Researcher: Omar Kahla
Project Duration: September 2023 – August 2024
Project Partner: Nebest
Research DESCRIPTION:
In the city of Amsterdam, where over 200 bridges have exceeded their lifespan and require intervention, the municipality is actively taking initiatives to implement circular design principles in asset management. However, assessing the circularity of historical bridges with the existing frameworks proves challenging. The existing framework requires an extensive amount of data for the assessment. In addition, historical bridges possess unique characteristics, such as their monumental status and uncertainties in components’ condition, which require a more specialised approach. This research addresses the gap by developing the Historical Bridge Circularity Indicator (HBCI).
The research design for developing the HBCI framework involves multiple steps: literature review, framework development, and framework validation. The literature review encompasses exploring the existing definitions and principles of circularity, existing circularity indicators, bridge preservation strategies, and examples of existing historical bridges. The literature review includes a critical review of the existing circularity indicators, examining their strengths and weaknesses when applied to historical bridges. Then, the framework is developed by defining the charachteristics of the framework and turning circular concepts into sub-indicators. The next step is determining the framework indicators by analysing the variables and the type of data needed for the framework to ensure their relevance, analytical soundness, timeliness, accessibility, etc. The next step is data normalisation to ensure that all inputs have the same measurement unit and can be aggregated together. Then, sub-indicators are weighted based on their influence on the asset’s circularity. Further, two case studies are applied to the framework, each serving a different purpose. Finally, a sensitivity analysis is conducted using the one-at-a-time approach to test the impact of changing the value of one parameter on the final score.
The framework features are determined using the taxonomy of circular economy indicators developed by Saidani et al. (2019). The framework assesses circularity on a micro level (organization, products, etc.), covering the full scope of the circularity feedback loops. The performance is captured on both intrinsic and consequential circularity. The framework is applicable to three different scenarios: general insight, strategic decision support, and deconstruction and demolition insight. The general assessment is a preliminary assessment of circularity potential for an existing situation. Strategic decision support is when the bridge requires interventions, and decisions need to be taken between different scenarios. Deconstruction and demolition is the end-of-life assessment to minimize waste generation and enhance resource efficiency.
The Historical Bridge Circularity Indicator (HBCI) assess the circularity level of historical bridges from 3 main perspectives: material, component, and bridge level. These main perspectives are assessed through the Modified Material Circularity Indicator (MMCI), Component Reusability Indicators (CRI), and Bridge Preservation Indicator (BPI). The MMCI captures the circularity performance on a material level by assessing the material flow, connection type, accessibility to material, and its availability. The CRI captures the circularity performance on a component level by assessing its dismantability, transportability, and health. Meanwhile, BPI captures the circularity performance on a system level by assessing how much is preserved from the original bridge and the ability of the bridge (potential preservation) to be widened and strengthened.
The framework has been used for two case studies. Case study A focused on the impact on circularity performance when an existing historical bridge is replaced but many of the original components are reused. The results showed an increase in the CRI and BPI scores due to better competent health and preservation capabilities. The MMCI score has decreased in the new bridge due to the addition of new virgin material. However, the sensitivity analysis revealed that changes in the virgin material fraction have a slight impact on the final output. Case study B tested the robustness and consistency of the framework by applying it to two different bridges that share similar characteristics and intervention history. Despite the two bridges sharing the same overall HBCI scores, differences were observed on layer, component, and material levels, demonstrating the framework's ability to capture circularity performance differences even among bridges with similar characteristics and histories.
In conclusion, future research can further refine the framework by developing standardised data collection protocols, mitigating subjectivity in expert judgment through a comprehensive framework, enhancing the quantification process, standardising the HBCI framework to be applicable to all historical infrastructures, and exploring integration with Life Cycle Assessment (LCA) for a broader environmental impact assessment. Additionally, practitioners can benefit by utilizing multiple expert opinions for subjective areas, exploring economic value metrics for components alongside mass, and integrating the framework with cost analysis to validate the financial feasibility of circular interventions. By implementing these recommendations, the HBCI framework can reach its full potential, promoting circularity in historical bridge management and decision-making while safeguarding their cultural heritage.