Abstract: The dynamic nature of the interaction processes and the diversity of interaction relationships within the project network contribute to the complex system characteristics of its structure. This paper employs the multi-scale theory of complex networks to construct a multi-scale analysis framework for project networks, ranging from macroscopic to microscopic levels, and empirically investigates the PPP project network. The study reveals that, at the global structural level, the PPP project network exhibits self-organizing characteristics, featuring two organizational collaboration mechanisms: project cooperation and strategic cooperation. At the community clustering level, the preferential attachment effect leads super-enterprises to develop increasingly stronger collaborative relationships in the project network, coupled with the geographical proximity effect shaping the clustering network structure. At the micro level, motifs form the foundation for contractual and non-contractual governance among organizations, while the embeddedness mechanism reveals the cooperative trajectories of PPP organizations at the micro level. Furthermore, under different payment mechanisms, PPP private-sector organizations, assuming higher risks, exhibit more pronounced characteristics in terms of strong alliances at the macro level, clustering features at the meso level, and motif composition proportions in the microstructure. The innovation of this study lies in uncovering cooperative mechanisms in the PPP project network at three levels, analyzing the evolutionary features in terms of time and multi-scale dimensions, and considering the multi-scale cooperative characteristics of PPP organizations under different payment mechanisms. This study provides a multi-scale framework for the government to analyze PPP project networks, aiding in understanding cooperative behaviors among PPP organizations. Additionally, it offers a comprehensive industry cooperation landscape for private-sector organizations and introduces a new perspective for the study of project network structures.

Key words: project network, multi-scale approach, PPP, motif, collaboration mechanism