CHAPTER 9 Simple checks to prevent the collapse of heavy historical structures and residual life prevision through a probabilistic model L. Binda, A. Anzani & E. Garavaglia Department of Structural Engineering, Politecnico di Milano, Milan, Italy. 9.1 Introduction A survey on approximately 60 Italian ancient towers, carried out to collect infor- mation on the most common symptoms of structural decay, particularly on the crack patterns, is described in this chapter. A simple procedure, aimed at achieving a pre-diagnosis of the tower structures and at identifying the cases where more detailed investigations are to be designed for defining the safety of the structure, is proposed, which local institutions might adopt. The vulnerability assessment of historic buildings towards the effects of persis- tent loading and the achievement of a reliable lifetime estimate on a deterministic basis is often very complex. Therefore, an attempt has been made at solving the problem through a probabilistic approach. 9.2 The safety of ancient towers Masonry towers are largely diffused in Italy and Europe and constitute an important part of our heritage which requires suitable protection. The problem of their safety, which became particularly evident after the collapses of monumental buildings mentioned in previous chapters [1, 2], has to be tackled by local public institutions, which not always can afford very costly diagnostic techniques. On the other hand, before large investments are made for monitoring and/or designing a repair intervention, a preliminary screening should be carried out to qualify the buildings depending on the estimated degree of damage. For this purpose, www.witpress.com, ISSN 1755-8336 (on-line) WIT Transactions on State of the Art in Science and Engineering, Vol 11, © 2007 WIT Press doi:10.2495/978-1-84564-057-6/09