drilled shaft fundation

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Progressive Collapse ODrilled Shaft Bridge

Foundation Under VeImpact


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Content

Abstract

Introduction

Site Description

• Piers and superstructure

• Ground conditions

Failure of the bridge under vessel

impact Drilled shafts and columns

Conclusions

References

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Abstract

On 1 !une "##$% a pier of the 1&$ m long !iu'iang (ridge near Gu

*as impacted b+ a vessel,

-he pier being impacted and t*o ad'acent piers collapsed in a se.ue

appro/imatel+ "## m of the bridge dec0 fell into the river,

ach of the three piers *as supported on a 1,$ m diameter% " / " dril

-he simulation model includes all three drilled shaft groups as an int

connected b+ a bridge dec0,

-he bending moment% displacement and soil reaction along the drillecomputed,

-he pier foundation being impacted collapsed 2rst,

-he failure of this pier *as initiated at the connections bet*een the p

drilled shafts and bet*een the pile cap and the pier columns,

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Introduction

(ridge piers ad'acent to navigation channels are usuall+ at ris0 of

collisions b+ errant ships,

Sometimes ships deviate from the navigation channel and collide

channel piers% *hich can lead to catastrophic conse.uences since t

channel piers are often designed *ith a relativel+ small lateral bea

Different structural s+stems e/hibit different degrees of sensitivit+

failure% *hich is often neglected in conventional design anal+sis,

-raditional design usuall+ pa+s more attention to the safet+ of ind

elements than to the safet+ of the entire structural s+stem,

As a result% failure of one member of a bridge s+stem ma+ cause th

collapse of several members or even the *hole s+stem,

-he purpose of this paper is to investigate the s+stem failure mech

foundations under vessel impact,

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6 Site Description

!iu'iang (ridge is part of 4ational 5igh*a+ G6"% *hich crosses

and connects !iu'iang and !iangmen Cit+ in Guangdong Province%

Fig, 1,

It is 1&$ m long and has 86 spans 9Fig, ":,

-he bridge has been on service since !une 1"% 1;


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Site Description7


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8 Site Description


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Piers and superstructure=

Piers no, "6% "8 and " had the same t+pe of structure,

ach consisted of four drilled shafts% t*o columns% one pile cap% an

as sho*n in Fig, 6, In the 2gure% S1% S"% S6% S8% C1 and C" repres

shafts and t*o columns,

-he piers are connected *ith continuous concrete bo/ girders,

-he cross section of the original bridge dec0 is composed of t*o b

9 Site Description


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Ground conditions=

-he site around the collapsed piers is underlain se.uentiall+ b+ a 2

gravell+ sand la+er and slightl+ or moderatel+ decomposed granite

-he ground conditions near Piers no, "6>" are sho*n in Fig, 8, -of the soil la+ers are summari)ed in -able ",

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13 Failure of the bridge under vessel impact

In the earl+ morning of !une 1% "##$% a vessel named ?4angui'i #

cargo of sand stra+ed from the navigation channel and struc0 on P

bridge pier ad'acent to the non3navigation channel,

ost part of the vessel sun0 into the *ater leaving the buttoc0 abo

9Fig, :,

-he vessel *as 1### tons in self *eight and the sand it carried *e

tons,

-he velocit+ of the vessel before impact *as estimated as appro/im

-he accident caused three piers% Piers no, "6% "8% and "% and appr

m bridge dec0 to fall into the river,


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16 Drilled shafts and columns

ach pier includes four drilled shafts% t*o pier columns% one pile c pier cap 9Fig, 6:,

-he dimensions of the cross sections and the arrangement of the st

reinforcement bars are according to the design in Section ",1 ?Pier

superstructure@ and Fig, 6,

-he properties of the concrete and steel reinforcement bars follo*

values,

-he compressive strength is 1&,$ Pa and the elastic modulus is "

-he stress>strain relationship of the steel reinforcement is assume

elastic% perfectl+ plastic,


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17 Conclusions

-he failure process of !iu'iang (ridge on 1 !une "##$ during a ves

is investigated b+ numerical anal+sis, -he main conclusions are as follo*s=

• -he static bearing capacit+ of the piers under static loading eithe

pile cap or pier cap is much smaller than the e.uivalent static lo

the vessel impact calculated using the AAS5-O method,

• -he failure of the pier sub'ected to vessel impact is initiated at th

connection bet*een the columns and the drilled shafts *here themoments are the largest and e/ceed the bending capacities of th

and drilled shafts,

• -he soil reactions are not full+ mobili)ed *hen the impacted pie


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18 Conclusions

• A failure process is proposed based on the results of detailed d+namic progressive failure *as resulted from the separation of structural elem

centrifugal forces of the falling bridge dec0,

• -he dec0 then rotated about one end of the ad'acent pier% *hich genera

centrifugal forces on the ad'acent pier,

• Subse.uentl+% the ad'acent pier *as pulled to failure b+ the centrifugal

leading to the cutoff of the bridge dec0 above the ad'acent pier,

•

In the same *a+% the nearb+ pier *as pulled to failure b+ the centrifugfrom the rotation of the falling bridge dec0,

• Such a progressive failure process stopped *hen a bridge 'oint *as en


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Than !ou

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drilled shaft fundation

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