Out-of-plane (OOP) collapse is one of the most observed damage types in masonry structures during strong earthquakes. OOP strength of a masonry wall depends on several parameters such as the dimensions of the wall, vertical restoring force, boundary conditions and material properties, which are parameters creating complex kinematics during an earthquake. Testing of OOP response of a masonry wall is thus a challenging task, also because additional to the complexities mentioned, the seismic forces triggering OOP are caused by inertia of the wall itself, a phenomenon that needs dynamic testing. All these facts make shake table tests of masonry walls for capturing the OOP response extremely relevant. This paper presents shake table tests on a total of four wall specimens, two of which were reference walls and the other two were strengthened solid masonry walls. The tested walls built to represent the characteristics of Groningen houses built before the Second World War and also the historical masonry structures in the region. The strengthening methods applied are the deep-mounted carbon strips embedded in flexible epoxy and helical bars applied in mortar beds. The shake table tests presented here show that OOP specimens not including the additional masses imposed by the floors may oversee important kinematic response characteristics of the walls. Furthermore, tests have also shown that even serious cracks caused by OOP response close when the shaking stops, which causes damage on the walls and significant decrease in the stiffness, but they are extremely difficult to be caught by human inspection. This has consequences in terms of ongoing damage inspection and compensation efforts taking place in the Groningen gas field. The strengthening methods applied to the two specimens have shown clear improvement in strength, and a partial improvement in progression of damage.
Two strong earthquakes hit Thessaly region on March 3rd, 2021 (Mw = 6.3) and on March 4th, 2021 (Mw = 6.1). The epicentres of the earthquakes were located at approximately 23 and 29 km respectively NW of Larissa, one of the most populous cities in Greece. Several aftershocks followed thereafter. Although no injuries were recorded, several structures suffered significant damage close to the epicentre, while some others collapsed. Approximately 300 residents of the village of Damasi were transferred to temporary settlements and tents. The event occurred during the COVID19 lockdown and created significant stress and disruption to residents. This paper focuses on the earthquake swarm itself as well as the damages observed in residential buildings, schools, and churches in the earthquake-stricken region. The earthquakes mainly impacted low-rise domestic masonry buildings, while the more modern reinforced concrete structures built following the recent seismic regulations were almost unaffected. The typology of buildings in the region, together with photographs demonstrating the extent of damage are presented herein. Despite the rather satisfactory performance of modern buildings in recent earthquakes in Greece, the preliminary investigations from the Thessaly Earthquakes showed that there is still a significant level of vulnerability in existing masonry building stock constructed using traditional methods and materials. This issue could re-emerge in future earthquakes striking other rural areas of Greece, something that needs to be addressed systematically in the future.
Masonry structures comprise a significant portion of the historical building stock all over the world. Previousstudies have clearly pointed out that unreinforced masonry buildings are vulnerable against extreme loadingconditions, such as seismic actions. Therefore, strengthening is inevitable in most cases for historical masonry towithstand severe loads. In this paper, the efficiency of fabric reinforced cementitious matrix is investigatedexperimentally by using diagonal tension tests. Fourteen wallets with a nominal size of 750x750x235 mm wereproduced with using solid clay bricks and a low-strength mortar. The bricks were collected from the structuralwalls of an early-20th century building under restoration. The low-strength mortar represents the historicalmortar commonly used in similar historical brick masonry buildings located in Istanbul, Turkey. By testing thespecimens under monotonic diagonal compression loads, the effects of different types of plasters on the walletsurface, varying types of fibers used in textile reinforcement and anchors used for the connection between FRCMand substrate are investigated. Although the wallet samples have inherent shortcomings in representing overallcomponent response accurately, still the qualitative findings are enlightening the effectiveness of the FRCMsystem by increasing shear strength, stiffness (shear modulus) and dissipated energy of the masonry wallets. Thestrengthened specimens were failed due to shear sliding along a bed joint and/or by a stair-shaped separationwhile the refence specimens were failed due to the splitting of the specimen into two parts in the stair-steppedshape and a slipping through a bed joint.
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A series of tests performed on as-built and strengthened timber joist-masonry-wall specimens. The test aims at providing a complete characterization of the behaviour of the timber-joist connections under axial cyclic loading. The obtained results will be used as inputs to calibrate numerical models to simulate the connection between the cavity wall and timber joist.
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.
Governments, fishermen, dredgers, nature organizations and researchers see that sand stocks are dwindling worldwide, while more and more sand from the North Sea will be needed to protect our coast against rising sea levels. We also extract a lot of sand in the Netherlands, especially from the North Sea. Every year we extract about 12 to 15 million cubic meters to protect our coast and about 15 million cubic meters as filling sand for roads and residential areas and for concrete and masonry sand. Every year we excavate a piece of seabed with the surface of the Schiermonnikoog island at a depth of about eighty centimeters. But our sand requirement continues to rise. Not only because we want to build more roads, homes and residential areas, but also because rising sea levels mean we need more and more sand for coastal protection. In this project a consortium of 21 partners and stakeholders will develop new knowledge and tools about the effects of sand extraction, with the goal to understand how it may be done sustainably despite the rising need for it. The project is led by Wageningen Marine Research and has been awarded funding under the ‘Onderzoek op Routes door Consortia’ (NWA ORC-call 2020/2021) scheme of the Dutch Research Council (NWO). Breda University of Applied Sciences will contribute with its MSP Challenge Simulation Platform, thereby developing and applying a bespoke sand extraction oriented North Sea edition, in close collaboration with data and simulation providing partners in the project.
