# Topology Optimisation in Structural Steel Design for Additive Manufacturing
## 2 Methods  
The literature research on Topology Optimisation was conducted between late November and early December 2020, encompassing Identification, Screening, Sorting, Eligibility Assessment, Information Extraction, Qualitative Synthesis, and Discussion Stages, as better depicted and systematised in Figure 8. While attending to this scientific field's case-specificity, compliance with well-established guidelines for systematic reviews, such as as in [152] was pursued. Inspiration was found in other recent Review Articles, such as in [153; 154; 155; 156]. Scientific literature has been searched with significant broadness. All published and peer-review items were considered, including Journal Research Articles, Conference Proceedings, Review Articles, Peer-reviewed Book Chapters, and Approved Master and Doctoral Theses. On the other hand, Technical Books, which are not necessarily peer-reviewed, were considered only for framing the research topic in the Introductory Section. Many notable books' unavoidability supports such a decision for defining Topology Optimisation, including [PERSON] [PERSON]'s _\"Topology Optimisation: Theory, Methods, and Applications\"_[113] with 7301 citations according to Google Scholar as of 28 November 2020. Figure 8: Search and systematic review methodology. For a more in-depth insight into the current research, industry developments, and future trends, EU-funded research projects as well as European, US, and worldwide patents were also investigated. The temporal scope for literature search has been set for the most recent 5 years (2015-2020), yet considering the Topology Optimisation novelty as a discipline (illustrated in Figure 3a), previous and very significant research items were investigated and considered for conceiving an explanatory Introduction. An encompassing fabric of data sources was put together for this endeavour. Thus, Journal Articles and Conference Proceedings were redundantly searched in Mendeley Desktop, Scopus Online, Springer Online, Taylor and Francis Online, and Willey online search engines. Moreover, most active research groups repositories were also investigated, including the DTU TopOpt group, Loughborough University, and the University of Leeds. Several universities Theses repositories were searched. However, literature findings through reading articles was not negligible and added to the former. Patents were found in Google Patents, Espacenet, and USPTO search engines. Research Projects were found in the European Commission projects database, and books were searched using the ProQuest online tool. Table 1 quantifies the search dimensions. A group of three basic keywords and 12 keyword strings were systematically used in all databases. The former included _\"Topology optimization\"_, _\"Design for Additive Manufacturing\"_ and _\"Topological optimization\"_, while the latter are _\"Topology optimization\"_ AND _\"Additive Manufacturing\"_, _\"Topology optimization\"_ AND _\"Steel Design\"_, _\"Topology optimization\"_ AND _\"Steel Detailing\"_, _\"Topology optimization\"_ AND _\"Steel Structures\"_, _\"Topology optimization\"_ AND _\"Structural Engineering\"_, _\"Topology optimization\"_ AND _\"Connections\"_, _\"Topology optimization\"_ AND _\"Construction\"_, _\"Topology optimization\"_ AND _\"Joints\"_, _\"Topology optimization\"_ AND _\"Review\"_, _\"Topology optimization\"_ AND _\"Civil Engineering\"_, _\"Topology optimization\"_ AND _\"Multiple Loading\"_, _\"Topology optimization\"_ AND _\"Robustness\"_. These keywords and strings have been selected to match the articles' Title, Keywords or Abstract, where such option is explicitly available, as it is the case of the Scopus search tool. The screening criteria for removal included duplicate items, the mismatch between title and content, corrupted files, and the impossibility of accessing the document.