## 2 Bridge Structural Health Monitoring (SHM) System
### The Importance of Using the SHM System
According to their findings after studying a considerable amount of literature on the topic, many elements of SHM approaches and technologies still need further research. Additionally, they have identified a few research gaps in the SHM approaches. [PERSON], and [PERSON] [38] presented a study on opportunities and challenges in SHM systems. They discussed conventional approaches to visual, destructive, and nondestructive evaluation in SHM systems. They also discussed how SHM can be used with IoT and what its pros and cons are based on what has already been conducted. After the final reviews, they decided that it was clear that SHM would benefit greatly from the IoT if technical problems like energy use, scalability, data security, and reliability were dealt with. In another review, [PERSON] et al. [39] reviewed the scientific research on the SHM systems that has been done on some US bridges over the last 20 years. A number of US monitored bridges were examined in terms of monitoring devices, monitoring scope, and key findings based on documentation in the scientific literature. [PERSON] et al. [40] introduced the development of a SHM and an event-based classification system for managing bridge scour. This system goes beyond and adds to the current risk-rating procedures by including information from different sensors and the different sources of uncertainty that affect scour estimates. Their proposed system was based on a probabilistic framework for estimating scour risk. This framework can be used to classify the scour risk of bridges in real time during a heavy flood. A summary of the process of evaluating the performance of bridges under a SHM system is shown in Figure 2.  
There are significant dangers to the current bridge infrastructure, such as damage and inefficiency. Natural or man-made disasters, such earthquakes and explosions, compound these issues. The reliability of public infrastructure like bridges is crucial in modern societies. Using these kinds of buildings, particularly in the aftermath of earthquakes and other natural catastrophes, helps to reduce the problems after these disasters as much as possible. In order to do this, the infrastructure's problems need to be diagnosed and figured out. The SHM of bridges can increase the service life of bridges and reduce the costs required to repair and strengthen the bridge structure [41; 42]. In fact, the use of SHM for bridges can reduce the unforeseen economic costs of maintenance, and by increasing the safety of bridges, it can prevent irreparable disasters. During the monitoring period, a full history of the bridges' structures can be gathered. This means that the technicians will keep a record of all the inspections done while the bridge is in use. All the documents related to these inspections will also be kept in these records. This makes it possible to predict damage more accurately [43]. Here, structural health monitoring may be used as a novel non-destructive test (NDT) or non-destructive evaluation (NDE). The technology depends on a number of things, such as sensors, the ability to send and receive data, smart materials, intelligent computations, and the ability to process structures [44; 45]. If bridges are not regularly inspected and maintained, they might become less effective, get damaged, or even be destroyed. This may have both immediate and long-term consequences for the individuals who rely on these systems in their daily lives and professional endeavors. Several disasters related to the lack of attention to structural health monitoring in recent decades caused a change in attitudes towards the importance of structural health monitoring. In the middle of rush hour on a warm day in 2007, the I-35W bridge in Minneapolis, Minnesota, crumbled into the Mississippi River below. Thirteen people were killed, and the collapse exposed to engineers how badly the U.S. [46]. infrastructure was aging. Because of this, engineers worked harder to control, fix, and improve the situation.