Smart reinforcement steel bars with low-cost MEMS sensors for the structural health monitoring of RC structures

Structural health monitoring (SHM) of civil structures and infrastructures is increasingly drawing the attention of stakeholders and of the research community because of the emerging need in the optimal maintenance and management of the existing assets. The monitoring of reinforced concrete (RC) structures through measuring local strains is a valuable procedure but only a limited number of alternative technologies are currently available, mainly including electric strain gages and fibre optic sensors. The difficulty of their installation, the high cost of their sensing and/or interrogating equipment and their uncertain long-term reliability push for alternative low-cost and distributed systems, easier to install and use. This paper presents a new concept of an instrumented reinforcement steel bar, achieving strain-sensing capabilities through the incorporation of an ordinary low-cost embedded Micro Electro-Mechanical Systems (MEMS) sensor. According to this concept, a sealed cavity is made in the bar, filled with a fluid and hosting the MEMS sensor; the temperature and pressure readings collected by the MEMS sensor are used to evaluate the cavity volume variations and are thus correlated with the bar axial deformation. The proposed smart system shows significant advantages over current strain-measurement devices, proving cheap, durable, easy to install, robust to mechanical shocks and chemical aggression. The theoretical framework of the new concept and the results of a preliminary mechanical test campaign are here presented and discussed.