Earthquake Risk Reduction in Buildings and Infrastructure Program

Objective:

The Program’s objective is to develop and advance knowledge which can improve codes, standards, and design guidelines for earthquake risk mitigation of buildings and infrastructure systems with the focus on recovery-based design. These efforts supplement NIST’s role as lead agency for the National Earthquake Hazards Reduction Program (NEHRP), and also improve the safety and economic security of the American public.

What is the Problem?  

Recent earthquakes indicate a growing pattern of vulnerability among U.S. communities to earthquake induced damage and loss, due to population growth in earthquake-prone areas, aging infrastructure, and increased interdependence among modern community networks, infrastructure, and supply chains . The average annual loss to earthquake hazards in the U.S. are estimated around $6.1 billion, with nearly 50% of all Americans at risk to damaging levels of ground shaking  (Fig. 1). While tremendous advances in earthquake science and engineering have been made over the past 50 years to reduce the collapse potential for U.S. buildings, recent earthquakes have demonstrated that even modern design practices may not protect against widespread damage and downtime. Indeed, the damage observed to buildings and lifeline infrastructure in the Loma Prieta, Northridge, and Christchurch earthquakes interrupted local economies, displaced families, and impacted community well-being for years after the event.

To help mitigate risks to the American public, new knowledge, tools, and codes and standards are required to improve the seismic performance of new and new and existing and new buildings and lifelines infrastructure systems to withstand earthquake shaking, quickly recover from damage, and support  nationwide community resilience and earthquake risk reduction. 

What is the Technical Idea?  

Improvements in engineering knowledge and practice are all needed to reduce risk, improve post-disaster recovery, and improve resilience to earthquake shaking. The Earthquake Risk Reduction in Buildings and Infrastructure Program addresses these needs by (1) developing key measurement science tools to mitigate seismic risk to new and existing buildings and infrastructure systems and (2) supporting the nation through development of improved building codes and new design approaches. This technical work is accomplished through four core projects, each strategically designed to produce specific improvements needed to enhance the seismic performance of the built environment, based on evidence and lessons learned from previous earthquakes. The projects described below are complementary and, when appropriate, research efforts are collaboratively integrated to achieve program goals.

CORE PROJECT 1: Functional Recovery of Buildings and Lifelines

Objective: To improve recovery time of  the built environment (including re-occupancy and resumption of services) after earthquakes through advances in 1) measurement science for assessment and design of buildings and lifelines for functional recovery, and 2) investigation of socioeconomic aspects designing beyond current codes and standards which impact achievement of risk mitigation.

CORE PROJECT 2: Building-Level Seismic Performance Assessment

Objective: To better understand the seismic performance of buildings designed in areas prone to moderate-to-severe earthquake shaking and to identify ways to enhance structural performance through low-damage design approaches and improved code provisions.

CORE PROJECT 3: Performance Criteria Development

Objective: To advance component-level seismic performance criteria in current design standards by conducting focused experimental and analytical studies on various structural components including materials of steel and concrete.

CORE PROJECT 4: Risk Evaluation and Mitigation of Structural Systems

Objectives: To improve techniques for risk evaluation and mitigation of structural systems and integrate them in the performance-based earthquake engineering (PBEE) framework. This is achieved through 1) improvements to quantification of uncertainty in structural response; and 2) advances in short- and long-term performance assessment of FRP retrofitted structures.

What is the Research Plan?  

The objectives of each research thrust are met through complementary research designed to advance in key strategic areas of need. The research tasks (RT) for each thrust are briefly described below.

CORE PROJECT 1: Functional Recovery of Buildings and Lifelines

Research Task 1-1: Buildings

To support future building codes targeting recovery-based performance objectives, this RT: 1) develops a framework to quantify prescriptive design criteria for buildings to meet specific  functional recovery targets, leveraging state-of-the-art performance-based earthquake engineering methods, 2) designs a large archetype set of reinforced concrete moment frame buildings and models to support recovery-based assessment, 3) quantifies performance and consequence data for critical nonstructural components based on ongoing experimental programs, and 4) provides initial recommendations for recovery-based design criteria targeting improved functional recovery performance of reinforced concrete moment frame buildings in high seismic regions. This research task is motivated directly by Congressional request in P.L. 115-307 (NEHRP reauthorization) and informed by a report to Congress on improving the functional recovery of the built environment (NIST SP-1254).

Research Task 1-2: Lifelines

The incorporation of lifelines and distributed systems is critical for achieving functional recovery goals and implementation. This RT advances multidisciplinary research across lifeline systems through subtasks that: 1) develop a tool that allows users to plan investments in enhancing earthquake performance and recovery time of highways, by advancing the recently developed FHWA resilience assessment tool and connecting to NISTS’s EDGE$ Economic decision guide software (Helgeson et al, 2020) as well as FEMA’s Hazus framework; 2) use advanced optimization and new machine learning techniques, as well as large datasets, to develop a framework to improve resilience and reduce recovery time of urban transit networks, while also incorporating various engineering and socioeconomic aspects of resilience; and 3) develop a functional recovery framework for water, wastewater, and electric power systems based on the intended functions of systems for users. This research task is motivated directly by Congressional request in P.L. 115-307 (NEHRP reauthorization) and informed by work performed for NIST SP-1254 under supervision by a Committee of Experts, as well as NIST GCR 16-917-39 and NIST GCR 14-917-33.

Research Task 1-3: Economic Evaluation

This project develops improved decision support methods and tools for earthquake risk reduction of buildings and infrastructure through the identification and quantification of potential benefits and costs from earthquake risk reduction activities. In particular, this RT provides a method for thorough economic evaluation that goes beyond initial costs and avoided damages, considering life-cycle parameters for each asset and for the system as a whole. This RT also provides worked examples and case studies of the benefit-cost assessment of recovery-based design alternatives compared to conventional code-conforming design across various building archetypes.

Research Task 1-4: Social Science & Communications

This RT focuses on the development of NIST communications on functional recovery and also the collection and distillation of stakeholder knowledge and input (social science data) integral to the development of functional recovery target recovery time frameworks.

CORE PROJECT 2: Building-Level Seismic Performance Assessment

Research Task 2-1: Seismic Performance of Low-Damage Rocking Systems

This RT aims to motivate wider implementation of low-damage rocking systems as a practical way to achieve functional recovery in buildings after being subjected to earthquake shaking. The present surge of interest in designing structures with consideration of post-earthquake functionality has created the opportunity for innovative approaches to be brought into the mainstream of structural design. Despite extensive research demonstrating the feasibility of rocking systems, wider implementation has been hindered due to a lack of knowledge, experience, and technical design guidelines.  

Research Task 2-2: Seismic Performance of the Built Environment in Central and Eastern United States (CEUS)

This RT addresses a geographical region of the US that has generally moderate seismic hazard, but high risk exposure due to large population concentration (about ¾ of the US population) and high monetary value of assets and functions. The first phase will focus on a suite of 16 steel buildings designed for 3 locations in the CEUS, where wind loads are dominant and control design, yet seismic demands may be significant, for both mid-1980s and the 2018 building codes. The second phase will engage a contractor to develop and host a theme-focused workshop to detail anticipated research topics, basic and applied research, and implementation activities to advance seismic design and construction practices for new and existing buildings and lifeline infrastructure located in the CEUS.

CORE PROJECT 3: Performance Criteria Development

Research Task 3-1: High-Strength Reinforcement (HSR) in Earthquake-Resistant Structures 

This RT consists of experimental and analytical research to investigate the seismic behavior of coupled RC structural wall (shear wall) systems constructed with HSR. The experimental phase focuses on quantifying the strength and deformation capacity of coupling beams with different reinforcing steel strengths (Grades 60, 100) tested under different axial restraint conditions (i.e., unrestrained, fully restrained).

Research Task 3-2: Assessment Criteria for Structural Steel Components Considering Loading History 

This RT aims to develop new component-level assessment criteria that account for loading history. It consists of conducting a series of experimental tests on eccentrically braced frame link beams using multiple loading protocols, and complementary analytical simulations using nonlinear finite element software to extend the results of the testing scheme to configurations not tested, and formulate an improved set of criteria for eccentrically braced frame link beams that explicitly captures loading history.

Research Task 3-3: Energy-Based Evaluation 

This RT develops an energy-based framework for evaluating structural performance and collapse due to seismic excitations. The structural response obtained from nonlinear dynamic analysis is evaluated based on the amount of energy stored in the system and that dissipated via damage to the components in the structure. This dissipative energy in turn is compared to the energy capacity of the components based on existing experimental data. Through this framework, an analytical tool will be developed to assess the state of structure and identify when collapse can occur, which is crucial in advancing performance-based seismic engineering. 

CORE PROJECT 4: Risk Evaluation and Mitigation

Research Task 4-1: Quantification of Material, Loading, and Modeling Uncertainties of RC Structural components and Systems

This RT develops a method to quantify the impact of three individual sources of uncertainty and their combined impact on seismic performance assessments of structures, associated with: (1) variability in construction material properties; (2) analytical model; and (3) seismic loading (i.e., record-to-record (RTR) variability). In the first phase, this RT developed a framework to incorporate uncertainty in seismic performance evaluations at a structural component level (i.e., bridge pier); in the second phase of the project, we will extend our framework to quantify the impact of individual and combined sources of uncertainty at the building level.

Research Task 4-2: Developing Intensifying Artificial Acceleration (IAA) for Rapid Risk Evaluation

The goal of this RT is to develop a series of design acceleration time histories using regional intensifying artificial acceleration (IAA) functions that can be applied for continuous limit state development and collapse evaluation of frame structures and lifeline systems. The results of the IAA method will be compared and validated with available techniques such as incremental dynamic (push-over) analysis, multiple stripe analysis and cloud analysis.

Research Task 4-4: Reliability of Fiber Reinforced Polymer (FRP) Composite Systems in Resilient Infrastructure This RT seeks to implement a strategic plan that prioritizes the current research needs for FR composites used in structural systems (NIST SP-1244). The research plan will: 1) investigate FR 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 laboratory tests and numerical analysis, and 4) develop a pre-standard for seismic assessment of FRP-retrofitted concrete structures.

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References:

ASCE/SEI (2010). Minimum Design Loads for Buildings and Other Structures. ASCE Standards ASCE 7-10, American Society of Civil engineers, Reston, Virginia.
ASCE/SEI (2013). Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-13). American Society of Civil Engineers, Reston, VA.
FEMA (2009) Quantification of Building Seismic Performance Factors (FEMA P-695) Federal Emergency Management Agency, Washington, D.C.

Harris and Speicher (2015). Assessment of First Generation Performance-Based Seismic Design Methods for New Steel Buildings Volume 1: Special Moment Frames (NIST Technical Note 1863-1) Gaithersburg, MD.
LATBSDC (2011). An Alternative Procedure for Seismic Analysis and Design of Tall Buildings Located in the Los Angeles Region, Los Angeles Tall Buildings Structural Design Council, Los Angeles. 
LA Times (2014) Older concrete buildings in Los Angeles, January 25, 2014 http://graphics.latimes.com/la-concrete-buildings/
Los Angeles (2017) Mandatory Retrofit Programs: Ordinance 183893 http://www.ladbs.org/services/core-services/plan-check-permit/plan-chec…

Seattle Times 2016, Buildings that kill: The earthquake danger lawmakers have ignored for decades, May 14, 2016
http://www.seattletimes.com/seattle-news/times-watchdog/buildings-that-…

Tall Buildings Initiative (2010). Guidelines for Performance Based Seismic Design of Tall Buildings, Pacific Earthquake Engineering Research Center, UC-Berkeley.