How do I calculate static equivalent load of a blast overpressure?

[Amr Abdelhalim]

Dear all,
I have a blast peak incident overpressure value Po= 5 kPa, and peak reflected pressure Pr= 12.5 kPa and the duration of impact to= 100 msec. How do I convert these loads into equivalent static loads according to ASCE Manual 42? I have an equation but it is somehow pretty hard to solve. Also should I use general dynamic loads conversion? I know that static equivalent load is not accurate and have some requirements, but I really need a help in it.
Thanks.

 

[WARose]

I suppose you could integrate the triangular function or perhaps apply a Dynamic Loading Factor (i.e. DLF, between 1-2) to the peak reflected pressure.

But it's rare to see anyone use a equivalent static force procedure for a blast loading anymore (unless it is far from the source). It just gets excessive. You may want to get 'Design of Blast Resistant Buildings in Petrochemical Facilities' by ASCE for a guide.

 

[Amr Abdelhalim]

Yes I know it is rare, but it is just a quick check I need to know. So it is just an integration for the triangle between pressure and time?
I searched for this book online I could not find any available online version for it.

 

[WARose]

I think a graphical solution might be easier (available in any Structural Dynamics text). If you have the ratio of ramp time to the fundamental period of the structure......you can get it that way.

 

[WARose]

See the link below for a chart showing DLF for a triangular impulse. t_d is impulse duration, and T is the fundamental period of the structure.

 

[bones206]

You can also set the static load equal to the load magnitude at the element's failure point (with capacity increased by SIF AND DIF). This approach is independent of the blast load and is useful for some design applications. You are basically saying this is the maximum force this element could deliver to its supports, regardless of the blast scenario.

 

[Anil Belani]

The formula for Equivalent Static Blast load is actually relatively quite easy to understand. The major factor affecting is time period. Alternatively, you can use Newmark's ASCE 1953 paper, from which this method is picked up.

Only caution is,in all normal buildings, that relected pressure worked out with equivalent static load should atleast be equal to or greater than original peak overpressure. Do let me know, if you face some issue, working out.
Regards,
Anil Belani

 

[ThomasH]

The figure that WARose provided is based on a linear system. If I remember correct, Manual 42 workes with a non-linear system and assumes an allovable dynamic displacement larger the yield displacement. That is a different approach.
I have only seen a old version of manual 42 but I don't remenber any equations that were very difficult to solve.

Edit: I just realized that this was a very old thread that had "woken up". Hopefully the problem is solved by now.

Thomas

 

[joya wehbe]

hi, im happy that i found someone who has done an exercice on converting the dynamic load of blast to an equivalent static load
can you please send it to me on my email if i passe it to you ? i really need help to make my final project i need an example because all the problems are solved with SDOF
sincerly
joya

 

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