Josipa Bošnjak1, Michael Stegmaier1, and Friedrich Grüner1
1)  Materials Testing Institute, University of Stuttgart
Pfaffenwaldring 4c, 70569 Stuttgart, Germany
e-mail: {josipa.bosnjak, michael.stegmaier, friedrich.gruener};

Keywords: Experimental investigations; natural stone masonry; pre-damage; compressive behavior

Abstract. The 800-years old “Blauer Turm” (eng. Blue Tower) in Bad Wimpfen, Germany, is one of the best preserved structures from the medieval Staufen-era. During its lifetime it withstood multiple fire accidents and natural hazards. These resulted in several major rehabilitations, whereby the top dome was generally adapted to the then prevalent architecture. The last major adaptation resulted in a change of load distribution, since the new heavy gothic dome is mainly supported by the outer leaf of the masonry. In combination with subsequent fire accidents the tower developed severe cracking along its 25 m high walls. Rehabilitation in 1970-ies further aggravated the situation, since a stiff mortar was used. In order to assess the load-bearing capacity of the tower, an extensive experimental campaign was undertaken. The tests were performed on half-scale masonry elements built using Triassic Muschelkalk similar to one found in the Blue Tower and the mortar was designed to correspond to the measured in-situ properties. The cracked stones were simulated by cutting the stones used in the test specimens. Six test series were performed to evaluate the effect of existing damage on the masonry performance. This paper reports and discusses the experimental findings from these tests.