BTP Presentation (1)

7/25/2019 BTP Presentation (1)

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Analysis and Design of Blast ResistantUnderground Shelters

Supervisor: Prof. T.K. Datta

Abhinav Agrawal



Introduction to the problem

ivil defense shelters are typi!ally built to provide prote!tion topersonnel and e"uip#ent against the effe!ts of weapondetonation.

Apart fro# the basi! ob$e!tive of preventing failure of thestru!ture itself% a #a$or !on!ern is the dyna#i! response of thestru!ture.

A rapid #ove#ent of the shelter #ay !ause in$ury to its hu#ano!!upants and !ause da#age to built&in e"uip#ent su!h asgenerators and ele!tri!al fittings.



'owever% the relevant infor#ation appears to be s!ar!ebe!ause of the !onfidential nature of the sub$e!t.

The present study tries to analy(e the response of anunderground shelter under the influen!e of blast wavesi#pinging upon it.



Description of Groundshock

Buried stru!tures !an be vulnerable to transient stressespropagated through the soil and ro!) in whi!h they have been!onstru!ted.

Sensitive e"uip#ent #ay suffer da#age fro# trans#ittedgroundsho!).

The isotropi! !o#ponent of the transient stress pulse !auses

!o#pression of the soil with parti!le #otions parallel to thedire!tion of propagation of the wave. These are )nown as!o#pression or *P+&waves.



The !o#ponent of the stress pulse !ausing shearing of the soil

with a parti!le velo!ity perpendi!ular to the dire!tion

propagation of the waves are )nown as shear or *S+ waves.

,ear the ground surfa!e parti!les adopt a !ir!ular #otion.

These are )nown as Rayleigh or *R+ waves.

P and S waves are attenuated #ore rapidly than R waves and

so R waves tend to do#inate at large range.



Characterization of Ground Shock

R Waves

(Rayleigh

S Waves

(Shear

Groundshock

Waves

Surface Waves

! Waves

(Compression

"ody Waves



#uantification of Groundshock

The propagation velo!ity of P&-aves

where K is the bul) #odulus and is given by

The ter# seis#i! velo!ity c is defined as

ρ K c p =

ν

ν

21

1

3

2

−

+c

ρ

E c =



$b%ectives of the &ork

odeling the underground shelter surrounded by ro!) and soilstrata and sub$e!t the syste# to a short duration% high intensityload% si#ulating a blast.

arry out the finite ele#ent analysis of the syste# using ABA/US.

Study the response in for# of stresses% strains% energies% et!.

of the syste#.

Use the obtained response in designing the stru!tural syste#resistant to the balst waves.



!recise ob%ectives of the &ork done

odeling the soil strata as a se#i&infinite #ediu#% #ini#i(ing

the disturban!es !reated by the presen!e of boundary

!onditions in the si#ulations.

Analy(ing the syste# by varying depth of burial% si(e of the

shelter and energy i#parted by the blast% et!.

Studying the differen!es in the stru!tural response in the above

s!enarios.



'aterial model used in the simulations

Under blast loading% the initial response is i#portant.

Beyond a !ertain distan!e% the response will not involve plasti!defor#ation.

The design stand&off distan!es are not short enough to !auseplasti! defor#ation very near the shelter.

3.0

/100.1

1800

28

3

=

×=

=

υ

ρ

mm N E

mkg



The !on!rete #aterial of the stru!ture is harder than the soil

#ediu#% the elasti! #odel without da#ping has been

!onsidered.

2.0

/20

/250005000

2400

2

2

3

=

=

≈=

=

υ

ρ

mm N f

mm N f E

mkg

ck

ck



oad )ariation &ith time



'odeling the soil as a semi*infinite medium

0n dyna#i! analysis% a fi!titious boundary would refle!t waves

originating fro# the vibrating stru!ture ba!) into the dis!reti(ied soil

region instead of letting the# propagate towards infinity.

0t is set at a suffi!ient distan!e where either the refle!tive waves are

not produ!ed or the effe!t of refle!tion on the response is not

signifi!ant.



Propagation of Stress -aves through soil #edia



+ime ,istories of !ressure at Critical ocations

Pressure variation at point 1 Pressure variation at point 2



+ime ,istory !lots of +otal and Strain -nergies

Total 3nergy of the syste# Strain 3nergy of the syste#



+he modified model &ith an e.tended boundary




o#parison of the e4tended #odel with a further

e4tension of the boundary to a larger distan!e





'odifying the depth of burial

There is a possibility that the stresses and strains generated in the

shelter !an be different at different depths of burial of the stru!ture.

This !an help in redu!tion of the vibrations whi!h o!!ur in response to

an e4plosive blast a!tion.

The effe!t of varying the depth of burial has been studied at 5 different

depths 6.7 #% 18 # and 12 #.



Stresses &ith variation in depth of burial

Depth of burial below surfa!e 9 12 #



Depth of burial below surfa!e 9 18 #



Depth of burial below surfa!e 9 6.7 #



$bservations

The plots indi!ate sharper and #ore pro#inent pea)s in the

shelters with a lesser soil overburden.

The !loser distan!e of the shelters to the !enter of detonation

whi!h !auses larger vibrations in the stru!ture

Also% the overburden stresses redu!e the vibrations o!!urring

in response to the stri)ing blast waves



Stresses at the critical points

Shelter Si(e 9 7# 4 7# Shelter Si(e 9 18# 4 18#



Shelter Si(e 9 7# 4 7# Shelter Si(e 9 18# 4 18#



$bservations

The pressure levels generated in the s#aller si(e shelters arelower in !o#parison to those in the larger one.

An analysis of the ti#e history of stresses also highlights lowerstress levels in s#aller shelter.

The pea)s are signifi!antly #ore pro#inent in si#ulation with as#aller shelter si(e.

Pro#inen!e of pea)s in the ti#e histories plots in the s#allershelters due to their lower #ass% #a)es the# undergo vigorousvibrations



Conclusions

An elaborate and e4tensive analysis of shelter response was!arried out using ABA/US.

0n the wor)% an elasti! soil #odel was adopted based on whi!ha 5&D stress analysis was perfor#ed.

The proble# of #odeling of soil as a se#i&infinite #ediu# wassolved.

The influen!e of the boundary of the soil #ediu# on the #odelwas eli#inated by gradually e4tending the #ediu# farther awayfro# the !enter of detonation of the e4plosive !harge.



Different !ases of buried shelters sub$e!ted to detonations were

studied

a; Different depths of burial indi!ated the stability of stru!tures buried

at a larger depth below the ground surfa!e with respe!t to the

stru!tural vibrations indu!ed in the#.

b; <arying the si(e on the shelter response observed to indi!ate that

shelters with a s#aller si(e undergoes #ore serious vibrations

when i#pa!ted by blast.



/uture &ork on the pro%ect

Study the syste# response with a !harge e4ploding within thesoil strata% by e4tending the syste# boundary either side of it.

Study of the effe!ts of variation para#eters li)e input energy%stand&off distan!e and shelter properties% et!. on the stresses at!riti!al points on the stru!ture.

Adoption of #ore !o#pli!ated non&linear soil #odels with the

ob$e!tive of obtaining a #ore realisti! representation and #orea!!urate analysis.

5&D #odeling of the syste# to study the stresses generated andhen!e designing the stru!tural syste#



References

=ang >hengwen% ?@inite ele#ent si#ulation of response of

buried shelters to blast loadings% Finite Elements in Analysis

and Design 1997; 24:113-132

S#ith P% 'etherington % ?Blast and Ballisti! Coading of

Stru!tures% 4ford: Butterworth and 'eine#annE 1FFG.

Cu =ong% ?Underground blast indu!ed ground sho!) and its

#odeling using artifi!ial neural networ)s% Computers and

eotec!nics 2""#; 32:1$4-7%

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