Peggi L. Clouston

Development of Laminated Bamboo Lumber: Review of Processing, Performance, and Economical Considerations

As focus is drawn toward more sustainable construction practices, use of bamboo as a structural building material is growing as a topic of interest. It is highly renewable, has low-embodied energy, and has the highest strength-to-weight ratio of steel, concrete, and timber. Composite lumber made from bamboo, termed laminated bamboo lumber (LBL), has gained the particular interest of researchers and practitioners of late, since it has bamboo’s mechanical properties but can be manufactured in well-defined dimensions, similar to commercially available wood products. Its primary drawbacks are that it is difficult to connect and is more costly than competing, locally available materials. This paper presents the advantages and challenges of embracing LBL as an alternative building material. Experimental and analytical data on production, performance, economics, and environmental impact of bamboo and LBL are reviewed, synthesized, and further analyzed to present an overview of the viability of using bamboo as a ...

A stochastic plasticity approach to strength modeling of strand-based wood composites

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. # 2002 Elsevier Science Ltd. All rights reserved.

Measurement and Stochastic Computational Modeling of the Elastic Properties of Parallel Strand Lumber

This paper describes a model for the spatial variation of the elastic modulus of parallel strand lumber (PSL) that is based on bending experiments and also describes a validated stochastic computational model that incorporates orthotropic elasticity and uncertainty in strand geometry and material properties. The PSL exhibits significant variability both within members and between members, but this variability is less than that of equivalent sawn-wood members, and decreases with increasing member size. The correlation length of the elastic modulus is found to be several meters and is independent of the cross-sectional size. The variance of PSL elastic modulus is found to scale inversely with the number of strands in the cross section. The validated computational model is flexible enough to allow preliminary exploration of the properties of new mixes of species and strand sizes in PSL material design.

Variability of the Compressive Strength of Parallel Strand Lumber

Measurement of the compressive strength of parallel strand lumber (PSL) 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.

Length Effects in Tensile Strength in the Orthogonal Directions of Structural Composite Lumber

The natural variation of strength properties within brittle materials leads to the phenomenon of size effect which causes the expected strength of a material to decrease as the stressed volume increases. An important implication of size effect is that size adjustment parameters must be incorporated into multi-axial constitutive and failure models used in numerical simulations such as those made using the finite element method. These size adjustments are based on the sizes of the individual elements, rather than the size of the structural member. This experimental study seeks to determine whether such a size effect is present in the orthotropic principal material directions of parallel strand lumber (PSL) and laminated veneer lumber (LVL), and, if the effect is present, to quantify it. Tensile tests were performed on specimens of different test section lengths oriented in the longitudinal, transverse, and through-thickness (PSL only) directions and size effect adjustment parameters were estimated. Statistical results indicate the existence of size effect in LVL and PSL for the longitudinal and transverse directions.

In-Plane Shear Properties of Laminated Wood from Tension and Compression Tests of Angle-Ply Laminates

AbstractExperimental methods for the characterization of shear strength and stiffness of both wood-based and glass-based or carbon-based composite materials are highly contested because shear prope...

Characterization and Probabilistic Modeling of the Mesostructure of Parallel Strand Lumber

AbstractParallel strand lumber (PSL) is a composite made of oriented wood strands that have been glued and compressed together. Its market share in the residential construction industry is considerable, being used primarily as main load bearing members such as beams and columns. Unlike the fast-paced market growth of these products, computational development has been slow. The highly heterogeneous mesostructure of this material must be known and quantified in order to develop advanced computational tools for limit state analysis of PSL. Void heterogeneities play an important role in determining the failure modes and strength of PSL, in addition to material phase aberrations such as grain angle variations and defects. In this study, two-dimensional (2D) and three-dimensional (3D) void characteristics were investigated. An experimental program along with a statistical survey was conducted to quantify the following 2D and 3D void characteristics in two 133×133×610  mm PSL billets: volume fraction, volume, al...

Computational Modeling of Laminated Veneer Bamboo Dowel Connections

AbstractLaminated veneer bamboo (LVB) is a relatively new building product made from layers of glued bamboo and used in applications similar to lumber. Few studies exist on its mechanical performan...

Modeling the Effect of Void Shapes on the Compressive Behavior of Parallel-Strand Lumber

AbstractSmall voids of varying shapes and sizes are an inherent part of the physical structure of parallel strand lumber (PSL) due to the material’s manufacturing process. To gauge the sensitivity ...

Torsional Shear Strength and Size Effect in Laminated Veneer Lumber

This study investigates the effect that specimen depth has on the torsional shear strength of full-size Eastern Species Laminated Veneer Lumber (LVL). Characterization of this effect is valuable for structural design purposes as well as for use in constitutive modeling when predicting member strength of one depth based on member strength of a different depth derived from testing. To this end, torsion tests were carried out on three depths (140, 184, and 235 mm) of 1.98 m long by 44 mm thick 1.9E Eastern Species LVL. The shear strength of each depth was determined based on homogeneous, orthotropic theory for beams of rectangular cross-section. Despite a perceptible trend of slightly decreasing shear strength with increasing depth, an analysis of variance test indicated that no statistically significant depth effect exists as it relates to torsional shear strength. Further, a three dimensional finite element model of the 44 mm by 140 mm specimen indicated that stresses are uniform within the shear span of 2 times the depth plus the grip distance away from each end of the specimen. The predicted average maximum shear stress in this region compared well to the maximum shear stresses obtained experimentally.