Modelling of the long-term behaviour of historical masonry towers

In March 1989 the Civic Tower in Pavia suddenly collapsed, killing four people and destroying part of the adjacent Cathedral, along with some of the buildings overlooking the surrounding square. No special event, to which the collapse might be attributed, was monitored in the preceding months. Also, no evidence of significant soil settlements was found. The results of a number of accelerated creep tests performed on samples extracted from the debris, along with finite element (FE) analyses of the tower, indicated that a possible origin for the collapse was the cumulation of creep-induced damage in time. Indeed, under sustained loading some of the specimens failed at stress levels comparable to the maximum values yielded by the numerical analyses. This remark was the starting point for an extensive research programme aiming at (1) characterizing the creep behaviour of ancient masonry; (2) developing theoretical models suitable to the description of creep evolution and creep-induced damage; and, finally, (3) assessing the safety of ancient masonry buildings subjected to heavy persistent loads through nonlinear structural analyses. In this chapter, a theoretical model developed by the authors is first described; the procedure employed to identify the model parameters from results of accelerated creep tests is also outlined. Then, the numerical results of structural analyses of two masonry towers are presented, with particular emphasis on the description of the damage evolution in time, up to the predicted creep time to failure for the building. Finally, the obtained results are critically reviewed, and future improvements for the theoretical model are pointed out