Resiliency and Recoverability of Concrete Structures
Zhishen Wu and Mohamed F.M. Fahmy
Human-constructed structural systems in normal operational conditions are operating under a daily load, and during long-term service they become subjected to environmental erosion and therefore will become overloaded. In addition, many structures are at risk of accidental effects, i.e., natural hazards or human disasters. All these factors cause gradual or immediate degradation of the performance of the available systems. In order to ensure that existing and modern structural systems perform the required functions and services, and retain their capacities during the life-cycle, numerous academic and field studies as well as lessons learned in times of crisis and natural hazards have produced detailed design recommendations and guidelines, taking into account several parameters: changes in the applied loads, weather impacts, and exposure to unconventional actions. At present, there is a general consensus among the academic community, professional engineers, expert construction industries, and civil society to work for the development of modern sustainable cities. In parallel, the fast-growing economy and the long-time investment in superior infrastructures all over the world are supporting sustainability during the normal operation time of the structures, and providing resilience under the effect of sudden disruptions and a quick recovery afterward. Sustainability, resilience, and recoverability (restorability) are three terms that were recently introduced to the field of civil engineering. The mutual relations between the three terms and structures need to be clearly established in order to identify the required sustainability, resiliency, and recoverability analysis methods, which in turn lead to the development of advanced design guidelines for sustainable, resilient, and recoverable structures.
This chapter provides a definition for the sustainability performance-based design of urban infrastructures, and briefly addresses the interrelation between the sustainability, resilience, and recoverability of structural systems. The global efforts made to enhance the resiliency of urban systems are presented in light of the design recommendations and considerations given by the available design codes. In addition, the academic literature concerning this endeavor is briefly presented in view of modern structural systems and the technologies proposed for the construction of resilient infrastructures. With respect to seismic forces as accidental actions, a mechanical model providing qualitative and quantitative measures for the seismic performance of urban structural systems is well-defined. The real situation of existing old and modern urban infrastructures is evaluated. Lastly, several models for the adoption of fiber-reinforced polymers (FRP) to enhance the recoverability/resiliency and control the performance of existing and modern reinforced concrete (RC) structures are comprehensively discussed.
Sustainability Design of Urban Structures
The holistic concept of sustainability depends on satisfying the needs of present and future generations, while creating a balance between society, environment, and economy direction. In addition, mutual influences between the three directions should be introduced so they can benefit from the positive aspects and keep negative impacts to a minimum. From the authors’ point of view, although there are a number of experiences that can be judged as promising and encouraging toward the construction of sustainable cities, ensuring that the concept of sustainability is more widely applied remains challenging. The sustainability of infrastructure provides one of the crucial practical challenges for transforming ideas and principles into concrete realities. In the field of civil engineering, there are many studies adopting new, renewable, and smart materials to reduce the negative impacts of available/ traditional construction materials on the environment and control construction costs, while raising the efficiency of the functionality of modern infrastructures. Moreover, numerous research deals with natural hazards and disasters associated with improper human actions to ensure the rapid recoverability/restoration of the functionality of critical infrastructures. Other studies have tremendously contributed to the development of effective health-monitoring methods and intelligent calculations for reliably following up on the states of structures. Bringing together the interactions among the scientific outputs available in abundance across many disciplines (structural, disaster prevention and mitigation, advanced materials application, information and communication technology, etc.) will have undeniable effects in bringing the design of a wide range of sustainable structures into reality.
Model for Sustainability Performance-Based Design of RC Structures
The authors here propose a sustainability-based design model for modern RC structures. This model includes several analysis/design approaches and design-based requirements that constitute mutually influent interactions among several design objectives to satisfy the three major pillars of sustainability performance-based design, i.e., economical and durable, green and healthy, and safety. This model also articulates design properties (characteristics) and the corresponding assessment indices (metrics) of sustainable structures, as shown in Figure 6.1.
Green, light-weight, and life-cycle cost analysis/design approaches can result in the protection of natural resources, development of high performance but environmentally friendly materials, and reduction in construction and maintenance costs of modern RC structures. Resilience-based design mostly emphasizes developing all the necessary measures to provide structures with deliberated protection systems/ elements/resources to meet the anticipated diversity of hazards/threats to ensure the long-term functionality of human-based constructions. The smartness of structures can be realized through the introduction of special components, special processing, and the adaptation of the materials-design. The longevity of a structure is dependent on the resistance of its components to harsh environmental conditions and natural hazards or human-made disasters. Therefore, the structural system should allow its components to be renovated, repaired, and replaced. That is, the longevity of a structure represents the outputs of the green-deign, the light-weight design, and the smartness and resilience-based design requirements. The positive impact of any design area on sustainability performance-based design cannot, in general, be guaranteed without taking into account the triple bottom line of sustainability (economic, environmental, and society). For example, durable, resilient, and reliable structural systems (based on advanced technologies, highly durable materials, and strong resisting systems) can satisfy the sustainability-based performance in some ways, but economic assessments may be exaggerated. On the other hand, other less expensive solutions can be applied, but may significantly harm the built environment. The society’s direction is directly or indirectly influenced by final decisions, and so mutual harmonization between findings/outputs at all design phases (planning and design, construction, and operation) is critical to balancing the three dimensions of sustainability.
FIGURE 6.1 Proposed model for the sustainable performance-based design of structures.
To ensure the sustainable performance-based design of modern structures, design of sustainable structures should be characterized by resourcefulness, reliability, redundancy, recoverability/restorability, robustness, intelligence, innovation, being environmentally friendly (eco-system), and having a low life-cycle cost (LCC), as shown in Figure 6.2. Resourcefulness means that established systems are based on renewable resources of materials, information, technical elements, recovery and maintenance plans, and management strategies to achieve certain goals and maintain the integrity of the system so it can be continued indefinitely. Reliability is the assurance that all components of a structure must function effectively throughout both the usual operating cycles and the times of pre-predicted perturbation events. It also ensures that the structure has a safe exit when entering the stage of functional-loss in the event of an unexpected external shock. Redundancy refers to the adoption of a set of systems/resources that jointly or sequentially support continuity of structure functions under any interrupted circumstances.
The Recoverability/restorability of a structure is determined when it suffers controlled damage during an interruption, and it is provided with deliberated plans and a collection of resources after the exposure to accelerate the speed of recovery of the structure’s functions. Robustness is a consistent principle in the design of the
FIGURE 6.2 Design properties (characteristics) for the sustainable-based design of structures.
components of a structure according to its assigned function toward providing protection systems against what is expected to happen, taking into account everything that is new and may potentially change in the future. Eco-system is based on the construction of structural and infrastructure systems that are environmentally friendly in terms of both the materials adopted in the different components and products over the structure’s lifetime, e.g., construction waste, production residues associated with structural function, and the impact of carbon emissions. The intelligence of a structure relies on the aggregation of data collected by all sensors that monitor the performance of all components for analysis allowing the highest possible efficiency during operation, saving energy, protecting all available resources, and ensuring constructive interaction between the various components. It predicts problems before they occur and provides advanced computational solutions to maintain functional efficiency over time. Innovation represents the extent to which advanced developments in materials, technology, and self-adaptation systems can be adopted by structures before and after construction. Following up on the continuous development in the field of energy-saving, the development of durable/cost-effective/light-weight building materials and innovative ways to accelerate construction and increase products’ efficiency have been created. In addition to the tremendous progress in digital data science to track the health of structures, many innovations associated with the creation of new' systems capable of adapting to the environment and its unpredictable changing conditions have emerged. Life-cycle cost links the outputs of all the proposed design methods with the design limit states of a structure in order to achieve the optimal continuous use of the structure and its components without any adverse economic impact of design limit states throughout the life-span of the structure.
Figure 6.1 shows that the sustainability of a structure is based on a very complex interaction between the characteristics of the proposed design approaches and the design-based requirements. This confirms that they must be completely interdependent in order to realize the required sustainability. In addition, in the design stage, the construction stage, the life-cycle stage, and the emergency stage (interruption actions) of RC structures, a large number of indices are necessary to assess the performance of structures designed using the proposed sustainable performance-based design model. Some of these indices are listed in Figure 6.1, such as the adoption of smart materials, the replacement ratio of natural resources with materials of renewable resources, the added value of renewable energy, the number of resistance systems and their interactions, acceptable design limit states under life-cycle loads, accepted maintenance planes (corrective, preventive, and predictive), and the application of advanced technology (ICT) in construction and during the life-cycle stage. In addition, in the life-cycle phase, other indices are very critical, such as the success of the applied health-monitoring system in tracking structural performance changes; the accurateness of the adopted calculations and possibilities to correctly activate mandatory maintenance, the readiness of the application of recovery plans in emergencies, and the applied technology should be evaluated for improvements.