Issue 47

V. Alecci et alii, Frattura ed Integrità Strutturale, 47 (2019) 161-167; DOI: 10.3221/IGF-ESIS.47.13 162 Plan irregularity is characterized by uneven plan distribution of earthquake-resistant structures or masses; vertical irregularity is due to mass, stiffness or strength discontinuities along the building height. Plan and vertical irregularities result in seismic over-demand into specific structures/elements which can lead to their early collapse, while not allowing the entire building structure to exploit its full seismic capacity. In fact, irregularity is one of the most frequent sources of severe damage during earthquake [1]. In 1985, during the earthquake of Mexico City, 42% of damaged or collapsed structures were corner buildings. Furthermore, many buildings failed in torsion due to asymmetric layout of masonry walls [2]. In the last decades, several studies on the design eccentricity were carried out [3-13]. Building irregularity - unknown concept in the classical and post-classical architecture - became a particularly widespread condition in postmodern and rational architecture. In fact, the famous "five points" of Le Corbusier’s architecture generated, for many decades, highly irregular buildings, characterized by free facades, soft stories with slim columns ( pilotis ), alternating to fully closed or/and opened floor plans, long strips of ribbon windows (and consequent short columns), etc. Otherwise, in the more remote past, wonderful "regular" buildings were built, based on obvious structural and constructive assumptions. In that period, architect and engineer coexisted and their contribution to the final project was perfectly integrated. In fact, in the past, a unique technician, combining creativity and structural knowledge, designed buildings with structural rigor but also expressing his own stylistic will. This condition, which allow architectural and structural issues to be perfectly integrated, played a crucial role for optimizing the final project. This kind of architecture/structure integration, desirable for the success of the project, is strictly necessary when designing in seismic zone, where the lack of architecture/structure integration can involve heavy losses in terms of human lives. In the last decades, the apparent rigor (more from an architectural than structural point of view, as we highlighted above) of postmodernist movements involved a sort of compositional anarchy that Rob Krier defined “the confusion in today’s art of building” and whose deconstructivist architecture is the maximum expression. Deconstructivism worked in pursuing architectural solutions based on the concept of “deconstruction” in place of “construction”, favoring non-rigid schemes, non-regular shapes and, more generally, avoiding geometric rules and classical canons of symmetry and regularity. The result of this philosophy is the growing proliferation of aesthetically spectacular buildings, with audacious shapes and impressive dimensions, supported by a clear propensity of contractors and funders to design and realize buildings outside the traditional and classical rules, gaining a “status symbol function” and getting a positive impact on their brand image. In this contest, it is not possible (and really desirable) to prevent the design of irregular buildings while it has to be pursued that designers know the consequences of their architectural design on a seismic and, more generally, structural field. The architectural designer would achieve a "seismic" training, with the aim at not forbidding his ambitions but at making him aware of the effects of his architectural choices. Figure 1 : Causes of structural irregularity. S TRUCTURAL IRREGULARITY he seismic vulnerabilities of a building depend on the morphological and structural condition and on the constructive details. The morphological irregularity is prodromal of structural irregularity and it is due to three main factors: economical, functional and aesthetical-formal (Fig. 1). An economical factor exists because, especially in densely populated urban areas, contractors try to fully exploit the available space in order to obtain the T