Rob Nijsse

Case-Study on the Application of Precast Double-Curved Concrete Elements for the Green Planet Shell Structure

Double-curved structures in general, and monolithic concrete shell structures more specifically, can transfer forces very efficiently. As a result, the thickness-to-span ratio can be very low, which, material-wise, can lead to a very economical design. However, the construction of shell structures is very labour-intensive and comes with high formwork costs and shells in modern building practice are rarely constructed. Concrete shell structures can be cast in-situ making use of temporary formwork and falsework, but they can be (partially) prefabricated as well, like the Palazzetto dello Sport in Rome. Although precasting is an effective technology for the repetitive production of concrete elements, for double-curved structures, having a large variety of shapes, the advantages of precasting seem to diminish quickly as a result of high formwork costs. Another disadvantage of precasting shell elements obviously seems to be the complexity of the required connections. For shell structures, the loss of stiffness of the connections might even lead to a crucial reduction of the buckling stability. A combination of both building methods, the prefabrication of the supportive structure and a finish with a cast in-situ layer, solves this before-mentioned issues and the advantages of both methods are combined: reduction of the complexity of the connections with an in-situ cast concrete layer and integration of the supportive structure in the design for a more cost-efficient erection. This paper describes the study of an innovative, partially precast, alternative solution for the construction of shell structures, and specifically addresses the influence of connections between precast elements on the overall shell behaviour. The Green Planet gas station along the A32 highway in The Netherlands was selected as a design case for such a building method.