## 3 Innovative SHM Techniques
### Distributed Sensors
It was found that the use of such smart textiles was a cost-effective solution to reinforce and, at the same time, monitor masonry and heritage structures, enhancing their ductility and providing an alarm signal in case of structural damage. Several novel sensors, data processing techniques, and adhesives were developed and prototyped. Product functionality and performance were evaluated with a series of laboratory field tests on masonry structures and geotechnical sites, as well as with numerical simulations. [PERSON] et al. [126] applied \"smart FRP devices\", consisting of FRP reinforcing sheets with embedded FBG sensors and FRP pultruded bars with DFOS, for reinforcing and monitoring some masonry vaults and buttresses of the Monastery of Sant'Angelo d'Ocre, L'Aquila. Before the installation, the efficacy of the multifunctional textile to correctly measure the strain of the structural elements was successfully assessed by performing flexural tests on small-scale reinforced masonry beams. [PERSON] et al. [127] reported the results of the POLYMAST project, which aimed to use a shaking table to test a two-storey stone building reinforced with a \"composite seismic wallpaper\" made of glass and polymeric multiaxial textile connected to the substrate using a cementitious matrix (see Figure 7). FBG sensors from different companies (some developed in the context of the POLYTECT project [125]) were embedded in the textile fabric, and their SHM capabilities were compared. It was found that, regarding the experimental modal analysis, not all sensors could capture the vibrations induced by the hammer tests. Regarding the strain measurement during the shaking test, the results showed a good correlation between strain measured by the different FBG sensors, and plastic deformations were also detected. The authors concluded that the system could effectively solve the seismic retrofit of existing masonry buildings. Furthermore, the embedded sensors proved to detect seismic-induced damages in terms of crack openings and residual strains. Figure 7: Application of the multiaxial textile with integrated SHM sensors on a stone masonry building within the POLYMAST project (from [127]). [PERSON] et al. [128] proposed an innovative seismic retrofitting and monitoring technique for masonries using glass fiber reinforced cement matrix (GFRCM) composites with an integrated fibre optic sensing system based on FBG sensors. The new combined system was designed and applied to an old masonry pavilion vault. The retrofitting technique's effectiveness and the FBG sensors' optimal position were verified through a nonlinear FE model. An experimental campaign verified the valuable information obtainable by the FBG sensors, even in the range of moderate deformations. Finally, the comparison between simulated and measured strain evidenced a reasonable agreement with the obtained results. It was concluded that this system demonstrated its capability to long-term and continuously monitor the mechanical behaviour of strengthened masonry structures and, in particular, to detect on-site masonry damage or detachment phenomena. The use of FBG sensors integrated with textile reinforced mortar (TRM) was also investigated by [PERSON] [129], exploiting the TRM composites developed by [PERSON] et al. [130] (Figure 8). Specifically, three optical FBG sensors were attached at the central roving point of the textile of a TRM coupon tested in tensile. The stress-strain curves of all three optical FBG sensors are presented and compared with the corresponding average response obtained by two LVDTs, showing a good agreement, mainly after the development of the cracking pattern of the TRM coupon. The authors concluded that using optical fibres for monitoring TRM jacketing externally applied to existing structures seems quite promising and worthy of further investigation in future research. Recently, [PERSON] and [PERSON] [131] analysed the tensile behaviour of a textile reinforced composite with DFOS embedded in the matrix.