Resilience (engineering and construction)
In the fields of engineering and construction, resilience is the ability to absorb or avoid damage without suffering complete failure and is an objective of design, maintenance and restoration for buildings and infrastructure, as well as communities.[1][2][3] A more comprehensive definition is that it is the ability to respond, absorb, and adapt to, as well as recover in a disruptive event.[4] A resilient structure/system/community is expected to be able to resist to an extreme event with minimal damages and functionality disruptions during the event; after the event, it should be able to rapidly recovery its functionality similar to or even better than the pre-event level.
The concept of resilience originated from engineering and then gradually applied to other fields. It is related to that of vulnerability. Both terms are specific to the event perturbation, meaning that a system/infrastructure/community may be more vulnerable or less resilient to one event than another one. However, they are not the same. One obvious difference is that vulnerability focuses on the evaluation of system susceptibility in the pre-event phase; resilience emphasizes the dynamic features in the pre-event, during-event, and post-event phases.[5]
Resilience is a multi-facet property, covering four dimensions: technical, organization, social and economic.[6] Therefore, using one metric may not be representative to describe and quantify resilience. In engineering, resilience is characterized by four Rs: robustness, redundancy, resourcefulness, and rapidity. Current research studies have developed various ways to quantify resilience from multiple aspects, such as functionality- and socioeconomic- related aspects.[5]
The built environment need resilience to existing and emerging threats such as severe wind storms or earthquakes and creating robustness and redundancy in building design. New implications of changing conditions on the efficiency of different approaches to design and planning can be addressed in the following term.[7]
Engineering resilience has inspired other fields and influenced the way how they interpret resilience, e.g. supply chain resilience.
Engineering resilience refers to the functionality of a system in relation to hazard mitigation. Within this framework, resilience is calculated based on the time it takes a system to return to a single state equilibrium.[17] Researchers at the MCEER (Multi-Hazard Earthquake Engineering research center) have identified four properties of resilience: Robustness, resourcefulness, redundancy and rapidity.[18]
Social-ecological resilience[edit]
Social-ecological resilience, also known as adaptive resilience,[19] is a new concept that shifts the focus to combining the social, ecological and technical domains of resilience. The adaptive model focuses on the transformable quality of the stable state of a system. In adaptive buildings, both short term and long term resilience are addressed to ensure that the system can withstand disturbances with social and physical capacities. Buildings operate at multiple scale and conditions, therefore it is important to recognize that constant changes in architecture are expected. Laboy and Fannon recognize that the resilience model is shifting, and have applied the MCEER four properties of resilience to the planning, designing and operating phases of architecture.[17] Rather than using four properties to describe resilience, Laboy and Fannon suggest a 6R model that adds Recovery for the operation phase of a building and Risk Avoidance for the planning phase of the building. In the planning phase of a building, site selection, building placement and site conditions are crucial for the risk avoidance. Early planning can help prepare and design for the built environment based on forces that we understand and perceive. In the operation phase of the building, a disturbance does not mark the end of resilience, but should propose a recovery plan for future adaptations. Disturbances should be used as a learning opportunity to assess mistakes and outcomes, and reconfigure for future needs.
Applications[edit]
International Building Code[edit]
The international building code provides minimum requirements for buildings using performative based standards. The most recent International Building Code (IBC)was released in 2018 by the International Code Council (ICC), focusing on standards that protect public health, safety and welfare, without restricting use of certain building methods. The code addresses several categories, which are updated every three years to incorporate new technologies and changes. Building codes are fundamental to the resilience of communities and their buildings, as “Resilience in the built environment starts with strong, regularly adopted and properly administered building codes” [20] Benefits occur due to the adoption of codes as the National Institute of Building Sciences (NIBS) found that the adoption of the International Building Code provides an $11 benefit for every $1 invested.[21]
The International Code Council is focused on assuming the community's buildings support the resilience of communities ahead of disasters. The process presented by the ICC includes understanding the risks, identifying strategies for the risks, and implementing those strategies. Risks vary based on communities, geographies and other factors. The American Institute of Architects created a list of shocks and stresses that are related to certain community characteristics. Shocks are natural forms of hazards (floods, earthquakes), while stresses are more chronic events that can develop over a longer period of time (affordability, drought). It is important to understand the application of resilient design on both shocks and stresses as buildings can play a part in contributing to their resolution. Even though the IBC is a model code, it is adopted by various state and governments to regulate specific building areas. Most of the approaches to minimizing risks are organized around building use and occupancy. In addition, the safety of a structure is determined by material usage, frames, and structure requirements can provide a high level of protection for occupants. Specific requirements and strategies are provided for each shock or stress such as with tsunamis, fires and earthquakes.[22]
U.S Resiliency Council[edit]
The U.S Resiliency Council (USRC), a non-profit organization, created the USRC Rating system which describes the expected impacts of a natural disaster on new and existing buildings. The rating considers the building prior to its use through its structure, Mechanical-Electrical systems and material usage. Currently, the program is in its pilot stage, focusing primarily on earthquake preparedness and resilience. For earthquake hazards, the rating relies heavily on the requirements set by the Building codes for design. Buildings can obtain one of the Two types of USRC rating systems:
Sustainability[edit]
It is difficult to discuss the concepts of resilience and sustainability in comparison due to the various scholarly definitions that have been used in the field over the years. Many policies and academic publications on both topics either provide their own definitions of both concepts or lack a clear definition of the type of resilience they seek. Even though sustainability is a well established term, there are generic interpretations of the concept and its focus. Sanchez et al. proposed a new characterization of the term ‘sustainable resilience’ which expands the social-ecological resilience to include more sustained and long-term approaches. Sustainable resilience focuses not only on the outcomes, but also on the processes and policy structures in the implementation.[33]
Both concepts share essential assumptions and goals such as passive survivability and persistence of a system operation over time and in response to disturbances. There is also a shared focus on climate change mitigation as they both appear in larger frameworks such as Building Code and building certification programs. Holling and Walker argue that “a resilient sociol-ecological system is synonymous with a region that is ecological, economically and socially sustainable.”[34] Other scholars such as Perrings state that “a development strategy is not sustainable if it is not resilient.”[35][36] Therefore, the two concepts are intertwined and cannot be successful individually as they are dependent on one another. For example, in RELi and in LEED and other building certifications, providing access to safe water and an energy source is crucial before, during and after a disturbance.[34]
Some scholars argue that resilience and sustainability tactics target different goals. Paula Melton argues that resilience focuses on the design for unpredictable, while sustainability focuses on the climate responsive designs. Some forms of resilience such as adaptive resilience focus on designs that can adapt and change based on a shock event, on the other hand, sustainable design focuses on systems that are efficient and optimized.[37]
Quantification[edit]
The first influential quantitative resilience metric based on the functionality recovery curve was proposed by Bruneau et al.,[6] where resilience is quantified as the resilience loss as follows.
where is the functionality at time ; is the time when the event strikes; is the time when the functionality full recovers.
The resilience loss is a metric of only positive value. It has the advantage of being easily generalized to different structures, infrastructures, and communities. This definition assumes that the functionality is 100% pre-event and will eventually be recovered to a full functionality of 100%. This may not be true in practice. A system may be partially functional when a hurricane strikes and may not be fully recovered due to uneconomic cost-benefit ratio.
Resilience index is a normalized metric between 0 and 1, computed from the functionality recovery curve.[38]
where is the functionality at time ; is the time when the event strikes; is the time horizon of interest.
![{\displaystyle R_{L}=\int _{t_{0}}^{t_{f}}[100\%-Q(t)]dt}](https://wikimedia.org/api/rest_v1/media/math/render/svg/d05e144b449152f0234a7156b4d5c21aa815a9a5)
