Analytical modelling of the creep-rotation rate for leaning towers

The role of geotechnical engineering in the preservation of historical towers is particularly relevant, not only for the definition of possible failure mechanisms of the soil-foundation system, but also for the prediction of the rotational rate of the structure with time (creep rate). This paper describes how the rotational creep process, based on a well-known creep model for a material volume element, can be extended to the “macro-element” model through a formal analogy, and thereby formulated in terms of generalised variables. The model needs to be calibrated against displacement-time data of real towers; much effort has therefore been devoted to collecting rotation records of historical towers. In this contribution, the creep rotational rate prediction has been developed for one of them: the Asinelli Tower in Bologna. The analysis shows that a reliable risk assessment of these structures is possible, provided that the evolution of the tower rotation is available accompanied by accurate monitoring of the current tilting rate. The use of modern monitoring systems is strongly recommended.