Underground structures are being constructed at an increasing rate in seismic prone areas, to facilitate the expanding needs of societies. Considering the vital role of this infrastructure in densely populated urban areas and interurban transportation networks, as well as the significant losses associated with potential seismically induced damage, its assessment against seismic hazard is of great importance for stakeholders, operators, and governmental bodies. This paper presents a state-of-the-art review of current developments in the assessment of seismic vulnerability of tunnels and underground structures. Methods for the development of fragility functions for the assessment of bored tunnels in rock or alluvial, and cut and cover tunnels and subways in alluvial, against ground seismic shaking and earthquake-induced ground failures are presented. Emphasis is placed on the estimation of the capacity of the examined structures, the selection of appropriate intensity measures to express seismic intensity, the development of rational probabilistic seismic demand models and the estimation of epistemic and aleatoric uncertainties, related to the seismic fragility of underground structures. Through the discussion, acknowledged gaps in the relevant literature are highlighted.

Infrastructure monitoring can facilitate the evaluation of capacity and functionality loss and therefore provide valuable data and evidence for reliable, lifetime and automated risk assessments. Terrestrial monitoring systems can provide information about assets and their condition. Yet, they fall short of engineering requirements related to the history of the asset loading, deterioration and potential damage, which is of paramount importance in risk-based decision-making by infrastructure operators. This capability gap can be filled by Persistent Scatterer Interferometry (PSI) Monitoring in conjunction with engineering forensics and judgment. This paper puts forward this hybrid approach to assess the structural condition of a landmark bridge by coupling advanced Differential SAR Tomography (D-TomoSAR) techniques with an adaptive deformation model, environmental measurements and engineering evidence and evaluations. A dataset of 360 Sentinel A &B images covering the period between 10/2014 and 2/2020 and temperature records to account for seasonal deformation were deployed. Displacement products, such as the development of annual displacement and time series were calculated demonstrating a strong correlation with temperature variation and resulting deformations of the asset. The spatiotemporally evolving deformation trends of the bridge superstructure were derived, and vulnerable deck locations were identified on the basis of engineering forensics, judgment and progressive displacements calculated from the D-TomoSAR technique. The vertical displacement profile at the critical deck location was developed reaching a displacement velocity of 1.8 mm/year and potential deterioration issues are manifested as potential causes of the observed geometric alterations. Based on the D-TomoSAR results matched with engineering evidence and on-site visual inspections and judgment, this study contributed to the decision-making process. This research is a pilot showcase of D-TomoSAR for the bridge monitoring, not only providing mm-level quantitative measurements of the bridge in a 6-year observation span using medium resolution Sentinel-1 SAR images alone but also indirectly identifying potential structural defects in the north section of the bridge. This research is a primer example of how we can deploy diverse evidence to facilitate targeted adaptation measures and prioritize restoration strategies to facilitate asset owners in better decision making.

The changing climate with resulting more extreme weather events will likely impact infrastructure assets and services. This phenomenon can present direct threats to the assets as well as significant indirect effects for those relying on the services those assets deliver. Such threats are path-dependent and place-specific, as they strongly depend on current and future climate variability, location, asset design life, function and condition. One key question is how climate change is likely to increase both the probability and magnitude of extreme weather events under different scenarios of climate change. To address this issue, this paper investigates selected effects of climate change and their consequences on structural performance, in the context of evolving loading scenarios in three different continental regions: Europe, North America, and Asia. The aim is to investigate some main place-specific changes of the exposure in terms of intensity/frequency of extreme events as well as the associated challenges, considering some recent activities of members of the IABSE TG6.1. Climate change can significantly affect built infrastructure and the society by increasing the occurrence and magnitude of extreme events and increasing potential losses. Therefore, specific relationships relating hazard levels and structural vulnerability to climate change effects should be determined.

One major issue when considering the effects of climate change is to understand, qualify and quantify how the changing climate will likely impact infrastructure assets and services as it strongly depends on current and future climate variability, location, asset design life, function and condition. Expected changes to local climatic conditions may potentially lead to changes in the degradation processes of building materials, affecting the durability and service life of structures. A key question is how climate change may produce changes of vulnerability owing to physical and chemical actions affecting structural durability or changes to exposure in terms of the intensity/frequency of extreme weather events. In this context, this article focuses on the impact on structural resistance and associated challenges, considering some recent activities of members of IABSE TG6.1. Several case studies of infrastructure assets worldwide are presented and discussed in this article.

Cable-stayed bridges have been used widely in the last 60 years in bridge construction practice and are key components of transportation networks. Therefore, the potential damages and losses, either in terms of economic cost or fatalities due to natural or man-made threats could become considerably large. Several researchers have identified the significance of risk assessment, especially to natural hazards and have proposed risk assessment frameworks for bridges. Recently, it has been identified that climate change affects the occurrence of extreme events and should be also incorporated in risk assessment. In the present research work, a risk assessment framework for cable-stayed bridges is proposed. The goal is to prioritize single and total risk to provide a useful tool in the decision-making process on the design and maintenance actions for cable-stayed bridges. Herein, the case study is an indicative design alternative of a cable-stayed bridge in a coastal area in the New York Region. which is expected to face sea-level rise due to climate change. Multi-hazard risk evaluation on the investigated bridge shows that it has low risk to the seismic hazard, while it has increased risk to hurricanes, which changes from low to high depending on the investigated sea-level rise projections and hurricane intensity levels. Hence, hurricane governs the resulting total risk of the case study bridge.