To date, several different structural representations of masonry are available for use in the numerical and analytical assessment methods, each calling for a distinct level of refinement regarding the material input. To determine material properties, in terms of strength, stiffness, and toughness under compression, bending, and shear loading, extensive experimental research is necessary. To minimise the burden associated with performing complex and invasive experimental studies, this paper investigated the possible correlations between different material properties, particularly toughness, which received limited attention in past research. The correlation study was mainly conducted on the rich database established from tests on laboratory-made as well as specimens extracted from unreinforced masonry structures built between 1910 and 2010 in the Netherlands. Considering the outcomes of the correlation study, this paper puts forward recommendations to indirectly derive elastic and toughness properties as a function of strength properties. In this way, a complete picture of material properties can be obtained, while minimising the number of experiments and the extent of their invasiveness.

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The shove test (ASTM Standard C1531) is an experimental technique aimed at studying the shear-sliding behavior of brick masonry. It can be executed according to various testing methods that differ in the way the vertical compression load is applied and in the way bricks and/or joints are locally removed for inserting jacks. One of the most critical aspects is the correct evaluation of the compressive stress state on the sliding brick. The objective of the present paper is to investigate the capability of the shove test in determining the shear strength parameters of brick masonries and to highlight the main advantages and disadvantages of the various testing methods. To this aim, nonlinear numerical simulations of the shove test were performed by adopting a brick-to-brick modeling strategy. The 2D numerical model was calibrated and validated through comparisons with experimental results of triplet tests and shove tests. The numerical analyses allowed to understand the influence the different testing methods and the masonry mechanical properties, such as dilatancy, may have on the test results. Based on the numerical outcomes, correction factors were calibrated for the proper evaluation of the compressive stress state on the sliding brick. Improvements with regards to the experimental procedures, i.e. additional test phases and measurements, were also proposed to enhance the results interpretation.

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Understanding the behaviour of unreinforced masonry (URM) structures requires in-depth insight into the mechanical properties of its constituents and their interaction under compression, tension, and shear loading. As a result, a complete picture of masonry characteristics, accounting for its full nonlinear response and its statistical distribution, has long been of scientific research interest worldwide. This has become a necessity for the Netherlands in recent years because of the induced seismicity affecting the vulnerable masonry building stock in the province of Groningen. The more rigorously the mechanical properties are determined, the more they engender confidence in the reliability of structural analyses. This calls for an interdisciplinary approach, whereby experimental research focuses on meeting the demands of structural analysts and numerical modellers. As a result, laboratory and in-situ testing campaigns can provide input parameters and a basis for the validation and calibration of the various models to be used in deterministic or probabilistic settings. Nevertheless, a thorough characterisation of the material properties of existing unreinforced masonry structures is widely acknowledged as a challenging task, given the quasi-brittle nature of masonry, a very diverse range of masonry types, a lack of reliable in-situ semi-invasive testing methods, and a large number of tests required to be carried out. To this end, both invasive and semi-invasive testing methods are adopted in this thesis. The former refers to tests on medium-sized samples, which follow the guidelines of the European standards for the selection of each sample’s size. The latter points to a novel testing method, whereby small-diameter cores are extracted perpendicular to the wall surface. In this thesis, the studied masonry types are either laboratory-made, replicating the five most typical Dutch masonry types, or field-extracted, from nineteen different URM dwellings and schools in the Groningen region, built between 1910 and 2010. The typical masonry types include clay brick masonry, calcium-silicate brick masonry and calcium-silicate element masonry. By performing 218 invasive tests on laboratory-made replicated masonry specimens, this thesis provides comprehensive insight into the behaviour of five masonry types and its constituents. It covers several aspects that have been addressed only partially in the literature: 1) investigating the response of masonry under different stress states, i.e. compression, bending, and shear; 2) analysing the complete nonlinear behaviour not only in the pre-peak but also in the post-peak regime; and 3) exploring the orthotropic response under compression and bending loads. Moreover, this lab-testing campaign has studied the influence of brick type, number of wythes, and joint thickness on the response of masonry. By performing 478 invasive tests on field-extracted masonry specimens, this thesis offers a regional dataset of material properties. This dataset, along with previously available data from the literature, has been transferred into material properties table that have been incorporated into the Dutch standard for the assessment of existing URM buildings subjected to induced earthquakes. Moreover, this research provides new insights into the inter-building variability of material properties and their statistical distribution. This thesis also investigates the suitability of a novel semi-invasive testing method, whereby 167 small-diameter cores were subjected to compression as well as shear-sliding load. To this end, a comparative study was conducted, in which the material properties obtained from tests on cores, namely strength, stiffness, and toughness, are correlated with those found from tests on companion specimens. Promising conclusions are drawn, indicating that this testing method can be regarded as a reliable and practical alternative to conventional flat-jack based in-situ testing methods. Considering the comprehensive dataset established and the study of different testing methods, this thesis ultimately formulates a strategy to characterise the material properties for assessment of existing URM structures. To this end, this research investigated the presence of relationships between different material properties, thus offering recommendations to indirectly derive elastic and toughness properties as a function of easy-to-obtain properties, i.e. strength found from testing cores and bond wrench tests. Moreover, this study introduced improved constitutive functions for compression, bending, and shear loading. Therefore, following this strategy, an acceptable level of knowledge on material properties can be gained, while intrusiveness and damage due to sampling remain limited. @en

In this study, tests on cores and companion tests on triplets are compared with respect to the evaluation of the nonlinear shear-sliding behaviour of masonry, including the determination of post-peak softening response. Due to its slightly-destructive sampling nature and its good agreement with triplet results, the core testing method is confirmed to be a competitive technique for the in-situ assessment of the cohesion, friction coefficient, and shear modulus of mortar. Additionally, the comparisons in terms of dilatancy and energy dissipation, novel aspects with respect to previous studies, provide interesting insights for further research on the cohesive and frictional mechanisms occurring at brick-mortar interfaces.@en

To assess the shear properties of masonry for existing buildings, the shove test method proposed by ASTM C1531 can be carried out, in which the load required to slide a single brick with respect to the surrounding masonry is measured. To control the vertical stress-state on the tested brick, two flat-jacks can be inserted in mortar bed joints in close proximity of it, thus prescribing a predefined level of compression. Although this test seems straightforward, uncertainties have not been resolved yet regarding the actual vertical compressive stress present on the tested brick and the effect of dilatancy. To gain a better insight into the shear-sliding behavior of masonry during the shove test, both experimental tests and numerical simulations were considered in the current research. To analyze these aspects and to precisely define a testing protocol, the experimental tests were performed in a controlled laboratory environment on a single wythe calcium silicate brick masonry wall. In parallel, numerical analyses were carried out using a simplified micro-modeling strategy, in which every brick was modelled, and the mortar joints were considered as zero-thickness interfaces. A composite interface model was used, including a tension cut-off, a Coulomb friction domain and a compressive cap. For the analyzed case study, the numerical results allowed to gain a better understanding of the aspects influencing the shear-sliding behavior of masonry during the shove test.

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Since the 1980s in the Netherlands, the demand for accelerating the construction process and subsequently reducing the construction costs has led to the replacement of traditional brick masonry with larger masonry units assembled with a thin mortar layer. Accordingly, different masonry unit sizes ranging from traditional bricks (210 × 70 × 100-mm) to larger elements (900 × 650 × 100-mm) have been produced by the calcium silicate industry and widely used for the construction of unreinforced masonry (URM) buildings. To properly assess the performances of URM buildings, numerical and analytical methods require a complete description of the mechanical behavior of masonry at material level. Despite the widespread application of both calcium silicate brick and element masonry, a refined characterization of the mechanical properties of masonry has not received much attention. As a result, an experimental study was conducted at Delft University of Technology for the material characterization of calcium silicate brick and element masonry, with a view to assessments for induced seismicity in Groningen. By using well-designed testing set-ups, the compression, shear and bending properties of calcium silicate specimens were measured, with an aim to understand the strength, stiffness as well as softening post-peak behavior in compression and in shear of both masonry types. This paper provides insight into the nonlinear behavior of the calcium silicate brick and calcium silicate element masonry as a support to the development and validation of numerical and analytical models for the seismic assessment of URM structures.

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This study investigates the applicability of the core testing method to assess the complete nonlinear behavior of masonry in compression. A comparative experimental approach was adopted performing compressive tests on cores and companion wallets. Via a correlation study on seven objects, including literature data, a one-to-one correlation for both compressive strength and Young's modulus is obtained, while further studies are necessary to evaluate peak strain and compressive fracture energy. Thanks to its limited invasiveness and the capability of capturing the post-peak response with standard equipment, the core testing method can be regarded as a practical alternative to conventional slightly-destructive techniques.@en

In recent years induced seismicity in the Netherlands considerably increased. This phenomenon has a wide impact on the built environment, which is mainly composed by unreinforced masonry (URM) structures. These buildings were not designed for seismic loading, and present peculiar characteristics include very slender walls (100 mm thickness and 2.5m in height), limited connections between walls and floors, and use of cavity walls. A large portion of the URM building stock consists of terraced houses in which the presence of calcium silicate (CS) masonry is often used. The CS masonry is used to build the loadbearing walls, which are part of the cavity wall system. The cavity walls are generally composed of two leaves of masonry separated by an empty cavity, having a thickness of 8-6 mm, and connected with steel anchors. On the basis of the construction year, different masonry unit were adopted to build the inner loadbearing leave: in the period 1960-1980 small CS brick and general purpose mortar were used, while after 1980, the presence of large CS elements and thin mortal layers is predominant. Although these materials are often used in the northern part of Europe, little information is available on their material and structural performance. In this paper, a comparison between the behaviour of CS brick and element masonry is presented. The results of two experimental campaigns carried out at Delft University of Technology are reported. Both masonry types have been characterised at the material level by performing standardised destructive tests, such as compression, shear, and bending tests on wallets. The characterisation at the structural level is carried out by performing quasi-static cyclic tests on full-scale two-story high assembled structures.@en

In recent years, induced seismicity in the north of the Netherlands significantly increased. As a consequence, the seismic assessment of the built environment, which mainly consists of unreinforced masonry (URM) structures not designed for seismic loads, became of high relevance. Within this context, an extensive multiscale testing program has been performed at the laboratory of Delft University of Technology since 2014 to characterize the behavior of URM buildings from structural down to material level and provide benchmarks for the validation of numerical and analytical models. The paper presents an overview on the experimental campaign, which was structured in three phases: characterization of existing buildings; study of the structural response up to near collapse on replicated specimens; study of light damage state, also on replicated URM walls. The experimental campaign was characterized by a multiscale approach, with tests at structural, component, connection, and material level. At structural level, the campaign comprehended two quasi-static cyclic tests on full-scale two-story high assembled structures and a large number of both in-plane and out-of-plane tests performed either on single piers or on walls with openings. The in-plane stiffness and capacity of as-built and retrofitted timber floors was also assessed. At material level, destructive and slightly-destructive laboratory tests were performed on both existing and replicated masonry and timber specimens. Existing and retrofitting connections between the leaves of cavity walls and between concrete slabs and masonry veneers were studied. To study the initiation and propagation of cracking in URM structures, Digital Image Correlation (DIC) was used during dedicated in-plane tests.@en

To accurately assess the performance of existing unreinforced masonry (URM) structures, the mechanical characteristics of masonry under compressive loading are required. The compression properties of existing URM can be evaluated through different methods, either performing destructive tests (DTs) or slightly destructive tests (SDTs). DTs can be performed in the laboratory on small-scale masonry samples. In practice, these tests are not easy to perform, due to technical challenges during sampling, packing and transportation. On the contrary, SDTs can be performed in-situ as proposed by the ASTM standard using double flatjack methods. Although the double flatjack method has the advantage of being less destructive and less time-consuming, the reliability of the results obtained from this method is still a matter of concern, in particular for masonry walls with low overburden that are typical for low-rise masonry houses in the Northern part of the Netherlands subjected to induced seismicity. As an alternative to the standardized DT and SDT methods, splitting tests on cylindrical cores have been recently introduced as a promising method to characterize the compression properties of masonry. Currently limited information is available about the suitability of the core testing method to evaluate the compression properties of masonry. To bridge these gaps, this research investigates the suitability of the double flatjack test and the core testing methods to characterize the compression properties of masonry. Calcium silicate brick masonry is considered as a case study. The results obtained by these SDT methods are correlated with the results of DT performed on companion specimens, aiming to suggest a quick and slightly destructive method for assessing the compression properties of masonry. Moreover, this paper addresses the effect of geometry and boundary conditions on the compression properties of masonry@en

Starting point in this research is to find a quick and non-destructive method to characterize the mechanical properties of existing masonry. Tests on cylindrical cores have been recently introduced as a novel in-situ testing method to identify the properties of existing clay brick masonry. Currently, some researchers reported promising results, showing that the adopted methodology causes minor damage to the structures and it allows a direct estimation of the mechanical properties. To evaluate the mechanical properties of masonry, cores extracted perpendicular to the surface of a wall are subjected to the splitting tests, by which the compressive and shear properties of the masonry can be estimated. In the first case, previous studies adopted different core configurations (i.e. size and joint pattern) subjected to compressive load. In the second case, cores with only a single bed joint were used. In the literature, the cores were tested in a way that the bed joint was rotated with respect to its original position. Consequently, a mixed compression–shear stress state is induced at the centre of the mortar joint.@en

Induced seismicity in the Groningen region of the Netherlands has led to a large scale testing campaign on Calcium silicate element masonry structures at Delft University of Technology. An overview of the finite element analysis (FEA) using an implicit solver, on the full scale quasi-static cyclic pushover test performed on a two-storey calcium sili-cate element masonry assemblage is presented in this paper. Tests have been performed in the experimental campaign at material, component, and structural level, of which the ma-terial tests like bond wrench tests, compression tests and shear tests are also briefed in this paper.@en

In the northern part of the Netherlands, The recent seismic activities have raised concerns about the behavior of unreinforced masonry structures which were not designed and constructed to resist seismic loading. The first step towards assessment of seismic behavior of masonry structures is to characterize the material properties. This characterization is the matter of importance, since the findings serve as input parameters for analytical and numerical models. To do so, destructive laboratory tests (standard and non-standard tests) have been carried out on samples extracted from existing masonry buildings. The compression, bending and shear properties of masonry were investigated in this research. The obtained properties were categorized with respect to masonry typologies and time periods.

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