Current literature on relationship management has focused on formal mechanisms such as contracts but has neglected the inter-organizational behavior that determines the effective adoption of relational mechanisms in the context of megaprojects. This study examines the antecedents and consequences of relational behavior of participating organizations in megaprojects based on the theory of planned behavior (TPB). A sample of 285 senior managers working on China’s megaprojects was surveyed, and the results were analyzed using partial least square structural equation modeling (PLS-SEM), revealing that: (1) the adoption of relational behavior is equally motivated by an organization’s behavioral intention and perceived behavioral control (PBC), and (2) relational behavior, especially information exchange, contributes the most toward achieving a high project relationship quality. A closer examination of the data found that two moderating effects, namely project culture and prior experience with other participating organizations, were particularly important. These findings contributed to four implications for project participating organizations to cultivate relational behavior and improve relationship quality in megaprojects, including identifying potential behavioral benefits, enhancing relational competence, establishing collaborative culture, and reinforcing information sharing.

Purpose: As each urban rail transit PPP (URT3P) project involves collaboration between public and private sponsors, a complex project-based collaborative network can emerge in the URT3P sector. However, the characteristics of such networks have not been thoroughly investigated from an inter-project perspective, particularly over an extended period, which poses problems for sponsors in formulating dynamic collaboration and market competition strategies. The absence of such understanding hinders sponsors from identifying how network positions affect their access to social capital, such as information, trust and collaborative opportunities, drawing on social capital theory. This study aims to elucidate the features of the project-based collaborative networks among public and private sponsors and their temporal evolution in the URT3P sector. Design/methodology/approach: A total of 76 URT3P projects in China are analyzed to reveal the dynamic characteristics of distinct collaborative networks by comparing their changes across three periods: 2010–2013, 2014–2017 and 2018–2021. Social network analysis (SNA) is used to examine two types of collaborative networks – public–private (Pub-Pri) and private–private (Pri-Pri) – at both the network and node levels. Furthermore, private sponsors have been classified into state-owned enterprises (SOEs) and non-SOEs based on organizational attributes, with six distinct types of organization identified for comparative analysis and discussion. Findings: From a network perspective, the Pub–Pri network analysis reveals that although sponsors have surged since 2014, collaboration between public and private sponsors remains limited due to low network density and extended characteristic path lengths in the second and third stages. At the node level, findings consistently indicate that Pub–Pri collaborations exhibit characteristics akin to those of a scale-free network. Here, a few sponsors with significant centrality wield substantial resources, granting them considerable competitive advantages. In the Pri–Pri network analysis, we observe the small-world property across the whole time period of 2010–2021, indicating a high degree of information exchange accessibility among private sponsors. At the node level in the Pri–Pri network, state-owned construction sponsors emerge as dominant players in the latter two stages, underscoring their robust market competition capabilities within a unified market structure. Originality/value: Unlike previous research, which has predominantly concentrated on sponsors’ collaborations within specific URT3P projects, this study delves into collaborative network structures across multiple URT3P projects from an inter-project perspective. This perspective will help public sponsors in partner selection while furnishing private sponsors with valuable insights into market positioning and corporate strategies. Furthermore, guided by social capital theory, this study reveals how the dynamic evolution of collaborative networks shapes the accumulation of structural social capital among URT3P sponsors, offering guidance to both public and private sponsors on the trends in sponsor engagement and future competitive scenarios.