Assessment of long-term stability of masonry structures: experimental research, non-destructive techniques and theoretical modelling. E. Verstrynge 1 , D. Van Gemert 1 , L. Schueremans 1 , M.A.N. Hendriks 2 1 Department of Civil Engineering, KULeuven, Belgium; 2 Faculty of Civil Engineering and Geosciences, TUDelft, the Netherlands Introduction The presented PhD research focuses on time-dependent deformations in masonry, which is subjected to high sustained stress levels. The damage accumulations which occur during creep deformations are usually within limits, but at high stress levels, these damage accumulations can result into partial or total collapse of the historical monument. Well known examples of historical monuments which collapsed due to creep damage accumulation are the Civic Tower of Pavia in Italy (1989), the Church of Kerksken in Belgium (1990), the St. Magdalena Church in Goch, Germany (1992), the Cathedral of Noto in Italy (1996) /1/, the Bell tower of the Sint-Willibrordus Church of Meldert in Belgium (2006) and the Medieval Maagden tower of Zichem in Belgium (2006) /2, 3/. These phenomena generally occur in tall constructions, such as bell towers or medieval city towers, as rather high stress levels are present at the base of these constructions due to the dead weight. Performing creep tests on masonry and modelling this time-dependent behaviour is rather complex, as masonry is very heterogeneous. Firstly, it contains different components (bricks and mortar) with different material properties and complex interface behaviour. Secondly, historical masonry often consists of multiple layers with different qualities (regular stone layers, rubble infill) and visible or invisible cracks, voids and cavities. The theoretical approach, used in the presented research, assumes isotropic material behaviour below certain stress limits and orthotropic damage accumulation at higher stress levels. In this paper, the experimental research, performed to obtain input parameter values for the model, will be described. Subsequently, a short overview of the data acquisition during the tests, including strain and acoustic emission monitoring, is presented. Then, the theoretical model will be presented and applied for a range of simulations. Finally, the applicability of the presented framework to be used for probabilistic analysis is indicated.