Out-of-plane retrofitting of masonry wall using engineered cementitious composites.
Bazkiani, Saeed Pourfalah
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The contribution of infill masonry walls to the overall behaviour of frame structures has been acknowledged through numerous published experimental and numerical investigations. Both the in-plane and out-of-plane response of such walls have a significant effect on the overall structural performance of frames and can be subjected to a range of in-plane and out-of-plane actions (e.g. wind, earthquakes, impact and blast loads) characterised by different time-histories, loading-frequencies and intensities. Infill walls are particularly vulnerable to the application of loads in the out-of-plain direction and often sustain significant damage (in the form of cracking) which can result in failure and collapse. It is interesting to note that after sustaining a certain level of damage due to the load applied in the out-of-plane direction, an infill wall can no longer contribute to the in-plane response of a frame. In an attempt to enhance the overall behaviour of infill walls, present work sets out to develop a method for improving the out-of-plain behaviour of such elements. This is achieved through the use of a thin layer of engineered cementitious composite (ECC) which is fully or partially bonded on the face of the wall which is in tension (opposite to the face on which the out-of-plane action is applied) or on both faces of the wall. For this purpose, an ECC mix is initially developed employing materials available in the UK. Its behaviour is then established experimentally under increasing loading rates and temperatures. This material is then used to strengthen a series of beam-like masonry specimens under different loading rates by conducting a series of static and dynamic 4- point bending tests. The test data obtained is then employed to develop a numerical model of the problem at hand capable of realistically predicting the experimentally established behaviour through the use of nonlinear dynamic finite element analysis. Both, experimental and numerical studies, reveal that in all cases considered the use of ECC resulted in a significant enhancement of the out-of-plain behaviour of the specimens in terms of strength, stiffness and ductility. Furthermore, the specimens with a partially bonded ECC layer performed better compared to those with a fully ECC layer. In addition, the performance of these specimens under impact load was further enhanced when adding a second layer on the other face of the specimen. Finally, a parametric numerical investigation is conducted to assess the effect of a range of parameters (associated with the boundary conditions imposed onto the specimen, the properties of the materials involved, the geometry of the specimen and loading rate) on the behaviour of the specimens.