# Recent Advancement in Assessment and Control of Structures under Multi-Hazard
## 7 Concluding Remarks  
This work is an attempt to summarize a vast body of research literature on multi-hazard effects on structures and their vibration mitigation measures. Aspects such as performance assessment, fragility modelling, life-cycle cost assessment, and vibration control in a multi-hazard scenario are covered. The main emphasis is on wind and seismic actions on major infrastructure, such as bridges, buildings, and wind turbine towers. Understanding of multi-hazard scenarios in a probabilistic sense and mapping them out for engineering design is an evolving field. At a local scale, multi-hazard mapping using the Analytical Hierarchy Process (AHP) is gaining popularity. Multi-hazard mapping at regional scales remains a challenging task, demanding more research on unifying frameworks that standardize and unify existing probabilistic hazard assessment methods used for different natural actions. Some recent advances in multi-hazard vulnerability of buildings include multi-dimensional vulnerability modelling. Fragility modelling in a multi-hazard scenario is still a growing field of knowledge, with many unresolved questions. Some examples of such unresolved issues relate to: (i) definition of intensity measures of hazards that might interact with each other, resulting in overall effects that are of different nature than those due to individual hazards; (ii) definition of joint probabilities of exceedances of intensities of different types of hazards; (iii) lack of empirical data on actual damage recorded in multi-hazard scenario, etc. Multi-hazard assessment of bridges is a widely studied topic. Most studies in this area focus on seismic loads and corrosion. Other effects, such as wind loads, scour, traffic loads, etc., in conjunction with seismic loads, have also been reported. Published literature on  
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bridges subjected to seismic loads and corrosion focus on the fragility assessment. Multi-hazard effects in such assessments are generally modelled through fragility increment functions, damage accumulation, and time-dependent fragility curves. Probabilistic load and resistance factors, for different hazards affecting bridges, is another widely reported research theme. In most cases, such fragility models are intended for a life-cycle cost and risk analysis. While multi-hazard fragility of individual bridges is widely reported, there are only a few deals with bridge networks. More research is needed in capacity modelling, risk metrics, stakeholder perceptions, and load combinations. The literature on multi-hazard effects on buildings is dominated by wind and earthquake loads. Performance-based engineering frameworks, progressive damage and collapse modelling, resilience assessment, multi-hazard performance evaluation metrics, etc., are some of the recent advances in damage risk and life cycle cost analysis of buildings. A variety of control systems such as passive TMDs, passive energy dissipation devices, viscous fluid dampers, multiple tuned passive TMDs, have been investigated in control of buildings subjected to wind and seismic forces. Some recent advances in this area seem promising and practically appealing: for example, sliding floor isolators, glass curtain wall TMDs, and variable friction cladding connections [VFCC]. While the literature on the vibration control of buildings subjected to wind or seismic action is vast, relatively few studies have addressed their simultaneous occurrence. More research is needed on probabilistic treatment of multi-hazard load cases, robustness of control devices against uncertainties in structural properties, as well as loading the feasibility of control from a life-cycle perspective. Seismic and wind forces are the two most considered environmental actions in the performance assessment and vibration control of wind turbine structures. Wave action, and effects of wave/wind misalignment in offshore wind turbines is also widely researched.