Materials and Structures for Resilience Program

Summary

The cost of disasters, in terms of human life and economic loss, continues to rise as natural hazards impact growing populations with increasing severity. Improving the resilience of buildings and infrastructure is key to reducing the impact of disasters, and understanding the changes in material and structural performance over the service life of a structure provides the foundation for its long-term resilience. A multi-scale approach is needed to understand the impact of material deterioration on the capacity of structural elements and the resulting performance of structural systems, so that the engineering community can design structures to be resilient and functional throughout their service life. The Durable Materials and Structures for Multi-Hazard Resilience Program leverages unique capabilities and expertise in the Materials and Structural Systems Division to characterize the aging of infrastructure materials, - quantify the loads hazards impart on structures, understand how environmental factors affect the long-term durability of structural components, and translate this knowledge to large-scale structural behavior to develop science-based methodologies needed to enable risk-informed design that accounts for the long-term performance of the structure.

Description

Objective
To improve building codes, standards, and engineering practice by developing and deploying advances in measurement science that enhance the robustness, resilience, and durability of materials and structures against natural and manmade hazards.

Technical Idea
The Durable Materials and Structures for Multi-Hazard Resilience Program will utilize the world-class expertise in materials characterization and structural testing to study the combined effects of structural performance given extreme loadings and aging due to chronic environmental exposure.

Research Plan
The fundamental new idea is that the robustness and resilience of buildings and infrastructure can be significantly enhanced by developing reliable capabilities to accurately characterize both the design hazards and to predict their effects on the performance of buildings and infrastructure, given the effects of long-term exposure to the environment on the aging of materials.

Track 1 – Structural Performance under Multi-Hazards:
This track will be achieved through a research program organized around two research thrusts. The first research thrust will focus on the development of analytical methods and measured data to characterize the hazard environment. The second research thrust will focus on performance-based design and evaluation of structures through the development of (1) validated physics-based models to predict performance of structures to failure; (2) testbeds, metrics, tools, and methodologies for quantification of in-situ structural capacity, including the effectiveness of structural repair and/or strengthening techniques, and evaluation of nonlinear structural performance; (3) acceptance criteria for differing levels of performance objectives; and (4) mitigation strategies based on evaluated performance. The scope of this program encompasses structural performance under aging effects: extreme winds, including tornadoes; mitigation of disproportionate collapse; and experimental structural research to advance the development of performance-based design standards.

(1) Develop measurement science and science-based methodologies for characterization of wind-related design hazards (wind speed, wind pressure, storm surge elevation, waves effects, and surge flow velocity) associated with synoptic and non-synoptic extreme wind events (hurricanes and tornadoes), with consideration of future hazard conditions. This research thrust consists of three elements:

• Develop an improved understanding of the current wind hazards to the built environment and the gaps between these hazards and existing design requirements as prescribed by current model building codes and national standards. The outcomes of this element will include: (1) risk-based techniques for improved quantification of tornado hazards (non-synoptic extreme wind events) and assessment of tornado loads for building design; and (2) innovative computational methods for accurate assessment of hazards associated with synoptic extreme wind events (design wind speeds, storm surge, flow velocity, surge-borne debris impact loading).

• Develop an improved understanding of temporal variations in wind and storm surge hazards across the U.S. (e.g., sea level rise, frequency, intensity, and duration of synoptic and non-synoptic windstorms).

• Develop science-based methodologies for quantification and projection of future wind-related hazards for incorporation into forward-looking building codes and standards.

(2) Develop validated tools and performance-based design guidelines that provide evaluation of performance of building systems (structural system and envelope) at pending failure (in non-linear range) under extreme loading conditions for safe and cost-effective design of new buildings and, where warranted, rehabilitation of existing buildings. This research thrust consists of four elements:

• Develop experimental procedure, wind loading protocol, and performance data for tall building’s connections and structural and cladding components to enable modeling of non-linear behavior in extreme winds of tall buildings.

• Develop validated structural response models that characterize structural response from initial loading to failure for individual hazards (e.g., wind) and within a multi-hazard context. The outcome of this element will be a rational assessment of safety and reliability of structures at specified performance levels for individual hazards and within a multi-hazard context.

• Develop improved analysis and design methods for performance-based design for extreme winds and for mitigation of disproportionate collapse of structures.

• Develop acceptance criteria for different performance levels. The outcome of this element will be published performance criteria for structures subjected to extreme loads and under disproportionate collapse that will enable the design of buildings and infrastructure with enhanced robustness and resilience against natural and man-made hazards.

Track 2 – Engineered Materials for Resilient Infrastructure:
This focuses on the aging mechanisms in concrete, including reinforced concrete, and polymeric materials. The metrology developed in this track is translated to the engineering community through the development of material durability test methods and standards. The output also helps develop structural tests needed to develop building codes that account for material aging.

Assuring the long-term performance of additively constructed structures: This project will address this by developing needed mechanical and durability test methods that provide assurance of performance for 3DCP, and will develop sampling strategies that achieve a balance of time, materials, and assurances of performance. To obviate the need for printing companion walls, real-time material property measurements will be developed for the purpose of identifying whether material properties have deviated from prescribed minimum values. Moreover, the testing will address the material properties that assure structural and durability performance. Ultimately, the project will develop the fundamental measurement science and new standardized test methods that will form the foundation for reliable building codes that enable AC industry growth.

Assessing Pyrrhotite in Concrete: Damage to concrete structures in residential and commercial construction in central Connecticut have been attributed to the iron sulfide mineral pyrrhotite. Iron sulfides in concrete aggregate are not desirable as their relative instability results in decomposition with associated staining, expansion, and pop-outs near concrete surfaces or, in severe cases, cracking of the structure. There are no standardized test methods to assess pyrrhotite occurrence and abundance in aggregate or in concrete. Suggested limits on aggregate include 1 % S (Sulfide) by mass in Europe, a Canadian (and now Connecticut and Massachusetts) limit of 0.1 % S or 0.23 % pyrrhotite, are very challenging to meet using current standard guides for petrographic analyses. Developing a standard test method, including a set of calibration reference standards will provide a means for accurate, consistent analysis of pyrrhotite in concrete. The pyrrhotite/aggregate/concrete reactions and rates will be documented so that the most deleterious reactions can be efficiently reduced or eliminated. This reaction and rate data in combination with the evaluation of proposed mitigation strategies, on both materials and structural levels, will be used to manage the deleterious effect of the presence of the pyrrhotite mineral as a component of the aggregate in concrete.

Reliability of Fiber Reinforced Polymer (FRP) Composite Systems in Resilient Infrastructure: This project will seek to implement a strategic plan that prioritizes the current research needs for fiber reinforced (FR) composites used in structural systems (NIST SP-1244). The research plan will 1) investigate FR composite use in the field, 2) design durability experiments of FR composite systems from micro to macro level that focus on the critical modes of failure identified, and 3) assess performance of FR composites in structural systems using existing data from laboratory tests and numerical analysis.

Metrology for Accelerated Laboratory Weathering: The NIST Accelerated Weathering Laboratory provides researchers with well-quantified accelerated-aging environments, using a unique SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) technology. The 2m SPHERE and the recently developed 6-port SPHEREs enable NIST to develop advanced metrology and methodology for accelerated laboratory weathering and service life prediction for engineered infrastructural materials, including composites for structural support, coatings for corrosion protection of structural elements, roofing, siding and sealants for the building envelopes. This project will investigate the effects of spectral power distribution, high UV irradiance, cycles of temperature, moisture and light exposure on long-term performance of engineered polymeric materials for the development of new standards for metal halide-based accelerated laboratory weathering devices and service life prediction procedures. The material degradation databases generated from this work will provide a better understanding on degradation mechanisms and failure modes of infrastructure materials, which is essential for industry to improve choices of materials and develop new materials for resilient infrastructure under chronic environmental hazards and natural disasters.

Assessing Steel Corrosion Risk in Innovative Cement Concretes: This project will investigate the corrosion mechanism of steel in concrete by combining measurements of the concrete pore solution chemistry with electrochemical impedance spectroscopy. These results will be used to develop models of the corrosion rate that incorporate environmental factors relevant to the corrosion mechanism of interest as input. The output of this model can inform structural engineers designing new structures about the hazard associated with corrosion and will inform the infrastructure stakeholders about the remaining service life of a structure. Developing this model requires a new approach to measuring corrosion and assessing the durability of concrete materials. Developing these measurements for the purpose of modeling will enable new standards for durability assessment that can be incorporated into existing building codes.