Blast loading on buildings from explosions in city streets

Abstract

The use of large vehicle bombs to attack city centres has been a feature of campaigns by terrorist organisations throughout the world during the last few years. Recent United Kingdom examples include the bombs in the City of London in both 1992 and 1993, the Docklands bomb of January 1996 and the explosion in Manchester city centre in June 1996. Such events cause damage—some of it very severe—and widespread disruption to the function of businesses in the vicinity of the explosion. The radius of damage to buildings experiencing the blast from such bombs is difficult to predict using simple techniques. Sometimes buildings quite close to an explosion experience relatively little damage while those at relatively long range suffer proportionately much higher levels as a consequence of the ‘channelling’ effect of city streets. This paper presents the results of an experimental study using scale models of simple generic urban geometries to provide assessment, both qualitatively and quantitatively, of the effect of such an environment on the blast resultants experienced by buildings in a city centre. In a pilot study, a simple straight street terminated by a rudimentary T-junction was investigated. In the main study, five configurations including a crossroads, a T-junction and a blind alley were constructed. In this phase, the pressure–time records obtained are explained by means of a ray-tracing technique which allows these histories to be reconstructed qualitatively leading to a better understanding of the complex processes involved in blast wave propagation in city streets. Results for these five configurations are presented quantitatively both in the form of contour plots of pressure and impulse compared with a ‘free air’ detonation and as graphs of pressure and impulse enhancement with scaled distance. The information presented demonstrates the channelling effect noted earlier and the consequent loading enhancement. In addition, for some experimental configurations, results are compared with those obtained from simulations using the AUTO-DYN3D code. Based on the results of this study, the paper makes recommendations about how the use of scale models, in conjunction with numerical simulation, could lead to a better understanding of the complex loadings experienced by buildings in a city, that could aid future building designers and urban planners.

Modelling blast loads on buildings in complex city geometries

“…Smith, et al [4] have presented the results of a small-scale experimental investigation of a number of generic street configurations. One of the experiments involved construction of a straight street model from reinforced concrete blocks, terminated by a simple T-junction formed from a cubic building made of steel.…”

“…Several experimental and numerical studies [2][3][4] have demonstrated that the blast loads on a building are affected by the presence of adjacent structures. Whether the blast loads are reduced due to shadowing by other buildings or augmented due to reflection and channelling of the airblast pressure is generally determined by the design of the buildings, the layout of nearby streets, and the location and size of the explosive device.…”

“…A limited number of experiments involving small-scale models have been conducted to validate numerical simulations of blast wave -multiple structures interaction [4,14].…”

Identification of the risk of blast-induced glass window failure in a complex environment

“…In this context, complex environments refer to scenarios where the blast wave impinges on structures that are in close proximity to one another such as a city, where complex phenomena of multiple reflections, channeling and shielding effects of adjacent structures must be accounted for. The advantages of the CFD technique have been demonstrated in an examination of blast characteristics in city streets (Rose and Smith 2002; Smith et al, 2001; Smith and Rose, 2006) in a study on the effect of street junctions (Rose and Smith 2003) and the effect of building arrays (Smith et al, 2003) and in an investigation on blast loading on a building at non-zero angles of incidence (Rose and Smith, 2004). Due to these important considerations, the CFD simulation is selected for the analysis of the risk of failure of glass windows in a complex environment.…”

Blast wave propagation in survival shelters: experimental analysis and numerical modelling

“…Confined explosions have, however, been studied in different settings such as urban environments [1,[5][6][7][8][9], tunnels [10][11][12], and small-size closed compartments and rooms [4,[13][14][15][16], where the flow of blast waves is constrained by obstacles and non-straight narrow paths.…”