Blast Resistant Design
341700 - The Blast Load Acting on a Structure in an Internal Explosion Scenario
Saturday, April 21
8:00 AM - 9:30 AM
In the case of a confined explosion, the resulting pressure signals are very complex, mainly because of the interaction between the shock waves and the surrounding room boundaries and the presence of openings. This problem of an internal explosion has been considerably less investigated compared to a free air explosion, and there are open basic questions concerning the parameters that affect the complex pressure-time history and their degree of influence. Ability to predict the pressure-time history with high fidelity is mandatory for any attempt to properly predict the dynamic structural response of the envelope panels and assess the damage caused by the confined explosion. The present research program comprises experimental, analytical, and numerical work.
The experimental part included a series of full scale tests of TNT confined explosions, carried out in a single room cuboid structure, specially designed and constructed to withstand repeated explosions without damage. This study yielded high quality pressure signals at different locations that were used as a data base for comparisons with the computational results and for the examination of the pressure distribution on the test room walls.
The analytical part focused at developing an extensive theoretical model for the prediction of the blast load, mainly characterized by the peak gas pressure and its decay with time. The developed theoretical model for the peak gas pressure prediction is based on the ideal gas equation of state, and is used to predict the gas pressure as function of the exploded charge weight per unit volume of the confined space. The model takes into account thermochemical processes, and uses the laws of thermodynamics to find the blast temperature. Moreover, a method for calculating the gas pressure decay, based on Bernoulli theory, was developed for a partially confined explosion. The derived formulas are found to yield gas pressure predictions that agree well with our experimental results and with experimental results available in the open literature. These new theoretical approaches explain numerous experimental results and agree very well with empirical results.
The experimental results were compared with numerical calculations performed using AUTODYN hydro-dynamic code, aiming at simulation of the experimental test cases. It clarified the behavior of the blast waves, the gas pressure and the effect of the detonation products afterburning on the acting pressures. According to the analytical work, the afterburning energy release, as a result of exothermic reaction of the detonation products with the oxygen in the air, at certain temperature conditions, helped to improve the numerical simulations when this afterburning energy was included into the equation of state of the explosive during an appropriate time interval.
This study contributes to understanding the relationship between explosion data and its results, and has a great value in advancing knowledge on this subject. Beyond that, it contributes to more accurately design of buildings subjected to such conditions discussed, which today are designed with simplified and approximate design tools which their suitability is questionable, as shown in this study.