Editorial - New Trends in the Numerical Analysis of Masonry Structures

The Special Issue of The Open Civil Engineering Journal entitled “New trends in the numerical analysis of masonry structures” provides an insight into the most up-to-date nu-merical techniques used at academic and professional level to perform advanced structuralanalyses on masonry struc-tures. Masonry is a building material that has been used for more than ten thousand years. In many countries, masonry structures still amount to 30–50%of the new housing devel-opments. Also, most structures built before the 19th century and still surviving are built with masonry. Masonry is usu-ally described as a heterogeneous material formed by units and joints, with or without mortar, and different bond ar-rangements. Units are such as bricks, blocks, ashlars, adobes, irregular stones and others. Mortar can be clay, bitumen, chalk, lime/cement based mortar, glue or other. The almost infinite possible combinations generated by the geometry, nature and arrangement of units as well as the characteristics of mortars raise doubts about the accuracy of the term “ma-sonry”. Still, much information can be gained from the study of regular masonry structures, in which a periodic repetition of the microstructure occurs due to a constant arrangement of the units (or constant bond). The difficulties in performing advanced testing and pro-viding sufficiently general numerical models for this kind of structures are basically due to the innumerable variations of masonry typologies, the large scatter of in situ material prop-erties and the impossibility of reproducing all in a specimen. Therefore, most of the advanced numerical research carried out in the last decades concentrated in brick / block masonry and its relevance for design. Accurate modelling requires a comprehensive experimental description of the material, which seems mostly available at the present state of knowl-edge. From a numerical point of view, masonry behaviour is quite complex to model, exhibiting non-linearity very early during the loading process, with softening in both tension and compression, low ductility and differed deformations under sustained loads. In addition, masonry is the result of the assemblage of bricks or stones, where mortar is laid, with common geometric irregularities adding further complexity to the problem. The special issue collects ninepapers from experts in the field, including contributions of researchers from six differ-ent countries (Czech Republic, Iran, Italy, Portugal, Spain, Switzerland), either devoted to the utilization of non-standard numerical models for case-studies or presenting new approaches for the interpretation of masonry behaviour in presence of different kinds ofnon-linearity. The effort is always to put the knowledge beyond the existing state-of-the art. Karbassi and Lestuzzi [1]present a fragility analysis per-formed on unreinforced masonry buildings, conducted by means of the so called Applied Element Method (AEM), to define fragility curves of typical masonry buildings which may be regarded as representative of building classes. A se-ries of nonlinear dynamic analyses using AEM are per-formed for a 6-storey stone masonry and a 4-storey brick masonry building using more than 50 ground motion re-cords. The distribution of the structural responses and inter-storey drifts are finally used to develop spectral-based fragil-ity curves for the five European Macro-seismic Scale dam-age grades. In the second paper, Milani et al. [2]perform a detailed non-linear analysis (both pushover and limit analysis) on the San Pietro di Coppito bell tower in L’Aquila, Italy, trying to have an insight into the causes of the collapse occurred dur-ing the devastating 2009 earthquake. Sykora et al. [2]review several topics related to the ho-mogenization of transport processes occurring in historical masonry structures. Particular attention is paid to variations of temperature and moisture fields, whose contribution to structural damage usually far exceeds the effects of me-chanical loadings. The concept of Statistically Equivalent Periodic Unit Cell (SEPUC) is reviewed and utilized to deal with historic masonry and random patterns. Accepting SEPUC as a reliable representative volume element, a Fast Fourier Transform to both the SEPUC and large binary sam-ples of real masonry is used to tackle effective thermal con-ductivities problems. Fully coupled non-stationary heat and moisture transport problems are addressed next in the framework of a two-scale first-order homogenization, with emphases on the application of boundary and initial condi-tions at the meso-scale.