In timber-concrete composite systems, timber and concrete are inherently brittle materials that behave linearly elastic in both tension and bending. However, the shear connection between the members can exhibit significant ductility. It is therefore possible to develop timber-concrete composite systems with ductile connection that behave in a ductile fashion. This study illustrates the use of an elastic-perfectly plastic analytical approach to this problem. In addition, the study proposes an incremental method for predicting the nonlinear load-deflection response of the composite system. The accuracy of the analytical model is confirmed with a computer model, and numerical solutions of the analytical model are compared to experimental results from the bending tests conducted by previous researchers. Reasonable agreement is found from the comparisons, which validates the capacity of the analytical model in predicting the structural behaviour of the timber-concrete composite systems in both elastic and post-elastic stages.
This book contains experiences and results of computer simulations in the field of research on glued laminated timber. Literature and references to the corresponding methodical approach are given to facilitate the access to the elementary basics. It also contains constructive explanations and critical annotations on modelling glued laminated timber for bending, tension and compression tests. Finally, the relevance of the simulation results for practical issues is discussed.
Cross Laminated Timber (CLT) is a lightweight construction material with a strength and stiffness comparable to Reinforced Concrete (RC). A crucial aspect of fully realizing the potential of CLT as a structural material is ability to interconnect it to similar and dissimilar materials. A study of connections was made through in-plane shear and tension tests on half-lapped and single-spline connections that make edge-toedge jointing between CLT panels using screws. A novel aspect of the study is investigation of how placing washers under screw heads alters stiffness and strengths of connections. Subsidiary axial load tests on screws assisted explanation of the shear and tension test results. Conclusions include the importance of accounting for large displacement effects on how screws transfer forces across joint-planes, and need to improve current generation connection design methods so that they account for effects of eccentricities that result from construction arrangement and detailing decision.
A new numerical model able to account for the interaction between tension and shear forces on typical hold-down connections used in CLT structures is proposed and discussed, starting from results of an experimental campaign conducted at University of Bologna. A specifically developed method appropriate to evaluate the main strength and stiffness parameters from the experimental cyclic force-displacement curves is presented, and the corresponding trilinear backbone approximation is defined. Parameters obtained from tri-linear backbone curves were used to define the effect of the tension-shear interaction on the behaviour of hold-down connections, particularly as far as yielding and peak strength and stiffness parameters are concerned. In order to numerically reproduce the behaviour of connections, a coupled zero-length element is developed and presented. The model is implemented in OpenSees and adopted to model single connection element. The model is calibrated referring to experimental results of specimens loaded only in tension. Then the model is validated referring to tests with increasing level of tension-shear interaction. The proposed model is able to reproduce the actual behaviour of hold-down connection with coupled tension-shear forces under monotonic load conditions. Finally, a first proposal for accounting the hysteretic behaviour is presented, and some preliminary results are shown.
On a number of occasions glued laminated timber breaks apart before the end of their service life. Examples in Germany (Frese M., Blaß H. J. [2011]) and Denmark (Hansson, Larsen [2005] ) show that this problem is real. In order to find the causes of the problem, extensive tests were conducted: 16 buildings with glued laminated timber were examined on the spot, calculations and laboratory work were carried out. These examinations told us that not only did the properties of the wooden material cause the damage, but the problems were also due to the wood used and the method of construction. In the calculations, the external load and residual stresses occurring in the glued laminated timber were included. Residual tensions in this timber were generated by climatic stresses and also due to the method of construction. These stresses also accumulated along with the stresses of the external load. Laboratory work was carried out to measure the delamination. We examined whether these analyses and calculations prove or disprove the results of the on- the- spot examinations.
Timber as a primary structural material has been forced to continually evolve to keep abreast with the changing demands of the construction industry. This paper presents further research undertaken by Queen’s University Belfast to evaluate the advantages provided by the post-tensioning of timber members using novel basalt fibre reinforced polymer (BFRP) rods. Using the high strength, low density, highly durable BFRP tendons experimental investigations utilising the four-point bending method were conducted and monitored. From the experimentation it was found that there was an increase in load carrying capacity, a more favourable ductile failure mode and a further benefit of less net deflection due to the precamber induced by the post-tensioning prior to load application.
Three-point bending tests were performed on specimens of glued laminated timber with diferent specimen heights to failure to determine the relationship between specimen height and bending strength under tension perpendicular to the grain. For the three-point bending tests, two types of glued laminated timber composed of homogeneous grade timber, as specifed in the Japanese Agricultural Standard, were used. The laminae used for the glued laminated timber were L80 grade Scots pine and L110 grade Scots pine. The specimens used in the three-point bending tests had dimensions of 105 mm (width) and 10–300 mm (height). The experimental results showed that the bending strength decreased as the specimen height increased, but the rate of decrease in the bending strength decreased with increasing specimen height when the specimen height exceeded 100 mm. From the relationship between the bending strength and specimen height, parameters that fit Bažant’s size-effect law were derived, and for a specimen height of approximately 100 mm, the bending strength was equal to the perpendicular-to-the-grain tensile strength.
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