The construction sector needs to reduce its material use and environmental impact, due to its significant CO2 emissions and energy consumption. Structural steel plays a significant role in this challenge while preserving a high carbon content. Moreover, many buildings and structures contain steel components that still possess substantial value. Steel reuse, also known as donor steel, involves harvesting steel elements from existing structures and using them in new projects, offering clear circular potential. However, despite the availability of innovations and technologies and increasing sustainability ambitions in the sector, donor steel is still not widely applied in practice.
This thesis researched how early-stage decision-making can support the integration of donor steel in circular construction projects. Therefore, the main research question states:
“How can applications of digital solutions and conditions for collaboration in the early design stages help to address the identified key obstacles to integrate donor steel in circular construction projects?”
To answer this question, a twofold approach was adopted: an exploratory approach and a case study approach. Data from exploratory interviews with construction stakeholders and multiple case studies were compared with the literature review, which identified five obstacles to donor steel. The following five obstacles were identified: supply and demand mismatch, certification and design standardization, the absence of legal frameworks, cost and economic uncertainty, and a lack of collaboration and transparency. The obstacles encompass technical, financial, regulatory, and organizational domains, indicating that technical obstacles alone do not hinder the widespread adoption of donor steel.
The exploratory interviews with stakeholders across the construction supply chain provided insights into how these obstacles manifest in practice. The interview data confirmed that ‘cost uncertainty’, ‘certification & design standardization’, and ‘supply & demand mismatches’ were the most significant obstacles in practice. The regulatory obstacle appeared less decisive than the literature review suggested, while several additional obstacles emerged, particularly related to client decision-making and timing. Additionally, ‘lack of collaboration and transparency’ was perceived as an obstacle in the interviews, but as an enabler in the case study research, showing the importance of strong collaborative structures in reuse projects. Moreover, the case study research provided further insights into how donor steel application is approached in real projects. The data showed that the key enablers were: early integration of digital and sustainability tools, strong collaborative structure with stakeholder engagement, and client sustainability ambitions. Showing the importance of digital solutions applications, such as BIM, MP’s, and material testing, supporting donor steel integration.
Overall, this thesis shows that the integration of donor steel is primarily constrained by early-stage organizational and economic conditions, rather than by technical constraints or the lack of digital solutions. The application of these digital tools is practical when embedded within the collaborative procurement process, early stakeholder engagement, and clear client commitment to circularity.
Finally, longitudinal, process-oriented research is recommended to generate more generalisable findings and to develop a coherent framework that provides actionable guidelines for future donor steel applications. Furthermore, practitioners should explicitly consider donor steel in the early design and procurement phases, support early stakeholder engagement, and integrate digital and sustainability tools early in a project to reduce uncertainty and prevent late-stage rejection. Additionally, policymakers must offer clarity and consistency in certification procedures and documentation requirements to reduce the perceived certification and regulatory risks.

Circular building adaptability (CBA) offers substantial benefits to the built environment, including reducing building costs through material efficiency and waste reduction, while enhancing the long-term value of structures through improved flexibility (Hamida et al., 2023). Next to this, CBA contributes to long-term sustainability in the built environment by making it possible to generate new business opportunities within the circular economy (CE). However, the Dutch building industry faces significant challenges in adopting CBA principles, particularly in the context of adaptive reuse (AR) projects. These challenges hinder the industry's transition towards a sustainable and circular built environment.

This research primarily concentrated on testing part of a relatively new framework that links determinants, strategies and the enabling and inhibiting factors of CBA in adaptive reuse projects to support the shift towards a circular economy. Accordingly, this study aimed to answer the following research question: “How can the applicability and effectiveness of design-oriented circular building adaptability strategies (CBASs) be promoted in adaptive reuse projects?”. A stepwise research design of two approaches was followed, namely case studies and Research-through-Design (RtD). The methods include archival research, field observations, semi-structured interviews with key informants, questionnaires, and workshops focused on practical design solutions.

The results indicate that the CBA-AR framework is a useful tool that integrates CBA-determinants, strategies, and associated enabling or inhibiting factors, and can be useful during early-stage planning and collaboration in adaptive reuse projects. Second, based on the findings of the case study, three strategies have been identified as the most applicable and effective, namely: opening the floor plan, providing multi-purpose spaces, and aligning the interconnection between floor plans. In contrast, the less applicable and effective strategies for the cases examined in this study are designing for mixed-use, modularizing spatial configuration, and designing for surplus capacity. Finally, the successful implementation of CBASs requires raising awareness among professionals, as the lack of knowledge often leads to missed opportunities for integrating adaptable and sustainable design strategies.

The scope of the research has been limited to the design-oriented (passive) CBASs, and therefore, directions for future research have been put forward in the conclusion. Moreover, the findings of this study are not generalizable because they are case-specific; however, they provide valuable lessons for future research, policy-making, and practitioners seeking to promote resource efficiency and future-proofing in adaptive reuse projects.

The architectural design Associations and Assemblages-A Pattern-based
Housing Complex, are followed by research on existing housing patterns
in Istanbul. Three types of housing forms: Self-built, Street apartment and
Highrise. For individual housing units, they are different in scale/volume/facade
composition/land occupation. When grouped housing units land on the terrain
of Istanbul, they form different patterns in plan and elevation.The research
finding can be concluded as: By figure ground plan, self-built houses are more
dense in land occupation, but have less demolish on original topography than
street apartments and high-rises. The collision of three patterns in my site
Yenidoğan, the most over-populated area of Istanbul, guides me rethinking how
they can coexist in a more topo-friendly way and create possible new housing
patterns.