EFFECTS OF AN EXTERNAL EXPLOSION ON A CONCRETE STRUCTURE

Abstract

Analysis for the structural behavior of reactor containments under Impact/Explosive loadings is an emerging field of research . The containment is the most important structure in a nuclear power plant. It is classified as a Seismic Category 1 Structure. Its protection against external aggression such as explosion, aircraft, missiles and fires is essential to keep the masses safe from the hazards of radiation. The present study has, therefore, been directed to study the effect of external explosion on a typical reinforced concrete containment structure. The general practice is to utilize the air blast pressure values in the structural analysis and design against external explosion. The ground shock parameters are usually neglected during blast resistant analysis and design. Many empirical relations have been proposed in the past to calculate the airblast pressure. Most of them, however, only predict peak pressure values. In this thesis, not only the airblast parameters have been studied but also the ground shock parameters have been dealt with. Therefore, the thesis deals with the experimental determination of relationships of following airblast and ground shock parameters against scaled distance on a reactor containment scaled model. Airblast Time History Parameters (a) Peak pressure (P so ) (b) Shock wave front arrival time (T a ) (c) Rising time (T r ) (d) Decreasing time (T d ) (e) Duration of the positive pressure phase (T ) Ground Shock Time History Parameters (f) Peak Particle Acceleration (PPA) (g) Arrival Time ( t a ) (h) Shock Wave Duration (t d ) (i) Time lag between ground shock and air blast pressure arrival at structures (T lag ) xviiiThe results have been compared with that of previous researchers and CONWEP. The variation of results is due to curved surface of containment model. In the second part of the study, full scale typical reactor containment has been modeled against external blast loads varying from 30 t to 160 t of Trinitrotoluene (TNT) at a detonation distance of 50-200 m using the above mentioned relationships. . . It is concluded that all the failure points lie either within the lowest 10m region or at top of the shell. It is observed that an increase of 5-20 MPa occurs with the simultaneous application of air blast and shock wave on reinforced concrete containment as compared to that of airblast only. It shows that an accurate analysis of structural response and damage of structures to a nearby external explosion requires application of ground shock and air blast pressure time history parameters at the same time. A comparative study has also been carried out to calculate the critical distance for the various external blast charges. The distances at which 90% of the shell elements have failed may be termed as critical distances. In the present study, the critical distances vary from 110 to 200 m for above blast charges. . The 70% of the shell elements are cracked on both faces and may be described as doubly cracked gauss points. These occur at the locations which have been crushed in the plastic range. The research work and the conclusions drawn may be utilized for evaluation of the effect of an external explosion on the reinforced concrete containments of other reactors.