论文翻译

Stress-Laminated Timber Decks Subjected to EccentricLoads in the Ultimate Limit StateIt is generally accepted that deflection in beams is highly dependent on the material property E L. For 3D plates, it is not quite as easy to identify the parameters that have a major effect on plate behavior. E L still has the greatest influence, because the stiffness in the longitudinal direction is several times greater than the stiffness in the transverse direction. The study of various material parameters revealed that the in-plane shear modulus, {GLT}, has a greater influence on deck deflection compared with the transverse MOE, {ET}. A reduction in GLT will increase the maximum deflection of the plate and thereby also the longitudinal bending moment. The twisting moment in the deck will be significantly smaller if GLT is reduced. The longitudinal out-of-plane shear modulus, GLH, was of little influence of the load distribution and the deflection values. Also the out-of-plane shear modulus in the transverse direction, GHT, has an insignificant influence on the load distribution. These values are obtained when the load is positioned at the very edge of the deck. However, this phenomenon can also be observed if the load is positioned further away from the edge, which was also shown by Karlsson et al. (2009). The difference between the first two material models [CEN (2004b) and Ritter (1990)] is not as great as that between materials 3 and 4 [Karlsson et al. (2009) and OHBDC (1983)]. The first two material models represent values which have been and are still being used in design. One plausible cause of the high and low values in Table 1 is the influence of the test methods. Full-scale tests perfumed by both Crews (2002) and Dahl et al. (2006) generally result in higher values for the mechanical properties of the deck than tests performed on smaller test specimens using the method proposed by Tsai(1965). The prestress also has an effect on the mechanical properties of the deck. However, this is not included in any design codes or recommendations.There is a significant difference between the first two equivalent beam models compared with the third equivalent beam theory studied. The maximum deflection obtained by the method in CEN (2004b) is 85% larger than the deflection according to Ritter’s method when the deck is loaded close to the edge (eccentric load). The difference in the deflection between Ritter’s and Crews’ method is much smaller. The two numerical plate theories formulated by Kirchhoff and Mindlin-Reissner result in deflection between that produced by the two equivalent beam theories. The variation in deflection between Kirchhoff and Mindlin-Reissner is fairly small, 55.7 and 52.4mm, respectively. Neither of the two plate theories is recommended for use when the deformation is lager than one-tenth of the thickness of the plate. The risk of the membrane effects on the plate becomes too great when the deformation is large. In the ultimate load test, the deflection was approximately a quarter of the plate thickness.From the results in the full-scale test by Ekholm et al. (2012), it was shown that the deflection become nonlinear at relatively low load levels. The nonlinearity started at loads of 150-200 kN, which corresponds to approximately 20% of the ultimate load. Furthermore, it was observed that the nonlinearity is directly dependant on the loadposition and the amount of prestress. When the load is positioned very close to the edge, the load-deflection curves are nonlinear. The test also showed that the deflection at the edge of the deck increases when the prestress is reduced. One plausible cause of this nonlinearity is horizontal interlaminar slip because of the twisting moment, as discussed by Ekevad et al. (2011). The maximum deflection from the test was 65.4mm immediately before failure, as shown in Fig.5. The linear design method with the beat prediction of the deflection was the equivalent beam theory, with a prediction of 61.5mm. Plate theory predicted that the deflection was between 52.4 and 55.7 mm. Ritter’s and Crews’ equivalent beam theory only predicted a deflection of 33.2-34.3 mm. Neither Ritter’s nor Crews’ method allows the load to be positioned this close to the edge and, as a result, their methods do not apply for an eccentric load very close to the edge of the deck. All five of the design methods underestimated the deflection of the tested deck. At the beginning of the load sequence, before interlaminar slip, the deflection in the tested deck could be predicted with plate theory. This was shown by comparing the deflection using plate theory with a test with a linear response, as shown in Fig. 6. When the load was positioned centrically on the deck, the results were quite different. The equivalent beam theory in CEN (2004b) now overestimated the deflection by more than 100%. Both Ritter’s and Crews’ equivalent beam theories, together with the two plate theories, now all predict the deflection fairly well.In several parts of the world, there are rail and curb systems, which also prevent the vehicle from driving at the edge. However, in some countries, such as Sweden, very small curbs are used and vehicles can drive very close to the edge. When the load in the numerical models was moved only half a meter away from the edge (toward the middle), the deflection and stress were reduced significantly. The maximum deflection was reduced from 52.4 to 34.8 mm. The deflection at this eccentric load position is only 12% lager than the deflection obtained from the centric load position. An eccentric load position like this is more similar to both North American and Australian standards. This shows that it might be more economical to introduce a wider curb to protect the deck from these extreme cases of eccentric loading. This would lead to a significant reduction in vehicle deformation of the deck.。