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.