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[SEAOC] Re: [SEAOC] [Q:] Explosion wave ---> Damping?

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Peter Rangelow wrote:
> 
> Hi,
> 
> Problem:        Design of the reactor containment of a NPP
>                 against explosion wave.
> 
> Question:       What factors should be taken in consideration
>                 when assuming the damping of the structure under
>                 this type of loading? 4 or 7 % of critical damping -
>                 how to rectify the higher damping value to be
>                 used in the calculation?
> 
>                 Does someone know of a paper/book or has experience
>                 in this field?
> 
> Thanks for any comment !
> 
> Best regards,
> 
> Peter Rangelow
> ====================================================
> Deutschherrnufer 29       tel  : + (49-69) 6199-1806
> 60594 Frankfurt am Main   fax  : + (49-69) 6199-1805
> GERMANY                   rangelow(--nospam--at)pop-frankfurt.com
> ====================================================

Hi, Peter

It is a general practice in impulsive load design to ignore damping because 
maximum response occurs at the beginning of the process.  This is generally 
true when the structure is sensitive to impulse and not to peak pressure.

The factor which determines impulse or pressure controlling is the ratio of 
dominant structural frequency to the duration of explosion wave.  It is 
tricky in determining the dominant containment frequency.  For example, if 
the explosion is due to hydrogen detonation at the center of the dome, the 
dominant frequency is axis-symmetrical membrane tension mode and can be very 
high.  However, if the explosion is due to hydrogen detonation on one side of 
the cylinder or due to external gas cloud explosion or other external 
reasons, the dominant mode can be a combination of nonaxis-symmetrical 
bending mode and axis-symmetrical bending mode.  

The duration of the explosion wave is usually influenced by the standoff 
distance.  For example, the standoff distance of hydrogen detonation is very 
small, while the standoff distance of external gas cloud explosion or other 
external reasons could be large.

Just in case you want to consider damping, it depends on the material of the 
containment, e.g., steel, reinforced concrete, or prestressed concrete.  In 
the case of double containment - steel containment with reinforced concrete 
shield building, the material for hydrogen detonation is steel and that for 
external gas clcoud explosion is reinforced concrete.  It also depends on the 
stress level in response to the explosion.  Most probably the response is 
beyond elastic limit.  Under this case, damping value corresponding to Safe 
Shutdown Earthquake (SSE) or higher can be justified.  This is assuming that 
you are performing a linear elastic analysis.  In case you are performing a 
nonlinear analysis, the above mentioned damping should be reduced to avoid 
double dipping because the nonlinear analysis takes care of most of the 
energy dissipation already.

Hope the above is helpful.

Aufwiederhoeren, 

Chang Chen, Ph.D., P.E.
Apollo Consulting, Inc.
e-mail: apollo(--nospam--at)epix.net

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