Damage Phenomena in Historical Masonry

Research focus

The Peer review has evaluated this group as Excellent

During their service life historic masonry structures, often characterized by non-homogeneous loadbearing sections, can be subjected to decay due to aggressive environmental attacks, aging and damage due to long term heavy loads. Salt crystallisation behind the surface causes delamination and crumbling of the masonry components and is one of the most frequent causes of damage in many environments. Together with other synergetic aspects, time dependent behaviour has proved to be involved in collapses of historical buildings occurred during the last twenty years. The research is developed jointly by the Historic Construction and the Mechanics of Materials and Structure Sections of the Department. The group is directly involved in mechanical, non destructive, and chemico-physical testing activities, as well as in the development of new mathematical models and software programs to describe the mechanical behaviour of rocklike materials, including masonry. The focus of the research team over the past four years addressed the following items: Pseudo-creep and long term tests on ancient masonry allowed to observe the influence of the loading rate, to catch the limit between primary and secondary creep phase and the damage development associated to an increase of the stress level. An inverse relationship was shown between time to failure and secondary creep rate which can be used to predict the residual life. When failure is approached, an increase of volumetric deformation through fracturing and crack opening develops. - A constitutive law with damage, based on a rheological model, has been formulated for the interpretation of the experimental results. The model consists of a Kelvin block connected in series with a Maxwell block, accounting for primary and secondary creep; tertiary creep is accounted for by the introduction of damage variables, governing the decrease in the stiffness and creep parameters. Applications to structural analyses aimed at predicting the service life of monumental buildings were also carried out. - Experimental tests were performed on three-leaf stone masonry specimens, consisting of two external leaves made of regular stone units masonry, and an internal rubble filling. The tests differed in terms of interface geometry, stone nature of the specimens and loading conditions. A numerical model characterized by a damage tensor was developed to predict the nonlinear response of the specimens and describe the damage-induced anisotropy accompanying the cracking process. More research is required to accurately describe the post-peak behaviour, by avoiding mesh-dependency effects related with the strain-softening behaviour of the material. - According to a crystallisation test on wallettes set up by TNO (Delft), experimental data were recorded in both indoor and outdoor laboratories over a number of years forming the basis of the investigation on reliability of masonry materials in time. A method for measuring the continuous decay also in situ was proposed based on the use of a laser profilometer. The high randomness involved in decay phenomena suggested to study these processes with a probabilistic approach. A model was applied to interpret sets of experimental data collected on: (i) samples of masonry subjected to salt crystallization and tested in laboratory through accelerated aging tests; (ii) full-scale masonry models exposed in Milan to a polluted environment and subjected to capillary rise of water and salt solutions; (iii) samples of historic masonry subjected to laboratory creep and pseudo creep tests. The prediction of the time needed to reach a given level of damage is an important issue in planning strategies for the maintenance and repair of existing buildings.

Dipartimento di afferenza

Dipartimento di Ingegneria Strutturale (DIS)

Docenti afferenti

Full Professors
Luigia Binda
Alberto Taliercio
Alberto Fontana
Associate Professors
Anna Anzani
Elsa Garavaglia
Assistant Professors
Antonella Saisi
Cristina Tedeschi
Giuliana Cardani
Alberto Drei