The Gothic tower of Freiburg Minster, Germany: analysis and repair

The filigree spire of the 116-m-high west tower of Freiburg Minster, Germany was completed around 1330 AD and is an architectural monument of the highest rank. At 45 m high and constructed using tracery throughout, the spire is the tallest of its kind ever built (Kayser, 2014). It has survived until the present without major damage or alteration. In 2010, after several flaws in the sandstone were detected, a detailed damage survey and a structural analysis were initiated. This paper provides a description of the construction of the spire, the damaged sections that were detected, the material tests and statical calculations undertaken and the implementation of repair measures. A three-dimensional digital model, showing all structural elements, historical alterations and damage, played a particularly important role in understanding the construction and the statical behaviour of the spire. Wind tunnel measurements and a series of material tests were conducted to ensure a realistic estimation of the stability under wind and seismic load. The analysis and the tests are still ongoing; nevertheless, some substantial results can already be presented.