Protecting Buildings from Bomb Damage Transfer of Blast-Effects Mitigation Technologies from Military to Civilian Applications (1995) / Chapter Skim
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4 Blast-Effects Mitigation Potential for Commercial Buildings
4 Blast-Effects Mitigation Potential for Commercial Buildings
Pages 49-70
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From page 49... ...
Also discussed are special considerations for blast-effects mitigation in commercial buildings, such as below-grade vulnerabilities and the stack effect in high-rise buildings (two areas of vulnerability shown dramatically in the World Trade Center bombing)
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From page 50... ...
Army Technical Manual TM 5-853 to a limited degree, though the planning techniques in this manual are strongest in the area of supporting access control to the facility. All such options can be applied in the normal design of a building, just as designers now routinely incorporate seismic, wind, and fire protection features and systems in buildings.
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From page 51... ...
The cost of land, however, must be considered in this measure. Control of surrounding streets and adjacent off-site parking is ideal, but rarely available to civilian commercial building owners.
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From page 52... ...
Frequently, these important utilities enter buildings near one another, are easily identified, and are relatively easily accessed by unauthorized persons. An explosion in the area of the utility service entrances could destroy all services in one stroke if they are all close together.
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From page 53... ...
Vehicle parking and loading operations within or under an occupied building pose a major hazard, since vehicle bombs can be very large and powerful. Vehicle bombs may also elude detection, especially in high-volume facilities where inspection of vehicles with any regularity or thoroughness may be operationally and financially unacceptable.
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From page 54... ...
Technical Manual TM 5-1300 "Structures to Resist the Elects of Accidental Explosions] discusses the use of blast valves for the controlled release of blast pressure from accidental explosions; Air Force Engineering and Services Center t1989]
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From page 55... ...
Defensive precautions, such as threat and vulnerability assessments, access control, and good intelligence and law enforcement, are always useful, but there are limitations to what building technologies can offer, and in some of these cases, the only option may be relocation. In addition to the architectural planning techniques discussed above, there are other means to harden typical existing civilian buildings against terrorist attacks.
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From page 56... ...
Quite obviously, anticipated loading conditions will influence the design, but reinforced concrete structures can be expected to be relatively thick (102 to 103 mm) to provide the mass and strength to resist blast pressures.
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From page 57... ...
Security windows and glazing are discussed in the U.S. Army Technical Manual TM 5-853 and Structural Design for Physical Security, Chapter S
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From page 58... ...
When designing for wind and earthquake loads, therefore, it is advantageous, especially for the upper levels, to use lightweight nonstructural building materials such as metal stud and drywall partitions instead of masonry. The dynamic loading on buildings caused by explosions differs in important respects from dynamic loads imposed by earthquake and wind.
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From page 59... ...
VULNERABILITIES OF NONSTRUCTURAL BUILDING SYSTEMS Recent instances of buildings that have suffered the effects of an explosion, such as the World Trade Center, have demonstrated that if the structure of the building survives and does not progressively collapse, the greatest problems are experienced during evacuation and rescue, when fire and smoke control and other critical building systems may not provide the necessary support. Most buildings are designed to resist events of seismic origin, fire, flood, wind, snow, and similar natural and human-caused events.
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From page 60... ...
2. The second group of nonstructural building systems may not in themselves play active roles in survival or rescue activities following an explosion, but they may attenuate, propagate, or contribute to the effects of an explosion: · Exterior wall systems consisting of interdependent subsystems: - wall construction-precast panels, metal panels, masonry, framed, and so forth-that is basically supported by the structural system; - sash supported by the wall system; - glazing supported by the sash, although polycarbonate glazing could hold the sash together; - sun-control system supported by the sash or soffit which could contain glass fragmentation, if in the form of a film or mesh, or contribute fragments, if in the form of blinds.
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From page 61... ...
· Interior mechanical and electrical distribution systems: heating, ventilating, and air-conditioning terminal units and ductwork supported by the structural system and perhaps easily dislodged by an explosion; electrical conduit usually hung under the structural system and possibly severed by structural failure or directly damaged by an explosion if it occurs nearby (exposed or ruptured power lines may pose a threat to occupants and emergency personnel, or contribute to fire) ; piping for water and gas under pressure usually hung under the structure, and, like conduit, possibly destroyed by the structure if it fails or is breached by the explosion itself (loss of fire-fighting water not only loses the fire-extinguishing function, but can pose a threat of flooding to occupants, other systems, and rescue personnel)
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From page 62... ...
If the room is located adjacent to or in the midst of the vehicle parking area, some of the main feeders from this equipment are also potentially exposed to an explosion from a vehicle bomb. If the building has a secondary power source from an alternative substation or even a power grid, the switchgear for that service is also typically placed in a similarly vulnerable location, if not in the same vicinity.
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From page 63... ...
Generator and switchgear rooms below grade are also vulnerable to water damage or flooding if an explosion ruptures water piping in the vicinity and there is insufficient drainage or pumping capacity. Building control centers for refrigeration and other building operating systems may also be located below grade in or near the central mechanical equipment room, if it is also below grade.
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From page 64... ...
Any basement vehicle parking areas, therefore, should be given particular attention when considering blast-hardening features or access control and detection, perhaps even at the expense of other measures when available funds are limited. PROTECTING NONSTRUCTURAL SYSTEMS Blast-resistant, reinforced concrete walls can be constructed to decrease the effects of an explosion in or around buildings, including protection of many of the critical systems discussed above.
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From page 65... ...
However, existing buildings have few if any options other than to construct stand-off barriers to keep vehicles as far as possible from elevators and stair shafts. STACK EFFECT IN HIGH-RISE BUILDINGS The vast majority of the injuries caused by the World Trade Center bombing were not the result of direct impingement of fire or explosion, but from smoke and dust inhalation.
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From page 66... ...
The economic factors in these two classes differ according to the owner's objectives. Buildings constructed by and for an owner include owner-occupied office buildings, such as corporate headquarters, warehouse and distribution facilities, process and production plants, and civilian government buildings.
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From page 67... ...
Appendix A compares the financial performance of a speculative commercial office building and the financial performance of the same building after it has incurred the additional costs of protection against attack. The discussion and accompanying cost models conclude that the construction premium for blasthardening does not materially impact the financial performance of a commercial building.
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From page 68... ...
Representatives of the building industry, such as the Building Owners and Managers Association, generally corroborate the observation that there is a low level of continuing public concern about terrorist attacks on commercial buildings in the United States. In the case of the World Trade Center, public attention and concern were very high in the months that followed, only to subside as time passed.
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From page 69... ...
Federal and state governments are also good candidates as agents of technology transfer, since they have a long-term concern to protect their own commercial office buildings. They are not subjected to all of the code issues that pertain to the private sector, and hence could incorporate blast-effects mitigation technology in their office buildings at a faster rate than the private sector.
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From page 70... ...
1995. Structural Design for Physical Security State of the Practice Report.
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