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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In Groningen, the Netherlands, induced earthquakes occur in a relatively densely populated area, the so-called Groningen gas field. Many houses and other buildings have been facing damage, from minor cracks to severe damage. The gas extraction company (NAM, a joint venture of Shell and Exxon Mobil) is held responsible for the earthquakes and has a legal liability to compensate for the damage. In addition to damage, several houses in the area are thought to be unsafe (not allowing occupants to leave their houses alive in case of a major earthquake). Both NAM and the Dutch government play a crucial role in the gas problems; where NAM is responsible for damage, the government has to guarantee citizens’ safety. Government has given orders to develop a strengthening operation for thousands houses.For many inhabitants, the practice of damage repair and strengthening has not been very effective and satisfying. First, the system of damage compensation, is neither simple nor expeditious; many citizens experience long waiting times, arbitrariness in causality and damage judgements and, as a result, unfair treatments. Second, after plans had been launched to inspect and eventually strengthen thousands of houses, the Minister decided to gradually reduce gas extraction. Immediately after that, he also decided to pause the intended strengthening operation, leaving many inhabitants in uncertainty about the current safety of their houses. In short, Groningen citizens don’t feel taken seriously by NAM, government and executing agencies, they are dissatisfied with damage settlements and their confidence in private (oil/gas companies) and public parties (government) has reached an all-time low. This situation has turned out to be very obstinate and difficult to turn. Our statement is that the architecture of the damage and strengthening operation is based on a systematic flaw. Although several minor changes have been made in the damage settlement and strengthening system, they have been limited to executing agencies and are not substantial. Therefore it is argued that, unless this structural flaw is being solved, the Netherlands will stay confronted with Groningen citizens whose trust in government is a far cry and will eventually lead to feelings of alienation.
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''Heritage buildings are often subjected to loading conditions that they were not exposed to in their earlier life span. Induced earthquakes in non-seismic regions caused by energy exploitation activities, or strains in the ground that are caused by the climate changes, are new phenomena that alter the usual loading situations for historical buildings.In this paper, monitoring results of a historical building in Groningen (Netherlands) in case of induced seismicity as well as climate change effects has been presented. Long-term monitoring results, detected cracks and relevance of the monitoring data are discussed. In the special case of Groningen, weak and agricultural soil properties dominate the structural response in the region. The gas extraction activities caused a soil subsidence in the giant Groningen Gas Field, resulting decameters of settlement in the entire area, thus an increase of the ground water level in respect to the ground surface. This is the reason why the heritage structures in the region are more vulnerable to soil-water-foundation interactions caused by climate change as compared to the time these heritage structures were constructed. The ground water monitoring as well as the interaction of soil movements with the structural response become important. The study presented here suggests ways on how to effectively monitor historical structures subjected to induced seismicity as well as harsh climate effects at the same time.It was shown here that the newly developed cracks on the structure were detected in a very narrow time window, coinciding with extreme drought and a small induced earthquake at the same time. One explanation provided here is that the soil parameters, such as shrinking of water-sensitive soil layers, in combination with small earthquakes, may cause settlements. The soil effects may superimpose with the earthquake effects eventually causing small cracks and damage. The effects of the climate change on historical buildings is rather serious, and structures on similar soil conditions around the world would need detailed monitoring of not only the structure itself but also the soil-foundation and ground water conditions.''
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Within the framework of resource efficiency it is important to recycle and reusematerials, replace fossil fuel based products with bio-based alternatives and avoidthe use of toxic substances. New applications are being sought for locally grownbiomass. In the area of Groningen buildings need reinforcement to guarantee safetyfor its users, due to man-induced earthquakes. Plans are to combine the workneeded for reinforcement with the improvement of energy performance of thesebuildings. The idea is to use bio-based building materials, preferably grown andprocessed in the region.In this study it is investigated whether it is feasible to use Typha (a swap plant) as abasis for a bio-based insulation product. In order to start the activities necessary tofurther develop this idea into a commercial product and start a dedicated company,a number of important questions have to be answered in terms of feasibility. Thisstudy therefore aims at mapping economic, organisational and technical issues andassociated risks and possibilities. On the basis of these results a developmenttrajectory can be started to set up a dedicated supply chain with the appropriatepartners, research projects can be designed to develop the missing knowledge andthe required funding can be acquired.
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.
