Use of RPAS (Drones) for the Inspection of Century-Old Metal Structures: Example of Application on the Requejo Bridge

Abstract

This article presents a technical analysis of the Requejo Bridge, an outstanding example of metallic engineering spanning the Duero River in Zamora, Spain.

Constructed between the late 19th and early 20th centuries, the bridge was designed to connect the regions of Sayago and Aliste, facilitating communication in an area defined by its challenging topography. The structure masterfully combines functionality and aesthetics, featuring a central metallic arch that supports the deck. Since its inauguration in 1914, it has been celebrated as a symbol of progress and Spanish industrial heritage.

The study focuses on inspections conducted to assess the current state of the bridge, with an emphasis on the use of drones (RPAS). These devices enabled a detailed and comprehensive visual analysis of the entire structure, overcoming the accessibility challenges inherent in historical constructions. The inspections revealed corrosion-related damage, particularly in hard-to-reach areas, as well as aging-related deterioration of the previously applied anti- corrosion protection system. While these issues did not immediately compromise the bridge’s functionality, they underscored the need for mid-term interventions to ensure its long-term preservation.

This work evaluates the effectiveness of drones as a tool for inspecting large heritage structures, highlighting advantages such as reduced risks to workers, lower costs and shorter execution times, and the ability to gather detailed data for use in management systems and condition monitoring.