Earthquake Risk Reduction in Buildings and Infrastructure Program

Objective:
To develop the technical means to mitigate the risk to the built environment from earthquake ground motions through improvements to building codes, applied research to identify new design approaches, development of fundamental information regarding behavior under strong earthquake shaking, and to lead the multi-agency National Earthquake Hazards Reduction Program (NEHRP) in providing information and tools for engineers, policy makers and the public to make informed decisions through a multi-faceted, coordinated outreach efforts.

What is the problem?  
Earthquakes represent one of the most destructive natural hazards on earth and while infrequent in any one location, are a high consequence, low-probability event of significant threat to the built environment. With the on-going concentration of global populations in cities, threats from strong shaking to these urban centers represent a growing problem. In the United States, strong earthquakes such as the 1811-1812 New Madrid, MO series and the 1906 San Francisco temblor raised some awareness, the real era of earthquake risk mitigation began with the 1933 Long Beach earthquake. Significant damage to schools resulted in the Field Act being enacted in California which improved structural design of K-12 schools and charted the course for improvements to building codes to mitigate risk. The 1971 San Fernando earthquake resulted in significant and unexpected damage to engineered structures designed to recent codes. The result was the National Earthquake Hazards Reduction Program enacted by Congress in 1977 to coordinate improvements to building codes and the built environment. 

Significant progress has been made by the United States over the past 40 years to improve design methods and building codes, to increase knowledge of structural behavior under extreme loads, to improve the characterization of seismic hazards and to take advantage of the greatly enhanced analytical abilities now available with modern computers and software. That said, much remains to be done. Knowledge of system level behavior of structures is limited principally to analytical simulations. With increased costs, economic considerations can constrain engineers using prescriptive building codes and force the use of performance based seismic engineering (PBSE), yet this approach is relatively new and requires on-going research to calibrate its methodologies. Furthermore, these same economic realities point to the need for improved knowledge of structural element behavior under loading together with the need for new, improved materials to provide cost-effective design solutions. 

The development of improved design approaches for new buildings has improved the quality of the building stock designed since the dawn of the NEHRP era in the late 1970’s. A larger and significant problem remains, that of existing buildings designed to older building codes. Studies published by the LA Times (2014) have shown the LA metropolitan region possesses over 2000 older reinforced concrete buildings that are considered structurally suspect given their age. A similar issue exists in Seattle where the Seattle Times (2016) has published extensively on the large numbers of unreinforced masonry buildings that remain in service. These examples point to the urgent need for improved methods to identify existing buildings needing assessment and to accurately estimate their likely performance under strong shaking and in turn to develop cost-effective means to strengthen these buildings. 

While buildings may perform adequately under strong shaking, the performance of interior systems also is important. Damage to nonstructural systems in buildings can represent economic losses and can require significant repair times to bring the building back into operation. Thus, these systems also must perform adequately to meet the intended performance of the building as a whole both during the event and after. 

Knowledge of the performance of soils under strong ground shaking remains an area of needed research. The 2011 Christchurch, NZ earthquake destroyed the central business district of the city when the soil liquefied under relatively modest shaking. Threats from liquefaction exist in many areas of the country including Memphis where the Mississippi River has deposited alluvial soil subject to liquefaction. Knowledge of the interaction of soil-foundation-structure systems remains a significant problem requiring on-going research and representing a significant opportunity for improvement by incorporating systems-level thinking in design.
Recent work at NIST into how to improve community resilience has dramatically shown the central role of lifelines in modern life. Improving the performance of isolated structures is important, yet without essential building services, these buildings may not be functional following an earthquake. Thus, improved knowledge of how lifelines perform under strong shaking is also needed. This knowledge includes not only the lifeline structure itself but the supporting geotechnical systems as well. 

Lastly, there is a shift in philosophy that has slowly developed in the United States since the Loma Prieta (1989) and Northridge (1994) earthquakes. In these two events, in general newer buildings performed adequately with a few exceptions. However, economic losses including direct losses from damage and indirect losses from business interruptions were significant. Historically, seismic design of buildings to ensure life safety has been the approach over time. With these two events, the question of business interruption and the need to improve building performance to minimize post-earthquake business interruption is now a common consideration. Moreover, with the greater awareness of resilience, the need for post-event building operation is gaining attention. How to achieve not only life safety but now an immediate occupancy level of building performance is an open question requiring consideration. The solution is not one of simply increasing design forces but requires systems level evaluation to achieve the needed performance levels. Adoption of immediate occupancy performance will represent a drastic shift in thinking requiring thoughtful development of supporting technical knowledge. 

Public policy also is an aspect of earthquake risk mitigation. While improvements to design methods and building codes are essential, adoption of stricter building codes and their enforcement also is important. Moreover, the existing building problem is a national issue that all jurisdictions face whether in areas of seismic risk or not. Existing buildings built to earlier, perhaps less stringent standards, are not required to be retrofitted unless repurposed or modified. Los Angeles is the first major city to address this issue with their landmark City Ordinance 183893 (LA 2017) requiring that buildings be evaluated within three years and brought up to minimum performance levels within 25 years. Public policy issues are not technical per se, but are at the heart of the existing building problem.
 

What is the technical idea?  
Improving the performance of new and existing buildings and lifelines to earthquake shaking is the overall goal of the program. That said, with finite resources a program to address this problem in a logical and effective manner has been developed in large part since NIST became NEHRP lead agency in 2004. What is proposed here is a modification of this approach to better utilize existing resources and focus on critical research needs. 

The technical idea involves four major efforts all aimed at improving the seismic performance of the built environment. These four efforts complement one another and are integrated so as to reach the overall program goal and include (1) Internal applied research efforts on specific topics, (2) extramural work to support NIST on specific topics, (3) leveraging NIST research efforts with partner organizations and (4) NEHRP lead agency roles and responsibilities including community outreach. The overall effort will continue to address important technical issues such as PBSE, developing basic performance data on structural elements and determination of the impact of uncertainty on design performance. New areas will include examination of collapse probabilities for buildings designed using PBSE or traditional prescriptive approaches, evaluation of next generation reinforcing steels and retrofit options for steel and concrete buildings. Working with partners such as the NIST-funded Center of Excellence in areas of common interest is an important way to leverage internal expertise. Lastly, study of public expectations of the condition of the post-earthquake built environment also will be begun. 
 

What is the research plan?  
There are two major components in the NIST Earthquake Risk Reduction in Buildings and Infrastructure: (1) development of measurement science tools for design of new buildings design and evaluation and retrofit of existing buildings, (2) NEHRP lead agency responsibilities including community outreach. A third area concerning assessing the seismic needs of lifelines will be in the planning process in FY2019. A third area concerning assessing the seismic needs of lifelines will be in the beginning planning process in FY2019.

These two major components are organized into four major thrust areas: 

Thrust 1 – Existing Buildings
Thurst 2 – Earthquake Design in Wind Communities
Thrust 3 – Perforamnce Based Design
Thrust 4 – NEHRP and the Statutory Work 

Development of Measurement Science-Based Tools 
This component of the program has the following thrusts: 

Thrust 1 – Existing Buildings: Evaluation Methods and Retrofit Methods. 
Nonductile reinforced concrete columns represent a significant concern in areas of the country of high seismicity. Los Angeles has over 2000 of these buildings designed in the 1960’s and 1970’s where design and detailing rules from that era do not meet current standards. Columns in these buildings represent a particular hazard and need to be evaluated. Research will be undertaken to improve existing analytical means to determine capacities in these columns. This work is being performed at NIST in collaboration with a team awarded an DRI/FFO grant. 

A complementary study is beginning its second year at NIST involving the Polymers, Materials, and Earthquake Engineering Groups to evaluate the use of fiber reinforced plastics (FRP) in strengthen concrete elements, specifically columns and structural walls.

A third study is being undertaken to examine the performance of pre-Northridge, that is pre-1994, panel zones in beam-column joints. The intersection of structural steel beams and columns is detailed to form a panel zone which is subjected to large demands during seismic response. The Northridge earthquake revealed serious deficiencies in panel zones designed in the 1960’s through the 1980’s resulting in improvements in design provisions. This study involves examination of existing buildings with these older panel zone designs to determine likely performance and how to retrofit these joints to improve performance. 
A fourth study involves testing of link beams for eccentric braced frames to obtain improved performance data for use in design and to suggest improvements in link design. These link beams are structural fuses in these systems, so their performance is critical yet data in the literature is limited. This study will be conducted in collaboration with researchers at the NIST Center of Excellence at Colorado State.

Thrust 2 – Earthquake Design in Wind Communities: Evaluation of Wind and Seismic Design Interaction in the CEUS. 
A suite of steel and concrete buildings will be designed for areas in the central and eastern US (CEUS) where wind loads are dominant and control design, yet seismic demands may be significant. Design for wind and for seismic represent two different design approaches and how these two conditions impact resulting building performance is not clear. Building collapse probabilities and fragilities will be determined. This work to be conducted in collaboration with the NIST Center of Excellence at Colorado State University. A suite of 16 structural steel buildings will be designed starting later in FY2018 for evaluation by EEG engineers to ascertain their performance and collapse probability as well as the interaction of wind and seismic demands. A suite of reinforced concrete buildings will be designed for three locations in Puerto Rico to ascertain their performance and collapse potential under the specific design conditions in Puerto Rico. The intent for both sets of buildings is to examine the interaction of these two different lateral load regimes and how the performance is impacted. 

Two projects associated with the NCST investigation are underway. EEG is providing engineering support for a project concering building performance during and after Hurricane Maria. A second project concerns the performance of lifelines in Maria. Details of this work can be found with the project descriptions for the NCST investigation. 

Thrust 3 – Performance Based Design: Calibration of PBSE,  and Prescriptive Design Methodologies a.nd New Technologies:
High Strength Reinforcing Bars in New Construction: The use of high strength reinforcing bars in reinforced concrete offers significant savings in construction costs. However, basic performance of reinforced concrete shear walls designed using these new bars is not known. A small study of elements constructed in the NIST Structures Laboratory will be made to determine how elements using these bars perform in comparison to existing approaches. The original thrust was column and beam applications but recent research conducted outside of NIST has lessened the urgency of that work, so work on walls is now proposed. 

Collapse Assessment of Buildings under Seismic Loading:  Performance Based Seismic Engineering (PBSE) has become an increasingly popular means of design of buildings in areas of high seismicity. Recent studies by Harris and Speicher (2015) have revealed that there appears to be an inconsistency between performance levels obtained using traditional prescriptive design approaches such as ASCE 7 (ASCE 2010) and newer PBSE methods using ASCE 41 (ASCE 2013). Collapse probability studies using the FEMA P-695 methods (FEMA 2009) will be employed to determine the efficacy of traditional and PBSE methods in reaching stated seismic performance goals. The suite of steel buildings analyzed by Harris and Speicher (2015) will be assessed using FEMA P-695 methods to determine the probability of collapse of these structures. Results will be compared with the target probabilities found in ASCE 7 and ASCE 41. 

Future studies will evaluate performance of archetype reinforced concrete buildings designed using three different PBSE standards: Tall Buildings Initiative (2010), LATBSDC (2011) and ASCE 41 (ASCE 2013) available to practitioners. Collapse probabilities and fragilities obtained for buildings designed using these different approaches will be compared to further calibrate PBSE methods against traditional prescriptive design using ASCE 7 (ASCE 2010). This work is planned for FY2020.

Quantification of Material, Loading, and Modeling Uncertainties of Reinforced Concrete Columns and Steel Beam-Columns under Seismic and Gravity Loads for Use in PBSE: There are a number of sources of uncertainty that can impact the accriacy of structural calculations. These include uncertainties in materials properties, loading and modeling. Earlier work completed under a NIST EL exploratory project exploredinvestigated uncertainty issues concerning steel beam-columns and established a framework to quantify uncertainty for structural components in PBSE. This project extends this work to quantify the influences of uncertainties in material properties, loads, and modeling techniques on the performance of reinforced concrete columns under lateral seismic and axial loads from gravity.

Energy-Based Collapse Assessment of Framed Structures for Performance-based Seismic Engineering:  The objective of this project is to develop a framework for evaluating structural performance and collapse due to seismic excitations based on an energy approach.  The structural response obtained from nonlinear dynamic analysis is evaluated based on the amount of energy stored in the system and the amount of energy dissipated via damage to the components in the structure.  This dissipative energy in turn is compared with 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 for the advancement of performance-based seismic engineering.  

Evaluation of Wind and Seismic Design Interaction in the CEUS. A suite of steel and concrete buildings will be designed for areas in the central and eastern US (CEUS) where wind loads are dominant and control design, yet seismic demands may be significant. Design for wind and for seismic represent two different design approaches and how these two conditions impact resulting building performance is not clear. Building collapse probabilities and fragilities will be determined. This work to be conducted in collaboration with the NIST Center of Excellence at Colorado State University. The suite of 16 structural steel buildings will be designed starting later in FY2019 for evaluation by EEG engineers to ascertain their performance and collapse probability as well as the interaction of wind and seismic demands. A suite of reinforced concrete buildings will be designed for three locations in Puerto Rico to ascertain their performance and collapse potential. The suite of 16 structural steel buildings will be designed starting later in FY2019 for evaluation by EEG engineers to ascertain their performance and collapse probability as well as the interaction of wind and seismic demands. A suite of reinforced concrete buildings will be designed for three locations in Puerto Rico to ascertain their performance and collapse potential. 

Evaluation Methods and Retrofit Methods. Nonductile reinforced concrete columns represent a significant concern in areas of the country of high seismicity. Los Angeles has over 2000 of these buildings designed in the 1960’s and 1970’s where design and detailing rules from that era do not meet current standards. Columns in these buildings represent a particular hazard and need to be evaluated. Research will be undertaken to improve existing analytical means to determine capacities in these columns. This work will be performed at NIST in collaboration with a team awarded an FFO grant. 

A complementary study is being started at NIST involving the Polymers and Earthquake Engineering Groups to evaluate the use of fiber reinforced plastics (FRP) in strengthen concrete elements, specifically columns and structural walls.

A third study is being undertaken to examine the performance of pre-Northridge, that is pre-1994, panel zones in beam-column joints. The intersection of structural steel beams and columns is detailed to for a panel zone which is subjected to large demands during seismic response. The Northridge earthquake revealed serious deficiencies in panel zones designed in the 1960’s through the 1980’s resulting in improvements in design provisions. This study will involve examination of existing buildings with these older panel zone designs to determine likely performance and how to retrofit these joints to improve performance. 

Experimental Evaluation of New Technologies. The use of high strength reinforcing bars in reinforced concrete offers significant savings in construction costs. However, basic performance of concrete beams and columns designed using these new bars is not known. A small study of elements constructed in the NIST Structures Laboratory will be made to determine how elements using these bars perform in comparison to existing approaches.

Thrust 4 - NEHRP lead agency responsibilities including community outreach 

NIST is the lead agency of the National Earthquake Hazards Reduction Program (NEHRP), which has four participating agencies: the Federal Emergency Management Agency (FEMA), NIST, the National Science Foundation (NSF), and the U.S. Geological Survey (USGS). Included in this project is leadership and technical support for the Interagency Committee on Seismic Safety in Construction (ICSSC), as required by Executive Order (EO) 13717.

The details of NEHRP lead agency statutory activities are discussed in a separate project write-up. 

Other work concerning social science considerations for mitigations efforts are being developed. These include what can be identified as “A second study will involve testing of link beams for eccentric braced frames to obtain improved performance data for use in design and to suggest improvements in link design. These link beams are structural fuses in these systems, so their performance is critical yet data in the literature is limited. This study will be conducted in collaboration with researchers at the NIST Center of Excellence at Colorado State.

Public Policy Issues: The Post-Earthquake Environment”. Traditional seismic design has been based on life safety whereby building occupants would be able to evacuate a building following an earthquake. The building could be seriously damaged resulting in lengthy and costly repairs or even demolition. Recent earthquakes such as Northridge and Loma Prieta have revealed the serious economic and social consequences of having large portions of the building stock out of service. Two related studies will be undertaken to research parts of this question. 

One study conducted by a new NIST/NEHRP AAAS fellow in collaboration with the NIST Center of Excellence at Colorado State will examine community expectations for building and community operability following an earthquake. The study will investigate the commonly held notion that buildings designed to building codes are “earthquake proof” and how the people expect their buildings and communities to perform. 

A second study will investigatewas concluded in May 2018 concering the research and implementation issues associated with development of a new Immediate Occupancy Performance Objective. This approach would offer building owners the choice to have their buildings designed in such a way that damage to structural and nonstructural components would be limited, permitting immediate occupancy following an event. Building utilities also would be required to be functioning so this new approach represents a profound shift in thinking. The initial study will investigated this question and identify identified needed tasks areas to be performed researched to actually develop this concept. The initial study of the IO question was completed in May 2018 and a report written. Publications and follow-on work related to that work will continue into FY2019. A second phase may be required depending on receipt of an assignment from Congress. 

REFERENCE DOCUMENTS:
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.