An innovative image processing-based framework for the numerical modelling of cracked masonry structures

A vital aspect when modelling the mechanical behaviour of existing masonry structures is the accuracy in which the geometry of the real structure is transferred in the numerical model. Commonly, the geometry of masonry is captured with traditional techniques (e.g. visual inspection and manual surveying methods), which are labour intensive and error-prone. Over the last ten years, advances in photogrammetry and image processing have started to change the building industry since it is possible to capture rapidly and remotely digital records of objects and features. Although limited work exists in detecting distinct features from masonry structures, up to now there is no automated procedure leading from image-based recording to their numerical modelling. To address this, an innovative framework, based on image-processing, has been developed that automatically extracts geometrical features from masonry structures (i.e. masonry units, mortar, existing cracks and pathologies, etc.) and generate the geometry for their advanced numerical modelling. The proposed watershed-based algorithm initially deconstructs the features of the segmentation, then reconstructs them in the form of shared vertices and edges, and finally converts them to scalable polylines. The polylines extracted are simplified using a contour generalisation procedure. The geometry of the masonry elements is further modified to facilitate the transition to a numerical modelling environment. The proposed framework is tested by comparing the numerical analysis results of an undamaged and a damaged masonry structures, using models generated through manual and the proposed algorithmic approaches. Although the methodology is demonstrated here for use in discrete element modelling, it can be applied to other computational approaches based on the simplified and detailed micro-modelling approach for evaluating the structural behaviour of masonry structures

Design of a smart lime mortar with conductive micro and nano fillers for structural health monitoring

Structural health monitoring is an essential tool for assessing the performance of buildings and infrastructure, especially after critical events or the application of structural interventions. When dealing with architectural heritage structures, both structural health monitoring instrumentation and intervention materials need to be as inconspicuous and unintrusive as possible, both in terms of mechanical compatibility and aesthetics. Therefore, the design of smart sensors based on construction materials used in conservation engineering promises to provide an acceptable integrated structural health monitoring and upgrading solution for historic structures. In this paper an experimental investigation of smart intervention materials for historic masonry structures is presented. The materials consisted of natural hydraulic lime mortars modified through the inclusion of electrically conductive micro- and nanofillers: graphite, carbon nanotubes and carbon microfibres. The fillers provide multifunctionality to the matrix material based on an enhancement of its piezoresistive characteristics. Further, they result in an improvement of the mechanical properties of the intervention material without compromising its mechanical and chemical compatibility with the original structure. The resulting materials were evaluated based on mechanical property improvement, piezoresistivity enhancement and ease of production

Quantification of damage evolution in masonry walls subjected to induced seismicity

This paper aims to quantify the evolution of damage in masonry walls under induced seismicity. A damage index equation, which is a function of the evolution of shear slippage and opening of the mortar joints, as well as of the drift ratio of masonry walls, was proposed herein. Initially, a dataset of experimental tests from in-plane quasi-static and cyclic tests on masonry walls was considered. The experimentally obtained crack patterns were investigated and their correlation with damage propagation was studied. Using a software based on the Distinct Element Method, a numerical model was developed and validated against full-scale experimental tests obtained from the literature. Wall panels representing common typologies of house façades of unreinforced masonry buildings in Northern Europe i.e. near the Groningen gas field in the Netherlands, were numerically investigated. The accumulated damage within the seismic response of the masonry walls was investigated by means of representative harmonic load excitations and an incremental dynamic analysis based on induced seismicity records from Groningen region. The ability of this index to capture different damage situations is demonstrated. The proposed methodology could also be applied to quantify damage and accumulation in masonry during strong earthquakes and aftershocks too

Experimental investigation on the shear behaviour of the brickwork-backfill interface in masonry arch bridges

This paper presents the results from an experimental campaign to characterise the shear behaviour of the brickwork-backfill interaction in masonry arch bridges. Two representative backfill materials found in real masonry arch bridges (compacted crushed limestone and clay) were sheared against brickwork masonry specimens with two different bond patterns (a soldier course bond and an English bond). The results demonstrated that the interface shear behaviour between masonry and backfill was different from the internal shear behaviour of backfill materials. When compacted crushed limestone was adopted as the backfill material, the ratio between the masonry-limestone interface friction angle (φi) and the internal friction angle (φ) of limestone was determined to lie within the range from 0.70 to 0.75. However, when clay was used as backfill material, the φi/φ ratio was much lower, and of the order of 0.51 to 0.52 under the assumption of zero-cohesion at the interface, or 0.35 to 0.39 if interface cohesion was considered. Moreover, the properties of the backfill material had a significant influence on the interface shear behaviour, whereas the effects of brickwork bonding pattern were marginal. This study provides valuable insight into the identification of brickwork-backfill interface parameters for the numerical analysis of masonry arch bridges

Soil Settlement and Uplift Damage to Architectural Heritage Structures in Belgium: Country-Scale Results from an InSAR-Based Analysis

Soil movement may be induced by a wide variety of natural and anthropogenic causes, which are detectable in the local scale, but may influence the movement of the soil over vast geographical expanses. Space borne interferometric synthetic aperture radar (InSAR) measurements of ground movement provide a method for the remote sensing of soil settlement and uplift over wide geographic areas. Based on this settlement and uplift evaluation, the assessment of the potential damage to architectural heritage structures is possible. In this paper an interdisciplinary monitoring and analysis method is presented that processes satellite, cadastral, patrimonial and building geometry data, used for the calculation of settlement and uplift damage to architectural heritage structures in Belgium. It uses processed InSAR data for the determination of the soil movement profile around each case study, of which the typology is determined from patrimonial information databases and the geometry is calculated from digital elevation models. The impact on the historic structures is calculated from the determined soil movement profile based on various soilstructure interaction models for buildings. The resulting damage is presented in terms of a numerical index illustrating its severity according to different criteria. In this way the potential soil movement damage is quantified in a large number of buildings in an easily interpretable and user-friendly fashion. The processing of InSAR data collected over the previous 3 decades allows the determination of the progress of settlement- and uplift-induced damage in this time period. With the integration of newly acquired and more accurate data, the methodology will continue to produce results in the coming years, both for the evaluation of soil settlement and uplift in Belgium as for introducing related damage risk data for existing architectural heritage buildings. Results of the analysis chain are presented in terms of potential current damage for selected areas and buildings

Macro-Modelling of Orthotropic Damage in Masonry: Combining Micro-Mechanics and Continuum FE Analysis

Due to the complex interaction of its constituent materials, arising from their brittleness and staggered geometric arrangement, masonry as a composite material is often characterised by pronounced orthotropy, both in elasticity and strength [20]. This orthotropy is particularly important in the study of earthquake induced damage and collapse mechanisms of large masonry structural elements [23]. Accurate prediction of the force capacity of masonry elements, therefore, relies not only on the careful mechanical character- isation of its comprising materials, but also on modelling their interaction at the material scale [32]. Finite element (FE) analysis of masonry structures can assume different levels of detail for the representation of the mechanical features and potential failure modes of the material. For example, in a macro-modelling approach the material may be treated as an isotropic [7] or orthotropic [26] continuum. The large number of material parameters in need of characterisation for the execution of these simulations has led to the development of experimental frameworks [12], empirical approaches [11] and numerically-driven calibration methods [16] for determining these parameters. While both approaches have been successfully used for nonlinear anal- ysis [8,21,28], it is the latter that provides a truer representation of the mechanical properties of masonry. Continuum modelling can be very attractive due to the geometrical simplicity of the resulting models and the reduced computational costs, especially for modelling large structures. However, orthotropic models must still rely on complex experiments, well-founded assumptions or ancillary computations for actually determining the orthotropic properties of the continuum. Stemming from the inherent attractiveness of continuum modelling and the need for deriving macroscopic orthotropy from ma- terials that are themselves often isotropic, constitutive approaches have been developed for taking into account the interaction of potential failure modes in regularly bonded masonry through a phenomenological or analytical rather than a detailed micro- mechanical approach [27,29]. While very promising, this approach does not directly provide comprehensive information on the stresses and strains in the material components comprising the masonry composite.Peer ReviewedPostprint (published version

Micro-mechanical homogenisation of three-leaf masonry walls under compression

Three-leaf masonry panels are typically composed of external leaves of irregularly bonded units and a rouble infill. The complexity of the response of these structures to mechanical loading arises from: a) the interaction of the leaves and b) the irregularity of the bond pattern of the outer leaves. This complexity makes analytical and computational modelling of these structures difficult and costly, respectively. This paper proposes a computational approach for the calculation of the mechanical properties of the three-leaf masonry from the properties of its constituent materials and its geometry. Using micro-mechanical analysis approaches applied in composite materials and accounting for the interaction of the leaves through a simple analytical approach, the homogenised elastic stiffness and strength of a representative volume element of three-leaf masonry can be calculated with very low computational cost. The analysis method is validated against experimental results from the literature. It is found that the proposed model provides accurate results for a relatively wide range of case studies. These results are expanded upon through a sensitivity study, highlighting the most important material and geometric parameters influencing the predicted compressive strength of three-leaf masonry walls

Micromechanical Homogenisation of Steel Bars in Reinforced Concrete for Damage Analysis

A homogenisation scheme based on inclusion modelling is coupled with constitutive laws for damage and implemented in a finite element model for the simulation of concrete and reinforcement bar damage in reinforced concrete structures. The scheme is employed for simulating the behaviour of evenly distributed reinforcement and adapted for the simulation of zones with concentrated reinforcement in structural members. The model is validated against experimental tests from the literature carried out on reinforced concrete members subjected to bending and direct tension. The model captures the main characteristics of the behaviour of and damage in the constituent materials of reinforced concrete without resorting to individual meshing of the embedded bars and with very low computational cost

Homogenisation of Masonry Structures Subjected to Seismic Loads through Matrix/Inclusion Micromechanics

The mechanical properties of masonry, both in the linear elastic range and after the onset of damage, are dependent on the geometric and mechanical properties of its constituent materials: the units and the mortar. Finite element micromodelling, while capable of providing accurate and comprehensive results, is associated with high computational costs and modelling effort. On the other hand, micromechanical homogenisation of the masonry composite provides an attractive alternative to detailed micromodelling, in which the stress and strain interaction between the material phases can be modelled without excessive computational cost and in which interpretation of the damage state of the phases is more straightforward. However, nonlinear micromechanical homogenisation of masonry elements through varied numerical and analytical approaches remains a subject of intense study. In this paper, an inclusion-based homogenisation scheme for masonry structures is proposed for plane stress conditions. The scheme is combined with constitutive laws for damage in the constituent materials of the masonry composite and implemented in finite element models. The proposed modelling approach is validated in terms of its capacity to predict the elastic properties against experimental results and a finite element benchmark. Finally, finite element analyses of walls subjected to in-plane shear under varying levels of vertical stress are performed and favourably compared with experimental results in terms of predicted capacity and obtained failure mode. The low computational cost of the proposed model makes it suitable for future application in digital twinning operations.Peer ReviewedPostprint (published version

Analytical Models to Determine In-Plane Damage Initiation and Force Capacity of Masonry Walls with Openings

Masonry panels consisting of piers and spandrels in buildings are vulnerable to in-plane actions caused by seismicity and soil subsidence. Tectonic seismicity is a safety hazard for masonry structures, whereas low-magnitude induced seismicity can be detrimental to their durability due to the accumulation of light damage. This is particularly true in the case of unreinforced masonry. Therefore, the development of models for the accurate prediction of both damage initiation and force capacity for masonry elements and structures is necessary. In this study, a method was developed based on analytical modeling for the prediction of the damage initiation mode and capacity of stand-alone masonry piers; the model was then expanded through a modular approach to masonry walls with asymmetric openings. The models account for all potential damage and failure modes for in-plane loaded walls. The stand-alone piers model is applicable to all types of masonry construction. The model for walls with openings can be applied as is to simple buildings but can also be extended to more complex structures with simple modifications. Model results were compared with numerous experimental cases and exhibited very good accuracy