Teoretiska beräkningar för infästning av takelement underifrån

Sammanfattning: Lättelement AB is a company that designs and manufactures prefabricated building parts in the form of roofs, walls and joists. Most of the productions is focused on roof elements and this is also what this study focuses on. At present all roof elements are mounted from above, screws are attached to the support through holes in the roof surface layer. Sometimes it can be problematic to install from above and this work must investigate whether it is possible to attach the roof elements from below. The study examines three different variants where the focus is on calculating which shear capacity and tensile you can count on. It is calculated for three different supports and they are wood, thick steel and thin steel rail. The first step is to calculate what capacity you can get with the company standard screws without changing anything in the construction of the element. The second step is to look at other screw models and see what capacity you can get without changing anything in the construction of the element. In the final step, what modifications and which screws are required to be able to handle 15 kN/m in shear and 5 kN/m in tensile. In order to solve this hand calculations according to Eurocode with certain assumptions, as well as proven theory of joints, have been used. Relevant results from the report is that it is not possible to attach screws to the element without modifying it, the reason is that the standard beams are to narrow. With a relatively simple solution in the form of an internal wooden beam and coarser screws one can achieve a characteristic shear- and tensile capacity of 19,2 kN/m and 27,0 kN/m for wooden supports. For a thicker steel support, a characteristic shear- and tensile capacity of 19,2 kN/m and 27 kN/m is achieved. For a thinner steel rail, thinner screws must be used and the characteristic shear and tensile capacity will be 8,4 kN/m and 28,2 kN/m. The conclusion is that it is possible to attach screws to the underside of the element if they are slightly modified, however, it would have to be investigated by testing, to what extent the steel sheet on the underside of the element reinforces the joint, and whether it is practically possible without pre-drilling.