ON THE USE OF PUSHOVER ANALYSIS FOR EXISTING MASONRY BUILDINGS

SUMMARY The application of nonlinear static (pushover) procedures for the assessment of existing masonry buildings has been introduced into seismic codes (e.g. EC8, new Italian Seismic Code OPCM 3274/03), but it still includes several critical points in the implementation to real structures. The three-dimensional model of a masonry building can be obtained by assembling frame-type macro-element models of the walls and orthotropic membrane elements in order to represent the mechanical behaviour of flexible floors. This modelling, although very effective in representing the actual behaviour, does not allow to use common simplifications such as rigid floor motion. Moreover, a 3D pushover algorithm requires a predefined pattern of horizontal forces to be applied to the structure and, keeping constant the relative force ratios, the horizontal displacement of a control node is incremented. A new displacement-based algorithm for the adaptive pushover analysis of masonry walls and buildings is presented: the load pattern, in this case, is directly derived, step-by-step, by the actual deformed shape evaluated during the pushover analysis. The proposed procedure seems to be very powerful for in-plane analyses of walls, whilst it requires some corrections in order to be applied to three-dimensional masonry buildings.