Effect of creep on the stability of leaning towers

Safety assessment of historical towers is an important challenge in the preservation of the national and worldwide artistic herit-age. This paper illustrates a novel unified methodology developed to evaluate the key phenomena governing the geotechnically related collapse of towers: bearing capacity failure, due to lack of strength of the supporting soil, instability of equilibrium, due to lack of foundation stiffness and a rotational creep process. The analysis, introduced in the framework of a strain-hardening plasticity model for shallow footings, shows that rotational creep is the main cause of the progressive deterioration of stability for real towers. The proposed analytical process is applied to the history of the Santo Stefano bell tower in Venice. This example demonstrates not only the potential of the proposed methodology but also the importance of past rotational records for the pre-diction of the eventual response of such a tower.