  The increasing urban population imposes a substantial and growing burden on
the supporting infrastructure, such as electricity, water, heating, natural
gas, road transportation, etc. This paper presents a Hetero-functional graph
theory (HFGT) based modeling framework for these integrated infrastructures
followed by an analysis of network robustness. The supporting infrastructures
along with the infrastructure repair facilities are considered. In contrast to
conventional graph representations, a weighted HFGT model is used to capture
the system processes and mutual dependencies among resources. To assess
robustness of the inter-dependent networks, impacts of complete/partial and
random/targeted attacks are quantified. Specifically, various contingency
scenarios are simulated and the vulnerability of the network is evaluated.
Additionally, several robustness metrics are proposed to provide a
comprehensive evaluation of system robustness. The proposed weighted HFGT
modeling and robustness assessment approach is tested using a synthetic
interdependent network, comprising of an electrical power system, a water
network, a district heating network, a natural gas system and a road
transportation network. Results demonstrate that system robustness can be
enhanced via securing system information and mitigating attack strength.
