A review on acoustic emission monitoring for damage detection in masonry structures

Acoustic emission monitoring is widely used for damage detection in materials research and for site monitoring. Its use for masonry structures is however challenging due to the highly heterogenic nature of masonry and rapid signal attenuation. However, the non-invasive nature and high sensitivity of the technique also provide interesting opportunities, especially for historical masonry structures, to locate damage, identify severity of damage and rate of deterioration. Aim of this paper is to provide an extensive literature review on the application of the acoustic emission technique for masonry structures, addressing specific challenges and recent findings. AE-based methods for damage assessment in masonry are discussed in view of monitoring approaches, wave propagation, source location and crack development under static, fatigue and creep loading. Site applications are discussed for identifying crack location and crack propagation in historical masonry towers, buildings and masonry arch bridges. The paper concludes with future challenges identified in this research field

Structural Analysis of Masonry Historical Constructions. Classical and Advanced Approaches

A review of methods applicable to the study of masonry historical construction, encompassing both classical and advanced ones, is presented. Firstly, the paper offers a discussion on the main challenges posed by historical structures and the desirable conditions that approaches oriented to the modeling and analysis of this type of structures should accomplish. Secondly, the main available methods which are actually used for study masonry historical structures are referred to and discussed. The main available strategies, including limit analysis, simplified methods, FEM macro- or micro-modeling and discrete element methods (DEM) are considered with regard to their realism, computer efficiency, data availability and real applicability to large structures. A set of final considerations are offered on the real possibility of carrying out realistic analysis of complex historic masonry structures. In spite of the modern developments, the study of historical buildings is still facing significant difficulties linked to computational effort, possibility of input data acquisition and limited realism of methods

The important role of diagnostics for the structural recovery of historic buildings

Diagnostic tests represent a fundamental phase of knowledge for historical masonry buildings. The correct design of structural recovery and seismic improvement work must be based on the results of the preliminary tests, for a better knowledge of the vulnerabilities and the mechanical characteristics of ancient masonry structures. The Italian technical codes have given great importance to the level of knowledge reached on the existing buildings, promoting the investment of diagnostics as a fundamental phase of the design work. Two case studies of multidisciplinary diagnostic tests, carried out on monumental buildings, are described for the preliminary evaluation of the quantitative and qualitative characteristics of the masonry structures. In both cases the tests allowed to better understand the vulnerabilities of the masonry section and to design the most appropriate strengthening work. The interpretation of the results coming from tests of different typologies allowed to investigate in depth the hidden peculiarities of the historical masonry structures

Discrete element modeling of masonry structures: Validation and application

The failure mechanism and maximum collapse load of masonry structures may change significantly under static and dynamic excitations depending on their internal arrangement and material properties. Hence, it is important to understand correctly the nonlinear behavior of masonry structures in order to adequately assess their safety and propose efficient strengthening measures, especially for historical constructions. The discrete element method (DEM) can play an important role in these studies. This paper discusses possible collapse mechanisms and provides a set of parametric analyses by considering the influence of material properties and cross section morphologies on the out of plane strength of masonry walls. Detailed modeling of masonry structures may affect their mechanical strength and displacement capacity. In particular, the structural behavior of stacked and rubble masonry walls, portal frames, simple combinations of masonry piers and arches, and a real structure is discussed using DEM. It is further demonstrated that this structural analysis tool allows obtaining excellent results in the description of the nonlinear behavior of masonry structures

Stochastic vulnerability assessment of masonry structures: Concepts, modeling and restoration aspects

A methodology aiming to predict the vulnerability of masonry structures under seismic action is presented herein. Masonry structures, among which many are cultural heritage assets, present high vulnerability under earthquake. Reliable simulations of their response to seismic stresses are exceedingly difficult because of the complexity of the structural system and the anisotropic and brittle behavior of the masonry materials. Furthermore, the majority of the parameters involved in the problem such as the masonry material mechanical characteristics and earthquake loading characteristics have a stochastic-probabilistic nature. Within this framework, a detailed analytical methodological approach for assessing the seismic vulnerability of masonry historical and monumental structures is presented, taking into account the probabilistic nature of the input parameters by means of analytically determining fragility curves. The emerged methodology is presented in detail through application on theoretical and built cultural heritage real masonry structures

Consolidation methods of Romanian historical building with composite materials

Timisoara is a growing city in the western part of Romania, in a seismic area, with a lot of masonry buildings with historical and cultural value, with interesting structural elements such as vaults, arches, slabs, walls, that were affected by earthquakes, subsidence of foundations, negative human actions or lack of interventions. Masonry historical structures in Banat seismic area present particular failure mechanisms, so there is a need for new, modern, fast, easy-to-apply and reversible consolidation methods. With this type of methods is possible to assure the local and global resistance, ductility, stability and rigidity for historical buildings. This article shows the consolidation methods that were applied on the buildings Sf. Gheorghe 3 and 4, in the historical centre of Timisoara, on masonry structures with historical value. The solutions that were applied are using new, innovative fibre-reinforced composite materials, in order to repair the existing damages and prevent further ones. The consolidation solutions with these new composite materials reduce the buildings vulnerability and present the advantage of being fast and easy to be executed

New Frontiers on Seismic Modeling of Masonry Structures

An accurate evaluation of the non-linear behavior of masonry structural elements in existing buildings still represents a complex issue that rigorously requires non-linear finite element strategies difficult to apply to real large structures. Nevertheless, for the static and seismic assessment of existing structures, involving the contribution of masonry materials, engineers need reliable and efficient numerical tools, whose complexity and computational demand should be suitable for practical purposes. For these reasons, the formulation and the validation of simplified numerical strategies represent a very important issue in masonry computational research. In this paper, an innovative macroelement approach, developed by the authors in the last decade, is presented. The proposed macroelement formulation is based on different, plane and spatial, macroelements for the simulation of both the in-plane and out-of-plane behavior of masonry structures also in presence of masonry elements with curved geometry. The mechanical response of the adopted macroelement is governed by non-linear zero-thickness interfaces, whose calibration follows a straightforward fiber discretization, and the non-linear internal shear deformability is ruled by equivalence with a corresponding geometrically consistent homogenized medium. The approach can be considered as "parsimonious" since the kinematics of the adopted elements is controlled by very few degrees of freedom, if compared to a corresponding discretization performed by using non-linear finite element method strategies. This innovative discrete element strategy has been implemented in two user-oriented software codes 3DMacro (Caliò et al., 2012b) and HiStrA (Historical Structures Analysis) (Caliò et al., 2015), which simplify the modeling of buildings and historical structures by means of several wizard generation tools and input/output facilities. The proposed approach, that represents a powerful tool for the structural assessment of structures in which the masonry plays a key role, is here validated against experimental results involving typical masonry monumental substructural elements and numerical results involving real-scale structures

Application of Acoustic Emission Technique in the Monitoring of Masonry Structures

The application of acoustic emission (AE) technique in monitoring the safe condition is a useful technique in steel and concrete structures, whereas its application is restrained in masonry structures due to the layered property. Qualitative and quantitative analyses were investigated in this research to improve the AE application in masonry structures. For quantitative analysis, an improved localization method is proposed to give more reliable crack localization results. In the proposed method, the parameter ξ on the behavior of inhomogeneity of the monitored structure could minimize the unavoidable propagation delay caused by the layers in the masonry structure. The rest results approved the reliability of the proposed method in masonry structures. For qualitative analysis, the parameter analysis, including the cumulative AE event, frequency distribution, time-scaling exponent, and b-value, was adopted to monitor one historical church and was approved to be useful

Challenges and perspectives for the protection of masonry structures in historic centers: the role of innovative materials and techniques

Lessons learned from natural events which caused severe damage to existing constructions have repeatedly shown the high vulnerability of historically important masonry, often worsened by inaccurate or dubious applications of modern or innovative interventions. Especially in the field of new technologies and materials applied to historical assets, experimental validation integrated at multi-disciplinary level is essential, to implement correct choices able to balance the respect of tradition and the requirements of innovation. The common objective is the transmission of educational values through the conservation of the historical identity of constructions which have survived over time and are still functional today. Planning agreements among academic and industrial research, management and governing bodies constitute preconditions for selecting consistent strategies for the protection of the built environment. However, the effects of technical advances and trends on historical assets should be carefully evaluated when influencing common practices, before recommendations, standards or execution protocols based on sufficiently long-lasting experience are available. This paper discusses a series of issues involved in the complex process of methodological and operative options currently feasible in the field of historical masonry structures. It also focuses on the progressive role of composite materials and the consequent implications on the implementation of preservation criteria