Keywords: unreinforced masonry, finite element method, macro modelling, textiles, retrofitting, fibres.

As unreinforced masonry is a heterogeneous building material with only low tensile strength and low ductility its resistance to dynamic horizontal loading like earthquakes is insufficient. Hence there exists a need for the use of modern retrofitting techniques especially for existing older buildings. The application of retrofitting techniques requires simulation models to calculate the load bearing capacity of retrofitted buildings. This paper deals with a numerical model for the retrofitting of unreinforced masonry by adhesive bonding of carbon fibres textiles. Practical knowledge showed that this retrofitting technique provides a good improvement of the ductility and the tensile strength of masonry.

The difficulties in adopting existing numerical tools from more advanced research fields, namely the mechanics of concrete, rock and composite materials, are hindered by the particular characteristics of masonry. Masonry is a composite material of units and mortar. Because of the specific material and bonding characteristic between the constituents it is difficult to predict its mechanical behaviour. One possibility for the numerical simulation is a detailed analysis on the micro-level, where the units, the mortar and the unit-mortar interface are modelled separately. As this approach is only suited for small structural elements with particular interest in strongly heterogeneous states of stress and strain, in large and practice-oriented analysis the knowledge of the interaction between units and mortar is, generally, negligible for the global structural behaviour.

In these cases a macro-modelling approach can be used, where the material is regarded as an anisotropic composite and a relation is established between average masonry strains and average masonry stresses. In the present work a two- dimensional non-linear macro-model for unreinforced masonry under dynamic loading on the basis of the concept of equivalent uniaxial strain using the biaxial Mohr-Coulomb failure criterion is exerted. This plain stress model was implemented into the Finite Element software tool ANSYS. It was verified and modified on the basis of results from literature.

In the next step the retrofitting with fibre textiles was added to this model. Therefore the tension stiffening due to the participation of the masonry between the cracks was modelled using a modified fibre characteristic curve similarly to the steel in reinforced concrete. The supporting points of the fibre characteristic curve thereby depend on the angle between the reinforcement and the masonry's main stress direction. The computational results accorded well with experimental data from literature.

Using these material models the capacity curves of a single building had been computed. By comparing the curves of the original and the retrofitted structure an expansion of the capacity could be shown which leads to an improvement in the seismic resistance.

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