Retrofit of unreinforced masonry (URM) buildings is continually attracting the interest of masonry professionals. This is because there are enormous URM building stocks in different parts of the world that have shown vulnerability to damage against out-of-plane actions due to having limited flexural strength and deformation resistance. As such, there is a global trend of promoting the development of different retrofit techniques for URM wall. Thus, this study proposed an experimental and numerical investigation into the possibility of retrofitting URM wall using oriented strand board (OSB) timber-panel. The aim is to estimate the improvements in the out-of-plane capacity of URM wall retrofitted with OSB panel. The study focuses on investigating out-of-plane behaviour because out-of-plane failure mode has been identified as the most critical failure mode of URM walls.
The proposed retrofitting approach is by securing an OSB/ type 3 timber-panel behind URM wall using threaded anchor rods together with an option of plastic plug or injection mortar. The methodologies adopted to deliver the overall aim and objectives of this study, as identified in this thesis were experimental tests and numerical analyses.
Flexural strength in the form of four-point bending tests has been obtained on nine small-scale masonry prisms (615 x 215 x 102.5mm) and six larger-scale masonry walls (1115 x 1115 x 225mm). The effectiveness of the proposed OSB-panel retrofit technique has been assessed in term of flexural strength, absorbed energy (toughness), out-of-plane load capacity and displacement. The test results show that OSB type 3 can considerably increase the load and flexure capacity of retrofitted masonry walls by (1.4 & 1.8), limiting toughness by (1.6 & 2.4) and overall toughness by (16 & 10) times that of plain wall subjected to out-of-plane loading for retrofit application on single (i.e tensile side only) and double-sides of the wall respectively. It can be concluded that the application of the proposed OSB retrofit technique greatly influenced the out-of-plane performance of the retrofitted wall and also prevents its quasi-brittle collapse.
Numerical analysis using commercial finite element software, ABAQUS was also performed and validated against the experimental data. The observed damage pattern and load-displacement plots compared with the experimental observations are in good agreement (within 5% difference). The calibrated model was then extended to parametric analysis to assess the model capability to simulate URM walls retrofitted with different OSB panel thickness, different connection spacing and different retrofit application position. The parametric analysis reveals that the thickness of the OSB timber is directly proportional to the out-of-plane load and displacement resistance of the system. It also shows that there is no enough composite action between the masonry and the OSB timber when the connection spacing is greater than 500mm. The parametric analyses revealed that the application of the retrofit on only the compression side does not improve the load capacity of the retrofitted walls significantly. Hence it is recommended that the application should be applied on the tensile sides of the wall or both sides where desirable.
Interestingly, the cost of applying this proposed OSB technique on a square meter of a masonry wall (materials and labour) is estimated to be £47 as against £152 estimated for typical fibre-based retrofit applications on 1m2 masonry wall using the market prices in England. The proposed retrofit technique in comparison with the other existing fibre-based retrofit techniques performed well in terms of increased capacity and it is cheaper and easy to apply.
