E-Paper
To study explosion impact, prediction of blast load must
TWO INDIAN Institute of Technology professors- Dr Sudhir K Jain and CVR Murty, while developing guidelines on measures to mitigate effects of terrorist attacks on buildings, under a project for the Gujarat State Disaster Mitigation Authority , discussed in detail the issue of ?possible damage to buildings under blast loading? in the second chapter of the comprehensive document. cording to the document, to study the impact of the blasts on structures, the blast loads on them needs to be predicted first.
TWO INDIAN Institute of Technology (IIT-K) professors- Dr Sudhir K Jain and CVR Murty, while developing guidelines on measures to mitigate effects of terrorist attacks on buildings, under a project for the Gujarat State Disaster Mitigation Authority (GSDMA), discussed in detail the issue of “possible damage to buildings under blast loading” in the second chapter of the comprehensive document.
According to the document, to study the impact of the blasts on structures, the blast loads on them needs to be predicted first. For exterior detonation, the blast pressure causes damage to the building and since the pressure over the exterior surface of the building varies with stand off distance, angle of incidence, and reflected pressure, the blast load should be predicted for multiple threat locations of the detonation and the worse case conditions used in the design.
In most cases, especially for design of single and isolated buildings, consultants use simplified methods to predict blast load, the document further reads.
However, while designing complex structures, refined estimates of the blast load on the structure are required. These methods could include computational fluid dynamics (CFD) for the analysis of the blast load factor. But this needed special equipment and skills, the document adds. For an identified potential threat from bombs of different sizes, the demand blast pressure on buildings could be estimated and damage sustainable building structures could be constructed, suggests the report.
Next, it was important to understand if the building could resist the demand safely. For this, history of the building must be studied to evaluate the adequacy of hardness provided in it.
The document further observes that though past experience suggested that the extent and severity of damage in a building could not be predicted accurately, some general indicative trends of overall damage could be ascertained, based on the size of explosion, stand of distance and assumption about the construction of the building.
Field-testing, nonlinear structural analysis or both could estimate the damage levels, the document adds. Testing was an active option for government and private agencies that develop specialised products related to mitigation measures.
The building designers should resort to detailed structural analysis, suggests the document. For greater reliability of these analyses, they must account for both time-dependent effects of the explosive event and nonlinear behaviour of the buildings. Advanced analytical tools are already in use in seismic design, particularly of special and critical structures like dams and nuclear power plants.
