Issue 51

M.G. Masciotta et alii, Frattura ed Integrità Strutturale, 51 (2020) 423-441; DOI: 10.3221/IGF-ESIS.51.31 424 relevant aspects about the effects of settlement-induced cracks on the modal blueprints of masonry arches. K EYWORDS . Masonry arch settlements; Dynamic behavior; Modal analysis; Linear perturbation; Model updating; Nonlinear elasticity. and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION asonry arches are among the most used structural systems in many worldwide historical buildings and bridges. The first arches appeared as early as the second millennium B.C. in Mesopotamian architecture. The great ancient civilizations, like the Egyptians, the Babylonians and the Assyrians, knew about the arch and began to exploit it as a basic structural system to span large areas and enclose spaces. However, the systematic use of masonry arches only started with the ancient Romans, who learned the arch from the Etruscans, refined it and tapped its full potential for above ground buildings and bridges, erecting arch structures throughout the empire [1]. Many of those structures have survived almost unimpaired for centuries and are still in use today. Indeed, the nature of the masonry material combined with the resistant virtues of the arch form makes these structural systems durable and surprisingly resistant to high compression loads. Yet, during their lifespan, masonry arches are exposed to several threats that can adversely affect their bearing capacity and stability, such as structural damages due to horizontal actions or excessive vertical loads originated by the increased traffic demand, materials degradation and springing settlements. In this regard, many research works have been devoted in the last years to investigating the mechanics of masonry arches up to failure for different loading conditions [2-7] and arch shapes [8] as well as considering the influence of geometrical irregularities [9, 10], materials nonlinearity [11], arch-fill interaction [11, 12] and localized damages [13, 14]. Apart from a few exceptions, a large amount of this literature focused on simplified uni- or bi-dimensional problems with the aim of shedding light on the collapse mechanisms of masonry arches to evaluate the minimum load multipliers and ultimate load carrying capacity. To this end, the most common approaches used by the international community working on these topics are the limit analysis and the finite element method, or a combination of both [15]. However, despite the great quantity of research devoted to the static and dynamic analysis of masonry arches, not all the aspects related to its structural behavior have been completely explored. For instance, studies on the actual response of arched structures subjected to springing settlements are still limited and mainly focused on the evaluation/prediction of the most probable failure modes for a variety of different semicircular or pointed arch geometries and settlement mechanisms [16-20], through analytical and/or advanced numerical procedures. Much less attention is paid to segmental masonry arches, which are indeed more prone to lateral movements of the abutments because of the higher horizontal thrust deriving from their shape (the flatter the arch, the greater the thrust). Furthermore, to the authors’ knowledge, no study on the effects of settlement-induced cracks on the dynamic blueprints of masonry arches has been ever addressed. As settlements represent one of the main causes of collapse in arched structures, the correct dynamic characterization of the nonlinear behavior of masonry arches undergoing this type of phenomena is fundamental to timely detect the stiffness degradation and consequent strength reduction resulting from the gradual progression of support displacements, thereby preventing local damages and unexpected failures. Indeed, the sensitivity of dynamic properties to structural damage is widely recognized within the scientific community and many works have demonstrated the importance of tracking such features to monitor the structural health and identify the onset of damage at the earliest possible stage, even when not yet detectable by visual inspections [21- 24]. In light of the above considerations, the present contribution aims at thoroughly investigating the three-dimensional dynamic behavior of a segmental masonry arch under increasing horizontal settlements of one support. To rigorously address this problem, the adopted strategy combines both experimental and numerical methods: the former for the real- time simulation of the studied phenomenon and the direct estimation of damage-sensitive dynamic features for the calibration of the subsequent numerical model; the latter for the correct reproduction of the actual dynamic behavior of the masonry arch taking into account the non-linear behavior of the materials and the effects that settlement-induced cracks have on the dynamic properties of masonry structures. Accordingly, the article is organized in two main parts: the first one is dedicated to the experimental analysis of the masonry arch and the second one focuses on the numerical simulations. The experimental investigations have been carried out in the Structural Laboratory of the University of Minho in Guimarães (Portugal) and the results obtained from the tests have been exploited as reference information for the subsequent modal analyses performed in the context of nonlinear elasticity through a non-commercial software developed by the Mechanics of Materials and Structures Laboratory of ISTI-CNR (Italy), namely the NOSA-ITACA code. The cross-validation with the M