Probabilistic Seismic Risk Assessment of Masonry

A huge amount of historical as well as modern structures is made of masonry which is usually notorious to have a low earthquake resistance limited by low shear strength and lowl ductility. In order to improve shear capacity and ductility, vertical local prestressing is considered. Static cyclic tests have shown the suitability of this method. A detailed investigation of the dynamic behaviour is demandable before using the strengthening method against earthquake action. The large quantity of necessary experimental tests is very expensive. This contribution presents possibilities, based on probabilistic numerical methods, to investigate the usefulness of vertical prestressing with particular emphasis on the dynamic behaviour as well as to estimate the risk. The work uses a risk based design, which accounts also for several damage stages, in order to assess the benefit of prestressing more in detail. For the transient earthquake simulations a macro modelling method by means of the material model of Lagomarsino and Gambarotta is used in combination with the finite element program ANSYS . This allows a prediction of damage via special damage parameters for units and mortar separately. Several detected factors that influence masonry behaviour and numerical results are investigated and discussed. The probabilities of damages are estimated by means of probabilistic methods. Thereto, Latin Hypercube sampling is applied by means of the advanced program optiSLang ® in combination with ANSYS, in order to carry out dynamic probabilistic analyses. With the calculated damage probabilities, the risks are estimated and the benefits of vertical prestressing in case of seismic action are compared.