Retrofitting of infilled RC frames using collar jointed masonry

Masonry is a composite material made of masonry units bonded together with mortar. A large number of historical buildings constructed using masonry can be found all over the world. Little or no seismic loading was considered when they were built. Therefore, masonry structures often need to be retrofitted or strengthened. This research proposed a new strengthening approach using a collar-jointed technique. Namely, the approach is implemented by building another masonry wall parallel to the existing single-leaf wall and bonding the two together using a mortar collar joint. Furthermore, collar-jointed masonry wall construction is also a popular construction system in reality. This thesis considers two different types of collar wall strengthening applications: pre- and post-damaged walls. The results found out that the pre-damaged strengthening could improve the lateral resistance by about 50% while the post-damaged retrofitting can only restore the initial strength.

A simplified micro-scale finite element model for fracture in masonry walls was developed. The mortar joints and the brick-mortar interfaces are taken to have zero-thickness. The bricks were modelled as elastic elements while the brick-mortar interfaces were represented using a Mohr-Coulomb failure surface with a tension cut-off and a linear compression cap. One feature of the research was to identify the material parameters for the constitutive model. The material parameters were tuned by minimizing the difference between the experimental and numerical results of a single leaf wall panel. The model was then validated by assigning the parameters to the single-leaf masonry wall as well as to the double-leaf wall to predict its mechanical behaviour. Good agreement with experimental results was found.

Furthermore, masonry is also widely used in the form of infill panels within RC frames. Therefore, the collar-jointed technique has also been extended and applied to the infilled RC frame. The numerical results showed that the collar-jointed technique could provide some benefits to the composite structure.