APPENDIX D (Continued)
As the blast wave continues to travel across the structure, the roof and sides and rear
walls are also loaded. These loadings are combinations of the incident pressure and the drag
Combined Damage Mechanisms. A structure subjected to an explosive blast receives
the effects of air blast, fragments, fire, and ground shock. Generally, the air blast is the dominant
factor in damage production. The size and construction of the target structure are factors that
affect the amount of damage produced. A large bomb will have a major effect on a small
building, while a small bomb will only affect a local area of a large building.
While a small bomb may only be capable of producing 5- or 10-percent total damage
to a building, there could be 100-percent damage over a local area.
There are a variety of building types and functions. Industrial buildings differ in
construction from an administrative office building and tend to be of simpler construction and
have a higher degree of ruggedness. Windows represent the most vulnerable element of a
building and are easily damaged at very low pressures.
Pressure Effects on Structures and Glazing. Glazing is usually the weakest element
of a structure. The area around a blast scene will contain numerous buildings with broken
windows, extending out to a distance of about seven times greater than that of the structural
damage. This means the blast area producing glazing damage will be about 50 times greater than
that subjected to other structural damage.
Blast Loading for Close Detonations to Structures. An explosion close to a building
will result in large variations in the pressure-time loading function at points on the building,
depending on the distance and angle of the explosive to a specific point. The effect is shown in
Figure D-3. The pressure-time loading function is again assumed to be triangular, as shown in
Figure D-1. The Tri-Service design manual, NAVFAC P397/TM5-1300/AFR 88-22, gives the
average peak pressure and impulse on a wall to be used for explosions close to a wall.