Lunds Domkyrkas takkonstruktion

Sammanfattning: Lund Cathedral was built in Romanesque style when Lund became an archbishopric in the early 1100s. The roof structure of the church then had a flat wooden roof on the inside with room for tension rods so that the roof structure only affected the masonry walls with vertical loads. After a major fire in the 1200s, where the church was almost completely destroyed, cross vaults were built. This meant that the roof structure also generated horizontal forces on the masonries. The masonries that were not designed for this were heavily affected and a system of buttresses around the church was built to remedy the problem. Lund Cathedral now had a Gothic style. This Helgo Zettervall would change when in connection with a renovation he reconstructed the Romanesque style in the mid-1800s. Helgo Zettervall built a modern roof structure of steel over the arches. The design and function of this steel structure have been studied in this degree project. A sub-question is if this roof can help stand the horizontal forces after the buttresses have been removed. Drawings of the existing roof structure have been produced with geometry data from an on-going scanning as a basis. The scanning aims to create a virtual 3D model of the church. An analysis of Zettervall´s steel structure shows that it can be divided into four structural levels. The first-order structure consists of Polonceau-trusses, the second-order structure consists of trussed beams, the third of smaller beams and the fourth of wood beams. Each level has been studied separately, and a preliminary analysis has been performed with PointSketch, a FEM - program that is suitable for rapid, qualitative analysis of trusses. The principle of the whole structure is to carry in tension and compression instead of bending. Apart from the self-weight of the truss, only the third and fourth-order structures are subjected to a distributed load between the joints. A more detailed, quantitative, numerical analysis has been performed using CALFEM. The results show that the roof structure is considerably oversized in comparison with today's building codes, provided that the steel is of a quality that was typically used during the period in question. The roof structure has the potential to counteract a horizontal support displacement caused by movement in the walls. In order to determine if the roof can really keep the walls together, one must also examine if the walls can transfer the horizontal force from the vaults up to the roof structure tension rods.