), the model is used to analyze the combined influence of these factors and to realize a calibration based on the experimental design approach. The commonly used thicknesses of timber elements and diameters of fastener are chosen in the study. The experimental design approach based on numerical results considers the main loading cases in timber connections. It is used to propose a simplified formula to predict the fire resistance of timber connections loaded in tension parallel to grain, perpendicular to grain or bending. The proposed formula is then applied to all the available experimental results to check its accuracy.
AbstractSince 1999, a long research program has been underway in France with the aim of better understanding the mechanical behavior of timber connections in fire situations. This work includes an ...experimental component, with the performance of numerous tests on timber connections subjected to an ISO fire, and a numerical component, aimed at better identifying the parameters influencing the fire resistance of connections. The final objective is to propose an analytical method for designing timber connections in fire situations that is easy to use by engineers and more precise and efficient than the current regulations, whose field of application is limited. In this study, a simple analytical method, based on the state of knowledge acquired over the last 20 years and the experimental data available in France and elsewhere, is proposed with the aim of improving the current regulations. The proposed method is explained, the experimental data used in its development are provided, and the results obtained from this method are discussed and commented.
•We examined the toxic potential of twelve aflatoxins and their precursors.•Cytotoxicity and the genotoxicity was evaluated with the γH2AX ICW assay.•Most genotoxic chemicals were in decreasing order ...ST, AFB1, AFL, AFG1 and VERA.•Some precursors of aflatoxins demonstrated genotoxic potential greater to AFB1.
Aflatoxins are found as food contaminant and some of them demonstrate a carcinogenic effect. The aflatoxins biosynthetic pathway involves 15 successive steps. The aim of this study was to compare the toxicity of aflatoxins and their precursors in three human cell lines. We tested the four aflatoxins and two of their metabolites; three early metabolic precursors and two late biosynthetic precursors. Cyclopiazonic acid, synthesized in parallel with aflatoxins, was also tested. The cytotoxicity and the genotoxicity was evaluated with the γH2AX assay in three human cell lines with different bioactivation capacities. Our results indicated that the most genotoxic chemicals in the three cell lines were in decreasing order sterigmatocystin (ST), aflatoxin B1 (AFB1), aflatoxicol (AFL), aflatoxin G1 (AFG1) and versicolorin A (VERA). Aflatoxin M1 (AFM1) demonstrated genotoxic property in only one cell line. The other tested compounds did not demonstrate any genotoxic activity. Overall, our results suggested different genotoxic mechanisms of action for the tested compounds, involving specific bioactivation pathways. Moreover, some metabolic precursors of aflatoxins demonstrated genotoxic potential equivalent or greater to AFB1. This should be taking into account for the development of new strategies intended to reduce the aflatoxins exposure and for human risk assessment.
•We examined the genotoxic potential of 27 HAPs.•Genotoxicity was evaluated with the γH2AX assay and was modelled with the Hill equation.•We developed for each compound, in each cell line, Genotoxic ...Equivalent Factor.•These new equivalent factor for PAHs may improve cancer risk assessment.
Polycyclic Aromatic Hydrocarbons (PAHs) form a family of compounds that are generally found in complex mixtures. PAHs can lead to the development of carcinogenesis. The Toxicity Equivalent Factor (TEF) approach has been suggested for estimating the toxicity of PAHs, however, due to the relative weakness of available data, TEF have not been applied for the risk characterization of PAHs as food contaminants in Europe. The determination of new TEFs for a large number of PAHs could overcome some limitations of the current method and improve cancer risk assessment. The present investigation aimed at deriving new TEFs for PAHs, based on their genotoxic effect measured in vitro and analyzed with mathematical models. For this purpose, we used a genotoxicity assay (γH2AX) with three human cell lines to analyze the genotoxic properties of 27 selected PAHs after 24 h treatment. For 11 compounds, we did not detect any genotoxic potential. For the remaining 16 PAHs, the concentration-response for genotoxic effect was modelled with the Hill equation; equivalency between PAHs at low dose was assessed by applying constraints to the model parameters. We developed for each compound, in each cell line, Genotoxic Equivalent Factor (GEF). Calculated GEF for the tested PAHs were similar in all cell lines and generally higher than the TEF usually used. These new equivalent factors for PAHs should improve cancer risk assessment.
A three-dimensional finite element model is developed to predict the thermo-mechanical behavior of steel-to-timber doweled joints in tension parallel to grain exposed to fire. To manage the plastic ...yielding of the materials, the mechanical model is based on the von Mises criterion for steel and the Hill criterion for timber. In fire, the material characteristics depend on the temperature. Two different meshes are used for the thermal and the thermo-mechanical models. The thermal model is continuous, to take account of the thermal continuity between the joint components. The thermo-mechanical model is discontinuous, to consider the contact evolution between the joint components. The thermal model is used to predict the evolution of the temperature field inside the joint which depend on the gas temperature. It is validated on the basis of measured temperatures during fire tests. The complex transformations in wood during fire are represented by apparent values of thermo-physical characteristics proposed in the bibliography and calibrated on the basis of the experimental measurements. The mechanical model is validated by comparison with the experimental results of joints in normal conditions. The thermo-mechanical model is validated by considering the experimental failure times of some joints. The numerical models showed a good capacity to simulate the behavior of the timber joints in cold and in fire situations. These developed and tested models can be used as a general tool to analyze the behavior of a large variety of joint configurations to constitute a data base that can be used in safe and economic practice of fire engineering of wood joints.
► A three-dimensional finite element model is developed to simulate the behavior of steel-to-timber joints in fire. ► The model is validated by comparison with test results in normal and fire conditions. ► The thermal model predicts the evolution of the temperature inside the joint well. ► The Hill criterion used for timber in fire represents the plastic behavior of the joint well. ► The thermo-mechanical model predicts the time to failure of the joints in fire well.
This paper presents a summary of experimental results from various studies conducted these twenty last years on the behaviour of steel-to-timber or timber-to-timber connections with dowel-type ...fasteners exposed to fire. The majority of the tested connections are loaded in tension parallel-to-grain and some of them loaded in tension at 45°, 90° and bending. The geometrical configurations of the tested connections are detailed and commented to facilitate further use. The tests in normal conditions are realized in order to obtain the real ultimate loads of the tested connections used as a basis to define the mechanical load in fire tests. Based on the fire resistance times of the tested connections, the experimental results are compared with those given by the design rules of EN 1995-1-2. The experimental results are presented in such a way that they can be used to validate numerical investigations that can be developed in order to understand the complex thermo-mechanical behaviour of timber connections. Thus, the paper provides to the researchers a database, of the main experimental results available in the world, related to the fire resistance of dowelled and bolted timber connection exposed to ISO fire.
•MICS on two ERT time-lapse monitoring.•Leachate flow behaviour.•Useful for hydrodynamic models.
Landfill bioreactors are based on an acceleration of in-situ waste biodegradation by performing ...leachate recirculation. To quantify the water content and to evaluate the leachate injection system, in-situ methods are required to obtain spatially distributed information, usually electrical resistivity tomography (ERT). In a previous study, the MICS (multiple inversions and clustering strategy) methodology was proposed to improve the hydrodynamic interpretation of ERT results by a precise delimitation of the infiltration area. In this study, MICS was applied on two ERT time-lapse data sets recorded on different waste deposit cells in order to compare the hydrodynamic behaviour of leachate flow between the two cells. This comparison is based on an analysis of: (i) the volume of wetted waste assessed by MICS and the wetting rate, (ii) the infiltration shapes and (iii) the pore volume used by the leachate flow. This paper shows that leachate hydrodynamic behaviour is comparable from one waste deposit cell to another with: (i) a high leachate infiltration speed at the beginning of the infiltration, which decreases with time, (ii) a horizontal anisotropy of the leachate infiltration shape and (iii) a very small fraction of the pore volume used by the leachate flow. This hydrodynamic information derived from MICS results can be useful for subsurface flow modelling used to predict leachate flow at the landfill scale.
Polycyclic Aromatic Hydrocarbons (PAHs) constitute a family of over one hundred compounds and can generally be found in complex mixtures. PAHs metabolites cause DNA damage which can lead to the ...development of carcinogenesis. Toxicity assessment of PAH complex mixtures is currently expressed in terms of toxic equivalents, based on Toxicity Equivalent Factors (TEFs). However, the definition of new TEFs for a large number of PAH could overcome some limitations of the current method and improve cancer risk assessment. The current investigation aimed at deriving the relative potency factors of PAHs, based on their genotoxic effect measured in vitro and analyzed with mathematical models. For this purpose, we used a new genotoxic assay (γH2AX) with two human cell lines (HepG2 and LS-174T) to analyze the genotoxic properties of 13 selected PAHs at low doses after 24h treatment. The dose–response for genotoxic effects was modeled with a Hill model; equivalency between PAHs at low dose was assessed by applying constraints to the model parameters. In the two cell lines tested, we observed a clear dose–response for genotoxic effects for 11 tested compounds. LS-174T was on average ten times more sensitive than HepG2 towards PAHs regarding genotoxicity. We developed new TEFs, which we named Genotoxic Equivalent Factor (GEF). Calculated GEF for the tested PAHs were generally higher than the TEF usually used. Our study proposed a new in vitro based method for the establishment of relevant TEFs for PAHs to improve cancer risk assessment.
► Examination of the genotoxic properties of 13 PAHs on two human cell lines. ► Modelization with a Hill model of the genotoxic dose–response. ► First investigation of the genotoxicity of benzocfluorene on human cell lines. ► Establishment of relevant TEFs for PAHs to improve cancer risk assessment.
•A new constraint methodology of hydrodynamic models.•Single and dual continuum approaches.•Hydrodynamic parameters.
Leachate recirculation is a key process in the operation of municipal solid waste ...landfills as bioreactors. To ensure optimal water content distribution, bioreactor operators need tools to design leachate injection systems. Prediction of leachate flow by subsurface flow modelling could provide useful information for the design of such systems. However, hydrodynamic models require additional data to constrain them and to assess hydrodynamic parameters. Electrical resistivity tomography (ERT) is a suitable method to study leachate infiltration at the landfill scale. It can provide spatially distributed information which is useful for constraining hydrodynamic models. However, this geophysical method does not allow ERT users to directly measure water content in waste. The MICS (multiple inversions and clustering strategy) methodology was proposed to delineate the infiltration area precisely during time-lapse ERT survey in order to avoid the use of empirical petrophysical relationships, which are not adapted to a heterogeneous medium such as waste.
The infiltration shapes and hydrodynamic information extracted with MICS were used to constrain hydrodynamic models in assessing parameters. The constraint methodology developed in this paper was tested on two hydrodynamic models: an equilibrium model where, flow within the waste medium is estimated using a single continuum approach and a non-equilibrium model where flow is estimated using a dual continuum approach. The latter represents leachate flows into fractures. Finally, this methodology provides insight to identify the advantages and limitations of hydrodynamic models. Furthermore, we suggest an explanation for the large volume detected by MICS when a small volume of leachate is injected.
The development of
in vitro genotoxic assays as an alternative method to animal experimentation is of growing interest in the context of the implementation of new regulations on chemicals. However, ...extrapolation of toxicity data from
in vitro systems to
in vivo models is hampered by the fact that
in vitro systems vary in their capability to metabolize chemicals, and that biotransformation can greatly influence the experimental results. Therefore, much attention has to be paid to the cellular models used and experimental conditions. Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic ubiquitous pollutants. Human exposure to PAHs is mainly from food origin. In this study, a detailed analysis of the biotransformation capabilities of three human cell lines commonly used for
in vitro testing (HepG2, ACHN and Caco-2) was undertaken using 3 model PAHs (benzo(
a)pyrene B(
a)P, fluoranthene FLA and 3-methylcholanthrene 3-MC). Concomitantly the genotoxicity of these PAHs was investigated in different cell lines, using a new genotoxic assay (H2AX) in 96-well plates. The metabolic rates of B(
a)P, FLA and 3-MC were similar in HepG2 and Caco-2 cell lines, respectively, though with the production of different metabolites. The ACHN cell line was shown to express very limited metabolic capabilities. We demonstrated that the PAHs having a high metabolic rate (B(
a)P and 3-MC) were genotoxic from 10
−7 molar in both HepG2 and Caco-2 cells. The present study shows that H2AX measurement in human cell lines competent for the metabolism, is an efficient and sensitive genotoxic assay requiring less cells and time than other currently available tests.
PDF
