Overpressure, structural damage caused

Table 6.10 presents some damage effects. It may give the impression that damage is related only to a blast wave s peak overpressure, but this is not the case. For certain types of structures, impulse and dynamic pressure (wind force), rather than overpressure, determine the extent of damage. Table 6.10 was prepared for blast waves of nuclear explosions, and generally provides conservative predictions for other types of explosions. More information on the damage caused by blast waves can be found in Appendix B. 

From Figure 6-23 the scaled overpressure is 0.055. Thus, if the ambient pressure is 1 atm, then the resulting side-on overpressure is estimated at (0.055)(101.3 kPa) = 5.6 kPa (0.81 psi). From Table 6-9 this overpressure will cause minor damage to house structures. 

The criteria selected for an overpressure hazard is normally taken as 0.2 bar (3.0 psio). Although fatalities due to direct effects of an explosion may require up to 2.0 bar (29.0 psio) or higher, significantly lower levels result in damages to structures and buildings that would likely cause a fatality to occur. An overpressure of 0.2 to 0.28 bar (3.0 to 4.0 psio) would destroy a frameless steel panel building, 0.35 bar (5.0 psio) would snap wooden utility poles and severely damage facility structures, and 0.35 to 0.5 bar (5.0 to 7.0 psio) would cause complete destruction of houses. 

Pressure-time histories caused by explosions may be nonuniform and subject to amplification because of secondary shocks and shock reflections. Current models can provide only one- or two-dimensional histories. Failure modes are typically permanent deformation (plastic deformation/buckling), stable cracking (leaking), and brittle failure. Table 2.3 (Theodore et al., 1989) describes expected damage estimates for humans, structural elements, and process equipment for particular overpressures. 

Most of the material damage from an airburst (nuclear weapon) is caused mainly by the shock (or blast) wave which accompanies the explosion. The majority of structures will suffer some damage from air blast when the overpressure in the blast wave, i.e. the excess over atmospheric pressure (101.3 kN/m at sea level), is about 3.5 kN/m or more. The distance to which this overpressure level will extend depends on the yield of the explosion and on the height of the burst. 

Rotation of brain on brain stem Forces exerted by blast overpressure can cause the rotation of the brain on the brain stem damaging structures of the medial temporal lobe. 

The main causes for mechanical failures other than overpressure include general wear and tear, collision with another vehicle, modifications in violation of original specifications, collision with a fixed object such as a bridge, collapse of a structure onto it, and damage by an external explosion. 

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