Building extension through additional CLT storeys

In the last decade, the use of cross-laminated timber (CLT) panels as load bearing elements have become a usual solution for buildings and structures with an upward trend internationally. This is because CLT has brilliant physical and mechanical properties and it is also an eco-friendly and renewable material. In addition, the prefabricated nature of the CLT panels in a controlled environment increases the overall building speed, reduces dramatically the erection time, and makes it an even more competitive structural material compared to more traditional ones like concrete and steel. Up until now, timber as a building material has mainly been used for roofs and pergolas in Greece. Concrete and steel have traditionally been the dominant building materials over the years. Timber is not such competitive mainly because there is not enough knowledge of abouttimber buildings. The fact that Greece is not a sawn timber producer affects this trend. Nowadays, the simple and cheap import of sawn timber, as well as the sensitiveness about the environment, are strong factors for introducing timber buildings to Greece. There is already a great demand for timber buildings, and an increase in the requests is expected.CLT panels are used in a wide spectrum of structural applications. They are used as structural components for houses, offices, multi-story buildings, schools, industrial halls, sports halls, and special structures [4]. Another innovative application of CLT is the renovation through vertical expansion with additional floors to existing buildings. This new and promising trend is becoming more and more frequent, especially in developing cities where there is a need for new houses in limited space. The low density of CLT and so the low overall weight of the additional structure, makes the CLT components a robust building solution for vertical renovation since there is usually no need for reinforcement of the foundations of the current building [15]. The aim of this study is to provide the author with the opportunity to deepen his knowledge regarding the special characteristics of CLT as a building material as well as to understand its mechanical properties and the theories which describe them. In addition, this study constitutes the first attempt at modeling and designing a timber structure made with CLT panels. Therefore, the knowledge gained about the special features in CLT modeling is a fundamental task. Finally, since the design of the CLT structure is based on the European design rules for buildings, the engagement with the appropriate Eurocodes, i.e. Eurocode 0, 1 & 5, is another critical task in this study. The structure under consideration is a two-story CLT structure which is a vertical expansion of a current composite (concrete-steel) building. The first additional floor will be used as an office area and the second one as a typical family house. Both additional floors are made of CLT elements and, where is necessary, glulam beams and columns are considered as reinforcement of the CLT panels and as supports, respectively. The design method includes finite element analysis (FEA) which is performed by the commercial structural softwareDLUBAL – RFEM [8]. In this study, the latter software is chosen for the design and the analysis of the structure since it is specialized software for timber structures made of CLT elements