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.
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.
The seismic assessment of unreinforced masonry (URM) buildings with cavity walls is a relevant issue in many countries, such as in Central and Northern Europe, Australia, New Zealand, China and several other countries. A cavity wall consists of two separate parallel masonry walls (called leaves) connected by metal ties: an inner loadbearing wall and an outer veneer having mostly aesthetic and insulating functions. Cavity walls are particularly vulnerable structural elements. If the two leaves of the cavity wall are not properly connected, their out-of-plane strength may be significantly smaller than that of an equivalent solid wall with the same thickness.The research presented in this paper focuses on a mechanical model developed to predict the failure mode and the strength capacity of metal tie connections in masonry cavity walls. The model considers six possible failures, namely tie failure, cone break-out failure, pull-out failure, buckling failure, piercing failure and punching failure. Tie failure is a predictable quantity when the possible failure modes can be captured. The mechanical model for the ties has been validated against the outcomes of an experimental campaign conducted earlier by the authors. The mechanical model is able to capture the mean peak force and the failure mode obtained from the tests. The mechanical model can be easily adopted by practising engineers who aim to model the wall ties accurately in order to assess the strength and behaviour of the structures against earthquakes. Furthermore, the proposed mechanical model is used to extrapolate the experimental results to untested configurations, by performing parametric analyses on key parameters including a higher strength mortar of the calcium silicate brick masonry, a different cavity depth, a different tie embedment depth, and solid versus perforated clay bricks.
Post-earthquake structural damage shows that wall collapse is one of the most common failure mechanisms in unreinforced masonry buildings. It is expected to be a critical issue also in Groningen, located in the northern part of the Netherlands, where human-induced seismicity has become an uprising problem in recent years. The majority of the existing buildings in that area are composed of unreinforced masonry; they were not designed to withstand earthquakes since the area has never been affected by tectonic earthquakes. They are characterised by vulnerable structural elements such as slender walls, large openings and cavity walls. Hence, the assessment of unreinforced masonry buildings in the Groningen province has become of high relevance. The abovementioned issue motivates engineering companies in the region to research seismic assessments of the existing structures. One of the biggest challenges is to be able to monitor structures during events in order to provide a quick post-earthquake assessment hence to obtain progressive damage on structures. The research published in the literature shows that crack detection can be a very powerful tool as an assessment technique. In order to ensure an adequate measurement, state-of-art technologies can be used for crack detection, such as special sensors or deep learning techniques for pixel-level crack segmentation on masonry surfaces. In this project, a new experiment will be run on an in-plane test setup to systematically propagate cracks to be able to detect cracks by new crack detection tools, namely digital crack sensor and vision-based crack detection. The validated product of the experiment will be tested on the monument of Fraeylemaborg.
This top-up project is related to the on-going RAAK MKB-project SafeGo (Seismic Monitoring, Design And Strengthening For thE GrOningen Region) . SafeGo combines knowledge of SMEs in the earthquake region of Groningen with innovative solutions and demonstration of technologies, to improve the process of seismic strengthening of houses. Innovative methods and approaches for monitoring and strengthening of structures are tested and further developed in SafeGo In the monitoring part of the project, SafeGo combines soil data, structural data and the sensor data to reach conclusions for the reasons behind observed damages in buildings. Fraeylemaborg, a castle-museum in Slochteren dating back to the 14th century, is used as a testbed. Various sensors are used for monitoring accelerations, tilt and water pressure. In the strengthening part of the project, masonry walls were built and strengthened by the participating SMEs. These walls are placed on the shake table and tested with real earthquake vibrations. A shake table is an accurate laboratory equipment which simulates earthquakes. Majority of the tasks in SafeGo are related either to the site or to the laboratory, which are environments outside of the school. Although an intensive student participation was initially planned, this was not achieved due to COVID19 crisis and the series of mobility restrictions, neither in the monitoring nor in the shake table testing parts of the project. This top-up project aims to transfer the knowledge and create interaction with the students for the SafeGo project. Visitation to the monitored building and presentations to the students on the monitoring system, visitations to the shake table laboratory and interactive events are planned within this project.
In recent years there has been an increasing need for nature inclusive solutions in the construction sector. The practice asks for new solutions contributing to the development of sustainable, resilient and liveable cities. Under the guidance of the Dutch government, greening of the cities has become one of the aims of municipalities in the Netherlands and the focus of some emerging companies and design offices. In cities, quay masonry walls, thanks to their close contact with water, have the potential to be ecologically engineered to favour vegetation, thereby contributing to the renaturing of urban areas. By building a prototype of an innovative masonry building system, this project aims to investigate the potential for improving the integration between masonry quay walls and vegetation. The set-up consists of a dry-stacking system for brick masonry: strong polyamide elements interconnect the bricks, providing strength to the masonry without the need for mortar. The space in between bricks, traditionally filled with mortar, is to be filled with compost material, providing an ideal substrate for plant growth and a buffer for water storage (figure 1). In addition to improved integration between masonry walls and vegetation, the proposed dry-stacking system allows for easy reuse of bricks, thereby contributing to circularity and sustainability of the building industry. The project broadens and strengthens the national network in the field of urban ecology by bringing together expertise from the fields of architecture, ecology and the construction sector, from both academia and practice.
