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This paper investigates the buckling behavior of three-layered cross-laminated timber (CLT) panels, from both the experimental and analytical standpoints. Two different series of specimens are considered: the homogeneous ones, which are entirely made of beech, and the hybrid ones, whose inner layers are made of Corsican pine. The experimental tests aim to evaluate the failure limit loads of the specimens, when loaded by an increasing compression tip force. The analytical formulation is first obtained for a panel with a generic number of layers and after it is specialized for a three-layered panel. Timber layers are modeled as internally constrained planar Timoshenko beams linked together by adhesive layers, which are modeled as a continuous distribution of normal and tangential elastic springs. A closed-form solution of the buckling problem is obtained. The achieved Eulerian critical load of CLT panels depends on two parameters, which account for (1) the interaction between timber layers (due to the glue tangential stiffness) and (2) the rolling shear stiffness of the inner layer. Three different failure criteria are introduced to estimate the limit load. Finally, the analytical limit loads and the experimental ones are compared. [ABSTRACT FROM AUTHOR]

Bamboo is a fast-growing biobased building material with a high strength-to-weight ratio, and the combination of bamboo and wood provides an environmentally friendly alternative for building construction. A new type of laminated bamboo–timber composite column was proposed to improve the compressive performance of timber columns, which was expected to obtain better mechanical performance. Bamboo scrimber and Douglas fir were combined to form laminated bamboo–timber composite columns for the experimental study. Axial compression tests were carried out on 5 groups of 15 composite columns. The failure modes of the composite columns were assessed. The laws of axial displacement, lateral displacement, axial strain, ultimate bearing capacity and stiffness were analyzed. Finally, the bearing capacity of the composite columns was calculated by referring to the design specification for timber structures. The results indicated that the composite columns exhibited three failure characteristics. The ultimate bearing capacity and stiffness of the bamboo–timber composite columns increased with increasing amount of bamboo scrimber. The ultimate load of the bamboo–timber composite columns was increased by 23.0–94.6%, while the stiffness was increased by 9.1–38.4%. In addition, the bearing capacity of composite columns was calculated according to two standards. The experimental values of the bamboo–timber composite columns are in good agreement with the theoretical values, and the errors are within 8%. [ABSTRACT FROM AUTHOR]

Predictive models of the moisture content of Para rubber timber were developed and validated using near-infrared (NIR) spectroscopy. A portable NIR spectrometer connected to a smartphone was developed to facilitate real-time moisture content determination of Para rubber timber. An android application was created to control the NIR spectrometer in acquiring, displaying, and processing the spectral data on the smartphone. Three predictive models for determining the moisture content of Para rubber timber were developed using partial least squares regression in the range 0–89% on a dry basis (%db), < 30% db, and > 30% db. The predictive model for moisture content in the range 0–89%db had a correlation coefficient of cross validation (Rcv) of 0.98 and a root-mean-square error of cross validation (RMSECV) of 5.48%. The predictive model for moisture content in the range less than 30%db had values for Rcv and RMSECV of 0.84 and 2.05% db, respectively. Lastly, the predictive model of moisture content in the range greater than 30% db had values for Rcv and RMSECV of 0.85 and 4.57% db, respectively. The performance of the predictive equation for determining the moisture content in Para rubber timber in the range less than 30% db was validated using unknown samples, which were not used in the model development, assigned as an external prediction set, which resulted in a root-mean-square error of prediction (RMSEP) of 1.44% db. The portable NIR spectrometer connected to a smartphone through an android application is a suitable system for practical application in sawn timber factories because it is cheap and conveniently portable. In addition, the calibration model should be updated and more samples added to cover the variation in growing season and growth area for greater robustness and accuracy of the predictive models. [ABSTRACT FROM AUTHOR]

In recent years, an increasing number of glulam structures have emerged in civil engineering, but their development is limited by durability issues. Degradations related to excessive moisture content (MC) or wetting/drying cycles were observed and can lead to severe structural damages. As a result, the development of continuous monitoring techniques of wood MC becomes essential. Currently, the mostly used MC control methods are based on electrical measurements (resistive or capacitive). Nevertheless, existing solutions are not practical to conduct measurements inside every lamella of glulam. In the light of these observations, it is proposed to transform glulam into “smart material” by embedding the MC monitoring system either inside or between lamellas, considering the major constraints of fabrication of this material (the small glue line thickness, the important bonding pressure, etc.). To achieve this, 4 measurement configurations using “pin-type” or “surface” electrodes were investigated with the following steps. First, a feasibility study was conducted to make sure of the good functionality of the measurement configurations. Thereafter, the selected configurations were used to monitor the MC variation (10-70%) in glulam specimens. At the same time, the influence of electrode spacing and bonding pressure on the electrical measurements was also investigated. Results show that the selected configurations are operational for the local MC measurement in the lamellas of glulam, regardless of the types of sensors used or the measured physical quantities (electrical resistance or capacitance). This study aims to provide valuable information for the future development of embedded MC monitoring system in glulam structures. [ABSTRACT FROM AUTHOR]

Timber is an desired material for structural applications due to its green credentials and attractive external appearance. Fire safety design of timber structures is largely limited to considering the exposure of elements to the standard fire, to which timber demonstrates exceptional resilience. This paper reports on a series of tests which were carried out with the intention of exploring the impact of non-standard fires on timber elements. Because of the natural variation in timber elements, the tests and the resulting analysis of the test results were conceived and designed in such a way that as much information about the statistical distribution of the response of the elements as possible could be obtained. The resulting testing programme comprised four furnace fire tests, each of eight loaded timber beams, with three different temperature time curves: two standard fire tests, one long-cool parametric fire and one short-hot parametric fire. The reduced cross section method for structural calculations is extended in this paper to parametric fire exposures, and the results of the tests are compared with this method. It is shown that the thickness of the zero-strength layer is dependent on the temperature time curve to which the timber is exposed in the furnace and that the 7 mm zero-strength layer prescribed in EN 1995-1-2 may be un-conservative for members in bending. For the cases studied, the zero-strength layer thickness in bending is shown to be around about 15 mm under standard fire exposure and 16 mm under exposure to a long cool parametric fire. Conversely, the zero-strength layer is only 8 mm deep under exposure to a short hot parametric fire. This has implications for the design of timber elements not only for parametric fire exposure in enclosures, but also perhaps for the use of timber elements in large open structures such as halls or arenas where more localised fire exposure or travelling fire exposure may be expected. [ABSTRACT FROM AUTHOR]

Understanding the inherent damping mechanisms of floor vibrations has become a matter of increasing importance following the development of new composite floor layouts and increased span. The present study focuses on the evaluation of material damping in timber beam specimens with dimensions that are typical of common timber floor structures. Using the impact test method, 11 solid wood beams and 11 glulam beams made out of Norway Spruce ( Picea abies) were subjected to flexural vibrations. The tests involved different spans and orientations. A total of 420 material damping evaluations were performed, and the results are presented as mean values for each configuration along with important statistical indicators to quantify their reliability. The consistency of the experimental method was validated with respect to repeatability and reproducibility. General trends found an increasing damping ratio for higher modes, shorter spans, and edgewise orientations. It is concluded from the results that material damping of timber beams of structural dimensions is governed by shear deformation, which can be expressed more conveniently with respect to the specific mode shape and its derivatives. [ABSTRACT FROM AUTHOR]

Moisture-induced stresses resulting from climate variations of the environment can induce cracks in timber members and thus affect the safety and serviceability. The present study highlights-by means of numerical simulations-the distribution and development over time of moisture-induced stresses in various glulam cross sections during wetting. The results show that local stresses may be significantly larger than average stresses, the extent of which strongly depends on the geometrical configuration of the glulam laminates. Suggestions are made on the design of glulam cross sections to minimize the arising local stresses. Furthermore, the studied wetting exposure results in local tensile stresses that exceed the tensile strength of the material. In smaller cross sections, this is the case within few days, while more time is required in wider cross sections. [ABSTRACT FROM AUTHOR]