Risk Assessment for Forward-Looking Building Standards

Objective
This project will significantly advance industry capacity for measuring and quantifying impacts from building damage/failure and develop guidance for the design and assessment of geotechnical considerations and multiple hazards that threaten buildings and infrastructure.

Technical Idea
To accommodate future needs from natural hazards and extreme events, significant measurement science and quantification are needed in key areas. NIST will produce:

• Documentation of the state of knowledge and guidance, and subject matter collaboration to produce recommendations identifying needs for guidance and best practices, for geotechnical design to ensure that consistent requirements can be implemented for effective mitigation of future risks with sufficient engineering rigor.
• Addressing future hazard conditions requires a reassessment of current engineering practices. Specifically, the safety margins reserved for structural members should be re-evaluated and adjusted to reflect the changing hazard conditions. This includes the calibration of load factors applied to nominal loads and resistance factors applied to nominal strengths so that the reliability index for all structural members consistently achieves the target value. Additionally, the uncertainty associated with these calibration factors should be assessed to support engineering decisions, facilitating a balance between forward-looking design strategies, societal risk tolerance, and cost efficiency.
• To support performance-based assessment of aging infrastructure, NIST will develop a computational framework that links corrosion progression in reinforced concrete with structural performance and service life prediction. This includes quantifying the effects of environmental exposure and extreme events on degradation, and producing guidance for integrating deterioration models into structural safety and resilience evaluations. 
   

Research Plan
The project includes two research tasks (RT): one on geotechnical considerations and potential impacts from geohazards (RT1) and one on the potential impacts from building damage and failure (RT2). RT2 has two sub-tasks, RT2-1 and RT2-2.

RT1: State of Practice Assessment for Improving Geotechnical Design Guidance for Buildings and Lifeline Infrastructure [Lead: Nikolaou]

The goal of RT1 is to advance the understanding of geotechnical performance of buildings and lifeline infrastructure subjected to future natural hazard stressors and conditions, with compounded effects from asset deterioration and other geohazards. For instance, future conditions of scour erosion due to floods (especially flash floods) elevate the risks of transportation systems. Flooding in the US causes an estimated up to almost $500 billion in damages annually, equivalent to 1-2% of our nation’s GDP in 2023. While this reflects all types of flood damage (e.g., infrastructure, commercial impacts, property damage, etc.), scour erosion contributes significantly to this economic effect as more than 80% of the nearly 600,000 bridges of the National Bridge Inventory are built over waterways. The same phenomenon affects foundations of buildings (especially in waterfront areas), as well as embankments and dams.

Geotechnical engineers are routinely faced with challenging problems relating to soil and water conditions in the natural and built environment (Culligan et al., 2019, Benedict et al., 2021). Without science-based guidance across the Nation, a patchwork of recommendations and requirements that vary significantly by state and by level of engineering rigor will remain. The five primary components of this research task are:

• Comprehensive literature review of codes, standards, guidelines, strategy documents, action plans, textbooks, and other relevant literature regarding the incorporation of impacts of variable or increasingly hazardous conditions in geotechnical engineering design and project implementation, assessing the current state of practice for geotechnical engineering and capacity to address future environmental hazards and conditions, to be published as a NIST SP report.
• Surveys and/or stakeholder focus groups to gather information from geotechnical engineering practitioners across the Nation. This effort will focus on: a) collecting and documenting available resources, b) discussing how variable conditions are considered in existing and planned projects in industry, and c) identifying needs in practice for incorporating impacts of variable or increasing future conditions in projects that can be addressed through cutting-edge research priorities, and will also be published as a NIST SP report.
• Develop a work plan to collect data for a priority future hazard and condition (e.g., scour erosion from floods). The data will include historical performance and hazard or condition data, failure cases, and maintenance logs from local/state authorities and federal agencies. It is expected that established collaborations with agencies and centers (NJ/CAIT transportation agencies, NCDOT, FHWA) will continue to support this activity.
• Develop geotechnical damage functions (“fragilities”) applicable to one or more infrastructure systems (e.g., bridge structures, retaining geosystems, embankments) based on the data collection, above and using an analytical evaluation of established national typologies for these assets.
• Generate recommendations on how the damage functions can be incorporated in guidelines and standards, connected to potential asset vulnerabilities and key performance parameters of scour susceptibility across typologies, foundation types, and hydrologic settings for specific characteristics and intensity levels of the future hazard or condition.

These tasks address an urgent need to update existing procedures and guidelines (the latest FHWA HEC-13 manual for scour assessment was published in 2012), with performance indicators and assessment procedures on both an asset and a system level. This project aims at supporting national, state, and local needs for technical guidance and prioritization of funding allocation based on risk-based scour evaluations and mitigation measures.

RT 2-1: Uncertainty Quantification for Forward-looking Building Design [Lead: Sattar]

Current building codes and standards are inadequate to protect people and assets from the increasing frequency and severity of natural hazard events. To address this limitation, a chapter is being introduced to ASCE 7-28 to account for projected changes in hazards such as wind, tornadoes, snow, and flood. However, the large uncertainty associated with future hazard conditions poses a new challenge to engineering design. The uncertainty is due to both natural variations in the hazard intensity (aleatory) and the limited ability to model future change in hazard intensities (epistemic). The uncertainty can vary by region and increase as predictions extend further into the future. Additionally, accelerated structural aging and material deterioration driven by increased temperature and humidity can reduce structural integrity, leading to decreased performance and increased safety risks. This research task will evaluate the impact of changed hazard conditions on design requirements and analyze the uncertainty of structural designs due to potential future hazard changes. Quantifying these uncertainties can avoid designs that are either overly conservative, resulting in excessive costs, or underly cautious, resulting in inadequate safety margins. The primary components of this research are:

• Conduct a detailed review of the methodologies, assumptions, and datasets referenced in building codes, standards, and provisions. The hazards to be examined include wind, flood, snow, ice, rain, temperature, and humidity, likely starting with the wind hazard. The assumptions and rationale underlying building codes will be examined to improve the understanding of design practices and to identify gaps and opportunities for future research and code refinement. According to the Structural Engineering Institute, the new chapter of ASCE 7-28 will affect 14 out of its 25 standards as well as 4 of its 8 Manuals of Practice. Therefore, this review can inform the development of standards and guidelines relevant to future hazards and provide a solid foundation for addressing emerging challenges.
• Employ the non-stationary reliability method for uncertainty quantification. The reliability method calibrates load and resistance factors to address uncertainties in the design process. It accounts for uncertainties in applied hazard loads, their effects on structural members, and the resulting member capacities. It can also incorporate uncertainties related to material deterioration and its impact on structural performance, a concept that has been proposed by previous studies but needs further validation. In addition, the deterioration effect is often neglected for buildings not subjected to extreme conditions. Therefore, this research task focuses on uncertainties in applied hazard loads. The objective of the calibration is to ensure an acceptable level of structural reliability over the structure’s design life. The target reliability index is derived from structural members of typical buildings that have demonstrated acceptable safety at reasonable construction costs. Note that the selection of reliability models and the models themselves can introduce uncertainties to the analysis results, which should be carefully assessed and mitigated throughout this process. For buildings with higher performance requirements, such as hospitals, the performance-based assessment methodology can be applied to conduct an in-depth uncertainty analysis. This research task will advance the understanding of uncertainties involved in designing and retrofitting buildings to withstand future hazard loads and support the adoption of forward-looking building standards in the context of deep uncertainty.

RT2-2 Service Life Assessment of Concrete Structures Under Corrosion [Lead: Sattar]

The deterioration of critical infrastructure systems—such as buildings, bridges, and transportation networks—has become a major challenge in the United States and globally. The cost of intervention (i.e., repair, maintenance, or replacement) is substantial, with over $2.6 trillion estimated to be needed for restoring deteriorating infrastructure in the U.S. over the next decade; a figure projected to rise to $5.6 trillion by 2040. Despite growing attention to this issue, current condition assessment standards and guidelines (e.g., ASCE/SEI 41-23, ACI 365.1R-17, ACI 369.1-22, and ACI 562-19) do not provide adequate methodologies for accurately assessing aging structures or predicting their remaining service life. The challenge is further exacerbated by the impact of extreme events, such as earthquakes and floods, which can accelerate degradation mechanisms.

Among mechanisms for deterioration in reinforced concrete (RC) structures (such as sulfate attack, alkali-aggregate reaction, chloride ingress, and freeze-thaw cycles), corrosion of steel reinforcement is the most prevalent, accounting for approximately 74–90% of cases. While significant advances have been made in understanding corrosion at the material scale (e.g., pore chemistry, electrochemical behavior), these insights are not yet fully translated into macro-scale structural performance modeling and assessment. With increasing concern about future hazards and aging infrastructure, there is a need for an integrated approach that bridges material-scale knowledge with structural-scale assessments. This project links experimental and theoretical research at the material scale with computational structural engineering analysis. The goal is to improve predictive capabilities and support informed decision-making regarding the safety, longevity, and resilience of infrastructure systems in real-world hazard scenarios.

Modeling corrosion in reinforced concrete structures is inherently complex, as the phenomenon is governed by environmental exposure, pore structure, ion diffusion, and chemical reactions involving both steel and concrete. While detailed meso-scale models can simulate these processes with high fidelity, their application to large-scale structures or distributed infrastructure assessments is computationally impractical. As a result, there is a pressing need for macro-level deterioration models that are computationally efficient, validated, and capable of informing structural performance metrics. The Infrastructure Materials Group (IMG) at NIST is currently undertaking extensive experimental and analytical research to understand the underlying chemical and physical processes of corrosion. However, the structural implications of this research—particularly in terms of fragility, resilience, and global performance—remain underexplored.

This project will develop a framework that connects experimentally validated material degradation models with structural-level performance indicators, tailored specifically to corrosion-induced deterioration in reinforced concrete structures. Rather than duplicating past research on general corrosion mechanisms, the emphasis will be on translating laboratory-scale measurements into actionable models for structural fragility. In corrosion-driven deterioration, the useful life of an RC structure is defined as the period during which it can fulfill its intended function without unacceptable loss in strength, excessive cracking/spalling, or violation of safety and resilience criteria. Research is required to define structural (remaining) useful life under various modeling assumptions, environmental exposures, and performance thresholds; understand how cover depth, concrete porosity, and environmental conditions (e.g., chloride exposure, carbonation) affect corrosion initiation and progression from a structural perspective; and analyze how external hazards such as flooding and earthquakes accelerate the corrosion process. Flooding increases moisture content and reduces electrical resistivity, while seismic events can introduce cracks that create rapid ingress pathways for corrosive agents.

The overarching goal is to develop a computational framework that supports aging-dependent service life prediction, integrates fragility and capacity models, and bridges materials research with structural engineering practice. Key steps necessary to produce this outcome include:

• Conducting a comprehensive literature review on corrosion modeling in RC structures, with a focus on structural performance impacts and aging-related deterioration.
• Develop a plan for determining how results from material-level experiments (e.g., accelerated corrosion testing, electrochemical analysis) to inform and calibrate structural-scale models, especially regarding initiation times and deterioration rates.
• Developing a state-of-the-art assessment of numerical modeling techniques for corrosion, identifying limitations in their application to structural performance evaluation and probabilistic failure analysis.
• A computational framework will be developed to quantify the remaining service life in RC structures, accounting for various parameters such as geometry and reinforcement layout, corrosion progression models, constitutive models for degraded materials, uncertainty in mechanical properties and their distributions, and time-varying environmental and structural loading.
• The research will also explore: (1) integration of diagnostic data (e.g., inspection, sensor readings) to refine degradation state estimation, (2) simulation of corroded RC members under a range of seismic (and possibly flooding) scenarios to assess synergistic effects on degradation, (3) evaluation of retrofit strategies implemented either during service life or post-event to improve performance and extend useful life, and (4) incorporation of decision-making tools and optimization routines to select the most cost-effective intervention strategies.