Discuss the principles of structural health monitoring (SHM) and its significance in ensuring the safety and integrity of civil engineering structures. Explore the various sensors and monitoring techniques used in SHM systems to detect structural damage, such as strain gauges, accelerometers, and acoustic emission sensors. Analyze the role of SHM in facilitating condition-based maintenance strategies and extending the service life of infrastructure assets. Consider the challenges and opportunities associated with implementing SHM in different types of structures.