facility and may approach close enough to cause damage on detonation of its
Retrofit Hardening of Existing Construction
Required Standoff for Level of Building Protection. Although the
windows and doors can be changed for existing structures to increase their
blast hardness, the only practical option for the rest of a building is to
maintain the required standoff distance between the facility and the point of
explosion, i.e., it is not normally practical to structurally harden existing
walls, ceilings, etc. The Navy Terrorist Vehicle Bomb Survivability Manual
provides a methodology to evaluate the vulnerability of existing structures
to bomb blast and to establish the required standoff distance. The reader is
referred there for details. Briefly, the maximum standoff distance that can
be attained for a given site is established first. Building components such
as walls, interior and exterior columns, beams, joists, and roofs are then
listed. For the blast design threat level, blast loading in various
structural elements is evaluated using data such as that shown in Figure 77.
Damage expected is then determined using diagrams as illustrated in Figure
84. The standoff distance can be iterated to obtain a tolerable level of
damage. Figure 84 shows a typical example of the rebuild/repair criteria for
charge weight versus standoff distance of a typical building. The "rebuild"
condition is left of the solid line. The "repair" condition is right of the
line. The numerical values on the chart (not on the axes) are percent of
damage value, i.e., the further one is away from the solid line, the less the
Vehicle Barriers. Vehicle barrier options for existing
construction are the same as for new construction, see par. 220.127.116.11.