Probabilistic strength prediction of adhesively bonded timber joints

In this study, an experimental campaign was conducted to characterize the length effect on the elasticity and tensile strength of clear spruce wood parallel to the grain direction. Four groups of specimens of different lengths, cut from the same log, were tested under the same conditions under longitudinal tensile loading. The cross-sectional area of the specimens was selected as being constant and sufficiently small to exclude the effect of variations of the properties in the transverse direction. Local deformations along the lengths of the specimens were recorded during the tests in order to characterize the spatial variability of the elastic modulus. A connection between the mesostructure of the clear wood and its local elastic modulus was observed. Statistics concerning the elastic modulus, strength and strain to failure and the effect of length change on these properties were extracted. The strength statistics were also used to examine the accuracy of the classical Weibull size effect law. The correlations between the strength, the elasticity and the density were obtained. The results show a variability of approximately 20% in the local elastic modulus. Also, the variability of the effective elastic modulus decreases with increasing length. The mean value of the strength has an upper bound when the length approaches zero, in contrast to the Weibull law, while its variability remains virtually unchanged for different lengths.

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“…In order to quantitatively examine the error involved in the prediction of the CWSEL, the following formula was used [12]:…”

Section: Comparison Of Experimental Results With Cwsel Predictionmentioning

confidence: 99%

Experimental characterization of longitudinal mechanical properties of clear timber: Random spatial variability and size effects

Moshtaghin

Franke

Keller

et al. 2016

Construction and Building Materials

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“…The CWSEL has been widely used to model the size effect on timber strength [2,[4][5][6][7][8][9][10][11][12]. According to this model, the material is considered as a structure made up of linked elements, which fails with the first element failure.…”

Section: Weibull Size Effect Theorymentioning

confidence: 99%

“…This is because testing a set of specimens with a constant volume suffices to determine the unknown parameter of the CWSEL. Thus, by fitting the Weibull distribution to the experimental data, the shape parameter is estimated, and the CWSEL is then used in the related application, such as estimation of a wooden joint capacity [4]. To the authors' knowledge, there are only two works [13,14] in which the effect of volume change on the longitudinal tensile strength of clear timber has been investigated experimentally.…”

Section: Modeling Size Effect On Longitudinal Tensile Strength Of Clementioning

confidence: 99%

“…The size effect on timber strength can be treated as a volume effect, for example see [3][4][5][6] where such an assumption was adopted for the failure analysis of adhesively-bonded, welded and dovetail timber joints and [7][8][9] in which the elastoplastic behavior of strand-based wood composites and laminated veneer was studied. The Weibull law was applied only in tensile mode, while plastic behavior was considered only in compressive mode.…”

Section: Introductionmentioning

confidence: 99%

“…In current practice using the CWSEL, a Weibull distribution is fitted to data obtained from experiments on specimens with standardized dimensions. Then, the CWSEL is used to predict the strength of pieces of timber either with higher volumes [2,10,11], like timber beams, or lower volumes [4,7], which are usually small elements considered in finite element analyses of timber structures. However, using experimental data from the literature [13,14], it is shown in the current study that this procedure can result in relative errors in the prediction of the size effect on timber strength as high as 400%.…”

Section: Introductionmentioning

confidence: 99%

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Random field-based modeling of size effect on the longitudinal tensile strength of clear timber

et al. 2016

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In the current study, a random field-based size effect model has been proposed for the longitudinal tensile strength of clear timber. Since the failure mode is brittle, the problem is basically an extreme value problem of finding the distribution of minima of strength fields for specimens of different volumes. The stochastic response has been evaluated based on the Monte Carlo method along with the weakest link theory. Within the framework of the spectral representation method, the Weibull distribution has been considered as the marginal distribution to generate realizations of the strength as a 3D random field. The squared exponential autocorrelation function has been used for the description of spatial variability. The error resulting from this model, as compared to existing experimental data in the literature, is much lower than that of the classical Weibull law. The results show that when one of the specimen's dimensions decreases to less than 10 times the correlation length of the strength field, the size effect starts to deviate from the classical size effect law. Moreover, a simple analytical approximation, which includes the correlation length as length scale, has been presented that facilitates the application of the proposed model.

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