Out-of-plane shake table tests on solid masonry walls with timber floors

Abstract

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.