Application of Smart FRP Devices for the Structural Health Monitoring of Heritage Buildings - A Case Study: The Monastery of Sant’Angelo d’Ocre

Abstract

The preservation of heritage buildings requires multidisciplinary skills ranging from materials and seismic design up to structural monitoring.One of the most interesting innovative solution that is being developing in the last years is based on smart FRP (FRP – Fibre Reinforced Polymer) devices, which can combine contemporary reinforcing and monitoring purposes. The use of composite materials has many advantages in comparison with traditional retrofitting techniques, such as low weight, high strength-to-weight ratio, ease of handling, drapability, speed of installation, low thickness and visual impact. At the same time, monitoring the structure during its lifetime (strain, cracks, temperature, etc.) and evaluating its in-service integrity, in order to predict possible anomalous situations, can be achieved by the combination of FRP materials and embedded fibre optic sensors into a smart FRP device, suitable for both reinforcing and monitoring purposes. Optical fibres can provide reliable measurement even in harsh environment, as they are chemically durable, corrosion resistant, stable and insensitive to external electromagnetic and environmental perturbations, allowing long distances signal transmission and several measures in different points along the same optical fibre (multiplexing). Furthermore, the embedding into composite material will preserve them from rupture during handling and installation.In the present work, the application of smart FRP devices for the structural health monitoring of the Monastery in Sant’Angelo d’Ocre, L’Aquila, performed in the framework of the national project PROVACI, is reported.Six Smart Patches, consisting of FRP reinforcing sheet with point FBG (Fibre Bragg Grating) sensors embedded were applied on the extrados of two different vaults, while four Smart Rebars, consisting in FRP pultruded bars with distributed optical fibres sensors embedded, were installed in four buttress of one same vault. All the smart FRP devices, after being cabled, have been connected to the relative control units (BraggMETER from Fibersensing for FBG sensors and OBR4600 control unit of Luna Technologies for the distributed optical sensors) connected with a remote server for on-line remote monitoring.Before the installation, the Smart FRP devices have been preliminary calibrated and tested in the laboratory in terms of mechanical properties, strain sensitivity and accelerated aging.The monitoring on the Monastery has been conducted for five months, showing the reliability of entire system and of the signal transmitted by each sensor over the time.