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Basic study of monitoring on fibre reinforced polymers: theoretical and experimental study

Recent research activities, technological utilization and commercialization activities in sensors and acquisition systems for monitoring have strongly supported the introduction of these innovations and new concepts in civil structural engineering. The impact of monitoring and assessing the health state of infrastructures, as well as new and old constructions, has become important and it seems to be one of the largest industries in the world. With the aim of monitoring new or repaired structures various monitoring systems have been extensively employed in recent years. In particular, in this paper attention is focused on the procedures usually adopted for monitoring the strengthening systems based on fibre reinforced polymers (FRPs) applied to civil structures. Electrical strain gauges are often used to detect strain variations, but on composite materials the measures can be affected by various factors, such as the characteristics of the resin coating, the type of glue and the gauge length. In this paper the measurement errors on FRP elements are studied, from a theoretical approach developed in previous work on a deterministic basis. This approach is extended to the probabilistic field, with the aim of performing a sensitivity analysis of the basic variables which can cause errors in strain measurements. Additionally, the previous approach is extended to study the effect of the deviation of the direction of the gauges from the longitudinal axis of the FRP sheets. Finally, a comparison with experimental data is performed.