EXPLOSION DESIGN

[civinco01]

Can anyone advice how to consider/evaluate explosion loads against buildings. This is required for the design of a Power plant to be built inside a LNG Gas Station Facility. What are the regulatory codes, typical values.

 

[plasgears]

In paint booth design we use blow out panels in the outside walls. This seems to be similar to your problem.

 

[civinco01]

Compared to normal panels are blow out panels more expensive?. Is this a specialized job or can normal cladding suppliers do it?

THnaks for your support

 

[SlideRuleEra]

Here are a couple of leads:

http://www.aisc.org/blast

http://www.nibs.org/Apr03.pdf

http://www.SlideRuleEra.net

 

[unclesyd]

Are you talking about blast resistant buildings, external pressure?

 

[AUCE98]

Design blast pressures typically would need to come from the owner, ie the power plant. I would suggest looking at TM 5-1300, "Structures Designed to Withstand Accidental Explosions", which is a technical manual published by the Navy.

 

[SperlingPE]

Also consult Corps of Engineers for design information concerning blast load pressures and required building performance.

 

[Lutfi]

AUCE98 and SperlingPE,

Both documents that you mentioned are not available to the public any more!

Regards,


Lutfi

http://www.cdeco.com

 

[bridgebuster]

civinco01

As mentioned by AUCE98, the owner has to provide you with the threat level, i.e. bomb size. In addition, THE OWNER has to determine what is an acceptable level of damage for the given threat level. The location of the threat in relation to the facility also comes into play.

Blast analysis IS NOT simple. It requires a lot of FEM analysis and experience in order to mitigate the effects. Most important, and with all due respect, if you don't have the experience get someone who does.

 

[btrueblood]

You can probably still obtain copies by directly contacting the Corps and/or Navy and formally requesting them; provided you are a US citizen or working for a US corporation. They aren't kept on "open" websites nowadays, for what should be obvious reasons.

 

[JStephen]

I'm not so sure the reasons are "obvious". Are they afraid Osama bin Laden is going to design a blast-resistant house that they can't blow apart? Or are they concerned that he will come up with a bigger bomb than what their naval bases are designed for? And do they assume that terrorists somehow overlooked downloading this vital information prior to 9/11?

By the way, seems like I have seen info like this on ASCE's site- check there, also. And with terrorist bombing being an issue, seems like this info would need to be MORE available, rather than less.

 

[unclesyd]

Other than the obvious over pressure event you have to contend with here is a little added information that you may be of use.

http://users.rcn.com/harwood.ma.ultranet/t17.html

 

[civinco01]

To all:

Thanks for the great support. The information we have received from our client is that the we shall consider an overpressure due to a blast of 4Kpa. On top of that our client require the buildings to be EMP- Protected

 

[pba]

4kPa is very low for a blast pressure - Are you sure there isn't a typographical error here?

 

[civinco01]

PBA:

You are right I've checked once again the spec and calls for an overpressure of 20KPA. Hope you can advice

 

[pba]

20kPa sounds about right.

I'll bow to other peoples experience if they wish to contribute...

Previously I've done similar design as follows:

The overburden pressure (OP) is treated as an exceptional imposed load and as such it is applied with a low partial safety factor. It is not usual to consider the OP with either wind, or seizmic effects. The force can be considered to act in the worst possible direction. Generally vertically down for rafters, floor beams etc. and Horizontal for walls. It's worth considering both for columns. Non-structural parts of the building may well be allowed to fail during the explosion and as such transfer lower forces, equal to their failure load. Your client should define what has to remain working after the explosion. Dynamic effects of the explosion are usually incorporated into the magnitude of the OP, so normally you're looking at static analysis only.

Normal imposed floor loads are typically 5kPa and there is a partial safety factor of 1.6 under the cods I use giving 8kPa. The OP of 20 would have a partial safety factor of 1.05 giving 21kPa. As you can see the OP will govern the design of the elements exposed to the force (wich is usually most of them).

One other thing to remember - Actual explosions consist of a positive force wave (acting outwards) followed by a negative force wave (acting inwards) as the air rushes back to fill the vacuum created at the centre of the explosion. - So you can't neglect to consider the reversal case.

I only have experience of once actual explosion and there the windows on the far side of the building were blown out but the windows facing the explosion wre left mostly intact.

Good Luck

 

[richardm]

I fear that both you and your client may be out of your depth, and I would strongly echo the advice from bridgebuster - get hold of somebody who knows about these things. Design of blast-resistant structures is a complicated business and if your client says the effect of a particular blast is equivalent to so many kPa, then he doesn't know what he's talking about. The response of a structural member to a blast is very dependant on the dynamic characteristics of that member (e.g. natural frequency). A blast load that lasts only milliseconds and seems like a static load of 20kPa to one member could seem like 40 kPa to another with a different dynamic response.

And I would also reiterate the point that a positive blast pressure is followed by a negative one, so slabs and beams have to be resistant to upward pressures as well as downward ones.

richard

 

[pba]

Richardm,

You are of course absolutely correct.

I have personally designed four significant structures using the approach I outline above. These were not small insignificant projects but large complex buildings and process platforms for serious and knowledgeable clients. The process of establishing the blast overburden pressure should include some consideration of the type of structure to which it will be applied. Coupled to the uncertainty of predicting how explosions actually impact on buildings the concept of an equivalent static load is surely not unreasonable?

I had the fortune some years ago to work along side (note not with) an engineer who modelled explosions and such like as his full time job. I didn't understand any of what he did but I do know that the sofisticated analytical models were all calibrated to empirical evidence gained from phorensic examination of actual explosion sites.

The end result of this work was loading data supplied to simple engineers such as myself and so called peak stress contour plots for elements such as blast walls

 

[AUCE98]

To All,

A couple of firms that our company has used as consultants are Baker Engineering and Risk Consultants, Inc. and Applied Research Associates. Both are well known and well versed in designing hardened structures for blast and progressive collapse.

Regards,

AUCE98

 

[bridgebuster]

civinco01

I'm not a blast expert but I am managing the design of a structure that will be blast hardened; it's not being designed by empirical methods. You need to be careful because the empirical methods are typically based on open-air blast for a particular threat level and standoff distance.

If there are buried components that need to be protected, these methods may not work.

Again, you need to discuss with your client the acceptable level of damage to the facility and, sorry to say, potential loss of life.