The spire of Freiburg Minster: Load assumptions and application for structural analysis

The spire of the 116 m-high west tower of Freiburg Minster can be dated to ca. 1300 AD and is not only the symbol of the city in southwestern Germany but also an architectural monument of highest rank. With its 45 m, the spire is the tallest ever built of its kind and still contains three-quarters of the original sandstone. In 2005, stonemasons in Freiburg detected a heavy fragment of sandstone on the viewing platform which had dropped overnight form the spire. At the end of 2009, after several systematic damages were identified, a structural and static analysis was initiated. Realistic load assumptions are an essential basis to evaluate causes of damages and to develop an accurate repair concept. The following report provides - after a short description of the construction and damage pattern - aspects of these approaches and their application with calculation models. Self-weight could be estimated by a stone-accurate, three-dimensional solid model, whereas wind forces were determined in extensive channel tests. An evaluation of these tests is being compared with present literature and building codes. Due to the inherent bearing behavior the loads are applied in a simplified way.