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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program Executive Summary The Blast Mitigation for Structures Program (BMSP) is a research and development activity conducted by the Defense Threat Reduction Agency (DTRA) to improve the performance of buildings that are targets of terrorist attack. The primary goal of the BMSP is to reduce loss of life and injuries to the occupants of these buildings through the development of innovative techniques for new structures and retrofitting existing facilities. The program encompasses the analysis, computational modeling, and physical testing of buildings and components, and structural and nonstructural systems. A report in 1995 by the National Research Council (NRC), Protecting Buildings From Bomb Damage: Transfer of Blast-Effects Mitigation Technology from Military to Civilian Applications, recommended that a research and development program be focused on the mitigation of blast effects and the transfer of relevant technology (NRC, 1995). Prior to the publication of that report, the NRC had published two studies, The Embassy of the Future, a series of recommendations for the design of future U.S. embassies (NRC, 1986), and The Protection of Federal Office Buildings Against Terrorism, a guide for federal agencies to improve the security of persons, buildings, and information from terrorist attack (NRC, 1988). Because of the NRC's expertise and long-standing involvement in this area, DTRA requested that the NRC review and assess the BMSP's implications for engineering, architectural, and building practices, disaster preparedness, rescue and recovery operations, and emergency medical services, and recommend appropriate research topics and a strategy for technology transfer. In response to that request, the NRC established the Committee for Oversight and Assessment of Blast-Effects and Related Research under the auspices of the Board on Infrastructure and the Constructed Environment. The committee was asked to: Assist in the development of a blast-effects research agenda and provide recommendations for activity priorities. This will include assessing the scope and focus of related, on-going research, both in this country and internationally, to assure that efforts are well-integrated; evaluating the capability of the existing research infrastructure to achieve research objectives; and determining the possible need for a national test facility to carry out the research program. Recommend appropriate mechanisms to achieve effective transfer of research results and existing technologies to civilian government agencies and commercial engineering and architectural practice; Develop recommendations for outreach and knowledge dissemination activities to be undertaken by DTRA and other agencies; Review and comment on proposed curriculum or training materials designed to enable civilian engineers and architects to apply the principles of protective design and analysis to civilian buildings and other constructed facilities. Provide a forum to enhance interaction and information sharing among other stakeholder government agencies such as the General Services Administration, Federal Emergency Management Agency, U.S. Army Corps of Engineers, Centers for Disease Control and Prevention, Bureau of Alcohol, Tobacco, and Firearms, Department of Transportation, Department of State, etc., and state and local governments. The committee's objective is to monitor and assist an evolving program that has activities subject to ongoing revision. DTRA anticipates that the BMSP will be funded through fiscal year 2003 (FY03) at an annual level of approximately $10 million and that the program could
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program potentially be continued beyond 2003. Because of the ongoing and long-term nature of the BMSP, in this first annual review the committee makes some broad programmatic observations and recommendations for improving DTRA's strategic planning, priority setting, and resource allocation over the life of the program. The committee's principal findings and recommendations are based on an analysis of current program plans, descriptions of work units, and budget allotments. Although the BMSP includes most of the activities the committee identified as necessary for a comprehensive program to improve the likelihood of survival of occupants of buildings subject to terrorist bombing, the committee did identify a number of specific areas where increased emphasis could bring immediate benefits and some current activities that should be reduced or redirected. In subsequent reports, the committee will evaluate in more detail how well the program objectives are being met and will suggest reallocations of the resources that will become available if the committee's recommendations have been implemented. The chapters in this report include additional observations and guidance on specific issues. CONCLUSIONS AND RECOMMENDATIONS Conclusion 1. The overall plan of the BMSP is appropriately focused on the explicit, and laudable, goal of protecting human life. Nevertheless, the BMSP would be improved by initiating a formalized strategic planning process for identifying and reaching consensus on knowledge gaps, reassessing them in light of lessons learned through individual program activities or studies outside the BMSP, refining or establishing new objectives, and identifying the activities that should be continued, initiated, or abandoned. Recommendation 1. The Defense Threat Reduction Agency should allocate sufficient time and resources to formalize a strategic planning process for reviewing and refining the Blast Mitigation for Structures Program on an annual basis. Planning of the next full-scale building test should be delayed until a strategic plan has been developed that defines the functions of the analytical and experimental components of the program in terms of overall program goals, and with respect to one another. The plan should also identify and establish pathways for developing the questions that may only be answered by large-scale building tests. Conclusion 2. Although the Program Master Plan includes many activities that could yield worthwhile benefits, the committee identified several modifications to the BMSP to be considered in the next program cycle. Recommendation 2a. All analytical and experimental activities should be designed to test a specific hypothesis about the outcome. With respect to full-scale tests, parametric studies should be conducted to determine what could be learned from the test on the basis of the proposed instrumentation. Recommendation 2b. The program should take full advantage of the advances in parallel-processor computing made by the U.S. Department of Defense and the U.S. Department of Energy to improve the capability and ease of use of computational tools for predicting structural responses to bomb blasts.
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program Recommendation 2c. The residual strength of blast-damaged structural components should be investigated more fully. For example, tests of full scale columns representative of buildings ten stories and more should be included, as well as a series of tests to evaluate how well common rebar splices and connections can function after being damaged by blasts. Recommendation 2d. The Blast Mitigation for Structures Program should consider conducting a series of tests on masonry structures, including tests of unreinforced masonry for benchmarking purposes and tests of a range of reinforcement techniques to improve protection. A series of tests on construction typical of long-span buildings should also be considered. Recommendation 2e. The Blast Mitigation for Structures Program should place a higher priority on the development and evaluation of retrofitting techniques —particularly on creative conceptual retrofitting measures that would prevent a life-threatening progressive collapse following a blast. Recommendation 2f. The Blast Mitigation for Structures Program should focus more attention on the behavior of nonstructural systems in the blast environment, including (1) tests of the effectiveness of various types of interior partitions or perimeter zones of “soft” space in protecting occupants and contents, and (2) comparisons of floor-based systems of mechanical and electrical distribution and typical overhead systems. Recommendation 2g. The Blast Mitigation for Structures Program should evaluate the key factors affecting the ease and rapidity with which trapped or injured occupants can be extricated from damaged buildings and whether rescuers can safely enter areas of the collapsed structure to render aid. In cooperation with urban search and rescue teams, the program should support simulated rescue and recovery operations to refine or improve rescue techniques. Conclusion 3. The design and engineering approaches favored by the industrial contractors and government laboratories that are implementing the BMSP may be more appropriate to traditional military and defense objectives despite the emphasis of the BMSP on nonstructural solutions, injury reduction, and improved rescue and recovery techniques. Recommendation 3. The contractor base should be broadened to increase the representation of the commercial architectural and engineering communities, as well as specialists in injury prevention, disaster medicine, and technology transfer, particularly in the planning phases of the program. Conclusion 4. The committee is in complete agreement with the BMSP's emphasis on determining progressive-collapse vulnerability of buildings in selected attack scenarios but believes this ability would be improved by fuller coordination of research activities. Recommendation 4. The Defense Threat Reduction Agency should adopt a balanced approach toward understanding and preventing the progressive collapse of buildings. This approach should include coordinated physical testing, experimentation, and analyses and should guide the planning of research activities and the interpretation and synthesis of the results.
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program Conclusion 5. Full-scale testing of structural systems has been overemphasized at this relatively early stage of the program at the expense of reduced-scale testing, the development of retrofitting techniques for existing buildings, the testing of nonstructural building systems, and the investigation of technologies related to injury prevention. Recommendation 5. The Defense Threat Reduction Agency should not construct another full-scale test structure until the results of previous experiments on Controlled Test Structure-1 (CTS-1) have been fully analyzed and understood. At this stage of the program, DTRA should rely more on experiments with scaled elements and scaled assemblies of elements wherever scale effects are well understood. Conclusion 6. Controlled Test Structure-1 has been underutilized so far; although it has been damaged in previous tests, it still has considerable value for testing full-scale structural components and nonstructural elements. Recommendation 6. Controlled Test Structure-1 should not be tested to failure because it can still be used as a reaction frame for component tests. Conclusion 7. Although, the inventory of existing buildings vulnerable to blast damage far exceeds the number of new buildings that will be constructed in the foreseeable future, the BMSP appears to have placed more emphasis on methods applicable to new construction than on retrofitting techniques for existing structures. Recommendation 7. The development of tools for conducting vulnerability assessments and strengthening existing buildings should be given a higher priority. Resources should also be allocated to investigating construction techniques that permit the rapid rehabilitation of blast-damaged buildings. Conclusion 8. The Blast Mitigation for Structures Program has a unique opportunity to determine how requirements and techniques for earthquake-resistant designs could apply to blast-resistant designs, as well as to identify and assess design features and materials that could improve building performance over a range of hazards (e.g.., earthquake, fire, flood, and extreme wind) that could impact the safety of the occupants. Recommendation 8. The Blast Mitigation for Structures Program should incorporate activities with the maximum potential for multihazard mitigation. Because design features that provide multihazard resistance are likely to generate more interest among designers and manufacturers than design features that promise only blast resistance, multihazard features could ultimately reduce the cost and increase the application of improved building practices and products. Conclusion 9. Data on blast-related injuries and building damage are limited and, therefore, have hindered the development of statistically valid damage-prediction and epidemiological models.
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program Recommendation 9. The Blast Mitigation for Structures Program should initiate an institutionalized process that can be quickly mobilized for collecting critical data related to blast damage and injuries in buildings that are subject to bomb damage. Conclusion 10. The barriers to the complete and effective transfer of the results of the BMSP will require considerable time and effort to overcome. A convenient way to reduce the transfer time would be to use existing institutional infrastructures (i.e., building code and standards-writing organizations, professional and technical organizations, universities, and research centers) to disseminate knowledge. Recommendation 10. A workshop to develop a road map for transferring technology for mitigating blast effects should be scheduled as soon as possible. To assist in the ongoing dissemination of information, the Blast Mitigation for Structures Program should consider sponsoring an annual or biennial conference devoted to all aspects of blast-mitigation design, engineering, injury prevention, and rescue and recovery. REFERENCES NRC (National Research Council). 1986. The Embassy of the Future: Recommendations for the Design of Future U.S. Embassy Buildings. Washington, D.C.: National Academy Press. NRC. 1988. The Protection of Federal Office Buildings Against Terrorism. Washington, D.C.: National Academy Press. NRC. 1995. Protecting Buildings from Bomb Damage: Transfer of Blast-Effects Mitigation Technologies from Military to Civilian Applications. Washington, D.C.: National Academy Press.
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