Comprising 516 pages, this tome is a compilation of contributions relating to structural health monitoring (SHM). In simple terms this book is about sensors, the acquisition of data and their interpretation. This is not a light bedtime read; it is both comprehensive in its coverage and rigorous in its explanation of theories behind the various techniques presented.
The introduction, ‘Structural health monitoring – a means to optimal design in the future', reveals much. The application of SHM is relatively new and future developments in both technology and asset management systems are needed to fulfil its potential benefits. All the lead authors but one (from the Bridges and Structures Division of the Government of Hong Kong), are University-based academics. Such an under-representation from those responsible for application of SHM is regrettable. Usefully, the introduction highlights the difference between non-destructive evaluation (NDE) and SHM, noting that ‘SHM requires diagnosis and prognosis (interpretation) of events or series of events with respect to parameters such as capacity and remaining service life'. Mere usage monitoring is not the goal of SHM.
Following the introduction, which is a worthwhile read, the first part of the book is devoted to various technologies (from Chapter 11 onwards it concentrates on examples of applications). The first chapter is a good introduction to potential applications and data analysis and is extensively referenced. There then follows a chapter that seeks to educate the reader in the highly theoretical electromechanical impedance technique for measuring the signature of a structure, a form of measurement that is unlikely to become main-stream in the near future. More promising as a future technology is the use of wireless sensors: the chapter on wireless sensors and networks contains a state-of-the-art review with sufficient detail not only to make it interesting to those who work in the technological area, but also informative for those who are responsible for implementing SHM strategies.
Chapter 4 outlines various remote sensing systems, including optical, radar including synthetic aperture radar (SAR) and light detection and ranging (LiDAR). It considers macro-scale usage of the techniques rather than those at micro-level (such as strain measurement) that are usually associated with SHM. In the following chapter magnetoelastic technology for monitoring cable forces in prestressed structures and bridges is explained. The theory is examined in detail and several examples of use are given, including the recently completed Stonecutters Bridge across Hong Kong's Rambler Channel. In Chapter 6 dynamic testing and vibration-based damage detection systems are explored, including a case study on a bridge rehabilitated with FRP composites. These techniques measure changes in stiffness over time. The following chapter discusses the use of operational modal analysis for vibration based SHM systems. This technique facilitates understanding of the overall response of a structure and estimation of its remaining capacity and future life expectancy. Unfortunately in this section far too much mathematical detail is used to explain ‘the frequency domain natural excitation technique' and not enough description or pictorial representation.
Chapter 8 explains the use of fibre optic sensors with a good balance of description, figures and mathematical theory. The historical background is interesting. The examples of strain measurement in bridge cables and detecting and measurement of cracks are relevant, although how the captured information can be used to estimate future life expectancy is not specifically explained. The following chapters describe data management and signal processing followed by statistical pattern recognition and damage detection. The transfer of data over the internet including security issues and the effective storage of data requirements are featured, as is possibly one of the most important considerations of SHM: having collected the data, how are significant changes in behaviour detected?
The final part, comprising one third of the book, comprises case studies of actual applications to bridges and to historical structures such as the Holy Shroud Chapel in Turin (Italy). Chapter 12, relating to cable-supported bridges in Hong Kong, is particularly interesting and comprehensive. It contains graphical displays of the wind-induced response of Tsing Ma suspension bridge and diagrammatic representation of the extensive monitoring systems installed on the Kap Shui Mun, Tin Kau and Stonecutters cable-stayed bridges. The book concludes with chapters on current SHM research in Europe and China.
This book is recommended reading for those seeking to gain a comprehensive understanding of the features, benefits, limitations and theories associated with SHM and for occasional reference by practising engineers and structure owners.
