Natural and manmade hazardous events can impose a devastating cost upon society. As Figure 1 shows, the costs of some of these disasters in the United States alone can be staggering. Stakeholders of civil infrastructure have a vested interest in reducing these costs by improving and maintaining operational and physical performance.
Throughout history, infrastructure resilience has been defined in numerous ways, the most widely used and most objective is by the National Infrastructure Advisory Council (NIAC*) (2009), which states:
"Infrastructure resilience is the ability to reduce the magnitude and/or duration of disruptive events. The effectiveness of a resilient infrastructure or enterprise depends upon its ability to anticipate, absorb, adapt to, and/or rapidly recover from a potentially disruptive event."
No city is immune to challenges, whether natural or manmade, and given the world's growing population, more people than ever are in the potential path of catastrophe. Fortunately, cities can become resilient and withstand shock and stress. As conditions change over time, cities that are resilient can evolve in the face of disaster and stop failure from rippling through systems; they can reestablish function quickly and avoid long-term disruptions.
This resource page explores different aspects of resilience management, to control and help reduce the rapidly increasing costs of manmade and natural hazards and ensure that civil infrastructure exhibits a high degree of resilience. A definition of resilience that incorporates using four components—robustness, resourcefulness, recovery and redundancy—is presented and its manifestation in building systems is covered.
Stakeholders of buildings stand to benefit from resilience management. Businesses locate where they can rely on critical infrastructure. Communities that become resilient will increasingly attract businesses because executives know they can rely on the services and workforce availability, even in the face of disruptive events.
Natural and manmade hazardous events are unpredictable, but they are still inevitable and impose a devastating cost to civil infrastructure. By improving and maintaining the operational and physical performance of our nation's building stock, strategies for resilience can be developed.
Components of Building Resilience
The NIAC (2009) determined that resilience can be characterized by four key features:
Robustness: the ability to maintain critical operations and functions in the face of crisis. This includes the building itself, the design of the infrastructure (office buildings, power generation, distribution structures, bridges, dams, levees), or in system redundancy and substitution (transportation, power grid, communications networks).
Resourcefulness: the ability to skillfully prepare for, respond to and manage a crisis or disruption as it unfolds. This includes identifying courses of action and business continuity planning; training; supply chain management; prioritizing actions to control and mitigate damage; and effectively communicating decisions.
Rapid recovery: the ability to return to and/or reconstitute normal operations as quickly and efficiently as possible after a disruption. Components of rapid recovery include carefully drafted contingency plans, competent emergency operations, and the means to get the right people and resources to the right places.
Redundancy, is proposed as another key feature, which mean that there are back-up resources to support the originals in case of failure that should also be considered when planning for resilience.
These four resilience features are simply called the 4Rs. Resilience is multidisciplinary and needs the cooperation of different disciplines for successful outcome. Without multidisciplinary cooperation and contributions, there cannot be successful or efficient resilient infrastructure.
A beneficial illustration of resilience was introduced first by Mary Ellen Hynes (2001) and then by Bruneau et. al (2003). Figure 3 shows graphically how to objectively estimate the resilience of an asset or community by utilizing resilience charts. The illustration shows how an undesirable event might affect two assets (or communities). The operations of asset (or community) "A" will immediately lose some operational quality, then start recovering until returning back to full operational quality. As for asset (or community) "B," it will lose much of its operational quality when subjected to the same undesirable event. It will recover but on a much slower pace than asset "A." Thus, it is concluded that "A" is more resilient than "B." The area under the curve describes the time-operational quality behavior of the asset or community to objectively assess the resilience of the asset or community.
Asset (Building) Resilience and Community Resilience
One of the objectives is to clarify distinctions and relationships between three of the emerging paradigms: risk, resilience, and sustainability. First, risk is expressed as the relationship between a particular hazard (or threat) that might degrade the performance of the infrastructure under consideration and the consequences that might result from a degradation of performance (Gutteling and Wiegman 1996, FEMA 2005, and NRC 2010). Most professional industries, such as engineering, finance, insurance and medicine, adopt a variant of this particular definition of risk (Gutteling and Wiegman 1996). In the building/infrastructure community, FEMA (2005) uses an objective risk definition that states:
Risk rating = function (Consequences, Threat, Vulnerability — C, T, V)
The type of risk function also depends on the desired degree of complexity of risk analysis.
It was established earlier that a reasonable resilience definition relates resilience to robustness, resourcefulness, recovery, and redundancy (the 4Rs). It can be shown that the 4Rs can be recast as a subset of C, T, V. Ettouney and Alampalli, 2012, proposed a relationship similar to that shown in Table 1. These relationships are illustrated in Figure 4.
Table 1 - Relationships Between Risk and Resilience
Resilience Management-Based Building Designs
There is an essential distinction between asset resilience and community resilience. As the label implies, asset resilience is the resilience of a single asset. For immediate purposes, an asset is considered to be an individual building. Note that other types of assets are also feasible such as bridges, mass transit stations, transmission towers, or tunnels. DHS (2009) and the American Society of Civil Engineers (ASCE) Report Card (2013), each contain a comprehensive list of types of assets.
Asset resilience is described using the resilience definition above with the 4Rs. Within an asset, different parameters (sometimes referred to as considerations) control asset resilience. These parameters can be categorized as components of one or more of the 4Rs. Table 2 shows a simplified example of building components and categorizations in an asset resilience setting. Note that Columns fit in more than one resilience component (robustness and redundancy). In addition to the categorizations of Table 2, a functional diagram, called a network or a graph, needs to be established. This network shows dependencies of different parameters. The dependencies are expressed by arrows from the controlling parameter to the dependent parameter. If there is no obvious dependence between two linked parameters, then a simple line connecting the two parameters is used. Figure 5 shows a simple network for an asset resilience of a tall building. Capturing important parameters (both operational and physical) as well as their interdependencies as shown in Table 2 and 5 are essential first steps for achieving successful asset resilience management.
Table 2 - Resilience Example of Individual Building as an Asset
|Building Parameters (Considerations)
Turning attention to community resilience—as the name implies, a community is comprised of several assets (nodes) that are interconnected via links that may be assets themselves. The nodes and links constitute a community's network. Community resilience is dependent on the resilience of the network's individual asset components (both nodes and links). As an essential step of community resilience management, a greater understanding of the resilience of nodes and links is needed. In addition, community resilience will depend on the topology of the network and how different nodes are linked together.
The size of the community is completely subjective. A community could be a simple campus comprising a small number of buildings (such as a small hospital or college). A community could be a transportation network, a small town, a region, a state, or even a whole country. Each of the 4Rs of community resilience is a function of all of the 4Rs of its nodes and links as well as the topology of the network. Figure 6 shows a simple resilience network for a small community.
Life Cycle and Cost/Benefit Considerations in Resilience-Based Designs
Incorporating resilience into new building designs, existing building retrofits, and ongoing building operations can carry significant costs. To justify investments in resilience it is imperative to evaluate the cost/benefit relationship of the investments over the full life cycle of the facility. To evaluate increasing resilience, it is necessary to identify performance (or for safety and security objectives, protection) levels and their impact on reducing risk and increasing resilience. With performance/protection levels identified, the costs associated with achieving the performance/protection identified can be calculated and used to evaluate the benefits of higher resilience. The relationships between functional performance, risk, resilience, and cost are identified in Figure 7.
Establishing the tradeoffs between performance and cost requires evaluating the relationships between the cost of providing building systems, their performance over the life of the facility, including response to undesirable events and the interrelationships between systems and performances. Traditional first-cost estimating approaches cannot effectively handle these evaluations. Evaluating Total Cost of Ownership (TCO) is a more effective way to analyze all of the cost factors identified in Figure 7. TCO is calculated by establishing capital cost for the building or improvement and then adding to it the discounted costs of future expenses (operations, maintenance, recovery) to arrive at a TCO. TCO can then be compared for different configurations to perform a cost analysis of the benefits of increasing performance to increase resilience. This methodology is implemented in a DHS project entitled Owners Performance Requirements for Building Envelopes. More information about the approach and access to a tool that implements it is available at www.oprtool.org.
Short-Term Versus Long-Term Resilience Planning
It has been shown that long-term planning can help immensely in cost savings (see FEMA  and MMC ). An objective way to accommodate such long-term cost savings is by following a reasonable resilience management procedure during planning, design, and throughout the life span of the building. Some details of resilience management components are offered in the Resilience Assessment and Resilience Acceptance information below.
Existing Structures Versus New Buildings
The options for enhanced resilience available to existing buildings are more limited than for new building construction. For existing buildings, an appraisal will help determine whether an economical upgrade may be constructed without adversely affecting the existing structure and whether the upgrade is economically feasible. This will help determine whether the risks are worth taking and whether the building is suitable for a proposed function. The structural engineer must evaluate both the risk and the economic feasibility.
If an upgrade is found to be worth pursuing, the engineer must determine the as-built building information, such as the type and arrangement of existing vertical and lateral-force-resisting systems, and the nonstructural components that either affect the structure's stiffness, strength, or the continuity of the structural load path. The as-built information primarily focuses on the load-resisting components, which include structural and nonstructural components that participate in resisting gravity loads, whether or not they were intended to do so by the original designers. This information typically identifies potential discontinuities in the load path, weak links, irregularities, inadequate strength, and stiffness.
The available construction documents may provide primary gravity and lateral-force-resisting elements, critical components, and connections. In the absence of a complete set of building drawings, the design team must perform a thorough investigation of the building. This typically requires the examination of concrete, reinforcing steel, and connector steel samples for physical condition. Generally, mechanical properties for both concrete and reinforcing steel can be established from combined core and specimen sampling at similar locations, followed by laboratory testing. Core drilling should minimize damage of the existing reinforcing steel as much as is practicable. Nominal material properties, or properties specified in construction documents, shall be taken as lower-bound material properties.
Structural steel components constructed after 1900 shall be classified based on ASTM specification and material grade and, if applicable, shape group. Lower-bound material properties may be taken for known steel materials or may be based on tests where the material grade or specified value is not known. The carbon equivalent of the existing components must be determined to establish weldability of the material.
The K factor is typically used to express the confidence with which the properties of the building components are known. The K factor is based on original construction documents or condition assessments, including destructive or nondestructive testing of representative components.
The first component in resilience management is to assess the resilience level of either the asset or the community of interest. Since resilience is a special representation of risk, it is natural to utilize risk assessment methods when trying to assess resilience. Some of the methods for assessing risk are based on subjective processes (Gutteling and Wiegman 1996), while others are based on objective processes (DHS 2011b, 2011c, and 2011d). There are detailed relative and absolute risk assessment methods available (Ettouney and Alampalli 2012a and 2012b). There are even probabilistic or deterministic risk assessment methods (Fenton and Neil 2013).
It is possible to use any or all of these methods for resilience assessment. Since resilience is based on the 4Rs, the parameters of each of the 4Rs in each asset need to be determined, and the desired methodology (which can be borrowed from any desired risk methodology) must be followed. After that, computing an objective or subjective resilience rating can be achieved in a simple and accurate manner. DHS 2011b, 2011c, and 2011d followed these procedures to compute resilience ratings for tunnels, subway stations, and buildings.
Assessing community and network resilience can be achieved using the resilience ratings from different assets and links between those assets in a network setting.
Setting acceptance thresholds is perhaps the most difficult step in asset (or community) management. Traditionally, a prescribed acceptance threshold was adopted in civil infrastructure projects and based on a reasonable, yet subjective, probabilistic non-exceedance1 value (Ettouney and Alampalli 2015a and 2015b). (Note that an example of probabilistic non-exceedance is stating that there is a 95 percent probability that the next flood in a particular area will not exceed a particular damaging level.) This practice was reasonable enough for its time, since civil infrastructure projects were mostly based on ensuring safety. With the advent of risk-based paradigms, where project decisions are based on safety as well as cost (both life-cycle costs and initial capital expenditures), setting risk acceptance thresholds has become more difficult to define. The same holds true for resilience. Objectively, what is a reasonable acceptance threshold for resilience of a particular asset or particular community? The answer to this question is as important as defining and assessing resilience. For without setting a threshold, resilience improvement projects could be either unnecessarily costly or result in reduced performance (see Figure 8). At the time of this writing, there were few objective methods available for setting reasonable resilience acceptance thresholds but some general suggestions can be made regarding methodologies for setting resilience thresholds. A simple approach is to try to set the acceptance threshold so as to minimize total costs, as illustrated in Figure 8.
- "A Framework to Qualitatively Assess and Enhance the Seismic Resilience of Communities" by Bruneau, M, Chang, S, Eguchi, R., O'Rourke, T., Reinhorn, A., Shinozuka, M., Tierney, K., Wallace, W., Winterfelt, D. Earthquake Spectra Journal Vol. 19, No. 4: 733-752, Earthquake Engineering Research Institute, 2003.
- ASEC Report Card for America's Infrastructure by American Society of Civil Engineers, Reston, VA: ASCE 2013.
- Costs and Benefits of Natural Hazard Mitigation by Federal Emergency Management Agency Report, Washington, DC: FEMA, 1996./li>
- Critical Infrastructure Resilience Final Report and Recommendations by National Infrastructure Advisory Council (NIAC), Washington, DC: NIAC, 2009.
- EM-DAT: The OFDA/CRED International Disaster Database by Université Catholique de Louvain. Brussels, Belgium: EM-DAT, accessed on April 2014.
- Exploring Risk Communications by Gutteling, J. and Wiegman, O. Dordrecht, The Netherlands: Kluwer Academic Publishers, 1996.
- High Performance Based Design for the Building Envelope: A Resilience Application Project Report, Building and Infrastructure Protection Series, Washington, DC: DHS 2011.
- Infrastructure Health in Civil Engineering: Applications and Management by Ettouney and Alampalli. Boca Raton, FL: CRC Press, 2012.
- Infrastructure Health in Civil Engineering: Theory and Components by Ettouney and Alampalli. Boca Raton, FL: CRC Press, 2012.
- Integrated Rapid Visual Screening of Buildings, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
- Integrated Rapid Visual Screening of Mass Transit Stations, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
- Integrated Rapid Visual Screening of Tunnels, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
- Multihazard Considerations in Civil Infrastructure by Ettouney & Alampalli. Boca Raton, FL: CRC Press, 2016.
- National Infrastructure Protection Plan by Department of Homeland Security, Washington, DC: DHS, 2009.
- Natural Hazards Mitigation Saves: An Independent Study to Assess the Future Savings from Mitigation Activities: Volume 1 - Findings, Conclusions, and Recommendations by National Institute of Building Sciences Report, Washington, DC: MMC, 2005.
- Personal Communications by Hynes, Mary Ellen. Vicksburg, MS: 2001.
- Review of the Department of Homeland Security's Approach to Risk Analysis, National Academic Press, Washington, DC: NRC 2010.
- Risk Assessment: A How-To Guide to Mitigate Terrorist Attacks, Risk Management Series, FEMA 452 by Federal Emergency Management Agency, Washington, DC: FEMA, 2005.
- Risk Assessment and Decision Analysis with Bayesian Networks by Fenton, N., and Neil, M. CRC Press, Boca Raton, FL: 2013.
- Risk Management in Civil Infrastructure by Ettouney & Alampalli. CRC Press, Boca Raton, FL: 2016a.