Val av stomsystem – vilka faktorer styr valet av system

Sammanfattning: Today there are various load bearing systems to choose from, concrete, steel, timber, or a combination of these. What determines the choice is usually the economy, which depends on the solutions in the different load bearing systems that will be made. Many of these choices are made based on previous projects and previous experience but do not always lead to the optimal solution. It is important to perform a detailed investigation of the existing possibilities for a specific project. Some of the key factors are construction time, installations, span, flexibility, sound and thickness. The purpose of this thesis is to study different solutions for load bearing systems, primarily on slabs, compare them from various aspects and to demonstrate the pros and cons of different choices. The report begins with a basic background and theory in the field, and then selects some solutions for design. For the results to be comparable, design is based on an existing building where there is access to drawings. Load bearing systems include the column and beam system, flat slabs and bearing walls. Slabs consist of concrete slabs and timber slabs. Concrete slabs are casted in situ, composite structures and prefabricated. Prefab slabs are composite structures, while hollow core slabs and massive slabs are prefabricated slabs. The result of the design indicates that prefab slabs, hollow core and timber slabs are three options that can handle different spans with different cross sections. Depending on the bearing system, all three slabs have been shown to be viable options. Design of flat slabs has also been performed based on both plasticity theory and elasticity. The results show that flat slabs can be the base for a load bearing system that fulfills requirements for flexible and open floor plans. An economic analysis of prefab slabs, hollow core slabs and timber slabs has been performed. The cost estimate includes the cost of materials, labor cost, subcontracting, and overhead expense. The results show that hollow core is cheapest. However, this does not reflect the total cost since different solutions have different effects on the remaining parts of the project. The final choice of load bearing systems depends on factors other than bearing capacity and deformation. Various solutions that fulfill the same requirements make it difficult to choose the best possible solution. This means that one has to identify all the important factors and then look at the available solutions and their consequences.