# A BIM-Enabled Workflow for the Rehabilitation of Heritage Steel Bridges
## 2 Current State of the Art
### Traditional Heritage Steel Bridge Rehabilitation Process  
As mentioned before, the rehabilitation of heritage steel bridges presents a range of technical challenges, primarily driven by structural deterioration, corrosion, and fatigue. Over time, these factors compromise the integrity and performance of bridge components, posing risks to safety and functionality. As the structure is subjected to loads from traffic and environmental forces, critical structural elements are subjected to wear and tear, weakening their capacity to withstand additional stress. Cracking, deformation, and material thinning are common issues that arise and they require rigorous inspection and repair strategies. For steel bridges, corrosion remains one of the most persistent challenges, especially in joints and connection points. Prolonged exposure to moisture and de-icing salts accelerates material degradation, compromising both structural integrity and durability. Corroded elements reduce load-bearing capacity, increasing the vulnerability of the structure. This degradation often complicates maintenance and repair efforts, as the weakened components carry a heightened risk of further damage during intervention. Corrosion can cause additional issues due to stuck bearings, which are meant to allow free movement (e.g., a simply supported bridge may be transformed into a double-pinned one). This unintended shift alters load distribution, increasing stress on certain components (e.g., piers), potentially leading to unaccounted failure modes. Another key issue of steel bridges is posed by fatigue (i.e., the repeated stress cycles from dynamic loads, leading to micro-cracks that propagate over time). This issue is particularly critical in bridges with high traffic volumes or those exposed to heavy vehicles. Fatigue-related failures are challenging to predict, requiring advanced monitoring techniques and detailed modelling to identify vulnerable areas. The rehabilitation of heritage steel bridges involves complex processes that require the integration of diverse data sources, stakeholder collaboration, and compliance with technical standards. Efficient and effective information workflows are crucial in order to streamline these activities, reduce uncertainties, and ultimately enhance decision-making. The general process is presented in Figure 2 and focuses on two key aspects: these are (i) structural integrity, emphasizing the technical assessments and interventions required to ensure the safety and functionality, and (ii) compliance with standards, ensuring that all legal and engineering requirements are met. The rehabilitation process starts with the identification of intervention needs, often prompted by routine inspections, structural performance reviews, or general safety concerns, as presented before. Next, phase 1 starts. Within this phase, a preliminary on-site visual inspection is performed that allows the study of the bridge's current state, followed by a thorough review of historical records, including design documents, maintenance logs, and past inspection reports, to piece together its operational history. Putting together all these details, a preliminary technical assessment is performed that focuses on visible issues such as corrosion, cracking, or noticeable deformations. If critical problems are identified, immediate safety measures are implemented, while further investigations are carried out. Next, phase 2 commences. The available information is assessed to determine whether it provides sufficient information to correctly evaluate the bridge's condition. When information is lacking, or it is unreliable, additional investigations are required. Along these lines, advanced technologies like laser scanning or drone surveys might be used to create precise geometric models, while detailed inspections with non-destructive testing methods, such as ultrasonic or radiographic tests, can offer deeper insights into the structure's material and overall health.