Unreinforced masonry (URM) has been traditionally used in structures as it offers considerable compressive strength. Nowadays, it is still in use either for structural elements in low seismicity areas or for secondary elements (e.g. infills) because it is easily available and cost-competitive. However, masonry's main defect is its lack of tensile strength and hence, failure is sudden with no considerable warning. The issue of upgrading masonry structures is of great importance as the vast majority of them are unengineered vernacular structures. Moreover, the latter combined with their deterioration due to ageing of materials, environmental induced degradation, experience of several earthquakes and lack of maintenance, contribute in their high vulnerability in seismic phenomena. Hence, there is a pressing need to increase their safety level and meet the current design requirements. Recently, an innovative structural material, the so-called Textile-Reinforced Mortar (TRM), was successfully developed for structural retrofitting of deficient masonry and concrete structures. TRM is an advanced sustainable material which offers well-established advantages (good behaviour at high temperature, compatibility to concrete or masonry substrates material high strength to weight ratio, corrosion resistance, ease and speed of application, minimal change of cross section dimensions) at a low-cost and mainly, it can be reversible. Over the last decade it has been reported in the literature that TRM is a very promising alternative to the FRP (Fibre Reinforced Polymers) retrofitting solution.
Researchers having studied the use of TRM on seismic strengthening of masonry structures concluded that TRM is a very promising alternative to the FRP retrofitting solution. However, development of reliable and accurate design models for masonry members strengthened with TRM is required for enabling their wide use in real applications. The available models in the literature are limited and in most cases, are validated only against few experimental data of single members.
An effort is put forward to develop a design model based on the characteristics of the textile material and the mortar strength and masonry able to describe the failure modes observed at masonry members strengthened with TRM jackets for in-plane and out-of-plane actions. The contribution of each component is taken into account additively (Figure). In this project, available data on masonry strengthened structural members (including piers and spandrel beams) and buildings retrofitted with TRM are used for developing and validating the proposed design models to calculate the capacity of the TRM strengthened members.
Finally, a clear basis to evaluate the efficacy and the design process of TRM strengthening strategy is provided focusing on a real URM full scale building strengthened with TRM and tested on a shaking table. Again the comparison with the actual performance of the structure shows the validity of the design process.
Normalised moment versus neutral axis for in plane failure: (a) masonry and TRM contribution, and (b) the sum of them.