»
t
‘
\
-
2 oar Ra Urs
"length ef the positive phat
oo.
effect with lead te a murned aiinval ce ci ptek po@amares ard the wus. 3 tw
rase in pressure, anateat of tne ideal er ances here. AY
wilt reau.t oF
siightiy greater distames, the tarma’ effe
Sehe
rise
socw
ly
compiet@
a
“han
a "partial shock" rather
further, the shock front will be sharp as sncvr Ap.t-
he fet
7
distances the negative phase increases ans eventually the pe 22 ite
and negative imputse urder the bias. was Poocme equa’
In trensiating these curies to hffernnt yholis, beth
the distance and tim boat be drrced @ wo 3, helidng preseurce
constant. In many cases, the sritecicr. for structure: damage is net
simply peak preasure, but the produit cf the alr density and the
square of the material velovity
4
ut, ti13 blast wind resulta
in a dynamic presswe on structures; the time vardaticn of this
dynamic pressuse may be teks: as appreximaely simihar te tne
preosure-time curece shewn here,
2.2.4
Tira ef Arrival
Figure 1 gives the time of arrisal of the shoek wars
as a function of distance. Thes2 curs a>? based on calsularion:
from peak pressures observed on tower shots, bul e€ in good agreemen.
with the time-of-arrival curve as predistiad from the IBM cuz using thic
yield,
Urdike peak preaturtss, the observed time of avrival should be
independent of the typs of surfaces.
2.2.5
Positive Duration
Figure & shows the duration of the positive phass ev toe
blast wave as a functicn of distante from the bomb. The upwea
swing of this curve at shert distances is aasetiaved with the hack
of a negative phase at this pcint. where a*curate encinanes of the
pressure decay is required 2* clese-in distan<s, tha precsy a -lm
curves may be fitted by a powrr law a seni-ieparithmic pict. Fee
example, the curve showr for 1,005 pai can ta fitted initaiv by
Pap 4°55 and later by Pow ifee® os & wee Be BT
2.2.6
Positive Impulse vs Distance
Figure 9 shows the positive impulse, cr I t af &
function of distance. If further information is desived, such as the
magative imulse, these values can be devived upon request.
2.3
Protestion frem Blast
2odok
Gereral Rules
As pointed out earlier, every reasonable precaution must
be taken against the blast effects and every method which ingenuity
suggest should ba used, but no prohibitive problems ave presanted by
blast. It is impossible te point out here the criterion fer all types
of structures, but the following discussicn shows tne general character
of the clenclusions which may be expected
It is cuggested that test
personnel consider their individual) structwes on the basia of the
field wariables given in Figs. i thre 10.