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Structural Performance Under Multi-Hazards (SPUMH) Program

The Structural Performance Under Multi-hazards (SPUMH) Program has an overall objective of addressing the gap between basic research and building codes, standards, and practice through measurement science research. It has a multi-phased mission to (1) predict structural performance up to failure under extreme loading conditions; (2) assess and evaluate in situ structural capacity using novel, smart sensing metrology and the ability of existing structures to withstand extreme loads; (3) design new buildings and retrofit existing buildings using cost-effective, performance-based methods; and (4) derive lessons learned from disasters and failures involving structures. The SPUMH Program accomplishes this with a staff of 13 with expertise in structural engineering, wind engineering, mechanical engineering, sociology, and geoscience, with assistance from five associates. Base funding is $4.15 million per year. Recent projects within the program include improvement in the nation’s wind design standards, development of design provisions for tornado-resistant design, research into the effects of alkali-silica reaction (ASR) in existing concrete structures, and development of performance-based fire protective design for structures.

All but two of the 13 staff hold Ph.D.’s, and these two are currently undergraduate students in civil engineering. Post-doctoral experience ranges from 1 year to more than 50 years. The program staff’s median experience level is 27 years, and the average is 25 years. Of the program’s 13 researchers, 2 are females. Collectively, the program staff has published more than 35 invited and/or refereed papers on their areas of research. Staff members have received 12 external awards, including a Gears of Government award for development and enhancement of the national wind design maps, PCI Journal’s George D. Nasser Award for work in developing robust precast concrete connections, the American Concrete Institute’s Arthur J. Boase award for work in assessing the effects of ASR, and the National Storm Shelter Association’s Keisling award.

The SPUMH Program consists of the following three research thrusts: (1) develop validated tools that predict structural performance to failure under extreme loading conditions; (2) develop validated tools to assess and evaluate the capabilities of existing structures to withstand extreme loads; and (3) develop performance-based guidelines for cost-effective design of new buildings and, where warranted, rehabilitation of existing buildings. The research thrusts have motivated a wide range of projects, including the investigation of the Joplin Missouri Tornado and Hurricane Maria; improvement in the nation’s wind design standards and practices; development of design provisions for tornado resistance; development of computational wind engineering procedures for using computational fluid dynamics; research into the effects of ASR in existing concrete structures; development of a life-cycle condition assessment platform; and continued work on developing robust, collapse-resistant structures, following on the World Trade Center investigations performed in the past. Collaboration with the EL fire science researchers would yield information on the effects of fire on structural performance.

The Structures Group’s research includes analytical and experimental studies performed with both intramural and extramural resources. Applied research associates support the group’s work in developing wind and tornado hazard maps. Together with the Earthquake Engineering Group, the Structures Group has recently commissioned the Performance-based Engineering Research for Multi-hazards (PERFORM) Laboratory. The PERFORM Structural Testbed will enable large-scale testing to

assess structural performance under extreme winds, disproportionate collapse, earthquakes, and material degradation.

TECHNICAL MERIT OF THE PROGRAM

Wind Hazards

Accomplishments

NIST has long led the nation’s research into wind hazards and design of structures for wind resistance. In recent years, NIST has performed a series of wind hazard studies that have resulted in updated wind hazard maps adopted by the building codes and nation’s standards. The staff’s national wind hazard study conducted in 2014-2015 resulted in adoption by the American Society of Civil Engineers (ASCE) standard ASCE-7-16 of a new set of wind design maps with substantially reduced design wind loads throughout much of the western United States, enabling development of buildings and structures at lower cost while maintaining desired protection again wind losses. More recent work will enable adoption by the ASCE 7-22 standard of long-return period maps, useful in performance-based wind design, as well as new maps for Puerto Rico and the U.S. Virgin Islands that represent substantially improved fidelity over prior maps.

The program staff’s study of the wind boundary layer’s variation with storm size has led to a proposal to modify the ASCE 7-22 study to include more accurate representation of wind-speed variation with elevation above ground. When adopted, this will result in the design of buildings for improved wind resistance reliability.

Recent research has focused on the development of computational wind engineering (CWE) procedures for using computational fluid dynamics (CFD) and the development of data-assisted design (DAD) tools. The staff has collaborated with Iowa State University and the engineering firm Walter P. Moore to import these procedures into ETABs, a popular structural-analysis software platform.

Challenges and Opportunities

With the adoption of a pre-standard for performance-based design of structures for wind resistance, the structural engineering profession is increasingly in need of tools to facilitate designs of this type. The staff’s efforts in CWE and DAD design holds promise to provide these needed tools. NIST has the opportunity to provide the technical guidance that the industry needs to avoid misapplications of this emerging technology that could lead to unfortunate results. The incorporation of DAD into ETABs has the potential to revolutionize wind design procedures. However, ETABs is just one of several proprietary software products used by industry. The selective teaming with one software vendor can be limiting to the broad adoption of this capability.

While CFD has promise as an important tool to permit building-specific assessment of wind effects, there is current widespread skepticism in the design community as to its validity. Unless addressed, this may inhibit the adoption of this technique in design practice.

Implementation of Joplin Tornado Recommendations: Moving Beyond Tornado Hazard Maps

NIST completed its investigation of the 2011 Joplin tornado and issued a final report in 2014¹. The report detailed 47 findings and 16 recommendations for improving the characterization of tornado hazards; the design, construction, and maintenance of buildings and shelters in tornado-prone regions; and emergency communications that alert and warn of imminent threat from tornadoes. The project’s objective is to implement all 16 recommendations from the NIST Joplin tornado investigation, at the earliest possible date, based on code and standard development cycles.

Accomplishments

Tornado hazards are not currently considered in the design of buildings, except for safety-related structures in nuclear power plants, storm shelters, and safe rooms. The inclusion of design criteria for tornados in building codes and design practice will be a significant accomplishment. The project has made progress on several of the recommendations provided during the first phase of the Joplin Implementation Project (completed in fiscal year 2019). Research and development for the tornado maps methodology, along with associated design provisions, has been completed, and submittals have been made to the ASCE-7 Wind Load Subcommittee and Main Committee for adoption into the 2022 edition of the standard.

Challenges and Opportunities

On the basis of feedback received from the ASCE 7 standards committee, the tornado hazard maps and design provisions were developed to target the same level of structural reliability provided by the building code for wind resistance. Because the probability that a building will actually be subjected to a tornado is very small, the protection is against only moderate tornado events (EF-I or II), even for important structures with large footprints. While the new requirements introduced by NIST into the standards will reduce tornado-induced losses, they will not prevent disasters of the scale of the Joplin event. Further work will be needed to enhance and improve the tornado design provisions so that they will have more substantive effect and benefit.

Alkali-Silica Reaction Research

The Alkali-Silica Reaction research program is funded by the U.S. Nuclear Regulatory Commission. The study’s objective is to develop the technical basis for evaluating effects of ASR on structural performance. This includes various experimental evaluations aimed at quantifying the effects of ASR on the following parameters: concrete mechanical properties; bond, anchorage, and flexural capacities; and seismic performance of concrete structural members.

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¹ The report is available at https://www.nist.gov/publications/final-report-national-institute-standards-and-technology-nist-technical-investigation

Accomplishments

This is an ongoing research area. Work accomplished to date includes completion of NIST technical notes—on assessing concrete mechanical properties² and bond/anchorage of reinforcement in ASR affected concrete.³ Physical testing is under way to assess seismic performance of concrete structural members. This includes the development of a methodology for assessing the degradation of seismic resistance of concrete walls affected by ASR.

Challenges and Opportunities

This is a topical and important research area that can greatly influence the evaluation of many types of structures, including commercial, industrial, and transportation structures. Although the effects of ASR have been known for a number of years, the discovery of ASR in commercial and state infrastructure has resulted in recent heightened media attention to this issue in some regions of the country. This presents an opportunity for NIST to expand the scope of investigation and recommendations on ASR beyond the nuclear industry to address these recent discoveries.

Robust Structural Systems for Multi-Hazard Mitigation

The Robust Structural Systems for Multi-Hazard Mitigation program’s objective is to develop performance-based design methodologies for structural systems to achieve robustness against multiple hazards. The program has focused on robustness against disproportionate collapse, following the work performed on the World Trade Center investigations, and has been recently extended to focus on performance-based design for extreme winds. The project approach is categorized into the following three components: evaluation of structural robustness based on experimental validation; enhancement of structural robustness through the development of improved structural connections; and technology transfer through the development of guidelines, standard provisions, and acceptance criteria.

Accomplishments

This is a developing research area that builds on the disproportionate-collapse work performed in the early 2000s related to the World Trade Center and Pentagon investigations. Research focused on robustness evaluation of concrete structures has resulted in several journal publications. NIST has coordinated with the Precast/Prestressed Concrete Institute (PCI) to develop improved precast beam-column connection concepts for future full-scale testing. NIST has also collaborated with the American Institute of Steel Construction (AISC) to develop improved steel gravity-frame connections that have been evaluated and designed based on computational modeling and component testing and will be demonstrated using full-scale testing. The program has made considerable contributions to future standards and guidelines, including the ASCE/SEI Disproportionate Collapse Mitigation Standard, ASCE/SEI Alternative Load Path Analysis Guidelines for Buildings and Other Structure, and the SSRC Guide to Stability Design Criteria for Metal Structures (7th edition).

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² National Institute of Standards and Technology (NIST), 2021, “Structural Performance of Nuclear Power Plant Concrete Structures Affected by Alkali-Silica Reaction (ASR) Task 1: Assessing In-Situ Mechanical Properties of ASR-Affected Concrete,” NIST TN 2121, Gaithersburg, MD.

³ NIST, 2021, “Structural Performance of Nuclear Power Plant Concrete Structures Affected by Alkali-Silica Reaction (ASR) Task 2: Assessing Bond and Anchorage of Reinforcing Bars in ASR-Affected Concrete,” NIST TN 2127, Gaithersburg, MD.

Challenges and Opportunities

This research program provides the opportunity for NIST to directly impact the design profession by providing structural connection and system solutions that enhance structural robustness and limit disproportionate collapse. This requires NIST to evaluate design solutions that not only meet various performance objectives, but also provide an economic and efficient design solution compared with current construction practices. Collaboration with other agencies (e.g., AISCand PCI) and design firms will be instrumental in accomplishing this goal.

A program goal that has not been accomplished is to encourage adoption by the building codes, or design criteria that would require minimum standards of robustness for all structures. NIST put substantial effort into accomplishing this goal in the period 2003-2006; however, the building industries and the building code development organizations were resistant to inclusion of such requirements. NIST has been working with the ASCE to develop a standard for design for structural robustness. This standard is now nearing completion. However, it is not clear whether the building codes will require use of this standard when it is available. Unless the building codes require use of these criteria, the effectiveness of this program will be limited.

PORTFOLIO OF SCIENTIFIC EXPERTISE

Accomplishments

The Materials and Structural Systems Division’s (MSSD’s) Structures Group has two primary areas of expertise: wind engineering and structural engineering.

The wind engineering personnel have deep expertise and experience in the engineering application of the science of wind. They have demonstrated through their successes that they have key roles in the development of the nation’s codes and standards related to wind and are highly regarded by the industry.

The structural engineering personnel address a broad range of topics that are generally associated with structural collapse issues. They have developed deep experience in studying structural failures, such as those associated with the destruction of the World Trade Center. They have demonstrated that they can address problems as diverse as ASR effects on the safety of nuclear facilities and the role of connections in preventing the collapse of steel or precast structures.

Challenges and Opportunities

Much of the program staff’s expertise lies in individuals who are approaching or beyond typical retirement age. As these individuals inevitably do retire, the program will lose substantive expertise.

The wind engineering personnel comprise approximately half of the Structures Group and have been extremely important and effective in the development and refinement of national wind standards. This success is highly associated with the effectiveness of individuals in the Wind Engineering Group. As with any small group, the loss of key individuals through retirement or other circumstances can have major effects. The Wind Engineering Group does have mid-career individuals who will have the responsibility of maintaining the group’s influence over the long term. They need to continue to develop and refine a long-term succession/talent plan.

The Structures Group also has challenges related to its small size and diverse demands. Because of the imbalance between potential demands and human resources, it is difficult to have a profound effect on the industry. A group multiple times the current size would still have limitations. This group has a unique and very important role through the statutory Disaster and Failure Studies Program. Historically,

understanding structural failures have led to advancements in the industry.⁴ There is no group or organization in the United States other than NIST that has the authority to independently investigate structural failures. It is not clear that the Structures Group is taking full advantage of its position.

ADEQUACY OF RESOURCES

Accomplishments

The MSSD Structures Group has a significantly updated and upgraded structural testing laboratory (PERFORM) that has recently been commissioned. It has a strong floor, modular strong walls, hydraulic actuators, hydraulic distribution system, and other components. It is roughly equivalent to the testing facilities at some U.S. research universities. There are larger structural testing facilities at a few U.S. universities and at overseas government laboratories and universities. The MSSD has high-quality equipment and can perform dynamic testing in addition to static testing. The facility has done testing related to the ASR study as well as some testing of precast concrete connections.

The Structures Group also has substantial computational resources that allow it to do computational demanding work in simulations for CWE and CFD as well as large and complex finite element modeling of structures and structural components.

Challenges and Opportunities

The ability to do in-house testing is important, and the testing should be done at the highest industry standards. There may be some testing that would be better done by other structural testing laboratories that have different or better facilities or special expertise. The presence of the PERFORM testbed should not influence the decision as to where to do testing if another laboratory is better equipped or has special expertise. It is also important that MSSD maintain active and ongoing relationships with other major U.S. structural testing laboratories and researchers.

EFFECTIVENESS OF DISSEMINATION OF OUTPUTS

Accomplishments

The Structures Group disseminates its research results through the following four primary means: publication of National Construction Safety Team Reports (NCSTARs) and technical notes; publication of papers and articles in journals and conference proceedings; best practices documents and guidelines, as well as pre-standards in partnership with industry; and working directly with standards development organizations and the model building code development organizations to introduce technical requirements into industry practices.

The group contributed to publication of a large series of NCSTARs associated with studies of the cause of collapse of the New York World Trade Center Buildings during the period 2002-2005. In March 2014, the group published a comprehensive report on the effects of the May 22, 2011, Joplin, Missouri, tornado. An investigation into the effects of Hurricane Maria on Puerto Rico in 2017, which involves several members of the Structures Group, is under way. The reports that have been published are comprehensive and identify the cause of structural failure and potential improvements in design and construction practice to avoid such failures in the future. In essence, these reports lay out a roadmap for improvement of the nation’s standards.

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⁴ H. Petroski, 1994, Design Paradigms, Cambridge University Press, Cambridge.

The reports associated with the 2001 attacks on the Pentagon and World Trade Center resulted in recommendations for incorporating structural robustness into building design. NIST made several attempts during the period 2003-2006 to insert structural robustness provisions into the International Building Code; however, the building community did not agree that this was necessary. Instead, a building industry coalition developed alternative, less impactful provisions that were adopted into the building code.

NIST has also worked with the ASCE to develop a best practice guide for design for structural robustness; a standard is being developed through the consensus committee process. It is not clear whether the building codes will require implementation of the standard.

The 2014 Joplin Missouri report recommended development of design and construction requirements to provide protection for buildings against tornados. NIST successfully worked with the International Code Council to develop a standard for design and construction of storm shelters⁵ that was adopted by the International Building Code. In addition, NIST has developed a set of probabilistic tornado hazard maps for the contiguous United States and introduced requirements for tornado-resistant design for inclusion into the ASCE 7-22 standard that will require design of important structures for resistance of moderate (EF-I and II) tornadoes. The earliest possible adoption of these criteria would be in the 2024 International Building Code.

For many years, the ASCE 7 standards committee has relied heavily on the NIST Structures Group for support in developing and maintaining the wind-resistant design criteria contained in the standard and adopted by the building codes. Both the 2016 and 2022 editions of these standards include major revisions based on the NIST work.

Challenges and Opportunities

The building industry is most open to major changes in practice following a substantive disaster, such as an earthquake, hurricane, wildlands-urban interface fire, or terror attack, when the public perceives that the performance of the built environment was sadly lacking and demands change. NIST has been effective at investigating deficiencies in the standards and practices associated with such disasters; however, the development of improved practice recommendations takes substantive time, typically measured in years. By the time recommendations that were motivated by the 2001 terror attacks and the Joplin tornado were ready for adoption, the public demand for change had waned, and the industry’s desire to offer construction at a low cost impeded the adoption of the recommendations. However, once requirements are adopted by the building codes and standards, NIST has had good success in making incremental improvements. Efforts to improve the nation’s building practice may be more effective if an iterative approach is used. This includes the rapid introduction of new requirements into the building codes and standards following an event, while the window of opportunity created by a disaster is still open, and refinements made in later years as research points to appropriate science-based criteria.

CONCLUSIONS AND RECOMMENDATIONS

Technical Merit of the Program

The statutory Disaster and Failures Studies Program puts the Structures Group in the unique position of being able to help the nation learn from structural failures. There are numerous structural collapses each year; some are related to major seismic, wind, or other environmental events, and some are isolated events.

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⁵ International Code Council, 2014, “Standard and Commentary: ICC/NSSA Standard for the Design and Construction of Storm Shelters,” ICC-500, Washington DC.

Systems engineering analysis is appropriately applied not only to such factors as loads and materials, but also to the element of human functions and tasks within the design process. Reliability studies properly include consideration of human reliability.

The code requirements for design of new structures are extremely complex and require deep knowledge of multiple codes and standards as well as the computer software needed to calculate the forces and design the members and connections.

Presently, the structural design profession faces a significant challenge because of a lack of database compatibility between various commercial structural engineering software programs. This leads to inefficiencies in U.S. design practices. NIST is in a unique position to offer standardized solutions to structural database interoperability.

Adequacy of Resources

A diverse staff often yields insights and perspectives that enhance the quality of research.

Effectiveness of Dissemination of Outputs

Interaction with organizations responsible for building codes development and implementation, benchmarking, design, and related research yields a two-way advantage—it provides knowledge to NIST researchers, and it enhances NIST’s reputation and influence.

A function of the Structures Group is to enhance the global competitiveness of U.S. industry through innovations in building materials and construction technology. Construction technology is very topical and drives many decisions related to the design and construction of structures.