The compressive behaviour of mortar under varying stress confinement

The confinement of mortar in masonry under compression is one of the key processes influencing the compressive strength of the composite material. It is triggered by the mismatch of elastic properties between units and mortar, coupled with deformation conformity between the two material phases. In cases where the mortar is particularly deformable compared to the units, this confinement results in a peak stress many times the uniaxial compressive strength of the mortar. Therefore, a careful examination of this effect is critical in understanding the failure mechanisms of masonry in compression.Mortar under compression can be modelled in a damage mechanics context, following the establishment of a) a constitutive stress-strain relation, b) a model for the increase of the compressive failure stress under lateral confinement and c) a model for the development (increase) of the Poisson’s ratio of mortar under different stress levels. The first aspect is approached using established hardening-softening curves used for quasi-brittle materials, such as concrete. The second aspect is dealt with through the adoption of a suitable and sufficiently flexible failure criterion. The third aspect is addressed through fitting against experimental data.The above aspects are expressed in a damage mechanics context, resulting in fast calculations of the compressive stress-strain curves for confined mortar. This approach allows the quantification of the development of damage in compression, the development of the apparent compressive strength and the relation between orthogonal strains in the mortar, leading to a full characterization of the stress, deformation and damage of the material. The analysis results are compared to experimental findings on different mortar types and are used for their interpretation and evaluation. The complexity of the behaviour of confined mortar is demonstrated, motivating the use of advanced numerical models for its accurate simulation and assessment.Peer ReviewedPostprint (author's final draft

Laser scanning, monitoring and analysis of a reconstructed masonry vault

Reconstruction of historic building elements is often necessary in adaptive re-use projects. Optimally this is performed with as much original material as can be sal- vaged. However, the use of hydraulic lime mortars in reconstructed masonry can lead to long curing time and excessive deformation under mechanical loadsThe authors would like to thank V. Wirix from Denys NV and F. Noë from VK Engineering for their support of the on-site work, and WTA-NL-VL for the financial supportPostprint (published version

The confinement of mortar in masonry under compression: experimental data and micro-mechanical analysis

The present paper deals with the behavior of several types of mortar in masonry under compression. The quantification of the response of mortar to triaxial confinement afforded by the masonry units in the composite subjected to compressive stresses is paramount in the determination of the peak stress of wallettes and pillars under compression. This behavior is greatly affected by the behavior of the mortar micro-structure and is manifested by the constrained lateral expansion of the mortar in the joint. A series of experimental results is presented, carried out on different assemblages of masonry composites (couplets and wallettes) with different types of masonry units and mortar, ranging in type from pure lime to cement based mortars. These experiments are subsequently simulated numerically using micro-mechanical techniques accounting for the shifting behavior of the Poisson's ratio of the mortar for varying levels of applied compression. Masonry is treated in a micro-mechanical framework as a composite material composed of two macroscopically distinct material phases: units and mortar. The experiments and their simulation provide insight into the complexities of masonry under compression that need to be accounted for in numerical analysis, including a discussion on the progression of damage in each material phase. The results and their analysis are further enriched through a comparative parametric study. A clear difference emerges between the assigned and the apparent Poisson's ratio for the material components.Funding for this work was procured through the GEPATAR project (“GEotechnical and Patrimonial Archives Toolbox for ARchitectural conservation in Belgium” BR/132/A6/GEPATAR), which is financially supported by BRAIN-be, BELSPO (Belgian Research Action through Interdisciplinary Networks, Federal Public Planning Service Science Policy Belgium).Peer ReviewedPostprint (author's final draft

Characterization of debonding in FRP-strengthened masonry using the acoustic emission technique

The acoustic emission (AE) technique is used for investigating the interfacial fracture and damage propagation in GFRP- and SRG-strengthened bricks during debonding tests. The bond behavior is investigated through single-lap shear bond tests and the fracture progress during the tests is recorded by means of AE sensors. The effect of hygrothermal conditions on the debonding characteristics and failure mode is also investigated by performing accelerated ageing tests. Accelerated ageing tests resulted in a change of failure mode in GFRP-strengthened specimens which helped in assessment of AE output in different failure modes, but no conclusive strength degradation was observed in the specimens. The results show that the average and cumulative AE energy are correlated to the FRP slip and debonding fracture energy in GFRPstrengthened specimens, respectively. The fracture progress and active debonding mechanisms are characterized using results from the AE technique. Moreover, a clear distinction between the AE outputs of specimens with different failure modes, in both SRG- and GFRP-strengthened specimens, is found which allows characterizing the debonding failure mode based on acoustic emission data. The tests performed in this study are also a contribution towards the application of AE techniques for on-site health monitoring of strengthened masonry structures.Fundação para a Ciência e Tecnologi

Macro scale material characterisation in support of meso scale modelling of masonry under uniaxial in-plane loading

The amount of detailed experimental data on the mechanical properties of brick masonry in the literature is limited regarding the orthotropic strength and fracture energy. A combined experimental/numerical methodology is proposed for the derivation of the macro scale properties of masonry. The experimental aspect deals with the mechanical characterisation of the individual materials, small masonry samples and masonry wallettes, including the relation of couplet to wallette strength. The numerical aspect is the calculation of the macroscopic properties of the masonry through discrete cracking calculations in two orthogonal directions. The numerical analysis results are compared with the experimental stress-strain results and Digital Image Correlation analysis. The Young's modulus and compressive fracture energy for the masonry composite are derived. The results are analysed in view of the resulting anisotropy of masonry and the obtained failure modes.Peer ReviewedPostprint (author's final draft

Crack monitoring in historical masonry with distributed strain and acoustic emission sensing techniques

The analysis of crack patterns and crack growth is one of the most important steps in the assessment of structural damage in historical masonry. In a search for integrated and accurate monitoring techniques for crack measurements in masonry, several novel techniques based on distributed strain monitoring and acoustic emission (AE) sensing have been investigated in an experimental test campaign. Aim of the test program was to develop integration procedures for the strain and AE sensors, analyse their use for crack monitoring specifically in historical masonry and assess their robustness and efficiency with respect to the experimentally observed crack pattern.This work is performed within the framework of the GEPATAR project (“GEotechnical and Patrimonial Archives Toolbox for ARchitectural conservation in Belgium” BR/132/A6/GEPATAR), which is financially supported by BRAIN-be, Belspo.Postprint (updated version

Numerical analysis of settlement-induced damage to a masonry church nave wall

Differential soil settlements can induce structural damage to heritage buildings, causing not only economic but also cultural value losses. In 1963, the Saint Jacob’s church in Leuven was permanently closed to the public because of severe settlement-induced damage caused by insufficient bearing capacity of the founda- tion. Currently, the church is stabilized using a temporary shoring system. This work aims at implementing a practical modelling approach to predict damage on church nave walls subjected to differential settlements. For that purpose, a finite element model of the Saint Jacob’s church nave was generated and validated through on- site monitoring data including levelling, damage survey and laser scanningThis work was done within the framework of the GEPATAR project (“GEotechnical and Patrimonial Archives Toolbox for ARchitectural conservation in Belgium” BR/132/A6/Gepatar), supported by BRAIN.be, Belspo.Postprint (published version

Crack growth in masonry::Numerical analysis and sensitivity study for discrete and smeared crack modelling

One of the most common obstacles faced by engineers when making numerical models to assess damage in historical masonry lies in defining the most suitable constitutive models when there is shortage of either material characterization or experimental data. This paper presents the implementation of a 2D finite element model (FEM) of a masonry wall by means of two strategies: a discrete cracking meso-model and a continuum smeared cracking macro-model. A sensitivity study is performed to investigate the effect of material properties variation on both modelling strategies, each of which considers the highly non-linear behaviour as well as the brittle cracking of the masonry. The numerical models are validated through the results obtained from an experimental testing campaign which considered a brick masonry wall subjected to cyclic three-point bending. The results of both modelling strategies compared with experimental results are presented, as well as the criteria considered for material characterization and the sensitivity analysis. Results indicate the suitability of both models to reproduce experimentally observed load capacity, failure mechanism and horizontal deformations. However, the meso-model showed higher accuracy in terms of failure mechanism and plastic deformations. The sensitivity analysis indicated that some material parameters, such as fracture energy, cohesion and tensile strength, significantly govern the final cracking. This is an important criterion for adequately choosing the parameters for further models in which crack width is considered, e.g. for settlement-induced cracking analysis.</p

Numerical Modeling of a Church Nave Wall Subjected to Differential Settlements::Soil-Structure Interaction, Time-Dependence and Sensitivity Analysis

Historic masonry structures are particularly sensitive to differential soil settlements. These settlements may be caused by deformable soil, shallow or inadequate foundation, structural additions in the building and changes in the underground water table due to the large-scale land use change in urban areas. This paper deals with the numerical modeling of a church nave wall subjected to differential settlement caused by a combination of the above factors. The building in question, the church of Saint Jacob in Leuven, has suffered extensive damage caused by centuries-long settlement. A numerical simulation campaign is carried out in order to reproduce and interpret the cracking damage observed in the building. The numerical analyses are based on material and soil property determination, the monitoring of settlement in the church over an extended period of time and soil-structure interaction. A sensitivity study is carried out, focused on the effect of material parameters on the response in terms of settlement magnitude and crack width and extent. Soil consolidation over time is considered through an analytical approach. The numerical results are compared with the in-situ observed damage and with an analytical damage prediction model.The authors acknowledge the funding received by BRAIN.be, Belspo in support of the GEPATAR research project (“GEotechnical and Patrimonial Archives Toolbox for ARchitectural conservation in Belgium” BR/132/A6/Gepatar).Peer ReviewedPostprint (author's final draft

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 soil-structure interaction models for buildings. The Declercqresulting 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.The authors wish to acknowledge the funding received by BRAIN.be, BelSPO in support of the GEPATAR research project (“GEotechnical and Patrimonial Archives Toolbox for ARchitectural conservation in Belgium” BR/132/A6/Gepatar)Peer ReviewedPostprint (published version