A stochastic finite element approach is presented herein for simulating the nonlinear behaviour o... more A stochastic finite element approach is presented herein for simulating the nonlinear behaviour of strand-based wood composites with strands of varying grain angle. The approach is based on the constitutive properties of the individual strands making it practical and versatile in application. It can be used to gauge the effects of varying strand characteristics in product manufacturing or it may be useful in the design of wood composite structures. Both 2 and 3 dimensional, stochastic, materially nonlinear finite element codes are developed. The nonlinear constitutive behaviour of the wood strands is characterized within the framework of rate-independent theory of orthotropic elasto-plasticity. The constitutive model employs the Tsai-Wu yield criterion with the associated flow rule of plasticity. Failure is marked by an upper bound surface whereupon either perfect plasticity or an abrupt loss of strength and stiffness ensues. This constitutive model is implemented into the finite element codes. The programs are based on the conventional displacement formulation using linear isoparametric elements. The nonlinearities are resolved by a modified Newton-Raphson procedure. The programs are further formulated in a probabilistic manner using random variables as input for principal material strengths and stiffnesses. To generate entire data samples for comparison with experimental samples, the programs were written with extended capacity to perform Monte Carlo simulations. The mechanical properties of the strands are derived through both experiment and analysis. An experimental database of principal material strengths and stiffness parameters is acquired for Douglas fir heartwood strands. Statistical parameters for shear strength and stiffness as well as the interaction parameter of the Tsai-Wu criterion are estimated, however, through a least square minirriization of error between simulated and experimental compression strength of [+15]s angle-ply laminates. Weibull weakest-link theory is employed t [...]
Interest in the engineering performance of bamboo is on the rise primarily due to its rapid regen... more Interest in the engineering performance of bamboo is on the rise primarily due to its rapid regenerative qualities and high strength-to-weight ratio. It has been a standard, sustainable building material for thousands of years in Asia and South America, where it grows naturally. Although there are many examples of magnificent bamboo structures, standards and documentation on safe and reliable bamboo design are scarce, particularly for connection design. Traditional connections involve friction-tight lashings (eg. ropes and cords of dried grasses) and pin-and-socket connections such as dowels and pegs, but more recent advances have involved integration with steel hardware and concrete. This paper presents bamboo as a feasible alternative building material and presents a review of past, current and emerging technologies to join hollow bamboo culms in structural applications. The paper's intent is to give an overview of the current state of bamboo connection technology and to promote developments in the emerging field of bamboo engineering. Recent technological advances and visionary architects have proven that it is possible to create safe structures that are not only sustainable but have tremendous potential for use in disaster relief and quick-build scenarios.
Today’s global automotive industry is gradually adopting more sustainable technologies particular... more Today’s global automotive industry is gradually adopting more sustainable technologies particularly in the form of natural fiber composites. From door panels to spare tire linings, a variety of modern day car parts are made with high-performance composites that are reinforced with plant fibers, such as hemp, flax, sisal and bamboo. Driving this trend is public awareness and demand for environmentally responsible consumer products, as well as governmental regulatory pressure, and competitive economics. Unlike conventional synthetic fiber reinforcement (glass and carbon), plant fiber is renewable, biodegradable, and carbon sequestering, in addition to being lightweight, economic and strong. This article presents a review of the industry’s recent movement toward using plant fibers in automotive composites including a detailed list of applications and projected future trends. Important aspects of composite development, such as fiber properties and composite processing techniques are also discussed.
A 3 dimensional stochastic finite element technique is presented herein for simulating the nonlin... more A 3 dimensional stochastic finite element technique is presented herein for simulating the nonlinear behaviour of strand-based wood composites with strands of varying grain-angle. The approach is based on the constitutive properties of the individual strands to study the effects of varying strand characteristics (such as species or geometry) on the performance of the member. The constitutive properties of the strands are found empirically and are subsequently used in a 3 dimensional finite element program. The program is formulated in a probabilistic manner using random variable material properties as input. The constitutive model incorporates classic plasticity theory whereby anisotropic hardening and eventual failure of the material is established by the Tsai-Wu criterion with an associated flow rule. Failure is marked by an upper bound surface whereupon either perfect plasticity (i.e. ductile behavior) or an abrupt loss of strength and stiffness (i.e. brittle behavior) ensues. The ability of this technique to reproduce experimental findings for the stress-strain curves of angle-ply laminates in tension, compression as well as 3 point bending is validated.
Journal of Structural Engineering-asce, Sep 1, 2005
This paper introduces a new, structural wood-concrete composite system. The system is formed by j... more This paper introduces a new, structural wood-concrete composite system. The system is formed by joining a wood component, such as a floor beam or laminated plate, to a concrete slab utilizing a continuous steel mesh of which one half is glued into a slot in the wood while the other half is embedded into the concrete. Two series of tests were performed and are presented: static push-out tests ͑to establish shear properties of the connector͒ and a full scale bending test with a span of approximately 10 m. Test results reveal that the steel mesh performs favorably-as a stiff yet ductile shear connector between the wood and the concrete. Design equations, per European standards ͑in absence of North American standards͒ are described and used to predict the failure load of the bending test. Calculations indicate that the tested beam performs with near full composite action-specifically, 97% effective stiffness and 99% strength of that of a beam with full composite action. This is a marked improvement in the efficiency of wood-concrete systems developed to date. The system shows itself to be superior to alternative systems in its high structural efficiency as well as being relatively easy to install and economic.
Journal of Engineering Mechanics-asce, Aug 1, 2001
A nonlinear stochastic model has been formulated to simulate the stress-strain behavior of strand... more A nonlinear stochastic model has been formulated to simulate the stress-strain behavior of strandbased wood composites based on the constitutive properties of the wood strands. Prediction models of this type save time and money in the development of wood composites by computationally gauging the effects of varying raw material characteristics with limited fabrication and testing of the full-scale product. The proposed model uses a stochastic-based materially nonlinear finite-element code with extended capacity to perform Monte Carlo simulations to predict the stress-strain behavior of [Ϯ15] s and [Ϯ30] s angle-ply laminates in tension and compression. The nonlinear constitutive behavior of the wood strands is characterized within the framework of rateindependent theory of orthotropic plasticity, where the plastic flow rule is in accordance with the Tsai-Wu criterion. Shear strength and stiffness of the strands, as well as the interaction parameter of the Tsai-Wu criterion have been estimated through a minimization technique developed in the present study. The model's accuracy was validated through comparisons of the numerical simulation results and experimental data. Excellent agreement was found.
Journal of Engineering Mechanics-asce, Apr 1, 2010
Measurement of the compressive strength of parallel strand lumber ͑PSL͒ is conducted on specimens... more Measurement of the compressive strength of parallel strand lumber ͑PSL͒ is conducted on specimens of varying size with nominally identical mesostructure. The mean of the compressive strength is found to vary inversely with the specimen size, and the coefficient of variation of the strength is found to decrease with increasing specimen size, and to be smaller than the coefficient of variation of strength for solid lumber. The correlation length of the compressive strength is approximately 0.5 m, and this correlation length leads to significant specimen-to-specimen variation in mean strength. A computational model is developed that includes the following properties of the PSL mesostructure: the strand length, the grain angle, the elastic constants, and the parameters of the Tsai-Hill failure surface. The computational model predicts the mean strength and coefficient of variation reasonably well, and predicts the correct form of correlation decay, but overpredicts the correlation length for compressive strength, likely because of sensitivity to the distribution of strand length used in the model. The estimates of the statistics of the PSL compressive strength are useful for reliability analysis of PSL structures, and the computational model, although still in need of further development, can be used in evaluating the effect of mesostructural parameters on PSL compressive strength.
Journal of Materials in Civil Engineering, May 1, 1998
A stochastic-based method of evaluating the interaction parameter (\iF\d1\d2) of the Tsai-Wu stre... more A stochastic-based method of evaluating the interaction parameter (\iF\d1\d2) of the Tsai-Wu strength theory has been presented in this paper. Treating all strength parameters of the strength theory as random variables, the mean and standard deviation of \iF\d1\d2, under plane stress conditions, have been estimated for Douglas-fir laminated veneer. This estimation has been managed through a nonlinear least-squares fit of the parameters to a cumulative probability distribution of off-axis tensile data. For the purpose of comparison, a sample evaluation of \iF\d1\d2 using deterministic methods has been presented. This evaluation showed strong dependence of \iF\d1\d2 on angle to grain. A subsequent sensitivity analysis of the off-axis tests on the value of \iF\d1\d2 indicated that data from 15° off-axis tensile tests were more stable in establishing \iF\d1\d2 than that of other angles tested: 30°, 45°, and 60°.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are
A stochastic finite element approach is presented herein for simulating the nonlinear behaviour o... more A stochastic finite element approach is presented herein for simulating the nonlinear behaviour of strand-based wood composites with strands of varying grain angle. The approach is based on the constitutive properties of the individual strands making it practical and versatile in application. It can be used to gauge the effects of varying strand characteristics in product manufacturing or it may be useful in the design of wood composite structures. Both 2 and 3 dimensional, stochastic, materially nonlinear finite element codes are developed. The nonlinear constitutive behaviour of the wood strands is characterized within the framework of rate-independent theory of orthotropic elasto-plasticity. The constitutive model employs the Tsai-Wu yield criterion with the associated flow rule of plasticity. Failure is marked by an upper bound surface whereupon either perfect plasticity or an abrupt loss of strength and stiffness ensues. This constitutive model is implemented into the finite element codes. The programs are based on the conventional displacement formulation using linear isoparametric elements. The nonlinearities are resolved by a modified Newton-Raphson procedure. The programs are further formulated in a probabilistic manner using random variables as input for principal material strengths and stiffnesses. To generate entire data samples for comparison with experimental samples, the programs were written with extended capacity to perform Monte Carlo simulations. The mechanical properties of the strands are derived through both experiment and analysis. An experimental database of principal material strengths and stiffness parameters is acquired for Douglas fir heartwood strands. Statistical parameters for shear strength and stiffness as well as the interaction parameter of the Tsai-Wu criterion are estimated, however, through a least square minirriization of error between simulated and experimental compression strength of [+15]s angle-ply laminates. Weibull weakest-link theory is employed t [...]
Interest in the engineering performance of bamboo is on the rise primarily due to its rapid regen... more Interest in the engineering performance of bamboo is on the rise primarily due to its rapid regenerative qualities and high strength-to-weight ratio. It has been a standard, sustainable building material for thousands of years in Asia and South America, where it grows naturally. Although there are many examples of magnificent bamboo structures, standards and documentation on safe and reliable bamboo design are scarce, particularly for connection design. Traditional connections involve friction-tight lashings (eg. ropes and cords of dried grasses) and pin-and-socket connections such as dowels and pegs, but more recent advances have involved integration with steel hardware and concrete. This paper presents bamboo as a feasible alternative building material and presents a review of past, current and emerging technologies to join hollow bamboo culms in structural applications. The paper's intent is to give an overview of the current state of bamboo connection technology and to promote developments in the emerging field of bamboo engineering. Recent technological advances and visionary architects have proven that it is possible to create safe structures that are not only sustainable but have tremendous potential for use in disaster relief and quick-build scenarios.
Today’s global automotive industry is gradually adopting more sustainable technologies particular... more Today’s global automotive industry is gradually adopting more sustainable technologies particularly in the form of natural fiber composites. From door panels to spare tire linings, a variety of modern day car parts are made with high-performance composites that are reinforced with plant fibers, such as hemp, flax, sisal and bamboo. Driving this trend is public awareness and demand for environmentally responsible consumer products, as well as governmental regulatory pressure, and competitive economics. Unlike conventional synthetic fiber reinforcement (glass and carbon), plant fiber is renewable, biodegradable, and carbon sequestering, in addition to being lightweight, economic and strong. This article presents a review of the industry’s recent movement toward using plant fibers in automotive composites including a detailed list of applications and projected future trends. Important aspects of composite development, such as fiber properties and composite processing techniques are also discussed.
A 3 dimensional stochastic finite element technique is presented herein for simulating the nonlin... more A 3 dimensional stochastic finite element technique is presented herein for simulating the nonlinear behaviour of strand-based wood composites with strands of varying grain-angle. The approach is based on the constitutive properties of the individual strands to study the effects of varying strand characteristics (such as species or geometry) on the performance of the member. The constitutive properties of the strands are found empirically and are subsequently used in a 3 dimensional finite element program. The program is formulated in a probabilistic manner using random variable material properties as input. The constitutive model incorporates classic plasticity theory whereby anisotropic hardening and eventual failure of the material is established by the Tsai-Wu criterion with an associated flow rule. Failure is marked by an upper bound surface whereupon either perfect plasticity (i.e. ductile behavior) or an abrupt loss of strength and stiffness (i.e. brittle behavior) ensues. The ability of this technique to reproduce experimental findings for the stress-strain curves of angle-ply laminates in tension, compression as well as 3 point bending is validated.
Journal of Structural Engineering-asce, Sep 1, 2005
This paper introduces a new, structural wood-concrete composite system. The system is formed by j... more This paper introduces a new, structural wood-concrete composite system. The system is formed by joining a wood component, such as a floor beam or laminated plate, to a concrete slab utilizing a continuous steel mesh of which one half is glued into a slot in the wood while the other half is embedded into the concrete. Two series of tests were performed and are presented: static push-out tests ͑to establish shear properties of the connector͒ and a full scale bending test with a span of approximately 10 m. Test results reveal that the steel mesh performs favorably-as a stiff yet ductile shear connector between the wood and the concrete. Design equations, per European standards ͑in absence of North American standards͒ are described and used to predict the failure load of the bending test. Calculations indicate that the tested beam performs with near full composite action-specifically, 97% effective stiffness and 99% strength of that of a beam with full composite action. This is a marked improvement in the efficiency of wood-concrete systems developed to date. The system shows itself to be superior to alternative systems in its high structural efficiency as well as being relatively easy to install and economic.
Journal of Engineering Mechanics-asce, Aug 1, 2001
A nonlinear stochastic model has been formulated to simulate the stress-strain behavior of strand... more A nonlinear stochastic model has been formulated to simulate the stress-strain behavior of strandbased wood composites based on the constitutive properties of the wood strands. Prediction models of this type save time and money in the development of wood composites by computationally gauging the effects of varying raw material characteristics with limited fabrication and testing of the full-scale product. The proposed model uses a stochastic-based materially nonlinear finite-element code with extended capacity to perform Monte Carlo simulations to predict the stress-strain behavior of [Ϯ15] s and [Ϯ30] s angle-ply laminates in tension and compression. The nonlinear constitutive behavior of the wood strands is characterized within the framework of rateindependent theory of orthotropic plasticity, where the plastic flow rule is in accordance with the Tsai-Wu criterion. Shear strength and stiffness of the strands, as well as the interaction parameter of the Tsai-Wu criterion have been estimated through a minimization technique developed in the present study. The model's accuracy was validated through comparisons of the numerical simulation results and experimental data. Excellent agreement was found.
Journal of Engineering Mechanics-asce, Apr 1, 2010
Measurement of the compressive strength of parallel strand lumber ͑PSL͒ is conducted on specimens... more Measurement of the compressive strength of parallel strand lumber ͑PSL͒ is conducted on specimens of varying size with nominally identical mesostructure. The mean of the compressive strength is found to vary inversely with the specimen size, and the coefficient of variation of the strength is found to decrease with increasing specimen size, and to be smaller than the coefficient of variation of strength for solid lumber. The correlation length of the compressive strength is approximately 0.5 m, and this correlation length leads to significant specimen-to-specimen variation in mean strength. A computational model is developed that includes the following properties of the PSL mesostructure: the strand length, the grain angle, the elastic constants, and the parameters of the Tsai-Hill failure surface. The computational model predicts the mean strength and coefficient of variation reasonably well, and predicts the correct form of correlation decay, but overpredicts the correlation length for compressive strength, likely because of sensitivity to the distribution of strand length used in the model. The estimates of the statistics of the PSL compressive strength are useful for reliability analysis of PSL structures, and the computational model, although still in need of further development, can be used in evaluating the effect of mesostructural parameters on PSL compressive strength.
Journal of Materials in Civil Engineering, May 1, 1998
A stochastic-based method of evaluating the interaction parameter (\iF\d1\d2) of the Tsai-Wu stre... more A stochastic-based method of evaluating the interaction parameter (\iF\d1\d2) of the Tsai-Wu strength theory has been presented in this paper. Treating all strength parameters of the strength theory as random variables, the mean and standard deviation of \iF\d1\d2, under plane stress conditions, have been estimated for Douglas-fir laminated veneer. This estimation has been managed through a nonlinear least-squares fit of the parameters to a cumulative probability distribution of off-axis tensile data. For the purpose of comparison, a sample evaluation of \iF\d1\d2 using deterministic methods has been presented. This evaluation showed strong dependence of \iF\d1\d2 on angle to grain. A subsequent sensitivity analysis of the off-axis tests on the value of \iF\d1\d2 indicated that data from 15° off-axis tensile tests were more stable in establishing \iF\d1\d2 than that of other angles tested: 30°, 45°, and 60°.
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are
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