A History of Research and a Review of Recent Developments

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Uniformly distributed pressures 73 the box and reaches the rear edge. It then spills down the back wall. On the flat roof and sides the instantaneous pressure rise is to p 0 (not p r), but because of the pressure difference at the junctions of the top and sides with the front face, vortices will be formed there. See, for example, the book by Norris et al. [4.1]. In determining the loads on the structure it is useful to consider the instant at which the shock front strikes the front face as t=0, and the time for reflection effects to clear the front face as t=t c, where t c =3s/ū. (4.2) In this equation s is the clearing height, taken as either the half width of the front face (B/2) or the full height (H), whichever is the lesser, and ū is the velocity of the shock front. Once the time t c is reached, the pressure on the front face (taken as uniform) is a combination of the gradually decaying incident pressure, p, and the dynamic pressure, q. The variation of dynamic pressure with time is usually given by the equation (4.3) which is similar to the expression for overpressure decay but with a different decay rate. From Eq. (1.28) we note once more that the dynamic pressure in psi at time t 0 is given by (4.4) To obtain a true measure of the dynamic loading due to the blast winds on the structure, it is necessary to multiply q by the drag coefficient, C d, for the shape under consideration. So the total front wall pressure (p s) from time t c onwards is given by p s=p+C dq. (4.5) For the front face of a rectangular box structure C d is often taken as 1.0, although wind tunnel tests show that the average pressure due to blast winds is rather less than 1.0 q. Some analysts therefore suggest C d=0.85 for the front face. When the shock wave reaches the rear wall of the structure distant L from the front wall, vorticity again occurs at the edges, causing a reduction in incident pressure due to suction. According to some authorities the overpressure on the rear wall reaches a maximum in a time given approximately by t (4.6) L =(L+4S)/ū. The sides and top of our simplified box are not fully loaded until the shock front has travelled the full length of the structure. The average pressure is therefore considered to be the shock overpressure plus the drag loading at a
74 distance L/2 from the front face. The loading increases from zero to the average value in a time L/2ū, so that, for the top and side faces and for the rear face Structural loading from distant explosions p s =[p+C d q] t=L/2ū , p s =[p+C d q] t=(L+45)/ū . (4.7) (4.8) Values of C d for the side, top and rear faces are known to vary with the dynamic pressure, q. In 1961 Newmark et al. [4.2] suggested that C d should be –0.4 for 0
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EXPLOSIVE LOADING OF ENGINEERING ST
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Explosive Loading of Engineering St
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Contents Preface vii Acknowledgemen
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Preface A long time ago I walked ov
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Acknowledgements The reports from w
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xii Notation m mass of projectile m
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xiv Notation Q work done during exp
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Introduction Explosions can threate
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Introduction xix Bertram Hopkinson
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Introduction xxi in the seventeenth
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Introduction xxiii own versions of
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Introduction xxv indoor shelters an
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Introduction xxvii explosions/ stru
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Introduction xxix particularly dama
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Introduction xxxi but the feeling i
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2 The nature of explosions propelli
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4 The nature of explosions or rathe
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6 The nature of explosions ogive, a
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8 The nature of explosions mass, an
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10 The nature of explosions Figure
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12 4 lb cylinders, TNT, 3.75 lb sph
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14 The nature of explosions As Figu
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16 The nature of explosions of the
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18 1.4 THE DECAY OF INSTANTANEOUS O
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20 The nature of explosions Figure
Page 55 and 56: 22 The nature of explosions where I
Page 57 and 58: 24 sometimes written in psi as The
Page 59 and 60: 26 The nature of explosions 1.20 Ki
Page 61 and 62: 28 The detonation of explosive char
Page 83 and 84: 50 Figure 2.18 Radius/time curve of
Page 87 and 88: 54 and 50%, rather than by a factor
Page 92 and 93: 3 Propellant, dust, gas and vapour
Page 94 and 95: Dust explosions 61 as the period 19
Page 96 and 97: Gas explosions 63 reported by Palme
Page 98 and 99: Gas explosions 65 workings in very
Page 100 and 101: Vapour cloud explosions 67 the leak
Page 102 and 103: References 69 in Los Angeles Harbou
Page 104 and 105: 4 Structural loading from distant e
Page 108 and 109: Table 4.1 Loading/time relationship
Page 110 and 111: Loading/time relationships 77 overp
Page 112 and 113: Loading/time relationships 79 side
Page 114 and 115: Loads on underground structures 81
Page 120 and 121: Loads on underwater structures 87 c
Page 122: References 89 4.12 Allgood, J. (197
Page 125 and 126: 92 Structural loading from local ex
Page 131 and 132: 98 The general empirical equation f
Page 133 and 134: 100 Structural loading from local e
Page 145 and 146: 112 Figure 5.16 Relationship betwee
Page 153 and 154: 120 Pressure measurement and blast
Page 155 and 156: 122 Pressure measurement and blast
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124 Pressure measurement and blast
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142 Penetration and fragmentation r
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144 Penetration and fragmentation p
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146 Penetration and fragmentation w
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148 Penetration and fragmentation T
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152 Penetration and fragmentation F
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152 Penetration and fragmentation n
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158 Figure 7.16 Penetration simulat
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162 Penetration and fragmentation b
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164 Table 7.1 Penetration and fragm
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168 Penetration and fragmentation I
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170 Penetration and fragmentation l
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174 Penetration and fragmentation p
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176 Penetration and fragmentation o
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178 Penetration and fragmentation o
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180 Penetration and fragmentation 7
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182 Penetration and fragmentation 7
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184 The effects of explosive loadin
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188 Table 8.1 It is worth noting th
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200 Table 8.5 The effects of explos
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216 Response, safety and evolution
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224 In the log-normal distribution
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230 Cole, R.H. 46, 48, 53, 55, 99 C
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232 Petry 143 Philip, E.B. 13, 14,
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Subject index Aircraft damage 207 A
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