## 4 Test Methodology and Evaluation Criteria of Data Interoperability  
One of the main novel aspects of this study was its attempt to fill this gap and to provide an overview of the current interoperability achieved via IFC among several commercial BIM-based CAx software, with specific attention paid to the structural analysis aspects in CAE environments of structures made of monodimensional members. This objective was pursued by analysing how geometric and non-geometric data were exchanged and the mechanisms that were involved in the failure of the data-exchange process. The specific perspective of the structural engineer was adopted, since the structural analysis and design of each construction is a diverse and key phase of every architectural project; therefore, an attempt was made to provide a picture of the interoperability involving structural data transfer. Furthermore, a cross-exchange between CAD systems was also performed, so that the up-to-date current status of the interoperability at the CAD level could be determined. Three levels of interoperability were selected: (i) CAD-to-CAD; (ii) CAD-to-CAE; (iii) CAE-to-CAE. An analytical and realistic approach based on the comparison of software capability and the key factors that differentiate software performances was adopted. The IFC object-mapping mechanism within some software packages was also a point of focus for repetitive self-tests. A selection of the most common BIM-based CAD and CAE software available on the market was made and is reported in Table 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Platform** & **Company** & **Software** & **Version (A)** & **Version (B)** & **Website** & **Ref.** \\ \hline \multirow{4}{*}{**CAD**} & Autodesk & REVIT & 2017 & 2021 & www.autodesk.com & [36] \\ \cline{2-7}  & NEMETSCHEK & Allplan & 2017 & 2020 & www.allplan.com & [37] \\ \cline{2-7}  & Graphisoft & ArchiCAD & 2017 & 24 & www.graphisoft.com & [38] \\ \cline{2-7}  & ACCA Software S.P.A. & Edificius & 2017 & 2020 & www.acca.it & [39] \\ \hline \multirow{4}{*}{**CAE**} & Autodesk & Robot Structural Analysis & 2017 & 2021 & www.autodesk.com & [40] \\ \cline{2-7}  & Trimble Solutions Corporation & Tekla Structures & 2018 & 2020 & www.tekla.com & [41] \\ \cline{2-7}  & Tecnisoft s.a.s. & ModeSt & 8.15 & 8.23 & www.tecnisoft.it & [42] \\ \cline{2-7}  & Dubal Software & RFEM & 5.14.02 & 5.23 & www.dubal.com & [43] \\ \cline{2-7}  & CSI & SAP2000 & 19.2.1 & 22 & www.csi-italia.eu & [44] \\ \cline{2-7}  & ACCA Software S.P.A. & Edilus & 2017 & 2020 & www.acca.it & [45] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of software packages adopted for the BIM tests. The assessment started at the end of 2017 and was updated until the most recent software releases (at the time of writing), so the evolution over time of the software performance was also reported. Version (A) and (B) in the tables indicate the starting releases and the final releases of the tested software packages, respectively (simply recalled as A and B in the following tables for sake of brevity). Tables 3 and 4 summarise the versions of the IFC formats supported by all software environments tested in the present work, for import and export, respectively. The tables show that some companies over the years extended their software's ability to work with IFC, including IFC 4, and their ability to handle structural analysis elements (labelled as Structural Analysis View in the tables) in both the IFC 2x3 and IFC 4 formats. In an ideal BIM-interoperability workflow, the end user should be able to work in any CAD system and transfer the model to any CAE system to run simulations; if changes are applied to the analytical model, it is expected that the model will be returned to the CAD level to update the corresponding architectural model. CAD-to-CAD and  
CAD-to-CAE data exchange can also occur in a large design context involving different computer-aided solutions.