Long-span Timber Roof Structure for the New Feyenoord Stadium

Abstract

Timber structures are experiencing a revelation in the build environment due to new technologies and production techniques. However, the longest spans created with timber structures still don't compete with the span widths of structures made of steel. This thesis provides a preliminary design for the long-span football stadium roof structure of The New Feyenoord stadium, which expends far beyond the existing maximum spans of timber structures. The aim is to provide insight in the feasibility of a long-span structure in timber. New Feyenoord stadium The city of Rotterdam is planning to built a new football stadium for the football club Feyenoord with a magnificent roof structure. This stadium is used to determine initial boundary conditions for the preliminary design in this thesis. A perfect bowl with an elegant flat, almost floating, roof that allows unobstructed viewing is desired. The playing field needs to be exposed to the weather conditions for the natural quality of the grass. The stadium will consist of three tiers with a total height of 40 metres, that need to be covered by a roof structure with a width of 205 metres, and length of 245 metres. Structural timber for a grand roof Timber has a high strength-to-weight ratio that is beneficial for long-span structures in which the self-weight of the structure is a significant part of the load. It has natural durability, a good performance in fire conditions, ease of workability, and a high ratio of prefabrication. The latter two result in an ease of construction and less human induced errors. Engineered wood products make it possible to create complex timber structures with more reliability than wood in its natural shape. The most promising are laminated veneer lumber (LVL) and glued laminated timber (Glulam), where LVL made of beech hardwood has the highest strength properties. Furthermore, new types of connections diminish the impact that connections traditionally have on the structural performance of timber structures. The enormous size of this stadium means that multiple connections are necessary due to dimensional restrictions for transport. Which reduces the amount of prefabrication. Structural systems for long-span stadium roofs Promising configurations for a long-span stadium roof structure are the single span, stress ribbon, shell roof system, and tension / compression ring. First, several existing stadium roof structures are presented to gain better insight on the possibilities of these systems. These stadiums are De Kuip, preliminary design of The New Feyenoord stadium by RHDHV, the Allianz Riviera stadium, the Wanda Metropolitano stadium, the Estadio Municipal, and the Tokyo National stadium. Initial designs are made for each structural system applicable to the case of the New Feyenoord stadium. These initial designs are explored on their structural behaviour and benefits for the case of the New Feyenoord stadium in combination with the material behaviour of timber. Structural forms for long-span timber structures Several structural forms are applied in long-span timber structures showing their applicability. These forms are the arch, box girder, truss, shell structure, space frame, and stress ribbon. This is explored by means of respective reference projects. These projects are the Multi-use Arena in Lisbon, Trade Fair Hall 11 in Frankfurt, the Anaklia-Ganmukhuri bridge in the Georgian Republic, the Maicasagi bridge in Nord-du-Quêbec, the geodesic domes in Brindisi, the Elephant House in Zurich, the Allianz-Riviera stadium in Nice, the Grandview Heights Aquatics Centre in Surrey, and the Essing bridge in Essing. These existing long-span timber structures mainly span only half of the required length of the New Feyenoord stadium. Possibility to create an efficient structural design for a long-span stadium timber roof structure After a rough assessment of the design concepts it is found that a combination between a tension / compression ring structure and a stress ribbon configuration shows the greatest potential for an efficient roof structure for the New Feyenoord stadium. Their are still many uncertainties for this type of structure for such a long span. There is no reference project and thus there can not be learned from mistakes. Also, the system is mathematically very complex because of its non-linear behaviour. Consequently, the structural system is modelled and verified in the parametric FEM environment of Grasshopper and Karamba3D. The found structural behaviour is verified by the strength verifications for timber structures. Tension / compression ring with radial stress ribbons The design consists of a triangular truss for the outer ring and a flat truss for the inner ring with radial stress ribbons in between. The structural design shows a feasible solution for the highest downward load, namely loads instigated by wind. The strength verification is performed on the maximum occurring force combination within a element group. Only the strength verification of shear stiffness in the bottom chord at the inside perimeter of the outer truss ring is not met. Which is a very localised effect and hence can be strengthened. Furthermore, the element groups of the rings show a undesirable utilisation distribution due to the non-circumferential perimeter of The New Feyenoord stadium. Large cross sections are required to provide stiffness to the entire structural system. The ribbons make use of their inherent bending stiffness to carry the loads in the long and short straight sides of the stadium. An elegant and stiff tensile force flow is found for the ribbons in the corners. At last, the designed connections for the ribbons which are attached to the timber fulfil the strength verifications. These connections consist of self-drilling dowels with slotted in steel plates, self-drilling screws, and glued in steel rods. Many steel fasteners are used to increase the efficiency factor of the joint. Suggested connections for the complex nodes in the ring trusses consist of slotted in steel plates with bolts and dowels, glued-in rods, and cast steel parts. The structural system is supported on roller bearings. The presented structural design only takes downward loading into account. Potential solutions for the severe upward loading are increasing the weight of the structural elements in the loaded area, tensile ties in the long and short side of the stadium, or tensile cables attached to the bottom side of the ribbons in the long and short side. An more in depth analysation of its stability against uplift forces and asymmetrical loading is needed to verify the proposed solutions. Recommendations are made to improve the design for The New Feyenoord stadium, for general possibilities for the chosen structural system, and for improvements and advice on the feasibility of special timber structures. It is concluded that a timber long-span stadium roof structure consisting of the chosen structural system shows potential to be a feasible solution for the New Feyenoord stadium. It will be a grand architectural statement that makes a stadium iconic, being the only timber tension / compression ring stress ribbon roof structure spanning with an exceptional distance.