Determination of shear strength values according to EN 408

This paper presents the results of 382 shear tests carried out according to EN 408. The test pieces consisted of spruce (Picea abies) and varied in density and ring width orientation (radial, tangential and at an angle of 45° to the steel plates). In addition pieces containing pith and knots were tested. The paper discusses problems observed when using this test configuration and shows that the test results do not support the characteristic shear strength values as given in EN 338. Moreover, the test results do not support the relationship between characteristic shear strength and characteristic bending strength as given in EN 384.

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Résumé Cet article présente les résultats de 382 essais de cisaillement menés conformément à EN 408. Les éprouvettes d’essai sont en épicéa (Picea abies) et présentent une variabilité en termes de masse volumique et d’orientation des cernes d’accroissement (radiale, tangentielle, à un angle de 45° par rapport aux plaques métalliques). Des éprouvettes supplémentaires contenant du cœur et des nœuds ont également été testées. L’article évoque les problèmes qui ont été mis en évidence lors de l’utilisation de ce dispositif expérimental et montre que les résultats expérimentaux ne sont pas en accord avec les valeurs caractéristiques de résistance au cisaillement données dans EN 338. De plus, ces résultats ne confirment pas la relation entre résistance caractéristique au cisaillement et résistance caractéristique à la flexion telle que stipulée dans EN 384.

     

Constructive quantum scaling of unitary matrices

In this work, we present a method of decomposition of arbitrary unitary matrix \(U\in \mathbf {U}(2^k)\) into a product of single-qubit negator and controlled-\(\sqrt{\text{ NOT }}\) gates. Since the product results with negator matrix, which can be treated as complex analogue of bistochastic matrix, our method can be seen as complex analogue of Sinkhorn–Knopp algorithm, where diagonal matrices are replaced by adding and removing an one-qubit ancilla. The decomposition can be found constructively, and resulting circuit consists of \(O(4^k)\) entangling gates, which is proved to be optimal. An example of such transformation is presented.     

Einfluß der Holzabmessungen auf die Zugfestigkeit von Bauschnittholz

The effect of timber dimensions on tensile strength was investigated in 750 and 200 tests involving spruce and Douglas fir respectively, with dimensions ranging in thickness from 30 mm to 70 mm, in width from 50 mm to 200 mm, and in length from 150 mm to 2,500 mm. Results show tensile strength to be essentially related to knot ratio and density and to decrease with increasing length, in accordance with relationship f _t,1=f _t,0·(l ₀/l ₁)^0.1. Since specimens tend to exhibit decreasing knot ratios with increasing width, tensile strength was shown to rise with increasing width. Apart from this relationship no significant effect of width and thickness on the 5-percentiles of tensile strength, as assumed e.g. in Eurocode 5, was detected.     

Coupling of skeletal muscle to a prosthesis for circulatory support

A durable bond between the end of skeletal muscles and prosthetic structures could, with appropriate linkage, allow circulatory support power by synchronous and/or sequential contraction of several in situ conditioned muscles. Potential advantages relative to a myoplasty wrap involve 1) less traumatic dissection, 2) efficient linear force development, 3) selectable contraction rate, 4) greater stroke work, 5) independent control of muscle pre-load and end diastolic pressure, and 6) independent control of duration of muscle tension and ejection time. However, no existing means of tissue-prosthetic bonding appears adequate. Practicality would demand that full tension bearing capacity by the bond take no longer than muscle conditioning. A prosthesis was developed to achieve those goals. As scaled for this study, it is made of 7,200-7,800 unspun, unplaited, 22 to 26 microns diameter polyester fibers swaged into four taper needles for weaving through distal muscle. The other end is formed into a polyurethane sheathed kernmantel cord for distal fixation. Devices were implanted in six 3 to 4 kg rabbits (unilateral posterior tibial tendon replacement, random side selection with contralateral dissection/closure controls), and their tensile strength was tested at 30 days. All healed well; leg movements were normal after 1 week. Limbs were frozen at -70 degrees C between death and testing. Control failure occurred at 243 +/- 94 N and experimental at 163 +/- 44 N (p = 0.065, t-test); highest estimated requirement was 17.2 N. Interface strength was adequate by 30 days. Continued investigations, addressing other questions, are warranted.     

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Ohne Zusammenfassung     

Verhältnis von Zug- zu Biegefestigkeit bei Vollholz

Zusammenfassung Nach EN 338 betr?gt die charakteristische Zugfestigkeit bei allen Festigkeitsklassen 60% der charakteristischen Biegefestigkeit. Die vorliegende Untersuchung an mitteleurop?ischem Bauschnittholz (vorw. Fichte, Picea abies) zeigt, da? das Verh?ltnis von Zug- zu Biegefestigkeit von der Holzqualit?t abh?ngt. Durch eine Modifizierung der klassischen Spr?dbruchtheorie kann das Verh?ltnis von Zug- zu Biegefestigkeit in Abh?ngigkeit der Biegefestigkeit ausgedrückt und damit ein Einflu? der Holzqualit?t deutlich gemacht werden. Insgesamt wurden zusammen mit verfügbaren Versuchsergebnissen aus der Literatur 2642 Zug- und 1739 Biegeversuche an Prüfk?rpern in Gebrauchsabmessungen ausgewertet, die in 28 bzw. 27 Einzelkollektive gleicher Abmessungen aufgeteilt waren. Für die charakteristischen Festigkeitswerte wird die Beziehung f _t,k /f _m,k =0,24 ·f _m,k ^0,28 bzw. f _t,k =0,24·f _m,k ^1,28 vorgeschlagen. Der Vergleich mit den derzeit gültigen charakteristischen Festigkeitswerten nach EN 338 zeigt, da? eine Berücksichtigung des Einflusses der Holzqualit?t aus Gründen der Sicherheit und der Wirtschaftlichkeit wünschenswert w?re.

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Summary Acc. to EN 338 the characteristic tensile strength is determined to be 60 percent of the characteristic bending strength for all strength classes. The present investigation involving timber from Central Europe (mainly spruce, Picea abies) shows that the relationship of tensile to bending strength is affected by wood quality. Through a modification of the classic brittle fracture theory this relationship can be expressed in terms of bending strength and hence the influence of wood quality can be shown. Together with available results from literature a total amount of 2642 tension and 1,739 bending tests divided into 28 and 27 subsamples respectively, were evaluated. A relation of f _t,k /f _m,k =0,24·f _m,k ^0,28 or f _t,k =0,24·f _m,k ^1,28 is suggested for the characteristic strength values. A comparison with the characteristic strength values acc. to EN 338 indicates that for safety and economy reasons the consideration of the influence of wood quality would be desirable.