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.