Thermal treatment of bamboo with flame: influence on the mechanical characteristics

The mechanical properties of bamboo are susceptible to degradation due to both physical and biological agents. Among the non-chemical treatments, we studied the influence of a short-time heat treatment, using an LPG-gas torch, on the mechanical properties of a bamboo (Phyllostachys viridiglaucescens) growing in Italy. The response was very encouraging as we found no significant reduction in either elastic modulus or tensile, compressive and bending strength. Several samples were subject to tension, compression and bending tests to compare the responses of the treated and untreated culms. The average tensile elastic modulus was slightly greater for the untreated culms. The average tensile strength of the untreated culms was only slightly greater, and the differences can be assumed to be insignificant from a structural point of view. The average value of the treated culms compressive elastic modulus was slightly greater than that of the untreated ones. The compressive strength was essentially the same. The bending mechanical behaviour was barely influenced by the thermal treatment. A microscopic investigation (optical and electron microscopy) was undertaken to investigate the possible deterioration of the bamboo microstructure due to the heat treatment. No appreciable damage was detectable in the treated material. The proposed heat treatments can be considered as a reliable and sustainable protection practice for bamboo culms

Rigid folding representation by the Stereographic Projection

The Stereographic Projection machinery is applied to the qualitative and quantitative description of the folding problem of an origami-like structure: the facets of a creased rigid sheet undergo successive rotation about several creases arbitrarily located in the three-dimensional space. The theoretical apparatus is revisited and some basic problems are depicted to emphasize both the simplicity and the great efficiency of the representation. Several original results, useful to simplify the trajectory tracing of the facet, are derived. The Representation of the Pole Path around a corner is finally presented as an alternative synthetic description of the folded configuration. An application to a multi-folded carton erection demonstrates the effectiveness of the proposed formulation

Discussion of "Simple Mechanical Model of Curved Beams by a 3D Approach"

The authors present a formulation of the static linear behavior of a non-homogeneous plane beam with large curvature: the displacement field is derived from the hypothesis of a rigid cross section in its plane (for axial and bending effects) and from a “pure torsion” case (for non-uniform torsion). Shearing strain is not taken directly into account so that shear forces are considered to be reactive. The governing equilibrium equations are derived from the Theorem of Minimum total Potential Energy. This discussion focuses on several consequences of the proposed theory with the aim to elucidate some aspects of the 3D behavior of a curved beam. (Discussion submitted to Journal of Engineering Mechanics ASCE, unpublished)

Exact deflation in the complex modal analysis of low-rank nonclassically damped structures

This paper presents the complex modal analysis for a proportionally damped structure equipped with linear non-proportionally damped viscous elements (substructures or discrete real devices) giving a low-rank contribution (r) to the non-proportional part of the damping matrix. Using the classical undamped modes and a special low-rank matrix update formulation of the original problem, the original Quadratic Eigenproblem (QEP) is hugely deflated, without approximations, to an equivalent Rational Eigenproblem (REP) of dimension r << n (Theorem 2), as an alternative to the linearized Standard Eigenproblem of order 2n over the complex field. The existence of classical modes in non-classically damped structures is also discussed. The REP is solved by the homotopy method: a robust predictor-corrector continuation algorithm is designed in order to determine the required eigenpairs. Some application to simple models of both traditional and base-isolated structures, together with an outline of future work, end the paper

Exact deflation in the complex modal analysis of low-rank non-proportionally damped structures

under submissio

Spectral Acceleration and Pseudo-spectral acceleration proximity

This paper deals with the deterministic relationship between spectral and pseudo-spectral acceleration, SA(csi,omega0) and PSA(csi,omega0) respectively, and gives the reason for their proximity on theoretical basis. The key step is to estimate the velocity at the acceleration extrema using the exact integral representation of the solution. When the product csi T0 < 1, each maximum displacement occurs csiT0/ Pi after each acceleration maximum. In this case the maximum displacement is evaluated in closed form as a simple function of the maximum acceleration: the well-known proximity between spectral and pseudo-spectral acceleration is thus quantified for the first time. As an alternative, a very simple procedure is presented using a “first-order” version of the motion equation; despite its coarseness the result agrees with the more complex analysis discussed previously. On the other hand, in Seismic Base Isolation systems (with large modal periods and damping ratios) a discussion of the relationship between PSA(csi,omega0) – giving the forces on the structure – and SA(csi,omega0) – governing the forces on the foundation – becomes crucial. Comparison of the obtained results with spectral quantities derived from a number of real accelerograms, along with a description of a typical counterexample in which displacement and acceleration extrema are not correlated, end the paper

Mechanical characterization of five species of Italian bamboo

High mechanical performance coupled with sustainability gives to bamboo a high potential to substitute conventional construction materials in various applications. In particular, there are countries in which this material has been used in construction for millennia and represents an asset, on the contrary, there are countries where there is still not enough knowledge of the structural properties of locally-grown bamboo. In these cases, it is important to extend the knowledge of the mechanical properties of local bamboo species supported by the development of suitable standardised testing procedures. In this view, the paper presents the results of an experimental study for the mechanical characterization of five bamboo species cultivated in Italy (Phyllostachys bambusoides, edulis, iridescens, violascens and vivax). For compressive tests, the used methodology is compliant with ISO Standards; for tensile test, the procedure suggested by ISO is very difficult to apply so different set ups have been proposed and in the second part of the paper a critical discussion about ISO methodology and its possible improvements are reported. The findings from this research shed light on current challenges and on the possible future steps for a wider uptake of natural materials in constructions

Large bending behavior of creased paperboard. II. Structural analysis

AbstractThe mechanics of a paradigmatic typical carton corner with five creases is analyzed theoretically, in closed form. A general kinematical analysis of the mechanism (in finite rotation) is presented, assuming the versor of the intermediate crease, s, as a 2-degree-of-freedom Lagrangian parameter. The rotation θc of the cth crease is derived, together with the existence domain and a discussion of the singular configurations.The actions, driving the carton during a prescribed quasi-static erection program, are derived in a very efficient manner using the Virtual Works Equation, taking into account a non-linear anholonomic bending constitutive law of the creased paperboard. In particular, the active and reactive components of the moment ϕ, driving s along its path, are identified. No resort to the tangent stiffness computation is required. Some numerical examples illustrate the rotation and the driving forces obtained for both monotone-loading and complex loading–unloading erection paths.The presented results, “exact” within the scope of the restrictive hypotheses assumed, may be used in a preliminary design approach as well as a benchmark for more realistic FEM or CAE simulators

Large bending behavior of creased paperboard. I. Experimental investigations

AbstractThe large bending behavior of a creased paperboard is studied in the range of rotation θ∊[0°,180°] – new results, apparently not reported previously in literature – with the aim to point out some crucial aspect involved in an adaptive robotic manipulation of the industrial cartons.The loading tests show a great variability of the mechanical behavior, depending dramatically on the crease indentation depth (also for the specimens obtained from the same carton): (a) when the damage induced during the crease formation is relatively small, the bending response is unusually complex: the moment constitutive function, mL(θ), presents (up to) two peaks followed by unstable branches; (b) for greater indentation, the mL(θ) is monotone.In the unloading case the response mU(θ) is always monotone and is practically independent of the formation conditions of the crease. These behaviors can be easily described analytically using (piecewise) third degree splines.In a companion paper, the erection of a typical carton corner with unstable constitutive behavior is fully analyzed to detect the possible criticalities