This thesis deals with the development of new construction methods for ice domes. Domes are esthetic, logical and functional load carrying systems, fascinating because of their shape, thinness and structure. Additionally, for the load transfer of a uniformly distributed load, the dome structure is the perfect choice because mainly normal forces occur in the cross-section. When building ice domes, use can be made of the superior load carrying system of dome structures. Since ice has low mechanical properties compared to other construction materials, it has to be deployed when low stresses occur.
Thus, the combination of dome structures and the construction material ice is definitely advantageous. The construction of ice domes, however, remains a challenging task.
Part 1 of this thesis consists of an introduction which provides an overview of the state-of-the-art of ice domes and gives an insight into the research topic. Two new construction methods for ice domes are presented in this thesis. The basic concept is similar for both construction methods: In the initial position the intended shell structure consists of a plane plate which is subsequently transformed into a shell. The first method to be presented is called Pneumatic Formwork Method - described in part 2. Using this construction method, the shell consists of individual plane elements, molded according to the final shape of the shell. Complying with this construction method, the elements are placed on a planar working surface and are assembled by means of tendons. In order to transform the flat plate into a shell a pneumatic formwork is used. While air is inflating the pneumatic formwork, the plane plate is transformed into a shell. First, the basic principle of this method is explained in detail and numerical und analytical simulations help to understand the stresses occurring during the construction as well as in the finished dome structure. An essential part of this construction method is the pneumatic formwork. The materials used and the considerations regarding the shape of the formwork as well as the loading are presented in chapter 5. The first approach for testing this newly developed technique was to carry out preliminary experiments. Two wooden models helped to gain a deeper understanding of the transformation process. Then, a thin concrete shell with a diameter of 8,4 m consisting of 96 individual precast concrete elements was erected. With the insights gained from the preliminary tests, the Pneumatic Formwork Method was tested on two ice shells. In their initial position both ice shells consisted of 96 plane ice elements assembled in such a way that circular plates with diameters of 6m and 13m were created.
Part 3 of this thesis presents a second construction method. Using this alternative technique, a flat plate is divided into segments which are distorted uniaxially and subsequently lifted into their final position.
This method is called Segment Lift Method. In order to distort the ice segments, these elements have to be lifted and kept in an elevated position so that the curvature produced, both by elastic deformation and creep deformation, can develop. For this purpose two different lifting methods are presented in this thesis - the Segment Lift Method with Pneumatic Formwork and the Segment Lift Method without Pneumatic Formwork. One way to lift the segments is by means of a pneumatic formwork which has to be placed underneath the ice elements before producing the ice plate. Another option is to lift them with a lifting device. In chapter 8, the basic principle of this method is explained and different shapes are taken into consideration. As the lifting of the ice segments and the creeping behavior of the ice are crucial factors within this technique, preliminary tests on ice beams were carried out to simulate parts of the subsequently built ice shells. In the winters of 2009/10 and 2010/11 large scale field tests on ice domes were carried out. First, the Segment Lift Method with Pneumatic Formwork was used and in the following winter season, the ice segments were lifted by means of a lifting device. Chapter 10 contains a detailed description of all construction stages of these two experiments as well as numerical and analytical simulations of the force and stress distributions during the different stages of the construction and in the finished structure. The successfully completed ice dome in the winter of 2010/11 was then monitored until the shell collapsed in spring 2011.
In part 4, advantages, disadvantages, achievements and limitations of the newly developed methods are discussed.