\Paper No.475

"SHOCK TRANSMISSION UNITS (STUs) FOREARTHQUAKE LOAD DISTRIBUTION ON THE

WORLD BANK FUNDED SECOND BASSEINCREEK BRIDGE IN MAHARASHTRA"t

By

D.B. DESHPANDE· , D.l PATEL·· & R.V. SAKHADEO·· ·

CONTENTS

1. Introduction2. Description of STU3. STUs for Strengthening of Existing Bridges4. STUs for New Continuous Bridges5. Procurement of STUs6. Selection of STUs for Second Bassein Creek Bridge7. Design Submission for STUs8. Load Testing of STUs9. Installation of STUs10. Conclusions

SYNOPSIS

Page202203205209212213215219224227

The Second Bassein Creek Bridge on National Highway 8 is among one of the fewbridges in the world constructed with Shock Transmission Units to distribute earthquake loadingamong piers installed with fixed and unidirect ional pot bearings. This is the first road bridge inIndia where STUs imported from overseas are installed.

There are only a few countries in the world where STUs are manufactured at present anduntil now the specificat ion for an STU is not covered in design codes of any country of theworld. Presently , efforts are being made to include specification for STU in the AmericanAssociation ofState Highway and Transportation Officials Specification (AASHTO) by ColebrandLtd. of UK. They asked the Highway Innovat ive Evaluation Centre (HITEC) - a service centerof the ASCE Civil Engineering Research Foundation to convene a panel of experts to developan evaluati on plan for their STU and to present to AASHTO.

STUs must be load tested before installation just like other bridge equi pment, such as,bearings, expansion joints. etc. Unfortunately, testing ofSTUs is quite an expensive business and

t Written comments on this Paper are invited and will be received upto 15th December, 200 I* Chief Engineer, National Highways Region , PWD, Mumbai, Maharashtra** Acting Team Leader/Resident Engineer, Lea International Vancouver , Canada*** S.E. & Project Director, National Highways Region, PWD, Mumba i, Mahara hstra

202 DESIIPANDE, PATEL & SAKIIADEO ON. CREEK BRIDGESTUs FOR SECOND BASSEIN

203

testing cost depends on the number and type of tests to be carried on an STU to be used for aparticular application. In the absence of specifications for the design and testing, manufacture rsof the STUs have to be relied upon to provide the appropriate STU and the relevant tests on theSTU for a particular bridge. The usage of STUs is presently growing as engineers round theworld have become aware of the advantages of using STUs for engineering structures. There is,therefore, intense competition among the few STU manufacturers of the world today.

The Second Badiwan Bridge at Baguio was the first bridge in Philippines where STUswere used first time in that country. The experience gained at Baguio by the co-author, Mr. DJ.Patel earlier on that Project helped in procuring, select ing, testing and installing the STUs on theSecond Bassein Creek Bridge.

This Paper is, therefore, written apart from providing technical and other informationwith a purpose to guide the future users of the STUs in procuring, selecting, testing and installingthe STUs in the absence of any specification for design and testing of the STUs.

I. INTRODUCTION

A Shock Transmission Unit (STU), also known as lock up device (LUD), isdesigned to be connected between bridge members to form a rigid link under rapidlyapplied loads, such as, braking and seismic, etc. but to move freely under slowlyapplied loads, such as, temperature and creep shrinkage. Such a temporary fixedconnection facil itated by an STU allows load sharing of a suddenly applied force .Longitudinal traction, brak ing forces, vehicle impact and seismic load, etc. areexamples of such short durat ion horizontal loads applied suddenly to bridge structures,transmitting short durat ion shock or impact forces . The unit is connected betweenelements of bridge structures at expansion joints or near the bearings between thesuperstructure and the substructure subject to long term separation movements due tocreep, shrinkage and temperature to beneficiall y share among them short durat ionloads applied to any one of the substructure elements. Shock transmission units workon the principle that rapid passage of viscous fluid through a narrow gap , orifice orvalve generates considerable resistance whil e slow passage gener ates only minorresistance.

Ever since the engineers started designin g mult i-span simply supported bridges,they felt a need for a device, such as, an STU .

Use of an STU was first made by Steinman, the designer of the CarquinezBridge on Interstate 80 in California, US, (Pho to I) in 1927 to distribute seismic loadsto more than one pier of this cantilevered stee l trusses with suspended span typebridge.

The next application of an STU in the US was for the San-Mateo HaywardBridge in 1967. 4 Oil-based STUs were installed at the expansion joint in the 230 mmain span. STUs have also been used in Europe. The 5 km long Oosterschelde Bridgecomp leted in the Netherlands in 1965, used STUs extensively. STUs were alsoutilized on the approach spans to the Kingston Bridge, completed in Glasgow in 1970.

. I terstate 80 in California, US,Th C quinez Bndge on n

Photo I. e ar STU was fir st usedwhere an .

. . I supported bridges, load sha~ng byIn new continuous and multl- span s;mPr~sulting in smaller design section for

means of STUs can be used advantageous~, f both steel and concrete cable stayedthe substructure elements. S!~S can be u~~s l~:ements of deck during an earthquake.and suspension bridges to ehmmate ~~ge ~ elevated light rail structures as well ~n~STUs can also be used in bascu.l~ bn ges a~hrou h an expansion jo int. F~r .o~he~ CIVilin bridge parapets to share colhslO~ f?rces STUs gcan provide additional n gldlty rn the

. engineering structures , such as, .bU11d.mg~~ s an structures and can also be used ~oframe structure, such as, parkmg. simp , p . event STUs are also used to resiststrengthen adjacent bui1din~s dunn~ a sels:~ water' industries. Light rail elevatedsurge forces at bends in plpehnes in g.as . (more cars) and take the increased

U rry a heavier tram b t turestructures with ST scan ca . without a change to the su s rue .braking forces associated with the load I~crea~e which have been found inadequateSTUs can be made to strengthen support~ng piers, which have sustained damage

. ti d braking forces, or . f STUsdue to increase m the trac IOn a~. t advantage is that the installatlon 0caused by corrosion. The other s\gmfiCa\ 'd to traffic unlike other methods forcan be carried out without c10smg the n ge

strengthening the piers.

2. DESCRIPTION OF STU

. machined cylinder with a transmissionThe STU as shown in Fig. 1 consists of a d at' the other end to the piston

d t the structure an Trod that is connected at one, en ?, the c linder is a specially fonnulated Sl Ic~neinside the cylinder. The mediuro wlthm ~ rmancv characteristics of a speCificcompound, precisely designed for the

d~er ~emperature chan ge in the structure or

project. During slow movements cause Y

207

P\l~ 3

.' B RIOG£BASS£IN CREEK

STUs FOR SECOND

p'\~~~JP\l~ 4. Sans

I .~ 111lQ111l1J1 !~IJ:\ inez Bridge - MaIn PFig. 4. Carqu

'-- '\, \ ."':""f=~;i~

Carquinez BridgePhoto 2. h fIrst major

d it was t e. z was initially rna ~ and its long span

rnk across the Carqume

f San Francisco .ay The later structureWhen thbeui~t over the deep wate\a~e_of_the-art at the t1m:~e identical in te~S

bridge to ~e \ truss was regarded a~; in looks; hence they The only exce ptIoncantilevere stee h the original bn ge d overall geometry .was des1gned to m~tc th span arrange ment anof structural form. eng ,

. transportationf the mam . d

. . 1958. It is one 0 as been deslgne

re recent structure bUl\t I~O The complete retr.o~t : ut the retrofittingand the other a;::~ Francisco and Sacran;~fo~r Beatty has carnelinks between M Hill. Contrac~o~

onsultant CH2 US$70 ml\hon.by c ost of someworkS at a c

DESIIPANDE, PATEL & SAKlIADEO ON

i iTYPICAL 5 SPAN. SIMPLY SUPPORTED BRIDGE

. ,

HORttoNTAL LOAD ON SUPPORT: tm TRACTlON/BRAXINC IN SPAN

B C D E ,A

AS 7 .~ i .~ 7.~ 7.~ 7.~ 7.~

Be 7.5 7.~ 7.~ 7.~ 7.~ 7.5

CO 7.5 7.5 7.5 7.5 7.5 7.~

DE 7.~ 7.5 7.~ 7.5 7.5 7.5

EF 7.5 7.5 7.5 7.5 7.~ 7.~

HORIZONTAL LOAD ON SUPPORT: tm TRACTlON/BR.IlINC IN SPAN

A B C D E P

AS .~ - - - - -Be - .~ - - - -CD . - .~ - - -DE - - - .~ - -EI' - - - - .~ -

ADDITION OF 5 STUs ·- EQUAL STIFFNESSES AT ALL SUPPORTS ASSUMED

TOTAL SUPPORT HORIZONTAL OESiGIl WII:IT'/ RUlUlRED FOIl TRACTION/Il'lEAKJNC. 7.~t +7.51+ 7.~1 +7.51 , 7.51>7.591 ·'51

Fig. 3. Usage of STUs on a Multi-Span Simp ly Supported Bridge

The Carquinez Bridge in California, Photos I & 2, is a good example ofstrengthening of an existing bridge for revised seismic loading. The Carquinezcrossing which carries Interstate 80 over the Carquinez Straits consi sts of two bridges- one dating back to 1927 designed by Steinman with STUs installed for the first time,

206

a total designed capacity of five times the requi red deck design braking and tractionlongitudinal loads. As shown in Fig. 3, by placing five new STUs at bearing level onthe free abutments and piers, it is possible to share out the traction and braking loadacting anywhere on the viaduct's deck among the' all four piers and both abutments.This results in reduction of pier and fixed abutments sizes and foundations significantlyto give a total designed horizontal load capacity only some 20 per cent of thatrequired initially.

208

209

4. STUs FOR NEW CONTINUOUS BRIDGES

STUs !'OR SECOND B ASSEIN C REEK B RIDGE

The site is very difficult for the construction of the Caissons , as there are dailytwo low tides and high tides in the creek, one followed by the other every six hours.There are occas ional windstorms which create high water currents with velocity of 3m/s and during the monsoon heavy floods are encountered. The depth of the water

Fig. 5 shows the General Arrangement of Second Bassein Creek Bridge . Theeight span igational spans in the middle of length 114.7 m each with two adjacentspans of length :'7 .35 m constructed as balanced cantilevers as seen in Fig. 5 andmade continuous by pour ing closure segment. The end spans comprise two cont inuou sspans with one span of 57.35 m and the other of 48.5 m making the total length ofthe bridge 555 .8 m. The cantilever box girder decks vary in depth from 7.0 m to3.5 m and are being constructed simultaneously using three travelling formworks, oneon each of the piers P3, P4 & P5. The box girder end spans have constant depth of3.5 m and are constructed using conventional method of ground supported staging andsteel trusses over the creek water supported on the piers. The total width of the bridgeof I 1.Om includes roadway width of 7.5 m and footway on either side of 1.5 m. Thebridge is supported over nine Caisson foundations of which three Caissons A I, A2& P7 are constructed as ground Caissons and the remaining six Caissons from P I toP6 as float ing Caissons sunk through creek water to basalt rock strata.

The bridge was designed by Consultants from India and proof checked by anagency from Australia. It is being constructed by Indian firm and supervised by theWorld Bank appointed Supervision Consultants of Canada in joint venture withAmerican & Indian Consultants.

4.1. Second Bassein Creek Bridge, Mumbai, India

The Second Bassein Creek Bridge is a good example of a new multi-spancontinuous bridge where installations of STUs have saved time and money inconstruction of the caisson foundations. It is located 25 m upstream beside theexisting bridge on Mumbai-Ahmedabad National Highway No.8 just outside Mumbainear Ghodbunder at the confluence of Ulhas river and the Arabian Sea.

Load sharing by means ofSTUs can also be used in new multi-span continuousbridges. On new structures, the force sharing made possible by the STUs allows acontinuous deck structure to be designed lighter , giving potential savings in piers andfoundations. Earthquake forces are a function of deck mass and generally results inforces well in excess of design braking and traction of traffic when the spans are big .The high earthquake loading necessitates the development of considerable longitudinalrestraint from the substructure at bearing level. Such a high earthquake force on abridge structure would overload the fixed piers or abutments and STUs can beadvantageously used to distribute the earthquake forces between the substructureelements resulting in considerable saving for the substructure elements and foundations .

D ES/IPANDE P, A TEL & S

A K/lI\ DEO ON

Photo J . I SOOtCapaCity STVs r.

or Ca r quinez Bridge

In. geometry is that tWIdth of just 12 rn he new bridge is 18 rn .spans of 152 m _ b~ Both have four spans _WIde compared With t ' .th.r~ugh cantilever /h have a main central p~o central spans Ofh;3~lglnal structu reWit concrete cais russ superstructure 0 er sUPPOrt and the rn and two sicspan~ between the sons. and steel piles n steel-braced trus Y both consist of ste(Intenor expan sion .C~ntl lever sections an~ :~~dations. Both sbS.~bstructure sUPPOrtmove during normJ~'ntS. These STU; W ~ to transmit 10 " ge~ use suspendc(an earthquake. a temperature variati:

redesIgned to allow ~gltudlnal loads acros,

ns, but provide structur:rPan~ionjoints tc'Apart fro COntinuity durin

retrofitting Workmti

strengthening of th ghYdraulic STU s Or the 1958 brid e superstructure d

s. ge structure inclUded r:pnl

the foundations thacement of .' e

b ' These eXisting ST the eXIstingndge as shou~ ' F' Us, located at th

Y· Id .,,, In Ig 4 ' e expa . .re .capacity of t . WhIch do not nSlOn Joints On t

capacIty, Photo he truss chords ar have enough ca aci he 335 m spans ofth

:;'";,~;";~~~~~::~O'%~';:'~~j~i;~~2db;;*';~:~~~},~:';':'~~';;o,b;;b;n ge structure in Ot STUs are . een Us Com an mr Venture - a

~~ at the Universi~he/;:;:Id to date. Extt;;:s hIghest.capaci; s~~ec.hstar and Italian2.Mhill. FUll Scale ~ Jlan in Italy by Al :vc testing of the unit s ~nstalled on any

consIsted of 18 OOOkNo:ces Wereapplied t ga under the superv' . s ad been carriedseconds before ~ever' Impact loads apPli~de~ch of the STUs in ;~IO~ of Caltrans and

, Smg from tension In less than 0 5 e est frame. Thesto compression. . second and held for;

II,

II~

2\\

ouring 'h' p"oIiminaty d"ign, ii 'w", found by 'h ' d"ign and p<oof cheek",n,ulta

n",hat 'h' , i'" of thoeai""n "qui"" f" picr P4 with 'h ' "X'd po' b",ring,

to ",i" 'h' fun ~i,mie loading of 9300 kN w"' 165m 0 .0· and that tho , i'" ofth'adj",nt eai"on' foe pi" P3 & P4 with unidi" e'ion' l pot b",in", w"' I I

5

10 0 .0.Th'y ""Ii' ol th' diffi",lty of ,on,tmding ,oeb a Ia,g' 16.5 10 Cai,,,,n in thi'difficult , ,,,,k eondi'io

n' and the ,o,"" ponding high eo" and d"id'd '0in'o",o" "

Shook T"n,m i" ion Uni" (STU') on pi" P3 & p5 to cr"''' ",mP""ty fixity " th' "pi' " doring "i,mie loading. Th' STU' on pi'" P3 & p5 woo

ldI"k op doring an"rthq~ke ,",n

t'hcr<bY di,tribu' ing the ~i,mie loading of about 9300 kN among

p,cr' P3, p4 & P5 "eoroing to thd' " ,p" tiv< ,tiffn"" Tlti' ",ul"d into ""o"io

n

of 'h' dia. of tho Cai"on foe picr p4 from 16.5 10 to 12.5 10 and incr"" in di'. ofth' C,i,,,,n, foe pi'" P' & p5 f,om 115 10 '0 12.5 n'· Th' hnri",ntal "i,mie lo,ding

Th' new b,idg' is d"ign'" foe tho lif< , pan of 100 y"" foe tue d"ig

n

liv<load of on' lan' of'RC Cia" 10R 0' two lane of IRC Cla,,·A whi,he

vcr

gov<m,.It is atso d"igo

olfoe v<,,,1 'olli,ion foe an impact fo<C' of 500

0kN a' Wdl Cap

mid d",th foe the main span pi'" p" P4 & P5 and fo<C' 0£2000

kN foe th' ",d , panpi'" PI , Pl, p6, p1. Th' site is I"at'" in mod""'" " i>tni' ",ne and the bridg' isd"ig

n'"

"",roingly

foe 0.015 ho'i",ntal "i'mi' 'o,ffid'nt indnding importa

n

",f"to' of \.5 . HoW'vcr, th' ho'i,ontal fo«" g'o,,,"d in a bridg' d"k 'obj'''ol '0an "'rthqo'k' ,hoek a" a fon"ion ofth' d"k lOa" and '0foe ,hi' b,idg' with h"'''''navigation ,pan' eacn of 114.1 10 , th' Cai,"" fooodation foe pi" P4 wi'h tho fIX,db",ring' ,,,,oi"d to '" d"ign'" initiany foe 9300 kN " i,mie hori",ntal lo,diog.

Whik th' Cai""n' ofth' new bridg' ,uff"'" ,,,''' p'obl,m' foetilt and ,hifl

duo to impmv'"

mod'''' m,thoda , it had its fair ,ha" of p<obl""" Two of thofloating eai,,,,n' got ,w,p' aW'Y during a ,to"" in Januaty 1999bu' w" , ,,'ov<"dlat«. On' 125m dia. Cai,,,,n had to be abandon"' "' it ",bm"g,d on 8th D",m""1999 do' to wa'" ",,,ring th' Cai"on doring th' high tid' whii' the ,,,,, lin<""qui"d as """,,,n,n' forro wo'" w,,, ",ing fabri"",d in tho ,,,,,k n'" tho

launching platform.

und" the twO ,,,,ual

navigation , p, n' is "ound '0 10 and tho av,,,g' ""iiy ,ida'variation is of tho onk' of 4.25 10 with an av""g' vd"ity of 2.4 mI' · An thes ,it<'onditio

n'

uav mad' tho Cai"on' ' on,,,,,,'ion a diff"un and ri'ky task foe tho",n,,,,m<. Th' "i"ing bridg' w"' originany d"ign'" "' ten ,pan ,imp'y ,upport'"PSC ai,d" Bridg' with dght middk ,pan' @ 57.35 10 and tho two end ,pan' @485 rn. How,"'" during th' ",n,,,,,'rion of tho bridg' 'h' d"igo of 'h' six int""a',pan' had to be ,hang,d with tbe two middk ,pan' in''''''''' from 57.35 10 <0 I 14.110 I'ngth duo to ",bm"g,n'" of two middk eai""n' during 'on,,,,,"ion in themon",on flood in 1964. Mo" of tho oth" Cai"on' "pw"'''''' h""" tilt and ,bifl,which "qui"" to be ,o_,ol by 10""" of k",tlolg' and ,inking m<thod'. The"i,'ing bridge took "v'" y" " to 'ompl"" duo to tho diff,,,,"i" 'n'oun.-l in

sinking the Caissons.

Cla:

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D ESIIPANDE P, ATEL & SAKHAD EO ON

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2\3

5. PROCUREMENT OF STUs

Today, STUs are manufactured in a few other countries apart from USA & UKand name and addresses of some of the major STU manufacturers around the worldcan be had from the Authors.

got distribut ed equally on the three piers having more or less the same stiffness from9300 kN initially on pier P4 to 3100 kN on each of the three piers P3, P4 & P5. Thisjust did not only make the Caisson construction manageable but also reduced the costof the Caisson foundations appreciably resulting into considerable cost saving.

There are presently two types of STUs available in the overseas market, onewith silicon putty based from UK and USA and Europe and other with oil based fromsome countr ies in Europe. However, these oil based STUs are much more compactthan the early oil and gas based STUs with many moving parts but the disadvantageof oil is that it is more likely to leak out rapidly from the cylinder than silicon puttywhich is like dough.

f Performance .Evidence 0 'I ' similar climatic

fi d satisfacton y 10 d fThe STU selected ~ust havbe P~e~~~ from manufacturer's recor 0

, . d this can econditIOns an .ous countries.

. STUs to vanexportm g

. 'R irements hDeSign equ , d d stroke of t e

' fj d deSign loa anwithstand the speci ie eck due to temperature,

The STU must . than the movement of d 'tudinal movement.piston must be blgg

i:each direction of the dec~'S ~~:~k Bridge is for the

shrinkage and creep for the Second Bassem t f the deck fromThe design requirements f 3I00 kN and movemen 0

f ch STU 0design .load or ea+40 mrn to -90 rnrn.

C EEK BRIDGES ECOND B ASSEIN R

STUs f OR

(c)

(b)

, For the Second Bassein

ed with by the supplter., 00 kN was US S, nd testing is strictly adhterof two STUs of capacity 3 I three specified tests

:slgn a .d e the average cos f h sTUs at the site by se~, h costs for the

;~e~o~.~o ~vhich inclu:ei~~~~~~~e~t t l:borat,Ory (aptWDUK~~:~:~n: :fMaharasuhtras)$, , d out at a db the client ' . ( st about

I be ~~rn\y three officers se\ecte .\ 'ft ed from UK to the site . co of the STUs atIpervlSIOn Id' down bolts air I 'for the installationrackets and ho 109 of a qualified supervisor

00) and assistance3500. f m the manufacturer. t countervailingre site ro d on CIF value and 16 per cen s But since the

There is 40 per~~;ta~~s~:o;~uty payab~ t~u~7::~a~~~~0:e~e exempted asd valorem on h World Bank ,ted

luty an , t was financed by ted eded to be importe .)ridge proJec t locally available an ne GEne STUs are no BASSEIN CREEK BRIO

sru- FOR SECOND ,6 SELECTION OF . I material protectIOn,. . h pe matena S, ketuch as, Size,sa , . day in the mar

Apart from other differenceds, s d oil based STUs avallabfile t~he STU and select'1' putty base an . proposal or

t there are Sl ICO~ btain more than one .e l~~e Therefore , it IS best to

hO

cost the following factors . ,p . . ' apart from t ethe one Judgmg

f the Manufacturer(a) Track Record 0 TU e manufactured

I the S s ar d, nee to check now ong nd the services an

It is of utmost Impo~a yother countries have fou to check the

and how the c1~en~em;~~facturer. It is also hnec~:~i~accreditation ofthe product 0 t f STU manufactured and t e qmaximum capacity 0 lity control and assurance .the manufacturer for qua I

D ESIIPA ND E, PATEL & SAKIIAD EO ON

The early STUs were relatively complex oil-filled or gas-filled devices with ahigh first cost and continuing need for regular and extensive maintenance andadjustment. In the 1960s a chemical compound, a boron-filled dimethyl syloxaneknown as silicone putty, was developed in the US and used in space exploration. TheUK Ministry of Transport realized that the new material was eminently suited toSTUs, offering a better and simpler filler material than the special oils then in use.They developed and patented in the UK an STU using the new silicone putty.Manufacturers in the USA also started making STUs with silicone putty. In 1982, theCalifornia Transportation Department (Caltrans) installed four STU units at twoexpansion joints that connect the main spans to the approach spans of the DumbartonBridge . This allowed seismic loading to be distributed to all the bridge piers in theevent of a seismic occurrence. This was the first silicon putty STU studied by Caltransand in 1996 Caltrans notified STU manufacturers in the US that silicon putty basedSTU was an approved product for California bridges.

The bridge contract was to be completed in three years but the contractor hasexperienced six months delay due to the problems involved in the construction of12.5 m dia Caissons. It can be concluded that the contractor would have experiencedgreat difficulty in constructing 16.5 m dia. Caisson in these difficult creek conditionsand would have been delayed much longer. The usage of Shock Transmission Unitsin this case not only decreased the cost of the foundations by about estimated elevenmillion Indian Rupees but above all made the Caisson foundations for the bridgefeasible by reducing somewhat unmanageable size of the Caisson for pier P4 from16.5 m dia. to 12.5 m dia.

212

There is keen competition among the few STU manufacturers and one cannegotiate for the best price keeping in mind that the required specification for the

215

7. DESIGN SUBMISSION FOR STUs

STUs are unidirectional devices for load transmission. If out of planeforces will be acting on the STU , the angular limits of these loads mustbe determined to assure the STU can withstand them. Generally , ball

Designer Notes

STUs fOR SECOND BASSEIN CREEK BRIDGE

(a)

7.1.

normal maintenance cannot be avoided. It is nece ssary to know themaintenance requirement for the selected STU including the recommendedfrequency of maintenance and a manual to be provided by themanufacturer that will include specific instructions to ensure propermaintenance and inspection procedures for the STU while it is in

service.

A critical factor in determining the success of an application of an STU on agiven bridge structure is a complete understanding on the part of the designer as to

the capabilities of these devices. Following are some cautionary notes for designers

to ass ist in proper life span performance:

The reason for giving the contractor the choice of making the final selection

from the two manufacturers was to expedite the delivery process and to award thecontract to the manufacturer who takes the shortest possible time to submit the design,manufacture and load testing of the STUs especially as the initial quotation from boththe manufacturers was more or less the same. The final choice of the contractor was

for Colebrand of UK to supply the two STUs each of capacity 3 I00 kN .

DESHPANDE, PATEL & SAKHADEO ON

Maintena nce Req .uirernents

While it is desirable to hav .e maintenance free STU but some periodi c

Load Testing Programme

The STU. must be tested d .achieved Th to eterrrune if th d .necessar; tes: i;~n~facturer must provide eevid:~::d perform.ance isas the tests independent laboratory in th of carrying outis necessaryatre rather expensive and may becoe country of manufacture

o test the STU . me more exp . . .testi ng facility . th m other country in th ~nslve If Itm e country of manufactu e case of inadequate

rer.

Installation Re quiirements

An installation manual sh .of adjustment of the S~wI;g the method of installation th hstorage ""d the details 0; ';:' temperature change, ",\u'ire;:::" od

sthl.p~mg and handling must beeavt~lmbPlorary support of the STUtss fi

for

rammg b at a e Sup .. orof install Yt. an expert from the manufac~r .ervlslOn of installation and

a Ion. er IS necessary in the country

Removability for Replacement

Th .e size and connection detailsreplac~d with ease in the futur of STUs must be such that the cSTU IS around 75 e, as the maximum lif Y an beperformed by the years subject to appropriate I e .expected for anowner. maintenance being

Protecti Tve reatment DetailsMaterials subject t d . . For tho S~ood B",,,io C",k Bridg', tho ,00tt'ctO' had ",bmitt'" p,opo><l,

sh Id 0 eten oration h ". 00 be protected a . . w m exposed to th . rom "" fol1ow

m, rnree m'oof"m"'"

interfere with th gamst such deterioration in e environmente perform a manner th t "II .,h,11 be protected fro """ of "'0 STU. Piston rods . at wi not (I) Col'b"md, UKable to accommodate ;,'Zi~;o" to tho environment hy',t:~:i~I"', (2) T~h"''', USAof"'0 outer surfaces of the S troke of the STU. Tho protective It' cover (3) M'u'" Sohoo, Gono,"Y

free for a lon g period. TU must be such that it remai " eatment

0' maintenance Tho pmpo"l, WOl' pom"d in dctaH wi'" "" above "I,"ioo f"'o" io miodand it was d,ddoo '0 "I~t Colob"od of UK ,od T~""'" of USA'" bo'" ",~,foood oqo.l1y ""p"blo by tho SopOlvi,ioo Cou,ol"""· Coltb"md of UK havem""of"m"d tho most oombOl of STU' but 'goo",l1y of "p"i!)' of upto 2500 kNwhi le T~h"M of USA h"o m""uf"m"d tho STU' of the hi..est "p"i!)' upto18000 kN for CMquioa B,idgo io cMomi,. It had taken 'oo'id,,'bl' 'imo for tho,"otrn'tu< to find out the ot'ooro'm"" to ,uppiy STU' and io gottiog quo

Ulioo,and

00" the 'oott'" was m,do with' m.ouro,m,,', there was furt,," tim' "",oi"d to,ppmV' the d"ign ,ubmi"iou of "'0 STU, m'ouf"m" of "'0 STU itself and lo,d

testing and transportation of the STUs from Overseas.

Mater ia l Requirements

The material used in "maximum " " manufacturing of th STstre anticipated life of the STU e U must ensure tha t

ngth stainless steel for th " could be achieved. Use of a h" C

recommended e piston rod and " Igh. connecting pins is

(i)

(h)

(g)

(I)

(e)

(d)

214

217

STU~ FOR S ECOND B ASSEIN C REEK B RIDGE

Submission of Requirements for STUs for the Second Bassein

Creek

Bridge

(a) Th,to"'l numb« of STU' mqui"d, indi~ting "too "paoity and rated

movement limits.(b) The plan view and section elevation view showing an relative dimension s,

including dimen sions for the anchorages.

The STU responds to impact type loading by locking. Thus, there is apo"ibility onoad ,mplifi~tiondue to tbe imp'" force Fm pmpo"" ofanalysis, the designer should assume an amplification of the rated(design) force , and should check the design of all related components(substructure, anchorage and all fasteners) for amplification of \.25

times the rated load.

The designer shall determine the maximum movement limits for the

proposed location of the STU.

STUs can be used to attach superstructure elements together, such as, atan expansion joint, or to attach superstructure elements to substructureelements. The designer must determine where and how the device canbe attached or anchored to the structure. Design ofthe actual connectionscan be by the design er or manufacturer, as specified in the contractdocuments. Modifications to design details where the STUs are connectedto the structure may be necessary due to heavy shear transfer especiallywhen an STU is to be attached between Superstructure and Substructure

elements.

7.2.

(h)

The following shall be specified (but need not to be limited for) on the working

drawings:

(g)

7.2. l . Working drawings : The manufacturer shall prepare and submit working

<hawing'for the STU' and ""hm.g'" Su,h d"wing' shall show the ",t_1

d,,,,iI'and dimensions of STUs and anchorages proposed for use and shall be approved bythe engineer prior to fabrication. Such approval shall not relieve the contractor of any",po"ibiiity under the "n.",t d""m,," for the ",,,,,,rul "mplction or the

work.

Once a manufacturer is selected to supply the STUs, it is necessary for the

~1"otOO STU m",uf",tu<tt to ",bmit the d"ign dctail' ofth' STU' togctW

with itsholding down ""t,m "mp",ing b""k'" at each end and the hoiding down bol",detailed load testing procedure and mode of transportation of the STUs from overseas.A"mdingly , the following ,ubtoi"ion mquimm,," were fmw,,",OO to the

manufacturer, Colebrand Ltd .

(D

D ESIIPANDE, PATEL & SAKIIADEO ON

For rail-road bridges th .forces in . ' e tracti on forces mmagnitude, and rna be . ay equal or exceed seiof the structure Th d . y applied many many ti sa,their rate of ap~licat~ones~~~e~umu.st ascertain the ma~:~~~:e;;~e Iiuse of an STU . ' ration of these I ds nri oadto distribute them. oa s pnor to specifyi-

The corro sion protection sused on the brid e T ystem used on STUs should bdurable reinforce~ ' he boot prote cting the piston d ~ the same ,pr t d neoprene material Th ro IS made ofof~:;~ ?y grease packed into the ne~pr e s~ain less steel piston rod i

the exp::~r:er to d.e~errnine if this 'protec:~oen o;tkIt i~ ~he r~sponsibi l itadditional con~ltlOns expected over the p ~ ag~ ISsatisfactory fo

. protection is required 't h service life of the STU Ispecial provision If ' ' I S all be so n t d . .of acceptance, th:\e~P~ClfiC durability testing is req:i~edm the pr~j.eca part of the order uirements shall be so specified by t:

s

d

a

c~ndltIOI. e eSlgner a!

Corrosion protection s st .Creek Bridge re ui y em ~pplied to the STUs for thpolyurethane pai~t :eydthot zinc spray followed by a ~Second Basseins em. ree-coat epoxyl

Environmental conditions to be .Industrial; Potential f . , considered are: Coastal ( .salts and mud (I' e dor pe~odlc immersion due to f1 d~anne salts );

. ., un erbnd . . 00 mg' D ..structure repainting' P' ge joints); Inadvertent sandbl .' elc~ngof the neoprene ' igeon nests; Ultraviolet light a d astmg dunng. n ozone exposure

~h~ designer should know that the S .esigned, manufactured and' TU IS a custom made .

site-specific load I" tailored to meet both mini umt that isirruts An STU . mum and m .temperature chan ' . IS designed assumi . aximumbasis for det . ~es at a given rate of moveme t ng bndges react to

to for the se~:~I~~et~~ '~:g~;~~e that sUbstru~~:: ~~~rb~:~~ji:c~~

Typically only STUof 1200F.'Units thatS;xposed t~ direct sunlight would resubjected to maxi ould be m the shade of th brid ach temperatures

th

aximum of 1000F If ' e n ge deck would beey can be . . Units areed'

reduce the e~:I~te~ a light colour to ref1ectX~ose to dir:ct sunlight,temperature of ~ 000 solar radiation. A maximu;at, or be .insulated too F would be appropriate for pre-qualification test

STUs so protected.

joints and/or additional d .these forces . evices, can be incorporated to properly transl

(e)

(d)

(c)

(b)

216

7.2 .2. Quality control and assurance

219STUs FOR SECOND BASSEIN CREEK B RIDGE

(c) Simulated Cyclical Force Transf er Test: Thi s test provides assurance thatas the rever se cyclic movem ent occurs during an eart hquake, the STUlocks as intended in eac h direc tion .

(b) Simulated Dynamic Force Transf er: This test determines the ultimateforce that the STU will trans fer upon lock up .

(a) Impressed Defl ection Test: This tes t ve rifies the rate at which normalmovements occur with in the device and the correspond ing 'Drag Force'generated du e to the movem ent. Th is drag force generated should belesser than the force required to mobilise the pot bear ing' s friction of52.5 tons at the maximum rate of mo vement of the superstruc tu re whenan STU is to co nnect superstructure elements to substructure ele me nts.

The manufacturer shall test one of the two STUs to be supplied under thecontract and submi t full details for the fo llowing tests:

D ESII PANDE, P ATEL & SK/lADEO ON

The type of materials to be used Ii\) STU d h. r s an anc orages.Corrosion protection system for Sl' .B id . I Us and anchorages. (Bassein Cre ek

n ge IS ocated over sea and . . . .C ive) the rnanne cnvironrnent IS highlyorros ive

Alignment plan s for the STUs sh .. owing tolerances for alignments in

whic h the STUs must be installed.

Complete installation schemes and detail f STU ' I. ai s 0 s In pace.Design calculations for the STUs a d hn anc orages.Complete anchorage details a d ddi .n a monal reinforcement details wherevernecessary.

The weight of each STU.Th "

(T: mlnll~lUm and m~x~mum temperatures, the STUs are designed for.

be maximum & rrurumum temp . at Bassein Creek Bridge site arc

a out +42°C & + lOoC d h .:an t e maxImum relative humidity about 90 per

cent).

(k) Lifting locations and mechanisms.

21 8

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(a) Th~ manu.facture~ is required to furnish a quality control certificate andan l~spectlOn certificate to confirm that an adequate system of continuousquality control was operating at his plant and to state the quality systemto be adopted.

The above submission received fro m the manufacturer was checked, amendedand approved but the STUs were to be approv ed pending successful load testi ng ata later date.

8. LOAD TESTING OF STUs

7.2.3. Special design requirements

(a)

(b)

(c)

(d)(e)

The STUs shall be designed to be attached with pins to the STUconnection brackets.

The desi~n ~f the STUs shall provide for quick adjustment of theirlen~t~, ~lthln plus or minus 0.25 inch , to compensate for errors inposrnonmg of the STU connection brackets.

Sphe.rical end joints may be required to accommodate out of plane endrotations depending on STU connection details.

The fil.ler ma~erial shall be silicone putty type.

Co rros ion resi stant high strength steel anchor bolts shall be used to holddown stee l brack ets connected to STU.

In 1996 , Colebrand Ltd ., the manufacturer for the ST Us for the Sec ond BasseinCreek Bridge, contracted with HITEC to develop a comprehensive evalua tion plan fortheir STUs. HITEC convened a panel of experts to develop the eva luation plan , whichcould be used as a basis to dem onstrate the capabilities of STUs for applica tion tohighway and railway br idge s.

Five spec ific tests we re conducted :

I. Seal Wear2. Cycl ic Load3. Drag Load4. Overload5. Fa tigue Load

.the pe~~~'a:c~t~~gsrequiremen~s : The objective; of the test plan are to evaluatewi ll not lock up the~~for :e;lgn conditiong consisting of slow mo vements that

temperatu re and loading cO:;i t i o~:t a~~::~:~~:1t~:tt::~~ ~~c~eu~r~~:ctS~~. within

Testi ng criteria were established for each test for which any potential user canevaluate their insta llations to insure devi ces provided met the intended design criteria .However, to pro vide confidence to potent ial use rs that STUs will, in fact . meet thesecriteria, the HITEC panel established a need for advance testing for four STUs wit hrated load capacities approx imating low er (50 kips), middl e ( 150 & 300 kips) andUpper (400 kips) potenti al dynam ic load ing limits.

220 DESlfPANDE, PATEL & SAKHADEO ONSTUs FOR SECOND BASSEIN CREEK BRIDGE

22\

The above test programme was carried out satisfactorily and it provi desassurance to the bridge owner that the product specified will provide the necessaryforce resistance and/or redistribution to ensure adequate dynamic load resistance fOrthe extrem e event design loadings. However, three project specific tests as speci fiedin Clause 7.2.4 - Testing Requirements were specified for these high capacity 3100kN STUs .

The life expectancy of about 75 years for STUs is mainly arrived from the loadtests. There are many STUs installed in UK , USA & Europe since 1970 which arestill functioning satisfactorily, however, the life expectancy of75 years in the field forSTUs still remain to be proved in the absence of the sufficient data.

When Colebrand Ltd. carried out the above five specific tests for includingspecification for STUs in AASHTO "LFRD Bridge Design Specification", the testsespecially for the Seal Wear and Fatigue strength as described below were carried outfor a life expectancy of 75 years .

Seal We ar Tes t: This test was carried out for 30000 cycles assuming that thepiston of the STU moved for the full design range of +2in to -2in in 24 hours, i.e,30000/365 = 82 years > 75 years of service assumed without any damage to seal dueto the movement which may allow silicone putty in the cylinder to leak out.

Fatigue Load Test: The panel of experts from HITEC appointed to develop anevaluation plan for STU to present to AASHTO had determined that a "worst case"scenario for service loading of the STUs is an application of braking loads equal tothe "lock up load" four times a day for the AASHTO LRFD specified design life of75 years service life. This is roughl y equivalent to 100,000 load cycles (4 cycles/dayX 365 X 75 years service life = 109,500 , say, 100,000 cycles). Accordingly, thefatigue load test was carried out on the test STU for 100,000 cycles for the maximumrated capacity of the STU and found satisfactory.

However , the corrosive environment may well determin e the longevity of anSTU if the steel component are not properl y galvanized and painted for the exposureconditions expected over the service life of 75 years. Then again, the protectivesystem needs to be maintained regularly over the service life of the STU.

Colebrand had in the past used the services of Bodycote Materials Testing Ltd.,Laboratory at Daventry, Northamptonshire, UK for load testing of the STUs whichhad the maximum capacity for testing an STU for only 2000 kN. Colebrand,therefore, had to arrange testing at Atomic Energy Authority Technology (AEAT), anindependent laboratory originally part of the United Kingdom Atomic Energy Authori tylocated at Risely , Warr ingto n, Cheshire, UK near Manche ster. AEAT laboratory hasServo-hydraulic fatigue machine manufactured by Schenck of Germany with amaximum load testing capacity of 6300 kN (Pho to A- I in Appendix-I) and has oneof the largest test spaces of any machine in the world.

. . d out in an independent laboratoryIt is necessary .to have \~ad tes~mgb~a.IT1ea certificate indicating satisfacto ry

. adequate testing capacity an 0 amhav lOg TU" rrnance of the tested S .pen o

. the Em loyer (PWD : Maharashtra), theThree engmeers one each from IPI d to Manchester UK to witness

ltd the Contractor trave e 'superv ision Con~u tan s an . h im orted STUs were going to be used onthe load ~ests a~ It wdas th~ firrtystt::

s::~ satisfied regarding the performance of the

a bridge in India an eac pa

selected STUs.

fthe ab

ove two independent laboratories for testing STU in U.K.,Apart rom , .

thers in Europe and America also.there are 0

8.1. Tes t Requirements

. . I to rove the operation of the S~UThe objective of t~e test s~hedu e d':~s fiPor seismic and thermal loadmg

if d d sign loading con monsagainst the speci ie e bli h th performance characteristics . Three testsexpected at the site and also to .est~ I~s b~oW and the results published by AEAwere specified as reproduced .m Ita ICS .Technolo gy pic and presented in App endIX-I .

. Load Test) : The STU shall have an8.1.1. Impressed defl ectIOn test (DO rag 40 m to 0 in not less than 10 hours

d .a . .r 0 to +40 mm to to - m h IIimpressed ejtection OJ • the im ressed defl ection cycle. the STU s aand not more than 24 hours . DurOl/lg t ~r the maximum design capacity of 3100develop no more drag force than I per cen oj

kN.. essive load could not be transmitted to

This test was specified to prove that ehxc. I ted daily temperature cycles. TheSTU it oves throug simu a

the structure by the as I m h tu to move through its entire movement. " uld be for t e struc re .

"worst case scenan o wo . . 24 hours which gives the conservativein one diurnal cycle , that ISto say, +40 mm m mIh 2621·n!hr This would be dueoX 4 -160/24 = 6 67 m r or . .rate of movement of 4 -. . . . and minimum temperatures that

. . d f lling to ItS maximumto the temperature nsmg an a I . I ds Additionally the structures

. d b fi e meteoro oglca recor . ,have been determme Yre erenc . I ' ible Therefore the test could be

. ' Id b ero - obVIOUS y irnpossrme. , . bthermal inertia wou e z . d g load criteria was establIshed Y

ti The maximum radeemed to be conserve Ive. . . f the bearings 10 per cent of the rated

. . f h s onding resistance 0 .consideration 0 t e corre p. f the brid e bearings of 52.5 tons and , therefore,capacity is less than the ~eslstance 0 'd d as having negligible effect on theif the STU met these cntcna It can be regar e

structure in normal service.

(a) Results commentary

in Appendix-l shows that the displacement of the STUThe graph in Fig. A.I

222 DESIII'ANDE, PATEL & SAKIIADEO ON STUs FOR SECOND BASSEIN CREEK BRIDGE 223

piston was constant with a constant resistance, or drag force. The test was accomplishedin approximately 18 hours . The load trace shows some "noise". This is due to the factthat since the load is so low the rig is required to work near the bottom of its range.During the final quarter of the test, the rig was given periodic manual adjustmentresulting in a smoother plot. The small irregularity at the end of the first quarter isdue to backlash in the rig being taken up. The duration of the test exceeded theminimum specified period of 10 hours and not more than 24 hours. During the cycle,the force required to move the STU was about 300 kN which is not greater than 10per cent of its design capacity of ±3 100 kN.

8.1.2. Simulated dynamic force transfer test: The STU shall be loaded intension from zero to the full design load of 3100 kN in less than 0.50 seconds andthe force sustained for 5 seconds. The load shall then be reversed to the full designload of 3100 kN in less than 0.50 seconds and held for 5 seconds.

The acceptance criteria for the above test shall be that the deflection during theloading of the positive force and the negative force shall be no greater than 6 mm andthe deflection during the sustained load portions shall not exceed 3 mm.

This test was specified to prove the lock-up capability of the device andestabli sh the stiffness under impulse and constant forces. It gives a clear demonstrationof any creep under high constant force.

(a) Results commentary

Fig. A.2 in Appendix-I shows the response of the STU to the applied load. Theload is applied in less than 0.50 seconds after about 4 seconds of logging . The sharpcrest at the top of both traces is overshoot necessary on this particular test machineto achieve the loading rate of 6200 kN/second. The STU piston response (thedisplacement trace) exactly copies the load trace. During this test, it can be seen thatthere is no "noise" on the load trace because the test machine is working in the middleof its range and can, therefore , be seen to be impressively stable . After approximately13 seconds of logging the load is released and applied in the opposite direction, againin less than 0.5 seconds. The graph is not completely symmetrical for two reasons.Firstly, due to the vertical test set-up, gravity will ensure that the weight of the testmachines piston and all the fixtures result in the application of a small compressiveforce on the unit when the rig is at rest. Therefore , when the load is applied there willbe a greater displacement in tension than in compression due to the backlash beingtaken up. There is also a very small amount of strain in the fixtures that is onlypossible in tension and a very small amount of free movement in the STU. Secondly,at the end of the tension loading phase the piston has displaced by a small amountdue.to creep. Therefore, the trace becomes "shifted" vertically. During the compressionloading, the load trace is not completely straight - a result of the control systemreacting and controlling the rate of load. Again, the STU piston response exactly

copies the load trace. A small degree of creep can be seen during the sustained loadportion of the test. This is, however, only IS per cent of the allowable value of 3 mm.

The maximum displacement recorded as the load was applied in tension was4.65 mm which is increased to 4.84 mm during the dwell period . The maximumdisplacement recorded as the load was applied in compression was -2.39 mm whichis increased to -2.60 mm during the dwell period .

8.1.3. Simulated cyclical force transfer test : The STU shall be tested byapplying 50 sinusoidal cycle s of load ranging between the maximum (lOO per cent)design tension and compression forces (±3100 kN) at a frequency of IHz. There shallbe no visible signs of distre ss or degradation as a result of 50 cycles of loading.

This test was specified to prove that the STU would function as intendedduring a seismic event. A IHz sinusoidal response of the structure to the groundmotion was considered to be an acceptable model for test purposes. This would resultin more than double the load application rate of the Simulated Dynamic ForceTransfer Test and prove the STU under the most demanding circumstance that it ispossible to test. The duration of the test was considered to be appropriate since itgreatly exceeds the likely demand on the STU in service.

(a) Results commentary

The ±3100 kN sinusoidal load input is shown on Fig . 3.A in Appendix-I. Thegraph commences at 40 seconds because the data logging was started before the testmachine was switched on. Also the load was increased form zero to ±3 100 kN overa few cycles and these are not included in the plot. The displacement graph can beseen to be symmetrical in this case because a small constant tension load wassuperimposed on the sinusoidal load to offset the gravitational effects.

The peak-to-peak displacement measured across the STU was typically7.6 mm. No visible signs of distress or degradation of the STU was observed.

8.2. Conclusion

The performance of the STUs can be verified after installation for the slowmovement due to temperature, shrinkage , creep, etc. by measuring the pin-to-pindistance between the bracket s holding the STU. The locking up of the STU due tobraking of vehicles, traction due to railway train can be verified by monitoring theSTU when such loads are applied on the particul ar bridge. However, for the SecondBassein Creek Bridge, the STUs are installed for the earthquake force of 3 100 tonsand it is only possible to check their performance for this sudden/dynamic load if sucha force can be applied to the deck in the horizontal direction. Unfortu nately, this israther a tall order. However, the perform ance and effectiveness of the STU (Lock-u p

224 DESIIPANDE, PATEL & SAKIIADEO ON STUs fOR SECOND BASSEIN CREEK BRIDGE 225

Device) under severe performance criteria in the laboratory was found satisfactoryand since there is no moving parts in the STU apart from the piston , and the patentedsilicone putty medium is thoroughly tested for performance for a wide range oftemperature, chances of its not performing for the cyclic earthquake force can be ruledout.

The device exceeded the prescribed parameters without degradation in responseand shows it's usefulness as a tool for the effective distribution of forces.

9. INSTALLATION OF STUs

While STUs require considerable amount of time in procuring, selecting, loadtesting and transportation, it is not always necessary to install STUs while a structureis under construction as long as the holding down anchor bolts and the bracketsrequired to fix an STU are installed in the structure during construction. The actualSTU can be installed soon after the structure is completed. The time can be furthersaved if the holding down anchor bolts and the brackets are not imported and arefabricated locally as per the specification.

The holding down anchor bolts and the brackets for the STUs for the SecondBassein Creek Bridge while manufactured in UK were air lifted and installed in timeand the STUs were to be installed later once the superstructure got completed in June2001. Once the holding down anchor bolts are installed , the installed length of theSTU may depend upon site conditions prevailing around the date of installation.Adjustment of the STU length for accommodating construction tolerances can beachieved by screwing and unscrewing the moving end clevis by a maximum of about± IOmm. Adjustment of the STU length by movement of the position requiresspecialist equipment or factory setting. Therefore, the manufacturer must be advisedbefore the STUs are transported if any adjustment in length is required due to siteconditions.

There are generally two ways STUs are connected to a structure to distributesudden ly applied load. One-way is to connect the superstructu re elements togethernormally at the expansion joi nts and the other way is to connect superstructureelements to substructure clements. Each type of connection of STU to a structuredepends up to what is required to be achieved. Some examples of STUs connectedat the expansion joints are Dockland Light Railway Viaduct, London, UK and TayRoad Bridge, Dundee, Scotland, UK, CR i l l Bridge, Suffock County, New YorkState, USA. This type of connection is very common for railway bridges where whenthe increased longitudinal traction and breaking load is applied to one particularviaduct, the load is transmitted through STUs connected across the expansion jointsand shared with adjacent unloaded viaducts. Fig. 3 shows such a connection withSTUs across expansion joints for a viaduct consisting of series of simply supporteddeck spans which increases its load capacity by sharing the loading of each deck with

Photo 4.

its neighbour' s piers. Photo 4 shows connection of an STU at the expansion joint forDockland Light Railway Viaduct, London , UK.

The second type of connection where STUs connect superstructure elements tosubstructu re elements is used for load distribution in continuous bridges. Here, theSTUs can be connected according to space available between the soffit of the deckand the top of pier. There are generally three ways in whi~h this con~ection can bemade. Fig. 7 shows STU connection for the Second Bassein Creek Bndge. Here t~e

STU is placed in a central gap in between the soffit of the deck and top o.f the pierbetween the pot bearings. One end of the STU is connected to the underside of thedeck diaphragm by means of the bracket, shear plate and anchor bolts and the otherto the top of the pier.

Photo 5 shows the STU connection for Arthur Laing Bridge, VancouverCanada. Here one end is connected to the pier face by means of a bracket with t~e

holding down bolts through the pier and the other end to the soffi~ of the deck. Thisconnection can be used when there is not enough place on the pier for the bracketconnection or when the gap between the pier top and the deck soffit is smaller thanthe STU height.

Fig. 6 shows STU connection for the New Badiwan Bridge. Baguio, Philippines.Here one end is connected to the pier top and the other to the soffit of the bottom slabof the box girder.

However. since there were more than one STUs on each pier (4 nos.-1600 k!,!on each pier) and bearings. the STUs could not be placed directly under the soliddiaphragm and so it was only possible to connect the STU to the superstructure by

STUs FOR SECOND BASSEIN CREEK BRIDGE 227

Photo S. Shock Transmission Unit (Lock up Device) Attached at Slide Bearing

226 DESHPANDE, PATEL & SAKIIADEO ON

-L----_..;/!rf -----:--i--I,III

I! " ~ 'M~

""'"I ,I LU-tt:,t.WM":';

puc" )"_ -'-- '1-' --!._

Fig. 6.

~1~SIl40'0SI

~"rOSlEMM,Af(

MUrlOlUlIII'GAWTI

r Un.r nm "'ATfS/ cO""crO"'''I<'

means of brackets to the thinner deck slab. To transmit the shear forces through theslab in the event of the earthquake, the deck slab at the connection needed to bestrengthened by providing additional reinforcement.

Some other examples of STUs connected in this manner are Mekong RiverFriendship Bridge, Korean High Speed Rail Project, Jamuna Multi Purpose Bridge,Bangladesh , Schuylkill River Bridge, Pennsylvania, USA.

9.1. Installation of STUs on the Second Bassein Creek Bridge

It is important that STUs are installed level. A tolerance of ±25 mm measureat the clevis pin locations is within the capability of the system. Tolerance for smallpositional errors are catered for in the STU clevis pin connections through theinclusion of spherical bearings, however, it is extremely important that the STUs areinstalled parallel to the longitudinal bridge central line at each pier for a straightbridge like the Second Bassein Creek Bridge. In order to achieve this, particular carewas given in installing the anchor bolts and the attachment plates . The holding downanchor bolts were installed during the construction of the pier and the first segmentof the box girder deck. A gap of 793 mm as shown in Fig. 7 between the soffit ofthe box girder diaphragm and the top of the pier was available which was sufficientto install the brackets with the STU at a later date in June 200 I when the deck wasplanned to be completed.

Here, the STU is installed in the gap between the pier and the deck as in thecase of the Badiwan Bridge. However, for the Badiwan Bridge the connection of theSTU is to the deck slab soffit while for the Second Bassein Creek Bridge theconnection of the STU is to the deck diaphragm which is fairly rigid compared withthe deck slab and thereby not requiring any additional strengthening to transfer theearthquake forces.

Once two steel brackets weighing about 0.25t each were connected to theanchor bolts through shear plates and aligned parallel to the longitudinal bridge centreline and the bolts tightened , the STU weighing about 1.0 tonne was connected to thebrackets at each end by means of the clevis pins. A rebate was formed in the pier headconcrete to facilitate the insertion of the clevis pin.

Photos 6 & 7 show the installation of the STUs for the Second Bassein CreekBridge.

10. CONCLUSIONS

STUs are very viable and economic means of retrofitting existing structuresand designing new structures for suddenly applied loads. They offer the opportun ityto upgrade existing structures with no impact on existing traffic conditions .

228 DESIIPANDE, PATEL & SAKIIADEO ON STU s FOR SECOND BASSEIN CREEK BRIDGE

Photo 6 Photo 7

229

Recent earthquakes in.India have provided a better knowledge of the magnitudeof the f?rce that must be resisted by bridge structures . Unfortunately, these forces aremuch higher than has been assumed in the past and has necessitated upgrading ~nheearthquake zones. As a result of this upgrading of the earthquake zones, significant

c.L PIERI I

-:! 1142 HIGH SlRENGlH S'TlIl ANCHOR BAR:-- 1m '/f.l.~.PPED fOIl CORROSIOO PROTtCl1ON

o j

mo

l.l COLEBRANO 31001cN lUD

15Dxl50x90THl<. GAlVANlSE~& \BUND THREADED ANCHOR Tt

~I

Fig. 7. STU Connection for the Second Bassein Creek Bridge

I IL--.L--

retrofitting of many bridges should be required all over India to reduce the possibilityof catastrophic collapse and loss of lives. Because of very large number of bridges,it is imperative that this retrofitting must be done in a cost effective manner and thiscan be achieved by means of STUs, which is one very economical means ofretrofitting existing bridges without closing the structure for traffic , that has also beenproven to be very durable.

There is an urgent need to make the consultants, contractors and the engineersof the Government Departments all over India aware about the economic benefits tobe derived by using STUs. This Paper is, therefore, a step forward in this directionand it is hoped that the experience gained in successfully installing imported STUsas described in this Paper may help the future users towards procuring the mostappropriate STUs for their structures.

ACKNOWLEDGEMENTS

The Authors are grateful to Shri A.B. Pawar, Secretary (Works) , PWD,Maharashtra, Shri Prafulla Kumar, Director General (RD) & Add!. Secy. (Retd) ,MORT&H , Shri S.c. Sharma, Director General (RD) & Add!. Secy., MORT&H fortheir encouragement. The assistance offered by Techstar Inc., USA and ColebrandLtd., UK in supplying information included in this Paper and cooperation receivedfrom Shri Tony Madathil, Managing Director, Shri Sunny Madathil, Director (projects) ,Bhagheeratha Engineering Company Limited is much appreciated and the Authors arethankful to them.

230 DESHI'AND E, PATEL & SAKIIADEO ON

REFERENCES

STUs FOR SECOND BASSEIN CREEK BRIDGE 231

Appendix-I

I. "Shock Transmission Units in Bridge Engineering" by Dinesh Patel, EngineeringWorld, OctoberfNovember 2000 Issue, Australia. India

Load Test Results for the STU for the Second Bassein Creek Bridge, Mu mbai,

2. "Shock Transmission Units (STUs) for Enhanced Strength of Structure s" byDinesh Patel, The Bridge and Structural Engineer, Vol. 30 No.1 (Part-II) FeblMarch 2000 issue.

3. Fairhurst et. al. "The Design and Construction of Kingston Bridge and ElevatedApproach Rroads" , Glasgow. Struct. Engr, January, 1971.

4. Pritchard. "Shock Transmission Units for Bridge Design, Construction andStrengthening", Constrn Repair, October, 1989.

5. Pritchard . "Stock Transmission Units for Bridge Strengthening". Congress onChallenges to Structural Engineering (International Association of Bridge andStructural Engineers), Helsinki, 1988.

6. Brown. D. "Bridge Strengthening with Shock Transmis sion Units", EleventhWorld Conference on Earthquake Engineering, Acapulco , Mexico , June , 23-28,1996.

7. Medeot, R., and Albajar , L., " The Evolution of Seismic Devices for Bridges inItaly", Tenth World Conference on Earthquake Engineering Madrid , Spain,July 1992.

8. Bertero, V.V., "Seismic Upgrading of Existing Structures", Tenth World Conferenceon Earthquake Engineering Madrid, Spain , July, 1992.

Photo-A.I. Photograph showing STU in 6.3 MN test ri g at AEA Tec hnology