# Structural Monitoring of a Drawbridge in Operation: Signal Analysis
## 1 Introduction  
Maritime transport, while not the most relevant type of passenger transport with a share of less than one percent in 2022 in the European Union [1], is responsible for over 80% of the world's merchandise trade by volume [2], representing over 60% of European freight transport during the same year [3]. This means that the smooth operation of ports and waterways is of utmost importance for global trade. On the other hand, bridges are a vital part of road transportation systems, being responsible for ensuring fast connections and connecting communities. Due to their operating principle, drawbridges, also known as bascule bridges, have to interrupt road-based traffic to allow larger vessels to pass, and thus can have a significant influence over both water- and road-based transport systems. Therefore, their continuous and predictable operation is paramount, especially for drawbridges located in ports. However, due to the fact that this type of bridge may have to open and close a number of times per day, they are subjected to more strain and wear than a typical bridge. Monitoring bridges is an essential and crucial activity in every type of bridge, but even more so in drawbridges, whose inoperability can severely impair trade and disconnect communities. Traditionally, this activity is performed manually and periodically, relying heavily on visual assessments to detect flaws that may already be at an advanced state of damage [4, 5]. [PERSON] et al. [6] performed a study on the research and innovation projects in new technologies for bridge inspection and monitoring in the European Union. This provides an overview of recent European policies aimed at promoting the implementation of innovative technologies in the inspection, monitoring, and maintenance of bridges. It highlights and evaluates Research and Innovation (R&I) projects pertinent to bridges, considering the financial allocations under the Horizon 2020 European Research Framework Programme, and concludes that, while research on this topic is substantial, data analysis should continue to be a relevant topic of research. The document also systematically examines the technologies and solutions produced by these projects, alongside assessing their level of technological maturity, and few of the analyzed projects reached the deployment phase. [PERSON] et al. [7] present a review of applications that use wireless smart sensors and wireless smart sensor networks (WSSN) for Structural Health Monitoring (SHM). Most of the full-scale SHM applications in bridges that were reviewed for the paper focus on measuring acceleration, and a few additionally measure strain and displacement. Although wireless sensors are becoming more and more common, are easy to install, and have lower costs than traditional wired counterparts, they still have some drawbacks. Among these, limited power resources, insufficient computing capabilities, and environmental vulnerabilities were identified as some of the most relevant. This work also highlights that WSSNs still do not meet the requirements for monitoring complex structures, especially metallic ones. [PERSON] et al. [8] propose a wireless IoT-based bridge health status monitoring and warning system focused on inclination measurements. Its main goals are, similarly to most SHM systems, reducing bridge maintenance costs, the extension of lifespans, and the enhancement of transportation safety through an early warning system. While it was developed and tested in lab conditions, it has not yet been deployed. [PERSON] et al. [9] present the lessons learned on Bridge SHM after decades of experience, where they highlight that it has been a valuable tool in better understanding the reality of their environment.