I was somewhat surprized with the fog in Groningen upon my arrival. This is notthe fog that covers the beautiful landscapes of the northern Netherlands in theevening and in the early morning. No… It is the fog that obscures the real aspectsof the earthquake problem in the region and is crystallised in the phrase “Groningen earthquakes are different”, which I have encountered numerous times whenever I raised a question of the type “But why..?”. A sentence taken out of the quiver as the absolute technical argument which mysteriously overshadows the whole earthquake discussion.Q: Why do we not use Eurocode 8 for seismic design, instead of NPR?A: Because the Groningen earthquakes are different!Q: Why do we not monitor our structures like the rest of the world does?A: Because the Groningen earthquakes are different!Q: Why does NPR, the Dutch seismic guidelines, dictate some unusual rules?A: Because the Groningen earthquakes are different!Q: Why are the hazard levels incredibly high, even higher than most Europeanseismic countries?A: Because the Groningen earthquakes are different!and so it keeps going…This statement is very common, but on the contrary, I have not seen a single piece of research that proves it or even discusses it. In essence, it would be a difficult task to prove that the Groningen earthquakes are different. In any case it barricades a healthy technical discussion because most of the times the arguments converge to one single statement, independent of the content of the discussion. This is the reason why our first research activities were dedicated to study if the Groningen earthquakes are really different. Up until today, we have not found any major differences between the Groningen induced seismicity events and natural seismic events with similar conditions (magnitude, distance, depth, soil etc…) that would affect the structures significantly in a different way.Since my arrival in Groningen, I have been amazed to learn how differently theearthquake issue has been treated in this part of the world. There will always bedifferences among different cultures, that is understandable. I have been exposed to several earthquake engineers from different countries, and I can expect a natural variation in opinions, approaches and definitions. But the feeling in Groningen is different. I soon realized that, due to several factors, a parallel path, which I call “an augmented reality” below, was created. What I mean by an augmented reality is a view of the real-world, whose elements are augmented and modified. In our example, I refer to the engineering concepts used for solving the earthquake problem, but in an augmented and modified way. This augmented reality is covered in the fog I described above. The whole thing is made so complicated that one is often tempted to rewind the tape to the hot August days of 2012, right after the Huizinge Earthquake, and replay it to today but this time by making the correct steps. We would wake up to a different Groningen today. I was instructed to keep the text as well as the inauguration speech as simple aspossible, and preferably, as non-technical as it goes. I thus listed the most common myths and fallacies I have faced since I arrived in Groningen. In this book and in the presentation, I may seem to take a critical view. This is because I try to tell a different part of the story, without repeating things that have already been said several times before. I think this is the very reason why my research group would like to make an effort in helping to solve the problem by providing different views. This book is one of such efforts.The quote given at the beginning of this book reads “How quick are we to learn: that is, to imitate what others have done or thought before. And how slow are we to understand: that is, to see the deeper connections.” is from Frits Zernike, the Nobel winning professor from the University of Groningen, who gave his name to the campus I work at. Applying this quotation to our problem would mean that we should learn from the seismic countries by imitating them, by using the existing state-of-the-art earthquake engineering knowledge, and by forgetting the dogma of “the Groningen earthquakes are different” at least for a while. We should then pass to the next level of looking deeperinto the Groningen earthquake problem for a better understanding, and alsodiscover the potential differences.
As part of the American Society of Civil Engineers E-Newsletter at page 5&6.
This paper presents a proof of concept for monitoring masonry structures using two different types of markers which are not easily noticeable by human eye but exhibit high reflection when subjected to NIR (near-infrared) wavelength of light. The first type is a retroreflective marker covered by a special tape that is opaque in visible light but translucent in NIR, while the second marker is a paint produced from infrared reflective pigments. The reflection of these markers is captured by a special camera-flash combination and processed using image processing algorithms. A series of experiments were conducted to verify their potential to monitor crack development. It is shown that the difference between the actual crack width and the measured was satisfactorily small. Besides that, the painted markers perform better than the tape markers both in terms of accuracy and precision, while their accuracy could be in the range of 0.05 mm which verifies its potential to be used for measuring cracks in masonry walls or plastered and painted masonry surfaces. The proposed method can be particularly useful for heritage structures, and especially for acute problems like foundation settlement. Another advantage of the method is that it has been designed to be used by non-technical people, so that citizen involvement is also possible in collecting data from the field.
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 project is devised for establishing pilot case studies in the Groningen gas field area for i) developing methodologies of proper evaluation of the monitoring data, ii) for establishing standards of structural monitoring in case of induced earthquakes, and for iii) increasing awareness among professionals on “why” and “how” to do structural monitoring in historical buildings in the region. The main focus of the project is both monitoring and also interpretation of results from the monitoring activities, which are the effects of maintenance and/or structural operations as well as the added value of monitoring in protecting historical buildings.
The structure will be monitored real-time and reasons behind the damages will be found. Proposals for protecting the structure against earthquakes will be made. - Damage scenario of the building, in relation to the induced seismicity effects on structures in the region- Establishment of a real-time structural monitoring toolThe building will be instrumented with accelerometers and displacement crack sensors. Additionally to the monitoring efforts, the structure will also be modelled in FE computer simulations in an effort trying to find out possible future response of the monument to strong earthquakes. The monitoring data will be combined with FE simulations in concluding the response of the structure to recursive induced seismic events.
