Modeling of multi-layer beam with interlayer slips

In the early 90th the IBOIS-EPFL developed a new kind of shell structure. The ribs were made with simple planks which are waved together to build a spacial ribbed shell. The first application was the Polydome in 1993, and the most fascinating has been the Expodach in Hannover in year 2000 [1]. However, the calculation and the realization of such structures requires particular knowledge and experience. That is’s why the construction of such structures is something exceptional. In addition to the anisotropy of material wood, the spatial structure of laminated and screwed beams has a structural anisotropy. They constitute highly unspecified static systems. Currently the engineer does not have any effective method to calculate these kinds of spatial structures, made out of curved screwed lamellate boards. The existing approximations for complex curved structures are not satisfying. The main differences are noticed especially upon the analysis of the stability of structures subject to horizontal loads. The following article will compare a 6-layered beam with inter-layer slips in different load cases and situations. The beam is composed of 6 planks with a section of 140/27mm. The connections between the layers are screws. The studied parameters are the distance between the connector, the length of the beam and 3 different load cases. A total of 24 elements have been tested and compared between the laboratory test and different theories. A very important parameter is the stiffness of the connector. Thus additional tests have been made to simulate the stiffness of the screws used. A bi-exponential law has been generated to be used in the theoretical evaluation of the tests. The actual theories which have been used to simulate the behavior of the sample are gamma- Method of Möhler-Schelling, Appendix F of the Germand standard E- DIN 1052 of Prof. Kreuzinger, framework systems developed by Kneidl and Hartmann and finally a multiy-layer finite element developed at the LSC- EPFL by Prof. Frei and Dr. Krawczyk.