Structural health monitoring of masonry structures using stress sensors: Experimental induced damage tests and proposed approach for real-time monitoring

The paper presents an experimental and numerical study investigating the effectiveness of two innovative stress sensors, i.e. piezoelectric and capacitive stress sensors, for use in Structural Health Monitoring (SHM). These sensors are installed within the mortar bed-joints and can measure vertical stress variations. The capability of the sensors in revealing stress state variations due to external events is experimentally tested by performing induced damage tests on two half-scale masonry wall specimens made of three piers and monitored by both the typologies of stress sensors. Two types of masonry, clay brick and calcarenite brick, are investigated. Experimental tests provided damage simulation by progressively reducing the cross-section of the central pier of the specimens by keeping the vertical load constant. Experimental sensor outputs are compared to those resulting from a reference refined finite element micro-model simulating the experimental tests. Simplified fiber-section equivalent frame modelling of masonry is finally proposed and tested as a computationally effective approach for real time monitoring. Results show that vertical stress variations in masonry structures can be effectively detected by the investigated sensors and potentially interpreted for the early prediction of structural stress-state modifications that can be eventually related to an ongoing damage.