Optimisation of Multi-type Sensor Placement for SHM based on application demands Rohan Soman PhD Candidate Cyprus University of Technology Limassol, Cyprus rohan.soman@cut.ac.cy Toula Onoufriou Professor Cyprus University of Technology Limassol, Cyprus Renos Votsis Post Doctoral Fellow Cyprus University of Technology Limassol, Cyprus Christis Chrysostomou Associate Professor Cyprus University of Technology Limassol, Cyprus Marios Kyriakides Post Doctoral Fellow Cyprus University of Technology Limassol, Cyprus Summary The research presents a multi-objective optimisation problem for a multi-type sensor placement for Structural Health Monitoring (SHM) on a long span bridge. The problem is formulated for simultaneous placement of strain sensors and accelerometers (heterogeneous network) based on the application demands for SHM system. The primary demands for SHM are Modal Identification (MI) and Accurate Mode Shape Expansion (AMSE). The optimisation problem is solved through the use of Integer Genetic Algorithm (GA) to maximise a common metric to ensure adequate MI and AMSE. The performance of the joint optimisation problem solved by GA is compared with other established methods for homogenous sensor placement. The results indicate that the use of a multi-type sensor system improves the quality of SHM and the use of GA improves the overall quality of the sensor placement compared to other methods for optimisation of sensor placement. Keywords: Long Span Bridge, Sensor Placement Optimisation, Mode Shape Expansion, Modal Identification, Modal Clarity Index, GA 1. Introduction The significant increase in the demands of the built environment observed over the last three decades, together with the limiting financial and natural resources have led towards the development of innovative techniques for monitoring the performance of structures. The methodology to monitor a structure through the evaluation of its in-service performance is known as Structural Health Monitoring (SHM). A proper SHM system can trigger alarms of structural deterioration early enough so as to schedule maintenance actions well in advance, thus reducing maintenance costs, and more importantly avoiding severe structural deterioration that can lead to collapse. This realisation has led to partial acceptance of the SHM systems for deployment on important infrastructure. The major hindrance in the widespread acceptance of SHM systems is the high cost of the SHM equipment. The aim of the bridge owners is to minimize the cost of the SHM system thus putting a restriction on the number of sensors used. This restriction makes it necessary to optimize the location of sensors for maximum information quality. Damage detection is a significant component of the function of the SHM. The traditional SHM systems typically monitor the global vibration characteristics of the structure like mode shapes and natural frequencies through the use of accelerometers or displacement transducers for damage detection. Due to the global nature of these properties, these systems are sensitive to large scale