[PATEL] Shock Transmission Units for Earthquake Load Distribution

\ Paper No.475

"SHOCK TRANSMISSION UNITS (STUs) FOR EARTHQUAKE LOAD DISTRIBUTION ON THE WORLD BANK FUNDED SECOND BASSEIN CREEK BRIDGE IN MAHARASHTRA"t By D.B . DESHPANDE· , D.l PATEL··

& R.V. S AKHADEO·· ·

CONTENTS Page

Introduction 2. Description of STU 3. STUs for Strengthening of Existing Bridges 4. STUs for New Continuous Bridges 5. Procurement of STUs 6. Selection of STUs for Second Bassein Creek Bridge 7. Design Submission for STUs 8. Load Testing of STUs 9. Installation of STUs 10. Conclusions 1.

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SYN OPSIS The Seco nd Bassei n Creek Bridge on National Highway 8 is among one of the few bridges in the world constructed with Shock Transmission Units to distribute earthquake loading among piers installed with fixed and unidirect ional pot bearings. This is the first road bridge in India where STUs imported from overseas are installed. There are only a few countries in the world where STUs are manu factured at present and until now the specification for an STU is not covered in design codes of any country of the world. Presently , efforts are being made to include specification for STU in the American Association of State Highway and Transportation Officials Specification (AASHTO) by Colebrand Ltd . of UK. They asked the Highway Innovat ive Evaluation Centre (HITEC) - a service center of the ASCE Civil Engineering Research Found ation to convene a panel of experts to develop an 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 joi nts. etc. Unfortunately, testing ofSTUs is quite an expe nsive business and

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

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DESIIPANDE, PATEL & SAKIIADEO ON

. CREEK BRIDGE STU s FOR SECOND BASSEIN

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testing cost depends on the number and type of tests to be carried on an STU to be used for a particular applicati on. In the absence of specifications for the design and testing, manufacture rs of the STUs have to be relied upon to provide the appropriate STU and the relevant tests on the STU for a particular bridge. The usage of STUs is presently growing as engineers round the world 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 STUs were 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 the Second Bassein Creek Bridge. This Paper is, therefore, written apart from providing technical and other information with a purpose to guide the future users of the STUs in procuring, selecting, testing and installing the 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), is designed to be connected between bridge members to form a rigid link under rapidly applied loads, such as, braking and seismic, etc. but to move freely under slowl y applied load s, such as, temp erature and creep shrinkage. Such a temporary fixed connection facil itated by an STU allows load sharing of a suddenly applied force . Longitudinal traction, brak ing forces, vehicle impact and seismic load, etc. are examples of such short durat ion horizontal loads applied suddenly to bridge structures, transmitting short durat ion shock or impact forces . The unit is connected between elements of bridge structures at expansion joints or near the bearin gs between the superstructure and the substructure subj ect to long term separation movements due to creep, shrinkage and temperature to ben eficiall y share among them short durat ion loads applie d to any one of the substructure elements. Shock transmission units work on the principle that rapid passage of viscous fluid through a narrow gap , orifice or valve generates considerabl e resistance whil e slow passage gener ates only minor resistance. 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 Carquinez Bridge on Interstate 80 in California, US , (Pho to I) in 1927 to distribute seismic loads to more than one pier of this cantilevered stee l trusses with suspended span type bridge. The next application of an STU in the US was for the San-Mateo Hay ward Bridge in 1967. 4 Oil-based STUs were installed at the expansion joint in the 230 m main span. STUs have also been used in Europe. The 5 km long Oosterschelde Bridge comp leted in the Netherlands in 1965, used STUs extensively. STUs were also utilized on the approach spans to the Kingston Bridge, completed in Glasgow in 1970.

Photo I.

. I terstate 80 in Califor nia, US, Th C quinez Bndge on n e ar STU was fir st used where an

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. . I supported bridges, load sha~ng by In new continuous and multl- span s;mPr~sulting in smaller design section for means of STU s can be used advantageous~, f both steel and concrete cable staye d the substructure elements. S!~S can be u~~s l~:ements of deck duri ng an earthquake. and suspension bridges to ehmmate ~~ge ~ eleva ted light rail structures as we ll ~n~ STUs can also be used in bascu.l~ bn ges a~hrou h an expansion jo int. F~r .o~he~ CIVil in bridge parapets to share colhslO~ f? rces STUs gcan provid e additional n gldlty rn the . engineering structures , such as, .bU11d.m g~~ s an structures and can also be used ~o frame structure, such as, parkmg. simp , p . event STUs are also used to resist strengthen adjacent bui1din~s dunn~ a sels:~ water' indu stries. Light rail elevated surge forces at bends in plpehnes in g.as . (more cars) and take the increased a heavier tram b t ture structures with ST U scan ca rry . without a change to the su s rue . braking forces associated with the load I~crea~e which have been found inadequate STUs can be made to strengthen support~ng piers, which have sustained damage . ti d braking forces, or . f STUs due to increase m the trac IOn a~. t advantage is that the installatlon 0 caused by corrosion. The other s\gmfiCa\ ' d to traffic unlike other methods for can be carried out without c10smg the n ge strengthening the piers. 2. DESCRIPTION OF STU

. machined cylinder with a transmission The STU as shown in Fig. 1 consists of a d at' the other end to the piston d t the structure an T rod that is connected at one, en ?, the c linder is a spec ially fonnulated Sl Ic~ne inside the cylinder. The mediuro wlthm ~ rmancv characteristics of a speCific compound , precisely designed for the ~er ~emperature chan ge in the structure or project. During slow movements caused Y

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. transport ation f the mam . d as been deslgne . . 1958. It is one 0 re recent stru cture bUl\t I~O The complete retr.o~t : ut the retrofittin g and the other a;::~ Francisco and Sacran;~fo~r Beatty has carne links between M H ill. Contrac~o~ onsultant CH2 US$70 ml\hon . by c ost of some work S at a c

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

a total designed capacity of five times the requi red deck design braking and traction longitudinal loads. As shown in Fig. 3, by placing five new STUs at bearing level on the free abutments and piers, it is possible to share out the traction and braking load acting 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 significantly to give a total designed horizontal load capacity only some 20 per cent of that required initially. The Carquinez Bridge in California, Photos I & 2, is a good example of strengthening of an existing bridge for revised seismic loading. The Carquinez crossing 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,

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is that t WIdth 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 re Wit concrete cais russ superstructure 0 er sUPPOrt and the rn and two sic span~ between the sons. and steel piles n steel-braced trus Y both consist of ste( Intenor expan sion .C ~ntllever sections an~ :~~dations. Both sbS.~bstructure sUPPOrt move during normJ~'ntS. These STU; W ~ to transmit 10 " ge~ use suspen dc( re an earthquake. a temperature variati: desIgned to allow ~gltudlnal loads acros, ns, but provide structur:rPan~ionjoints tc' Apart fro COntinuity durin retrofitting Work m strengthening of th g hYdraulic STU s tiOr the 1958 brid e superstructure d s. ge structure inclUded r:pn the foundations th lacement of .' e the eXIsting b ' These eXisting ST ndge as shou~ ' F' Us, located at th ' e expa . . · Id .,,, In Ig 4 Yre . WhIch do not nSlOn Joints On t .capacity of t capacIty, Photo he truss chords ar have enough ca aci he 335 m spans ofth In. geometry

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4. STUs FOR NEW CONTINUOUS BRIDGES

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

4.1.

Second Bassein Creek Bridge, Mumbai, India

The Second Bassein Creek Bridge is a good example of a new multi-span continuous bridge where installations of STUs have saved time and money in construction of the caisson foundations. It is located 25 m upstream beside the existing bridge on Mumbai-Ahmedabad National Highway No.8 just outside Mumbai near Ghodbunder at the confluence of Ulhas river and the Arabian Sea. The bridge was designed by Consultants from India and proof checked by an agency from Australia. It is being constructed by Indian firm and supervised by the World Bank appointed Supervision Consultants of Canada in joint venture with American & Indian Consultants. Fig. 5 shows the General Arrangement of Second Bassein Creek Bridge . The eight span igational spans in the middle of length 114.7 m each with two adjacent spans of length :'7 .35 m constructed as balanced cantilevers as seen in Fig. 5 and made continuous by pour ing closure segment. The end spans comprise two cont inuou s spans with one span of 57.35 m and the other of 48.5 m making the total length of the bridge 555 .8 m. The cantilever box girder decks vary in depth from 7.0 m to 3.5 m and are being constructed simultaneously using three travelling formworks, one on each of the piers P3, P4 & P5. The box girder end spans have constant depth of 3.5 m and are constructed using conventional method of ground supported staging and steel trusses over the creek water supported on the piers. The total width of the bridge of I 1.Om includes roadway width of 7.5 m and footway on either side of 1.5 m. The bridge is sup ported over nine Caisson foundations of wh ich three Caissons A I, A2 & P7 are constructed as ground Caissons and the remai ning six Caissons from P I to P6 as float ing Caissons sunk through creek water to basalt rock strata.

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CapaCity STVs r. or Ca r q uinez Bridge

The site is very difficult for the construction of the Caissons , as there are daily two 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 curre nts with velocity of 3 m/s and during the monsoon heavy floods are encountered. The depth of the water

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D ESIIPANDE,

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und" the twO ,,,,u navigation , p, n' is "ound '0 10 and tho av,,,g' ""iiy ,ida' al of 4.25 10 with an av""g' vd"ity of 2.4 mI' · An thes ,it< variation is of tho onk' 'onditio uav mad' tho Cai"on' ' on,,,,,,'ion a diff"un and ri'ky task foe tho ",n,,,,m