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Jin-guang Teng - One of the best experts on this subject based on the ideXlab platform.
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Analysis-Oriented Stress-Strain Model for Concrete under Combined FRP-Steel Confinement
Journal of Composites for Construction, 2015Co-Authors: Jin-guang Teng, Guan LinAbstract:AbstractExtensive research has been conducted on fiber-reinforced polymer (FRP)-confined plain and RC columns, leading to a large number of stress–Strain Models. Most of these Models have been developed for FRP-confined plain concrete and are thus applicable only to concrete in FRP-confined RC columns with a negligible amount of transverse steel reinforcement. The few Models that have been developed for concrete under the combined confinement of FRP and transverse steel reinforcement are either inaccurate or too complex for direct use in design. This paper presents an accurate design-oriented stress–Strain Model for concrete under combined FRP-steel confinement in FRP-confined circular RC columns. The proposed Model is formulated on the basis of extensive numerical results generated using an analysis-oriented stress–Strain Model recently proposed by the authors and properly captures the key characteristics of FRP-steel-confined concrete as revealed by existing test results. The Model strikes a good balanc...
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Stress–Strain Model for concrete in FRP-confined steel tubular columns
Engineering Structures, 2013Co-Authors: Jin-guang TengAbstract:Abstract Concrete-filled steel tubes (CFTs) are widely used as columns in many structural systems. In CFTs, degradation in steel confinement, strength and ductility can result from inelastic outward local buckling. To overcome this deficiency of CFTs, external confinement of CFTs with an FRP jacket has been explored in recent studies. This paper presents a theoretical Model in an incremental–iterative form for circular FRP-confined CFTs (CCFTs) under monotonic axial compression, with the focus being on the stress–Strain behavior of the confined concrete. The proposed stress–Strain Model for concrete in CCFTs is based on the same approach as that commonly adopted by existing Models for FRP-confined concrete and includes three components: (a) an active-confinement Model; (b) a lateral Strain equation; and (c) equations for determining the total confining pressure from the steel tube and the FRP jacket. It is shown that the lateral dilation behavior of concrete in CCFTs differs significantly from that of FRP-confined concrete in the initial stage because the former experiences more severe micro-cracking than the latter in the initial stage of loading; this difference is reflected in the proposed Model. In general, the predictions of the proposed Model are in close agreement with existing test results. The proposed Model provides a useful tool for a parametric study on the stress–Strain behavior of confined concrete in CCFTs to produce results for the formulation of simple stress–Strain Model in closed-form expressions for design use.
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Stress–Strain Model for FRP-confined concrete under cyclic axial compression
Engineering Structures, 2009Co-Authors: L Lam, Jin-guang TengAbstract:Abstract One important application of fibre-reinforced polymer (FRP) composites in construction is as FRP jackets to confine concrete in the seismic retrofit of reinforced concrete (RC) structures, because FRP confinement can enhance both the compressive strength and ultimate Strain of concrete. For the safe and economic design of FRP jackets, the stress–Strain behaviour of FRP-confined concrete under cyclic compression needs to be properly understood and Modelled. This paper presents a stress–Strain Model for FRP-confined concrete under cyclic axial compression. The Model consists of the following major components: (a) a monotonic stress–Strain Model for FRP-confined concrete developed by the authors in a previous study for predicting the envelope curve; (b) new algebraic expressions for predicting unloading and reloading paths; and (c) predictive equations for determining the permanent Strain and stress deterioration, with the effect of loading history duly accounted for. The capability and accuracy of the proposed Model in predicting the complete stress–Strain history of FRP-confined concrete under cyclic axial compression are demonstrated through comparisons between predictions of the proposed Model and test results.
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Refinement of a Design-Oriented Stress–Strain Model for FRP-Confined Concrete
Journal of Composites for Construction, 2009Co-Authors: Jin-guang Teng, Linda Lam, T Jiang, Yaozhi LuoAbstract:This paper presents the results of a recent study conducted to refine the design-oriented stress–Strain Model originally proposed by Lam and Teng for fiber-reinforced polymer (FRP)-confined concrete under axial compression. More accurate expressions for the ultimate axial Strain and the compressive strength are proposed for use in this Model. These new expressions are based on results from recent tests conducted by the writers’ group under well-defined conditions and on results from a parametric study using an accurate analysis-oriented stress–Strain Model for FRP-confined concrete. They allow the effects of confinement stiffness and the jacket Strain capacity to be separately reflected and accounts for the effect of confinement stiffness explicitly instead of having it reflected only through the confinement ratio. The new expressions can be easily incorporated into Lam and Teng’s Model for more accurate predictions. Based on these new expressions, two modified versions of Lam and Teng’s Model are present...
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Three-Stage Full-Range Stress-Strain Model for Stainless Steels
Journal of Structural Engineering, 2008Co-Authors: W.m. Quach, Jin-guang Teng, Kwok-fai ChungAbstract:Advanced numerical Modeling of cold-formed stainless steel members, from manufacturing to full-range response under applied loading, requires knowledge of the stress-Strain relationship of the material over a wide range of tensile and compressive Strains. Although a number of stress-Strain Models have been developed for stainless steels, they are only capable of accurate predictions either over a limited Strain range or for the tensile stress-Strain behavior only. This paper presents a three-stage stress-Strain Model for stainless steels, which is capable of accurate predictions over the full ranges of both tensile and compressive Strains. The new stress-Strain Model is defined using the three basic Ramberg-Osgood parameters and is based on a careful interpretation of existing experimental data. The accuracy of the proposed Model is demonstrated by comparing its predictions with experimental stress-Strain curves. These comparisons also clearly demonstrate the advantage of the proposed Model over the only existing full-range stress-Strain Model.
J G Teng - One of the best experts on this subject based on the ideXlab platform.
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stress Strain Model for concrete in frp confined steel tubular columns
Engineering Structures, 2013Co-Authors: J G TengAbstract:Abstract Concrete-filled steel tubes (CFTs) are widely used as columns in many structural systems. In CFTs, degradation in steel confinement, strength and ductility can result from inelastic outward local buckling. To overcome this deficiency of CFTs, external confinement of CFTs with an FRP jacket has been explored in recent studies. This paper presents a theoretical Model in an incremental–iterative form for circular FRP-confined CFTs (CCFTs) under monotonic axial compression, with the focus being on the stress–Strain behavior of the confined concrete. The proposed stress–Strain Model for concrete in CCFTs is based on the same approach as that commonly adopted by existing Models for FRP-confined concrete and includes three components: (a) an active-confinement Model; (b) a lateral Strain equation; and (c) equations for determining the total confining pressure from the steel tube and the FRP jacket. It is shown that the lateral dilation behavior of concrete in CCFTs differs significantly from that of FRP-confined concrete in the initial stage because the former experiences more severe micro-cracking than the latter in the initial stage of loading; this difference is reflected in the proposed Model. In general, the predictions of the proposed Model are in close agreement with existing test results. The proposed Model provides a useful tool for a parametric study on the stress–Strain behavior of confined concrete in CCFTs to produce results for the formulation of simple stress–Strain Model in closed-form expressions for design use.
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refinement of a design oriented stress Strain Model for frp confined concrete
Journal of Composites for Construction, 2009Co-Authors: J G Teng, L Lam, T Jiang, Yaozhi LuoAbstract:This paper presents the results of a recent study conducted to refine the design-oriented stress–Strain Model originally proposed by Lam and Teng for fiber-reinforced polymer (FRP)-confined concrete under axial compression. More accurate expressions for the ultimate axial Strain and the compressive strength are proposed for use in this Model. These new expressions are based on results from recent tests conducted by the writers’ group under well-defined conditions and on results from a parametric study using an accurate analysis-oriented stress–Strain Model for FRP-confined concrete. They allow the effects of confinement stiffness and the jacket Strain capacity to be separately reflected and accounts for the effect of confinement stiffness explicitly instead of having it reflected only through the confinement ratio. The new expressions can be easily incorporated into Lam and Teng’s Model for more accurate predictions. Based on these new expressions, two modified versions of Lam and Teng’s Model are present...
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stress Strain Model for frp confined concrete under cyclic axial compression
Engineering Structures, 2009Co-Authors: L Lam, J G TengAbstract:Abstract One important application of fibre-reinforced polymer (FRP) composites in construction is as FRP jackets to confine concrete in the seismic retrofit of reinforced concrete (RC) structures, because FRP confinement can enhance both the compressive strength and ultimate Strain of concrete. For the safe and economic design of FRP jackets, the stress–Strain behaviour of FRP-confined concrete under cyclic compression needs to be properly understood and Modelled. This paper presents a stress–Strain Model for FRP-confined concrete under cyclic axial compression. The Model consists of the following major components: (a) a monotonic stress–Strain Model for FRP-confined concrete developed by the authors in a previous study for predicting the envelope curve; (b) new algebraic expressions for predicting unloading and reloading paths; and (c) predictive equations for determining the permanent Strain and stress deterioration, with the effect of loading history duly accounted for. The capability and accuracy of the proposed Model in predicting the complete stress–Strain history of FRP-confined concrete under cyclic axial compression are demonstrated through comparisons between predictions of the proposed Model and test results.
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design oriented stress Strain Model for frp confined concrete in rectangular columns
Journal of Reinforced Plastics and Composites, 2003Co-Authors: L Lam, J G TengAbstract:The behavior of fiber reinforced polymer (FRP)-confined concrete in circular columns has been extensively studied, but much less is known about concrete in FRP-confined rectangular columns in which the concrete is nonuniformly confined and the effectiveness of confinement is much reduced. This paper presents a simple design-oriented stress-Strain Model for FRP-confined concrete in rectangular columns. To this end, existing theoretical Models are first reviewed. A database of existing test results collected by the authors is next presented, which is then augmented by a new set of results from tests conducted by the authors. The augmented test database is next employed to assess the existing theoretical Models. Finally, a stress-Strain Model is presented, which is an extension of a recent design-oriented stress-Strain Model developed for concrete uniformly-confined with FRP based on test results of circular concrete specimens. The proposed stress-Strain Model is shown to provide satisfactory predictions of ...
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design oriented stress Strain Model for frp confined concrete
Construction and Building Materials, 2003Co-Authors: L Lam, J G TengAbstract:Abstract External confinement by the wrapping of FRP sheets (or FRP jacketing) provides a very effective method for the retrofit of reinforced concrete (RC) columns subject to either static or seismic loads. For the reliable and cost-effective design of FRP jackets, an accurate stress–Strain Model is required for FRP-confined concrete. In this paper, a new design-oriented stress–Strain Model is proposed for concrete confined by FRP wraps with fibres only or predominantly in the hoop direction based on a careful interpretation of existing test data and observations. This Model is simple, so it is suitable for direct use in design, but in the meantime, it captures all the main characteristics of the stress–Strain behavior of concrete confined by different types of FRP. In addition, for unconfined concrete, this Model reduces directly to idealized stress–Strain curves in existing design codes. In the development of this Model, a number of important issues including the actual hoop Strains in FRP jackets at rupture, the sufficiency of FRP confinement for a significant strength enhancement, and the effect of jacket stiffness on the ultimate axial Strain, were all carefully examined and appropriately resolved. The predictions of the Model are shown to agree well with test data.
Youyi Wei - One of the best experts on this subject based on the ideXlab platform.
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Unified stress–Strain Model of concrete for FRP-confined columns
Construction and Building Materials, 2012Co-Authors: Youyi WeiAbstract:Abstract This paper presents a unified stress–Strain Model of concrete for circular, square, and rectangular columns confined by fiber-reinforced polymer (FRP) jackets. Through the unification, the variation of parameters is continuous and consistent, which overcomes the inconsistency or discontinuity in the results predicted by all existing Models. The unification also improves the performance of the stress–Strain Model by greatly extending the range of the parameter space, thus allowing a clearer picture of the trends and variations in the results. The new Model is developed based on a large and up-to-date database that includes data from both the authors’ own tests and that collected from the literature, involving circular, square, and rectangular short columns and carbon FRP, glass FRP, and aramid FRP jackets with a wide range of parameter values. The proposed stress–Strain Model is compared with existing Models, showing good agreement with the experimental results and improved performance.
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unified stress Strain Model of concrete for frp confined columns
Construction and Building Materials, 2012Co-Authors: Youyi WeiAbstract:Abstract This paper presents a unified stress–Strain Model of concrete for circular, square, and rectangular columns confined by fiber-reinforced polymer (FRP) jackets. Through the unification, the variation of parameters is continuous and consistent, which overcomes the inconsistency or discontinuity in the results predicted by all existing Models. The unification also improves the performance of the stress–Strain Model by greatly extending the range of the parameter space, thus allowing a clearer picture of the trends and variations in the results. The new Model is developed based on a large and up-to-date database that includes data from both the authors’ own tests and that collected from the literature, involving circular, square, and rectangular short columns and carbon FRP, glass FRP, and aramid FRP jackets with a wide range of parameter values. The proposed stress–Strain Model is compared with existing Models, showing good agreement with the experimental results and improved performance.
Jean-françois Chastang - One of the best experts on this subject based on the ideXlab platform.
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Psychosocial work factors of the job Strain` Model and all-cause mortality: The STRESSJEM prospective cohort study
Psychosomatic Medicine, 2020Co-Authors: Isabelle Niedhammer, Allison Milner, Thomas Coutrot, Béatrice Geoffroy-perez, Anthony D Lamontagne, Jean-françois ChastangAbstract:OBJECTIVES: The objectives were to examine the prospective associations between psychosocial work factors of the job Strain Model and all-cause mortality in a national representative cohort of French employees using various measures of time-varying exposure. METHODS: The study was based on a sample of 798,547 men and 697,785 women for which data on job history from 1976 to 2002 were linked to mortality data from the national death registry. Psychosocial work factors from the validated job Strain Model questionnaire were imputed using a job-exposure matrix. Three time-varying measures of exposure were explored: current, cumulative, and recency-weighted cumulative exposure. Cox proportional hazards Models were performed to study the associations between psychosocial work factors and mortality. RESULTS: Within the 1976-2002 period, 88,521 deaths occurred among men and 28,921 among women. Low decision latitude, low social support, job Strain, isoStrain, high Strain, and passive job were found to be risk factors for mortality. The Model using current exposure was the best relative quality Model. The associations of current exposure to job Strain and mortality were found to be HR=1.30 (95% CI: 1.24-1.36) among men and HR=1.15 (95% CI: 1.06-1.25) among women. The population fractions of mortality attributable to job Strain were 5.64% (95% CI: 4.56%-6.71%) among men and 4.13% (95% CI: 1.69%-6.71%) among women. CONCLUSIONS: This study supports the role of the psychosocial work factors of the job Strain Model on all-cause mortality. Preventive intervention to improve the psychosocial work environment may help to prevent mortality in working populations.
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Psychosocial factors at work from the job Strain Model and preventable mortality in France: the STRESSJEM prospective study
Preventive Medicine, 2020Co-Authors: Isabelle Niedhammer, Allison Milner, Thomas Coutrot, Béatrice Geoffroy-perez, Anthony D Lamontagne, Jean-françois ChastangAbstract:The study aimed to explore the prospective associations between psychosocial factors at work from the job Strain Model and preventable mortality, including smoking- and alcohol-related mortality as well as external causes of death. The study was based on prospective data and relied on a sample of 1,511,456 individuals for which data on job history, mortality and causes of death were linked over the 1976–2002 period. Exposures were the factors from the job Strain Model imputed through a job-exposure matrix. Various time-varying measures of exposure were used including current exposure and two measures of cumulative exposure. Preventable mortality was defined using the OECD/Eurostat list of preventable causes of death. The associations between exposures and outcomes were studied using Cox proportional hazards Models. Effect modification by gender was also assessed. Over the study period, 57,264 preventable deaths occurred before the age of 75 years. Low decision latitude, low social support, job Strain, iso-Strain, passive job, and high Strain were associated with preventable mortality, and associations of stronger magnitude were found for job Strain and isoStrain among men. Stronger associations were observed for alcohol-related mortality than for smoking-related mortality and external causes of death. The fractions of preventable mortality attributable to current exposure to job Strain and isoStrain were significant among men only (5.1% and 3.3%). Psychosocial factors at work from the job Strain Model may play a role on preventable mortality. Intensifying research and prevention towards the psychosocial work environment may be helpful to reduce risky health-related behaviours and related mortality.
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Psychosocial work exposures of the job Strain Model and cardiovascular mortality in France: results from the STRESSJEM prospective study
Scandinavian Journal of Work Environment and Health, 2020Co-Authors: Isabelle Niedhammer, Allison Milner, Thomas Coutrot, Béatrice Geoffroy-perez, Anthony d. Lamontagne, Jean-françois ChastangAbstract:Objectives The study aims to explore the prospective associations of the psychosocial work exposures of the job Strain Model with cardiovascular mortality, including mortality for ischemic heart diseases (IHD) and stroke, using various time-varying exposure measures in the French working population of employees. Methods The study was based on a cohort of 798 547 men and 697 785 women for which job history data from 1976 to 2002 were linked to mortality data and causes of death from the national death registry. Psychosocial work exposures from the validated job Strain Model questionnaire were assessed using a job-exposure matrix (JEM). Three time-varying measures of exposure were studied: current, cumulative, and recency-weighted cumulative exposure. Cox proportional hazards Models were used to examine the associations between psychosocial work exposures and cardiovascular mortality. Results Within the 1976-2002 period, there were 19 264 cardiovascular deaths among men and 6181 among women. Low decision latitude, low social support, job Strain, iso-Strain, passive job, and high Strain were associated with cardiovascular mortality. Most of these associations were also observed for IHD and stroke mortality. The comparison between the different exposure measures suggested that current exposure may be more important than cumulative (or past) exposure. The population fractions of cardiovascular mortality attributable to job Strain were 5.64% for men and 6.44% for women. Conclusions Psychosocial work exposures of the job Strain Model may play a role in cardiovascular mortality. The estimated burden of cardiovascular mortality associated with these exposures underlines the need for preventive policies oriented toward the psychosocial work environment.
Matthias F Bickelhaupt - One of the best experts on this subject based on the ideXlab platform.
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the activation Strain Model and molecular orbital theory
Wiley Interdisciplinary Reviews: Computational Molecular Science, 2015Co-Authors: Lando P Wolters, Matthias F BickelhauptAbstract:The activation Strain Model is a powerful tool for understanding reactivity, or inertness, of molecular species. This is done by relating the relative energy of a molecular complex along the reaction energy profile to the structural rigidity of the reactants and the strength of their mutual interactions: ΔE(ζ) = ΔEStrain(ζ) + ΔEint(ζ). We provide a detailed discussion of the Model, and elaborate on its strong connection with molecular orbital theory. Using these approaches, a causal relationship is revealed between the properties of the reactants and their reactivity, e.g., reaction barriers and plausible reaction mechanisms. This methodology may reveal intriguing parallels between completely different types of chemical transformations. Thus, the activation Strain Model constitutes a unifying framework that furthers the development of cross-disciplinary concepts throughout various fields of chemistry. We illustrate the activation Strain Model in action with selected examples from literature. These examples demonstrate how the methodology is applied to different research questions, how results are interpreted, and how insights into one chemical phenomenon can lead to an improved understanding of another, seemingly completely different chemical process. WIREs Comput Mol Sci 2015, 5:324–343. doi: 10.1002/wcms.1221 For further resources related to this article, please visit the WIREs website. Conflict of interest: The authors have declared no conflicts of interest for this article.
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the activation Strain Model and molecular orbital theory understanding and designing chemical reactions
Chemical Society Reviews, 2014Co-Authors: Israel Fernandez, Matthias F BickelhauptAbstract:In this Tutorial Review, we make the point that a true understanding of trends in reactivity (as opposed to measuring or simply computing them) requires a causal reactivity Model. To this end, we present and discuss the Activation Strain Model (ASM). The ASM establishes the desired causal relationship between reaction barriers, on one hand, and the properties of reactants and characteristics of reaction mechanisms, on the other hand. In the ASM, the potential energy surface ΔE(ζ) along the reaction coordinate ζ is decomposed into the Strain ΔEStrain(ζ) of the reactants that become increasingly deformed as the reaction proceeds, plus the interaction ΔEint(ζ) between these deformed reactants, i.e., ΔE(ζ) = ΔEStrain(ζ) + ΔEint(ζ). The ASM can be used in conjunction with any quantum chemical program. An analysis of the method and its application to problems in organic and organometallic chemistry illustrate the power of the ASM as a unifying concept and a tool for rational design of reactants and catalysts.
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the activation Strain Model of chemical reactivity
Organic and Biomolecular Chemistry, 2010Co-Authors: Willemjan Van Zeist, Matthias F BickelhauptAbstract:Herein, we provide an account of the activation Strain Model of chemical reactivity and its recent applications. In this Model, the potential energy surface ΔE(ζ) along the reaction coordinate ζ is decomposed into the Strain ΔEStrain(ζ) of the increasingly deformed reactants plus the interaction ΔEint(ζ) between these deformed reactants, i.e., ΔE(ζ) = ΔEStrain(ζ) + ΔEint(ζ). The purpose of this fragment-based approach is to arrive at a qualitative understanding, based on accurate calculations, of the trends in activation barriers and transition-state geometries (e.g., early or late along the reaction coordinate) in terms of the reactants’ properties. The usage of the activation Strain Model is illustrated by a number of concrete applications, by us and others, in the fields of catalysis and organic chemistry.
