Infoscience

Thesis

Analyse non-linéaire des coques géodésiques multicouches à joints semi-rigides

In the 90ies the IBOIS-EPFL developed a new kind of shell structure. The ribs were made with simple boards waved together to form a spatial rib shell. However, the engineer currently does not have any effective method to calculate these kinds of spatial structures, which are made out of curved screwed lamellate boards. The existing approximations for complex multi-layered structures are not satisfying. In an initial step, our study compares a 6-layered beam with inter-layer slip in different load cases and situations. Existing theories were then used to modelise the different cases and situations tested previously, namely: the γ-Method of Prof. Möhler and Prof. Schelling, the appendix F of the German standard E-DIN 1052 of Prof. Kreuzinger, the framework systems developed by Dr. Kneidl and Dr. Hartmann and, finally, a multi-layer finite element developed at the LSC-EPFL by Prof. Frey and Dr. Krawczyk. To follow up on this observation, a range of tests were carried out. The studied parameters were the distance between the connectors, as well as the length of the multi-layered element. A total of 24 elements were tested and the test results were then compared with the different theories listed above. An important parameter in our analysis was the stiffness of the connectors. Therefore, additional tests were made to simulate the stiffness of the double-sheared connectors used. A bi-exponential law was generated specifically for the evaluation of the tests. Another step was the linearization of the non-linear law in order to account for the fact that some theories work only with linear stiffness law, like for instance the analogy method and the γ-method. The final step of this study was the analysis of multi-layered beams working in a network. To that aim, a large scale prototype known as unstable was built. Based on the form of a sphere, it had a span of 10,0m for a height of 0,75m. The tests were carried out until rupture to evaluate the structural behaviour and the critical load of the prototype. This enabled us to compare the measured results with the calculated ones of digital models.

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