Stability and strength analysis of leaning towers

Abstract

Many ancient towers are afflicted by stability problems. The evaluation of the overall safety of historical towers is one of the most important items in the preservation of the national and worldwide artistic heritage. This thesis is concerned with models appropriate for the stability assessment of tower foundations, which is related to: bearing capacity failure, due to lack of soil strength, and instability of equilibrium, due to lack of soil stiffness. Both of these hazards are tackled using a work-hardening plasticity model for surface footings. New developments have been introduced into the foundation modelling in relation to prediction of displacements and creep behaviour. These improvements have been used develop a methodology that can deal in a unified way with the two major failure mechanisms of such foundations. Finally, a new interpretation of the influence of creep on tower stability is explained. Such an analysis provides not only a complete framework within which both possible collapse mechanisms can be assessed but also a prediction of which of them is most likely to occur. The analysis, which has been developed in the form of a Mathematica notebook, and applied to the Pisa Tower and the Santo Stefano bell tower, can be also used to study the influence of foundation strengthening procedures.