Post-earthquake structural damage shows that out-of-plane wall collapse is one of the most prevalent failure mechanisms in unreinforced masonry (URM) buildings. This issue is particularly critical in Groningen, a province located in the northern part of the Netherlands, where low-intensity ground shaking has occurred since 1991 due to gas extraction. The majority of buildings in this area are constructed using URM and were not designed to withstand earthquakes, as the area had never been affected by tectonic seismic activity before. Hence, the assessment of URM buildings in the Groningen province has become of high relevance.Out-of-plane failure mechanisms in brick masonry structures often stem from poor wall-to-wall, wall-to-floor or wall-to-roof connections that provide insufficient restraint and boundary conditions. Therefore, studying the mechanical behaviour of such connections is of prime importance for understanding and preventing damages and collapses in URM structures. Specifically, buildings with double-leaf cavity walls constitute a large portion of the building stock in the Groningen area. The connections of the leaves in cavity walls, which consist of metallic ties, are expected to play an important role. Regarding the wall-to-floor connections, the traditional way for URM structures in Dutch construction practice is either a simple masonry pocket connection or a hook anchor as-built connection, which are expected to be vulnerable to out-of-plane excitation. However, until now, little research has been carried out to characterise the seismic behaviour of connections between structural elements in traditional Dutch construction practice.This thesis investigates the seismic behaviour of two types of connections: wall-to-wall connections between cavity wall leaves and wall-to-floor connections between the masonry cavity wall and timber diaphragm, commonly found in traditional houses in the Groningen area. The research is divided into three phases: (1) inventory of existing buildings and connections in the Groningen area, (2) performance of experimental tests, and (3) proposal and validation of numerical and mechanical models. The thesis explores the three phases as follows:(i) An inventory of connections within URM buildings in the Groningen area is established. The inventory includes URM buildings of Groningen based on construction material, lateral load-resisting system, floor system, number of storeys, and connection details. Specific focus is given to the wall-to-wall and wall-to-floor connections in each URM building. The thickness of cavity wall leaves, the air gap between the leaves and the size and spacing of timber joists are key aspects of the inventory.(ii) Experimental tests are performed on the most common connection typologies identified in the inventory. This phase consists of two distinct experimental campaigns:o The first experimental campaign took place at the laboratory of the Delft University of Technology to provide a comprehensive characterisation of the axial behaviour of traditional metal tie connections in cavity walls. The campaign included a wide range of variations, such as two embedment lengths, four pre-compression levels, two different tie geometries, and five different testing protocols, including both monotonic and cyclic loading. The experimental results showed that the capacity of the wall tie connection is strongly influenced by the embedment length and the tie geometry, whereas the applied pre-compression and the loading rate do not have a significant influence.o The second experimental campaign has been carried out at the laboratory of the Hanze University of Applied Sciences to characterise the seismic behaviour of timber joist-masonry cavity wall connections, reproducing both as-built and strengthened conditions. Twenty-two unreinforced masonry wallets were tested, with different configurations, including two tie distributions, two pre-compression levels, two different as-built connections, and two different strengthening solutions. The experimental results highlighted the importance of cohesion and friction between joist and masonry since the type of failure mechanism (sliding of the joist or rocking failure of the masonry wallet) depends on the value of these two parameters. Additionally, the interaction between the joist and the wallet and the uplift of the latter activated due to rocking led to an arching effect that increased friction at the interface between the joist and the masonry. Consequently, the arching effect enhanced the force capacity of the connection.(iii) Mechanical and numerical models are proposed and validated against the performed experiments or other benchmarks. Mechanical and numerical models for the cavity wall tie and mechanical models for the timber joist-masonry connections were developed and verified by the experimental results to predict the failure mode and the strength capacity of the examined connections in URM buildings.o The mechanical model for the cavity wall tie connections considers six possible failures, namely tie failure, cone break-out failure, pull-out failure, buckling failure, piercing failure and punching failure. The mechanical model is able to capture the mean peak force and the failure mode obtained from the tests. After being calibrated against the available experiments, the proposed mechanical model is used to predict the performance of untested configurations by means of parametric analyses, including higher strength of mortar for calcium silicate brick masonry, different cavity depth, different tie embedment depth, and the use of solid bricks in place of perforated clay bricks.o The results of the experimental campaign on cavity wall ties were also utilised to calibrate a hysteretic numerical model representing the cyclic axial response of cavity wall tie connections. The proposed model uses zero-length elements implemented in OpenSees with the Pinching4 constitutive model to account for the compression-tension cyclic behaviour of the ties. The numerical model is able to capture important aspects of the tie response, such as strength degradation, unloading stiffness degradation, and pinching behaviour. The mechanical and numerical modelling approach can be easily adopted by practitioner engineers seeking to model the wall ties more accurately when assessing URM structures against earthquakes.o The mechanical model of timber-masonry connections examines two different failure modes: joist-sliding failure mode, including joist-to-wall interaction and rocking failure mode due to joist movement. Both mechanical models have been validated against the outcomes of the experimental campaigns conducted on the corresponding connections. The mechanical model is able to estimate each contribution of the studied mechanism. Structural engineers can use the mechanical model to predict the capacity of the connection for the studied failure modes.This research study can contribute to a better understanding of typical Groningen houses in terms of identifying the most common connections used at wall-to-wall and wall-to-floor connections in cavity walls, characterising the identified connections and proposing mechanical models for the studied connections.
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Post-earthquake structural damage shows that out-of-plane (OOP) wall collapse is one of the most common failure mechanisms in unreinforced masonry (URM) buildings. This issue is particularly critical in Groningen, a province located in the northern part of the Netherlands, where low-intensity induced earthquakes have become an uprising problem in recent years. The majority of buildings in this area are constructed using URM and were not designed to withstand earthquakes, as the area had never been affected by tectonic seismic activity before. OOP failure in URM structures often stems from poor connections between structural elements, resulting in insufficient restraint to the URM walls. Therefore, investigating the mechanical behaviour of these connections is of prime importance for mitigating damages and collapses in URM structures. This paper presents the results of an experimental campaign conducted on timber joist-masonry cavity wall connections. The specimens consisted of timber joists pocketed into masonry wallets. The campaign aimed at providing a better understanding and characterisation of the cyclic axial behaviour of these connections. Both as-built and strengthened conditions were considered, with different variations, including two tie distributions, two pre-compression levels, two different as-built connections, and one strengthening solution. The experimental findings underscored that incorporating retrofitting bars not only restores the system's initial capacity but also guarantees deformation compatibility between the wall and the joist. This effectively enhances the overall deformation capacity and ductility of the timber joist-cavity wall system.
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In recent years, the number of human-induced earthquakes in Groningen, a large gas field in the north of the Netherlands, has increased. The majority of the buildings are built by using unreinforced masonry (URM), most of which consists of cavity (i.e. two-leaf) walls, and were not designed to withstand earthquakes. Efforts to define, test and standardize the metal ties, which do play an important role, are valuable also from the wider construction industry point of view. The presented study exhibits findings on the behavior of the metal tie connections between the masonry leaves often used in Dutch construction practice, but also elsewhere around the world. An experimental campaign has been carried out at Delft University of Technology to provide a complete characterization of the axial behavior of traditional connections in cavity walls. A large number of variations was considered in this research: two embedment lengths, four pre-compression levels, two different tie geometries, and five different testing protocols, including monotonic and cyclic loading. The experimental results showed that the capacity of the connection was strongly influenced by the embedment length and the geometry of the tie, whereas the applied pre-compression and the loading rate did not have a significant influence.
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From the article: Abstract. This exploratory and conceptual article sets out to research what arguments and possibilities for experimentation in construction exists and if experimentation can contribute towards more innovative construction as a whole. Traditional, -western- construction is very conservative and regional, often following a traditional and linear design process, which focuses on front-loaded cost savings and repetitive efficiency, rather than securing market position through innovation. Thus becoming a hindrance for the development of the sector as a whole. Exploring the effects of using the, in other design-sectors commonly and successfully practiced, “four-phased iterative method” in architectural construction could be the start of transforming the conservative construction industry towards a more innovative construction industry. The goal of this research is to find whether the proposed strategy would indeed result in a higher learning curve and more innovation during the - architectural- process. Preliminary research indicates that there is argumentation for a more experimental approach to construction.
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The seismic assessment of the out-of-plane (OOP) behaviour of unreinforced masonry (URM) buildings is essential since the OOP is one of the primary collapse mechanisms in URM buildings. It is influenced by several parameters, including the poor connections between structural elements, a weakness highlighted by post-earthquake observations. The paper presents a mechanical model designed to predict the contributions of various resisting mechanisms to the strength capacity of timber-joist connections in masonry cavity walls. The research presented in this paper considers two different failure modes: joist-wall interface failure, and OOP rocking behaviour of the URM walls. Consequently, two mechanical models are introduced to examine these failure modes in timber-joist connections within masonry cavity walls. One model focuses on the joist-wall interface failure, adopting a Coulomb friction model for joist-sliding further extended to incorporate the arching effect. The other model investigates the OOP rocking failure mode of walls. The combined mechanical model has been validated against the outcomes of an earlier experimental campaign conducted by the authors. The considered model can accurately predict the peak capacity of the joist connection and successfully defines the contribution of each mechanism in terms of resistance at failure.
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The assessment of the out-of-plane response of unreinforced masonry (URM) buildings with cavity walls has been a popular topic in regions such as Central and Northern Europe, Australia, New Zealand, China and several other countries.Cavity walls are particularly vulnerable as the out-of-plane capacity of each individual leaf is significantly smaller than the one of a solid wall. In the Netherlands, cavity walls are characterized by an inner load-bearing leaf of calcium silicate bricks, and by an outer veneer of clay bricks that has only aesthetic and insulation functions. The two leaves are typically connected by means of metallic ties. This paper utilizes the results of an experimental campaign conducted by the authors to calibrate a hysteretic model that represents the axial cyclic response of cavity wall tie connections. The proposednumerical model uses zero-length elements implemented in OpenSees with the Pinching4 constitutive model to account for the compression-tension cyclic behaviour of the ties. The numerical model is able to capture important aspects of the tie response such as the strength degradation, the unloading stiffness degradation and the pinching behaviour. The numerical modelling approach in this paper can be easily adopted by practitioner engineers who aim to model the wall ties more accurately when assessing the structures against earthquakes.
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The majority of houses in the Groningen gas field region, the largest in Europe, consist of unreinforced masonry material. Because of their particular characteristics (cavity walls of different material, large openings, limited bearing walls in one direction, etc.) these houses are exceptionally vulnerable to shallow induced earthquakes, frequently occurring in the region during the last decade. Raised by the damage incurred in the Groningen buildings due to induced earthquakes, the question whether the small and sometimes invisible plastic deformations prior to a major earthquake affect the overall final response becomes of high importance as its answer is associated with legal liability and consequences due to the damage-claim procedures employed in the region. This paper presents, for the first time, evidence of cumulative damage from available experimental and numerical data reported in the literature. Furthermore, the available modelling tools are scrutinized in terms of their pros and cons in modelling cumulative damage in masonry. Results of full-scale shake-table tests, cyclic wall tests, complex 3D nonlinear time-history analyses, single degree of freedom (SDOF) analyses and finally wall element analyses under periodic dynamic loading have been used for better explaining the phenomenon. It was concluded that a user intervention is needed for most of the SDOF modelling tools if cumulative damage is to be modelled. Furthermore, the results of the cumulative damage in SDOF models are sensitive to the degradation parameters, which require calibration against experimental data. The overall results of numerical models, such as SDOF residual displacement or floor lateral displacements, may be misleading in understanding the damage accumulation. On the other hand, detailed discrete-element modelling is found to be computationally expensive but more consistent in terms of providing insights in real damage accumulation.
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At this moment, no method is available to objectively estimate the temperature to which skeletal remains have been exposed during a fire. Estimating this temperature can provide crucial information in a legal investigation. Exposure of bone to heat results in observable and measurable changes, including a change in colour. To determine the exposure temperature of experimental bone samples, heat related changes in colour were systemically studied by means of image analysis. In total 1138 samples of fresh human long bone diaphysis and epiphysis, varying in size, were subjected to heat ranging from room temperature to 900 °C for various durations and in different media. The samples were scanned with a calibrated flatbed scanner and photographed with a Digital Single Lens Reflex camera. Red, Green, Blue values and Lightness, A-, and B-coordinates were collected for statistical analysis. Cluster analysis showed that discriminating thresholds for Lightness and B-coordinate could be defined and used to construct a model of decision rules. This model enables the user to differentiate between seven different temperature clusters with relatively high precision and accuracy. The proposed decision model provides an objective, robust and non-destructive method for estimating the exposure temperature of heated bone samples.
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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.
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Light scattering is a fundamental property that can be exploited to create essential devices such as particle analysers. The most common particle size analyser relies on measuring the angle-dependent diffracted light from a sample illuminated by a laser beam. Compared to other non-light-based counterparts, such a laser diffraction scheme offers precision, but it does so at the expense of size, complexity and cost. In this paper, we introduce the concept of a new particle size analyser in a collimated beam configuration using a consumer electronic camera and machine learning. The key novelty is a small form factor angular spatial filter that allows for the collection of light scattered by the particles up to predefined discrete angles. The filter is combined with a light-emitting diode and a complementary metal-oxide-semiconductor image sensor array to acquire angularly resolved scattering images. From these images, a machine learning model predicts the volume median diameter of the particles. To validate the proposed device, glass beads with diameters ranging from 13 to 125 µm were measured in suspension at several concentrations. We were able to correct for multiple scattering effects and predict the particle size with mean absolute percentage errors of 5.09% and 2.5% for the cases without and with concentration as an input parameter, respectively. When only spherical particles were analysed, the former error was significantly reduced (0.72%). Given that it is compact (on the order of ten cm) and built with low-cost consumer electronics, the newly designed particle size analyser has significant potential for use outside a standard laboratory, for example, in online and in-line industrial process monitoring.
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