Multi-scale structural integrity assessment of a series of identical components in cultural-heritage structures: The case of the Clifton suspension bridge

Cultural-heritage structures may be characterised by structural elements that are geometrically identical for cosmetic or functional reasons but can be subjected to a significant variable stress distribution because they are located in different positions on the structural system. This can lead to a variety of damage and failure phenomena that will probably occur asynchronously. Damage occurrence triggers discussions among the stakeholders and decision-makers. For heritage structures, repair and restoration actions are costly and constrained by laws regulating grade-listed systems. Therefore, it becomes imperative to understand if such actions are necessary and to identify the most suitable intervention. The research question is: how can future maintenance costs be minimised while preserving the historical value of legacy structures? The answer lies in the reduction of uncertainties using a multi-scale approach that combines: (a) multi-scale knowledge of the material nature and fabrication, (b) multi-scale empirical evidence on material mechanical properties, (c) detailed geometrical description of the system, and (d) multi-scale numerical models. The challenge is finding the optimal trade-off between maintenance and historical value. Such a multi-scale framework is applied to the parapet stanchions of the Clifton Suspension Bridge in Bristol, UK. Stanchions are vertical cast-iron structural elements providing: (a) lateral support to parapets and anti-climb barriers and (b) partial support to the maintenance under-deck gantry. There are 162 identical parapet stanchions on the bridge. These structural elements may suffer heavy damage due to wear and tear. The damage consists of cracking in zones of stress concentration. This damage is unrepairable, and stanchions must be replaced when cracks appear. Their substitution is operated by the Clifton Suspension Bridge Trust (CSBT), which is particularly interested in science and technology for conservation and awareness. By applying the proposed multi-scale assessment framework, we provided essential insights into the structural integrity of such elements that are fundamental for informed decision-making.