From: G Vishwanath <gvshwnth(--nospam--at)yahoo.com>
Date: Sun, 29 Jul 2001 07:18:24 -0700 (PDT)
Date: Sunday, July 29
Sub:Blast Resistant Doors
I last did blast resistant design about 15 years ago.
For the past few years, I have not done any
design(blast or even plain static) as my job nowadays
is administrative and management/marketing related.
I am sorry, I also do not have material ready to share
with all of you after the passage of so much time. The
documents related to the design that I did are also
protected as the design was done for a defence project
and they are not in my custody.
However, I do remember the following : This is not
confidential and does not compromise secrecy. I hope
We had consulted some academics for this job and were
advised that in our particular case, we could proceed
on the basis of an equivalent static load.
The criterion for determining if the equivalent
static load approach could be adopted was that the
Time period of the structure should be at least 10
times the duration of the load.
If this condition was satisfied, the equivalent static
load could be determined by the equation :
ESL = Impulse * Angular Frequency of the structure
Impulse = Area under the curve when pressure is
plotted against time
Angular frequency = 2 * Pi * f where f = natural
frequency of the structure.
The contractor is not right in submitting calculations
only for the highest pressure. This need not be the
governing case .
I remember that the design was quite challenging.
Providing a stronger member was not necessarily safer.
The natural frequncy also went up and the equivalent
static load would also go up ! It was like chasing
your own shadow.
I had used an old 8 bit micro- computer and a Fortran
programme to try out various combinations. Today, I
can do the same in a jiffy using a spreadsheet.
I remember I had consulted a book on Structural
dynamics authored by Biggs where there is reference to
I wish I could give you more information.
I am a quack in Structural Dynamics. Please do not
accept whatever I have written without question. There
may be more knowledgeable people in this forum and
in case they differ in opinion , I will not be able to
stand by what I have written. If I am wrong, I would
like to be corrected. However if I am right, please
confirm. That will make me more confident next time !
Fi Sofex Limited
Electronics City, Bangalore, India
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