Seismic Performances of Thin-Bed Layered Masonry Walls Made of Clay Blocks and Comprising a Door Opening

Abstract eng:
Seismicity level in North-European countries is obviously lower than in other well identified seismic countries like Greece or Italy. Significant earthquakes can however occur, even if they are more spaced in time. On the other hand, traditional masonry construction in countries like Belgium, Netherlands or UK exhibits some aspects that are not particularly suitable for earthquake resistance purposes. One point is that no confining elements are used. Another point is that the wall is structured as follows: a facing wall with no structural role, a gap for insulation purposes and a bearing wall with rather limited thickness (between 10 and 20 cm). The use of such thin structural walls implies that they must be realised with material exhibiting a relatively high resistance, in particular when used for building made of bearing unreinforced masonry up to 4 to 5 levels, which are nowadays common. To this purpose, clay block manufacturers are producing units made of pure clay that can exhibit nominal resistance up to more than 20 MPa but that have as a counterpart a relatively brittle behaviour, thus a priori less suitable for earthquake conditions. However, the recent transposition of Eurocode 8 for low-to-moderate seismicity areas implies that some seismic guarantees need to be given. The use of conservative models considering masonry structures as a set of cantilever walls does often not allow justifying the seismic resistance of usual buildings even with design accelerations only up to 1 m/s². It is therefore necessary to consider the coupling effects of lintels and spandrels and to consider the structure as a frame. According to design codes, this is however only allowed if the lintels and spandrels are "regularly bonded and correctly connected". In this perspective, this contribution presents in a first part results of cyclic tests carried out on 5 walls with dimensions 3,0 x 2,8 m (one full wall and 4 walls including a door opening with different configurations of lintel). It presents then a comparison of experimental and numerical results both in terms of stiffness and resistance. Two types of models are considered, i.e. 2D-membrane elements (using FE software Lagamine) and equivalent frame model (using AmQuake software). The first objective is to identify experimentally the actual behaviour of walls made of high-strength clay blocks including a door opening with a focus on the efficiency of the coupling by the spandrel. The second objective is then to validate numerical models that could be used for the seismic safety assessment of entire unreinforced clay masonry structures typical from North-western European countries.

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