Why We Need Structural Health Monitoring? Owners and maintenance managers of capital-intensive assets are looking for cost-effective and reliable inspection and monitoring solutions to ensure safety and reliability of these structures. Modern design codes are now looking in a much longer service life. For example, The Canadian Highway Bridge Design Code (S6-14, 2014) considers a service life of 75 years for newly constructed bridges. One good example in this case is the New Champlain bridge in Montreal, Canada which is designed for a 125 years in service. Moreover, municipalities, provincial and federal government are becoming interested in the concept of “Smart City”. This vision aims at implementing advanced technologies to create value-added services for citizens and administration of the city (Bui et al, 2014). In the context, proper inspection and maintenance become more important than ever. Modern Structural Health Monitoring (SHM) and innovative Nondestructive Testing (NDT) solutions have been developed in response to such a need.
Another important application of Structural Health Monitoring is to improve reliability of existing infrastructure. Existing infrastructures in North America are rapidly approaching the end of their design service life. According to ASCE 2017 infrastructure report card, nearly 10% of bridges (about 56,000 bridges) in the United States have some sort of structural deficiency, which makes them vulnerable. The conditions in Canada is not much better. There are about 75,000 highway bridges in Canada; According to the National Research Council of Canada (NRCC 2015), almost one third of these bridges have structural or functional deficiencies. The collapse of Ponte Mirandi in Genoa, Italy in August 2018 clearly shows that existing infrastructure require immediate attention. With limited resources available to governments, the questions is how implementing SHM systems can help maintenance managers and decision makers prioritize rehabilitation and replacement programs.
But What is Structural Health Monitoring?
Structural health monitoring (SHM) refers to an array of connected sensors to collect and analyze data, at every moment during the service life of the structure. The goal of such system is to identify and quantify any damage or deterioration state that might occur over the service life (Balageas, 2006). While SHM systems might vary in their architecture and deployment, they all encompasses four distinct subsets (Chang, 2003):
- Periodic measurement by an array of sensors;
- Structural identification;
- Processing data to identify damages;
- Analysis of results and Decision making.
Implementing SHM systems is a step forward towards proactive maintenance systems. Existing maintenance protocols are generally based on reactive strategy; it means that repairs and interventions are usually performed when a damage has already happened. From a life-cycle cost analysis perspective, this can be a more expensive option for the organization. These interventions often come with unplanned downtime of the structure or facility, and the repair solutions are not as effective. SHM systems can help identify and quantify these structural defect in early stages, when repair and rehabilitation will be more cost effective, and more efficient.
Depending on the structure type, its environment, and different aspect of structural and durability performance, an array of sensors are used in SHM systems. sensors can be as basic as temperature and humidity, or advanced vibration monitoring, or acoustic emission systems.
If SHM is Good, Why Are we Not Using it?
While structural health monitoring solutions look to be promising, there has been a number of issues that have limited their use in real engineering practice. In this section, we will review some of these aspects.
Cost of SHM Systems
The deployment of structural health monitoring systems has not been widespread, mainly due to the cost associated with the technology and installation of these systems. Most existing SHM solutions are relatively expensive.
What Sensors to Use
Another aspect of SHM system which remain confusing for many owners and maintenance managers is the type of sensors that are needed. The selection of a good array of sensors is an important task, and requires solid structural, material, and environmental engineering.
Installation of SHM Systems
Existing practice for structural health monitoring (SHM) solutions heavily rely on tethered (wired) systems (Lynch and Kenneth, 2006), where extensive wiring is required to collect various information at element level and transmit to a centralized data acquisition system. This has made installation and implementation of SHM relatively time consuming, labour-intensive, and expensive.
Interpretation of Test Results
Using SHM systems mean collecting a large amount of data in real-time. Analysis and interpretation of test results has remained a challenging issue. It is specially challenging to identify data related to changes in the environment, from those that are from defects in structural components. Decision making based on this data requires special set of skill.
The Future is Bright
Recent advancements in sensing technology (i.e. MEMS, Acoustic sensors, fiber optics) and latest developments in the Internet of Things (IoT), mobile networks (5G), and wireless connectivity (Wi-Fi, Bluetooth 5) are finally creating a promising platform for the inspection and evaluation of structural systems. SHM systems based on these new technologies have the potential to collect precise information about every event and pave the way to create proactive maintenance systems. The architecture of structure and environment friendly SHM systems looks very promising for the first time, and is about to disrupt the old-fashion inspection and monitoring forever.
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