Abstract:
Explosive and car bomb blasts have become day-to-day affairs in some of
the co_untries highly affected by war and terrorism. Even peace loving
countries are not free from this type of threat and fear. Oklahoma city
bombing in 1995, Khobar Tower bombing in 1996, the WTCbombing in
1999 and 2001 are all incidents of blast of different kind in the world.
Recent HSBC bank bombing in Turkey and Australian Embassy bombing in
Indonesia are examples of ever increasing incidents of blast. Bangladesh is
not totally free from this type of threat or incidents. Though of small scale,
Mymensingh theatre hall bombing in 2003 made a deep imprint on many
people. Therefore, the need for research on dynamic blast load has become
a priority in Bangladesh as well. In order to provide protection for theaters
and halls in Bangladesh and to minimize casualty one must fIrst assess the
degree of vulnerability of these structures, which entails a thorough
research and investigation. Practical experiment with real blast on
prototype structure is not always possible. So, this study is carried out by
fmite element modelling of the structure and thus applying the dynamic
blast through transient dynamic analysis.
This thesis focuses on the building frame analysis due to an external blast
load on a popularly known theater hall type of structure, called the Osmani
Auditorium. The most renowned reference of US Army, Navy and Air Force
manual, TM 5-1300 and ASCE publications have been thoroughly studied
and applied in this work. Basing on the actual condition of the auditorium,
blast loads from various standoff distances have been considered and
applied to the structure. Blast is a very short duration dynamic load of 10
to 100 milliseconds depending on the location of blast and target. As such,
structure also behaves differently due to different orientation of blast and
structural condition and strength. Various factors like reflection, fa\(ade
condition, venting and structural properties affect the blast response of a
building.
The numerical modelling and transient dynamic response analysis of the
Osmani Auditorium reveals that blast can create catastrophic effects due to
both shear and moment failure at different external locations of a building
frame. Since the structure allows a standoff distance of about 50 feet,
therefore, loads are applied from 50 to 500 feet standoff distances and the
structural responses are analysed basing on 4000 lbs of TNT.It is clear that
shear failure occurs at a distance of 300 feet where as moments are
tolerable up to a distance of 200 feet standoff. It is also evitab1e that the
columns and beams of the roof are all affected if blast of 75 feet standoff is
considered with 4000 lbs of charge weight, which can be easily carried, by a
small truck or SUY.
Based on the findings of the study some recommendations regarding the
safe distance of approaching vehicles are suggested to safeguard the
structure. Some indications are also given regarding retrofItting measures
to increase the structural capacity against blast loads and few design
criterion.
