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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program 2 The Blast Mitigation for Structures Program PROGRAM REVIEW Program Goal and Objectives The overall goal of the BMSP is “to protect people inside buildings from terrorist bomb attacks” (DTRA, 1999). The program seeks to achieve this goal by focusing on two primary areas: (1) reducing the likelihood of structural collapse and (2) minimizing the hazard from flying debris.1 Specific program objectives are listed below (DTRA, 1999): Establish tri-service and interagency collaboration on the program. Develop cost-effective methods to retrofit existing structures to mitigate the effects of blast. Develop design guidance for new construction to mitigate the effects of blast. Test and evaluate commercial-off-the-shelf (COTS) products for their capability to increase the resistance of a structure to blast effects. Develop industry standard models for the prediction of blast effects on structures and generate computer modules for use by government and industry. Define and produce joint service/agency design and assessment tools (to be defined by the user community). Develop simplified injury prediction models so that the benefits of blast mitigation design and retrofits can be evaluated in terms of human injury avoidance. Program Activities To implement the BMSP, DTRA has issued numerous contracts and work orders for analyses, computational modeling, and reduced-scale and full-scale physical experiments. Physical testing has been carried out primarily at two sites, White Sands, New Mexico, and the U.S. Army Engineering Research and Development Center (ERDC) in Vicksburg, Mississippi. At White Sands, DTRA Field Command has constructed a full-scale prototype of a concrete flat-slab structure called Controlled Test Structure-1 (CTS-1) to test windows, walls, and structural elements under realistic threat conditions (i.e., the blast effects of large vehicle bombs [equivalent to ~5,000 pounds of TNT]). The large blast and thermal simulator (LBTS), a very large shock tube originally constructed at White Sands to simulate the effects of nuclear 1 The committee believes that the direct effects of explosions on the human body are a potentially significant cause of injuries and death. However, the committee also believes the emphasis of the BMSP on secondary effects (i.e., the response of the building and its subsystems to blast) and their potential to cause injury and death is well focused given the state of knowledge regarding secondary blast effects.
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program weapons, has proven to be valuable for simulating conventional blast effects on complete curtain-wall assemblies for public and commercial buildings. A complementary program of reduced-scale and component testing is being conducted at the ERDC Structures Laboratory, which has a long history of model and component testing under blast conditions. The ERDC has also organized the Blast Mitigation Action Group (BMAG) to identify and evaluate commercially available (commercial-off-the-shelf or COTS) products. The BMAG web site provides sources of blast mitigation products and services for new construction and retrofitting existing structures (BMAG, 2000). The BMSP has also made extensive use of private contractors with expertise in structural engineering, structural dynamics, and computational modeling to design experiments and analyze their results. Program Organization and Funding Profiles The three primary “tasks” of the BMSP are: (1) technology and construction evaluation; (2) technology development and application; and (3) computer support, technology transfer, administration. Approximately 11 per cent of program funds are unallocated as “reserves.” Total program funding for fiscal years 1999 (FY99) through FY03 is anticipated to be $54 million. Funding in FY99 was $8.3 million; funding for FY00 through FY02 is projected to remain level at $12 million, and funding for FY03 is expected to drop to $10 million. DTRA, the parent organization of the BMSP, anticipates that the program will continue beyond FY03 at an annual funding level of $8 million to $10 million. The overall task structure and funding profiles of the BMSP are summarized in Tables 2-1 and 2-2. TABLE 2-1 Funding Levels by Major Component Task Percentage of Funding 1 technology and construction evaluation 8 % 2 technology development and application 64 % 3 computer support, technology transfer, administrationa 17 % Reservesb 11% a Includes operations and maintenance support for contributing military services b Unallocated funds Source: DTRA, 1999b. TABLE 2-2 Funding by Fiscal Year ($000's) Task FY99 FY00 FY01 FY02 FY03 FY04 1 $894 $1,246 $825 $750 $625 $4,340 2 $5,529 $8,914 $8,915 $6,724 $4,650 $34,732 3 $1,880 $1,840 $1,840 $1,845 $1,845 $9,250 Reserves $420 $2,681 $2,880 $5,981 Totals $8,303 $12,000 $12,000 $12,000 $10,000 $54,303 Source: DTRA, 1999b.
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program Task 2, the principal technology-development component of the program, consists of four subtasks, which involve a number of work-unit categories (groups of work units) (see Table 2-3). Figure 2-1 shows relative funding levels for the Task 2 subtasks for FY99 through FY03. TABLE 2-3 Task 2 Subtasks and Work-Unit Categories Subtask 2A: Loading Definition (11 % of Task 2 funding) Work Unit Percentage of Subtask Funding Blast wave propagation 36% Blast wall effectiveness 64% Subtask 2B: Structural Collapse (62 % of Task 2 funding) Work Unit Percentage of Subtask Funding Flat-slab construction (CTS-1)a 21 % Load-bearing wall construction 9% Roof slabs 7% Blast-resistant construction (CTS-2)a 12% Seismic construction (CTS-3)a 12% Steel-frame construction (CTS-4)a 18% Other structures 21% a Denotes a full-scale field test Subtask 2C: Debris Hazards (25 % of Task 2 funding) Work Unit Percentage of Subtask Funding Windows and doors 16% Exterior walls 51% Building internals 14% Injury studies 19% Subtask 2D: Internal Detonations (2 % of Task 2 funding) Source: DTRA, 1999b. PROGRAM ASSESSMENT The committee was asked to determine whether the BMSP Master Plan, as prepared by DTRA, provided sufficient guidance for the research and development elements of the program (DTRA, 1999). To aid in this determination, the committee superimposed the BMSP on a basic logic diagram for program development (i.e., statement of purpose, project identification, priority setting, and implementation) as shown in Figure 2-2. The committee also assessed the extent and balance of the technical activities in the Program Plan. The six major activities, defined by the committee in ascending order of cost and time (but not necessarily value), are listed below: review of literature (lowest cost) analysis and calculation reduced-scale testing full-scale component testing computational modeling full-scale structural testing (highest cost)
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program FIGURE 2-1 Relative funding levels for Task 2 subtasks and work-unit categories. FIGURE 2-2 Framework for defining and refining the BMSP.
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program Observations At the higher program levels (i.e., program purpose and focus areas), the committee believes that the BMSP program is focused correctly on protecting people first and physical assets second. Epidemiological studies after the bombing of the Alfred P. Murrah Building in Oklahoma City have shown that building collapse was the primary cause of death and that flying debris was the primary cause of nonfatal injuries in that event (Mallonee, et al., 1996). Studies of the attacks on the Khobar Towers complex and the U.S. embassy in Nairobi also suggest that, in the absence of structural collapse, flying debris was the primary cause of death and injury (U.S. Department of State, 1999). Based on these findings, the BMSP has focused its efforts on reducing both the probability of progressive collapse and the production of hazardous debris. The committee notes, however, that the program has not developed a formalized strategic planning process for identifying knowledge gaps and assessing them in light of what has been learned by individual program activities, as well as outside the BMSP. A formalized planning process would enable DTRA to refine objectives or establish new ones and determine, on an annual basis, which activities should be continued, initiated, or abandoned. Annual reviews wouldensure that the program remains sufficiently robust to resolve problems that will take several years of study and sufficiently flexible to address emerging issues. The committee believes annual assessments are a key element in the development of a successful program and recommends that DTRA allocate the time and resources to put in place a continuing process for reviewing and refining the BMSP. The committee also believes that questions must be resolved at an appropriate level of inquiry. In other words, if a short review of the literature and one or two physical experiments at reduced scale will satisfy a particular hypothesis at a 90–95 percent confidence level, there is no need to carry out full-scale experiments. However, some structural phenomena (e.g., phenomena involving the effects of gravity) can only be satisfactorily modeled at full scale or under very sophisticated experimental conditions. The committee believes that the BMSP Master Plan does not yet provide sufficient rationale and guidance to suggest the appropriate analytical or experimental approach on a consistent basis. For this reason the committee recommends that all proposed activities be guided by clearly stated objectives and working hypotheses. Ultimately, the behavior of a full-scale, fully loaded structure in a high-intensity blast environment may be the only acceptable demonstration of proof of concept—in a political, if not an engineering context. However, full-scale testing is very high in value (and cost) in the experimental hierarchy. Therefore, the practical equivalent of live-fire testing should only be undertaken on full-scale structures as the culmination and validation of a chain of supporting analyses and experiments. Full-scale structural tests should not be used to gain new knowledge but to confirm what has been learned and demonstrate measures that should work in similar conditions. 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. In the following chapter, the committee addresses technical activities and project-specific aspects of the BMSP and recommends modifications and activities that DTRA should consider for the next program cycle.
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Blast Mitigation for Structures: 1999 Status Report on the DTRA/TSWG Program CONCLUSION AND RECOMMENDATION 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. REFERENCES BMAG (Blast Mitigation Action Group). 2000. BMAG. Available on line at: http://bmag.nwo.usace.army.mil DTRA (Defense Threat Reduction Agency). 1999a. Blast Mitigation for Structures Program Master Plan, June, 1999. Alexandria, Va.: Defense Threat Reduction Agency. DTRA. 1999b. Blast Mitigation for Structures Program Review, August, 1999. Alexandria, Va.: Defense Threat Reduction Agency. Mallonee, S., S. Shariat, G. Stennies, R. Waxweiler, D. Hogan, and F. Jordan. 1996. Physical injuries and fatalities resulting from the Oklahoma City bombing. Journal of the American Medical Association 5: 382–387. U.S. Department of State, 1999. Report of the Accountability Review Boards on the Embassy Bombings in Nairobi and Dar es Salaam on August 7, 1998, January 1999. Available on line at: http://www.state.gov/www/regions/africa/accountability report.html
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