Segmental Box Girdersfor the High LevelWest Seattle Bridge

Rising 150 ft (46,State of Washingispan of the West:example of efficieilong-span structur

the structure’s deE

For many years two bascule bridgesover the west waterway of the

Duwamish River were the only directlink between West Seattle, Washington,and the downtown area. Busy maritimetraffic and an ever-increasing vehicularvolume on the bridges caused serioustraffic congestion, making the need for ahigh level structure apparent.

On June 11, 1978, a fully-loaded12,000 ton (10,900 t) freighter slammedinto the north bascule bridge, severelydamaging the superstructure and powerhouse wall and rendering the bridgeinoperable. This accident left only thesouth bascule bridge, with its four-lanecapacity, to handle all traffic, creating aneven more acute need for a high levelreplacement bridge.

LChing K. Yu, P.E.ManagerContech Consultants, Inc.Seattle, Washington

The initial planning for the ensuingreplacement project has been describedpreviously.1

As shown in the vicinity map (Fig. 1),the entire project was divided into fourunits: West Interchange, Main Span,Harbor Island Approach and East Interchange. A paper published in theNovember-December 1983 PCI JOURNAL describes the design and construction of the three approach structureunits2 This article presents a detaileddiscussion of the main span.

Structures selected for final design included three types: (1) steel box girderswith an orthotropic steel plate deck, (2)cast-in-place segmental prestressedconcrete box girders, and (3) precastsegmental pre stressed concrete box

girders. Only the superstructmof the two concrete altematecovered in this article.

Fig. 2 shows the general planvation of the concrete bridge, wa span arrangement of 375-5(114-180-114 m). The superstnrigidly connected to the tw(piers. The bearings at the end ifree to slide in a longitudinal cbut restrained laterally. The ceniare designed to withhold the tture, creep, and shrinkage deforof the center span.

The overall outlines of the siare identical for both the cast-iand precast schemes. Howev

52 PCI JOURNALJJUIy-August 1984

Rising 150 ft (46 m) over the Duwamish River in theState of Washington, the recently completed mainspan of the West Seattle Bridge is an excellentexample of efficient use of prestressed concrete for along-span structure. This article presents highlights ofthe structure's design and construction.

girders. Only the superstructure designof the two concrete alternates will becovered in this article.

Fig. 2 shows the general plan and ele-vation of the concrete bridge, which hasa span arrangement of 375-590-375 ft(114-180-114 m). The superstructure isrigidly connected to the two centerpiers. The bearings at the end piers arefree to slide in a longitudinal directionbut restrained laterally. The center piersare designed to withhold the tempera-ture, creep, and shrinkage deformationsof the center span.

The overall outlines of the structureare identical for both the cast-in-placeand precast schemes. However, the

minimum concrete strengths at 28 daysare 5000 and 6000 psi (35 and 41 MPa)for the cast-in-place and precast alter-nates, respectively. This allows a thin-ner bottom slab for precast segments atthe center piers. Otherwise, all the con-crete dimensions were kept uniform forboth construction methods. Unlessotherwise stated, the descriptionhereinafter applies to both superstruc-ture alternates.

The bridge section is composed of twin

single cell boxes of trapezoidal shape(Fig. 3). The total deck width of 104 ft 5in. (32 m) provides a roadway of six traf-fic lanes and shoulders. Following aparabolic curve at its soffit line, the

GG^ HARBOR ISLAND

'syWEST SEATTLE

WEST INTERCHANGE MAIN SPAN 4 HARBOR ISLAND EAST1340 \ I INTERCHANGE

5600

Fig. 1. Vicinity map of West Seattle Bridge.

SEATTLE

PCI JOURNAL/July-August 1984 53

U1Af Pier 15 Pier 16 Pier 17 C Pier 18

Duwamish RiverWest Waterway o

West Seattl [QBarrier

Seattle

Expansion \ o ExpansionJoint \\ Joint

375-0 59 -0" 375-0"Span

S 00

125 -0" 125'-0"o Clearance

Envelope

.I. tai/pp rox. Existing Future Channel Elev.0.00Ground

I

Future City DatumWaterway

Fig. 2. General plan and elevation of main spans.

C-0C

zDC

DCc

ODcoA

52-21/2

Box Girder

2" WearingSurface 2.0/.

HL.rn oN r

_

m U—H I 0I I

I ^TYp. 01' N U

mv a

^

0 0co n

17'-83/4"

Section

At Piers 16 and I7

Fig. 3. Typical sections of main spans.

WSB Line52'- 21/2'^

Box Girder

2.0

O

N

24'-II1/4"

Section

At Mid-Span

C

55'-0"

15 1-0 5'-0° 15-0 5-0' 5'-0°

12151<121 5K 121.5 K 12,51<2151< 121.5K 121.5K

8 Axles at 21.5 K each; 172 K TotalTransver wheel spacing 0-8' O.C.Tire pressure 80 psi, width 12"

Vehicle Load

57'-6"

3.0 1</ft..HHHH.3.0 K per linear foot x 57.5'= 172 K Total -may be used where wheel loads do not govern.

Eauivalent Uniform Load

Fig. 4. Assumed overload due to vehicle load and equivalent uniform load.

depth of the girder varies from 30 ft (9.1

m) at center pier to 12 ft (3.7 m) atmidspan. The slightly arched form of thesuperstructure provides not only effi-cient use of concrete materials and pre-stressing, but is also aesthetically ap-pealing.

Design CriteriaIn general, the structural design fol-

lows AASHTO Standard Specifications.3For subjects not covered by AASHTO,other commonly used codes for seg-mental construction were adopted.4•5,6

In application of AASHTO loadingcombinations, the transverse design in-

cluded a temperature differential of 10deg F(6 degC) warmer or5 deg F(3 degC) cooler at the outside than the insideof the box. A temperature for the top slab18 deg F (10 deg C) warmer or 9 deg F (5deg C) cooler than the rest of the sectionwas incorporated into the longitudinaldesign.

In addition to the interstate highwaybridge loadings specified in AASHTO,Article 1.2.5(G), the bridge was also de-signed for an overload vehicle or itsequivalent (Fig. 4).

Allowable concrete stresses in tensionspecified in AASHTO, Article 1.6.6,were modified to account for frequentsegmental joints in the superstructure

56

)overn

ad

9quivalent uniform load.

emperature differential of 10:g C) warmer or5 deg F (3 degit the outside than the insideA temperature for the top slab.OdegC)warmeror9degF(5ler than the rest ofthe sectionorated into the longitudinal

ion to the interstate highwaydings specified in AASHTO,.5(G), the bridge was also der an overload vehicle or its(Fig. 4).

le concrete stresses in tensionin AASHTO, Article 1.6.6,

iified to account for frequentjoints in the superstructure

and to provide better control over deckslab concrete cracking. Table 1 showsthe allowable prestressed concrete tensile stresses for cast-in-place construction, applicable to the design of bothtransverse deck and longitudinal crosssections.

The precast design’s allowable stressfor the transverse deck section remainsthe same as in Table 1. However, in recognition of reinforcement discontinuityat segmental joints, allowable longitudinal tensile stress requirements aremore stringent. In fact, minimum compressive stresses are required for this direction (Table 2). Allowable compressive stresses for each construction are inconformance with AASHTO requirements.

A dense concrete or latex-modifiedconcrete wearing surface of 2 in. (51mm) nominal and 1Y2 in. (38 mm)minimum thickness over the bridge

deck was specified. An additionalsuperimposed dead load of 25 lb per sqft (1.2 kN/m2) of deck surface was designed for as a future surfacing allowance.

Construction SequenceAs shown in Fig. 5, the suggested con

struction sequence may be divided intofour stages:

Stage 1: Casting the pier table overboth the north and south columns at theeast side of the river. Post-tensioning allthe tendons in the pier table and placingtwo sets of form travellers in position,one pair for each box girder. For thepurpose of reducing the unbalancedpier moment, the pier table is offset ahalf segment length from the centerlineof the pier.

Stage 2: Performing the balanced freecantilever construction by casting 16 ft 6

Table 1. Allowable tensile stresses in psi (fe) for cast-in-placeconstruction.

All tension forceNo additional resisted by additional

Loading combinations reinforcement reinforcement

Dead+ Liveor 0 O<ft<3f7

Dead + Construction

All other combinations 3 3 ,J7 < f < 6 J7Note: f = compressive strength of concrete in psi at 28 days or, for dead and

construction load combination, at time of stressing.

Table 2. Minimum compressive stresses in psi for precastconstruction (longitudinal design only).

Deck slab Deck slablocal stresses local stresses Other

Loading combinations not included included area

Dead ÷ Liveor 200 100 30

Dead + Construction

All other combinations 30 30 30

Note: 1 psi = 0.006895 MPa.

‘IPCI JOURNAL/July-August 1984 57

r-

Th Forroveller

CE Pier 17(East)

j L c5outh Colurns

Stage I - Build East PierTable

SpanPierl6(West

in. (5 m) segments on alternate sides ofthe pier table. Stressing half of thetransverse tendons in each girder fromthe outboard edge of the deck slab, asshown in Fig. 6. The other half will bestressed only after the longitudinal clo-sure between the two girders is cast.

Progress of the two parallel girdersshould be approximately the same, witha difference of no more than two seg-ments. This is to minimize possible mis-alignment of the continuous transversetendons due to concrete creep effect.

Stage 3: After the balanced cantilevers

375-0" , 590,-0°

375-0

t North Columns

^i '1TemporarySupports

dge

.J ® 4a ^ rLongitudinal Closure Pour Closure PourDiaphragm 0

Ex ponsion ExpansionJoint Joint

Stage 4-Complete the whole Bridge

Fig. 5. Suggested construction sequence of main spans.

Stage 2-Free Cantilever Const ructEast Side

ri

Stage 3- Complete East half of Bri

58

reach their limits, moving the centerspan form travellers to the west piertable, installing temporary supports nearthe edges of the side span cantileversand continuing segmental constructionuntil the girders land on the end pier.

Stage 4: Repeating the construction asdescribed above for the west half of thebridge. Pouring the center and lon-gitudinal closures, stressing all the con-tinuous transverse tendons and com-pleting other work.

The construction sequence for theprecast scheme is basically the same asdescribed above. However, to facilitatetransportation, handling and erection of

the precast units, the segment length isreduced to between 6 ft (2 m) at pier and12 ft (4 m) at midspan.

Prestressing SystemLongitudinal tendons consisting of 12

x 0.6 in. (15 mm) diameter strands werespecified in the design. As shown in Fig.7, the cantilever tendons are anchored,three at each web, on the bulkhead faceof each segment, the continuity tendonsat buttresses built up from the slab. Thecantilever tendons follow the profilegrade and the continuity tendons followthe soffit line.

Stress after completion Longitudinal Closure Pourof Segment

II

II

4-1IIA

Stress after Longitudinal Closure Pour

Plan

WSB LineBox Girder

Box Girder3'-6°(Closure)

TiDiscontinuous

ons

Section A-A

II Stressing EndI Dead End

Fig. 6. Plan and section of transverse tendon details.

PCI JOURNAL/July-August 1984

59

rn0

26-1/4

1 1/4 " Dia.Deformed BarBox Girder

(Transverse Tendon) Anchor Plate Longitudinal Tendons Symm. abt.

!''." °O oo 0 00000

00 0 001 000000° o

012x0.6°Dia. Strands ° 1(Cantilever Tendon) °

11 1 1/a° Dia. Bar (Vertica

11 Web Tendon )

11 Typ. Stressing Buttress

11 Anchor Plate

1 ^ o ;.. 0 0 0 0

12x 0.6" Dia. Strands (Continuity Tendons)

Fig. 7. Tendon arrangement inside box segment.,

Straight tendons are preferred fortheir ease of installation and ability tominimize friction losses. They also pre-vent the necessity of having a wide webto accommodate the anchor plates, asthey are all anchored away from thewebs.

Additional longitudinal bar tendonsare installed across the deck slab of theclosure segments. They are required toresist the negative moments induced bylive loads before creep-induced mo-ments settle in.

For transverse and vertical tendons,1 1/4 in. (32 mm) diameter deformed highstrength bars are preferred. The screwtype bar tendon anchorages reduce theseating loss to about lho in. (2.5 mm),rendering them most effective forshort-length prestressing. However,

strand and wire systems providingequivalent effective forces are also per-mitted.

Corrosion ProtectionFor corrosion protection of reinforcing

bars and prestressing tendons, aminimum concrete cover of 1Y2 in. (38mm) was specified for the deck slab inaddition to the wearing surface. Epoxycoating was required on all top mat deckbars as well as web bars having less than3½ in. (89 mm) concrete cover, mea-sured from the top of the monolithical-ly-cast deck slab. To eliminate the needfor epoxy coating long web bars, a spe-cial detail was developed (Fig. 8).

One of the following measures mustbe taken to protect the transverse ten-

PCI JOURNAL/July-August 1984 61

dons, depending on the type of tendonsused: (1) epoxy coating the deformedhigh strength bar tendons, (2) usingplastic ducts with spiral corrugations,either polyethylene or polyvinyl-chloride, (3) using epoxy coated metallic

ducts.Because the longitudinal tendons are

located well below the riding surface,galvanization of the metallic ducts isconsidered adequate for their corrosion

protection.

Special RequirementsThe following prestressing-system

related requirements were specified:

1. Pull-out tests: If epoxy-coated flator plastic ducts are used for transversetendon sheathing, pull-out tests must beperformed to prove the bonding-strength adequacy of the ducts. Thetests should show that a force equal to 40percent of the ultimate tensile strengthof the tendon, 0.4 fpu A,,, can be trans-ferred from the tendon through the ductto the surrounding concrete at a lengthof 2 ft 6 in. (0.76 m). A total of 12 pull-outtests should be conducted of which 10must pass the bonding requirement.

2. Lift-off tests: As short tendons areapt to lose too much prestressing forcedue to slip at anchorages, tendons short-er than 20 ft (6 m) must be equipped

with an anchorage device which allowslift-off checks and restressing. This re-quirement applies to most vertical ten-

dons.

3. Water freezing prevention: Covers

and plugs should be provided to preventrain water from entering vertical ducts.As a complete seal of ducts at deck levelis always difficult, some water will in-evitably be collected, and its sub-sequent freezing could cause cracks inthe webs or delamination of the bottomslab. Unless a complete seal can beachieved, the ducts should be filledwith a mixture of glycol antifreeze andwater when the temperature falls below

45 F(7C).

Design ConsiderationsAlthough sections subjected to pre-

stressing forces were designed accord-ing to allowable stress requirements,their ultimate strengths must bechecked by load factor design, asspecified by AASHTO. For the lon-gitudinal direction, allowable stresschecks are performed at all constructionstages, i.e., when a new segment isadded, a form traveller advanced or re-moved, additional tendons stressed anda closure poured. In addition, stressconditions at completion of the bridge,18 months after completion, and at in-finity must be evaluated to insure thesoundness of the structure with all pre-stress losses and creep effects consid-ered.

In the transverse direction, the crosssection was analyzed as a frame struc-ture. In order to take longitudinal dis-tribution of wheel loads into considera-tion, influence surfaces prepared byHomberg7 were used to determine theequivalent beam fixed end momentsprior to the frame analysis. The methodis described in detail in the PTI BoxGirder Bridge Manual."

The load factor method was used fordesigning reinforcement in the websand bottom slabs, whereas allowablestress design was used to determine thetransverse tendon spacing and profiles.Since only half of the transverse tendonsrun continuously across the longitudinalclosure, dead load stresses and second-ary moments introduced by the discon-tinuous tendons need to be estimated.This is done by using a separate struc-tural model consisting of only one boxgirder section.

Vertical bar tendons were selected asthe main reinforcement for shear force.However, in applying AASHTO designequations specified in Article 1.6.13,half of the nonprestressed reinforce-ment required for transverse flexure de-sign is considered effective in resistingshear forces. This is justified, since po-

62

Approach Structure Main SpanI ft

1rD

End Pier

D=8+0.02L+0.08HD1 = D/4

where D and D i are in inches.L Length of bridge deck between

expansion joints, in feet.H= Pier height in feet

Fig. 9. Minimum gap and seating length requirement.

tential shear failure normally originatesat the half-depth location of the webwhere transverse bending stresses arenot critical.9

For seismic design, recommendationsdeveloped by the Applied TechnologyCouncil (ATC-6)10 were followed. Thedesign objective is to ensure that in anearthquake, with a 50-year probability ofoccurrence, the bridge will remain usa-ble for emergency passage, although itmay suffer repairable damage. This cor-responds approximately to designingthe ultimate strength of the bridge for aload equivalent to that induced by anearthquake of a 500-year return period.The structure is designed to allow plas-tic hinge formation at the pier top andbottom only when its failure mechanismis reached.

Special consideration was given to theearthquake requirements for expansionjoints and restrainers. Fig. 9 schemat-ically shows the gap and seating lengthas specified in the design. The

minimum seating length, D, was estab-lished in accordance with Article 4.9.1of ATC-6, and the gap distance, D l , waspredicted by response spectrumanalysis." This provision stipulates thattemperature induced movements mustbe added to D, in determining the de-sign expansion joint gaps.

To provide a positive horizontal link-age between the main span structureand the approaches, earthquake re-strainers were installed at each expan-sion joint. A sufficient number of earth-quake restrainers were selected at

each expansion joint to provide a totalultimate strength equal to 15 percent ofthe weight of the main span structure.The length of the restraining cables issuch that they will accommodate with-out rupture to the total joint movementduring an earthquake. In order to trans-mit this restraining force to the remain-der of the superstructure, additionaltendons were provided at the weak partsof the side spans.

PCI JOURNALJJuly-August 1984 63

Contract AwardingA total of six bids was received on

October 1, 1980: five for cast-in-placebox girders and one for steel box girders

with an orthotropic steel plate deck. Nobids were received for the precast con-crete superstructure alternate. The bidsfor the concrete structure varied fromapproximately $24 to $28 million, and

375'-0" 590'- 0 375'-0"

CE North Columns

^S olumns

Stage I - Build East Pier Table

O Formtroveller

(jSponPier 16 Q Pier 17(West) I (East)

104 -S

0

Stage 2 - Free Cantilever Construction,East Side

11

L .l

Closure PourO

Stage 3 - Complete East Half of Bridge Falsework

Expansion Joint O Closure Pour Expansion Joint

Stage 4 - Complete the whole Bridge

Fig. 10. Actual construction sequence.

64

Table 3. Comparison of tendon system from as designed and as built condition.

Tendon location As designed As built

Longitudinal 12 x 0.6 in. (15 mm) 0 strands 19 x 0.5 in. (13 mm) (A strands

Transverse Epoxy coated 1'/a in. (32 mm) 4) 4 x 0.6 in. (15 mm) 4) strands

deformed bar with epoxy coated flat duct

Vertical 1' in. (32 mm) 4) deformed bar 6 x 0.5 in. (13 mm) 0 strand

the sole steel bid was approximately $40million. The winning bid put the con-struction cost of the structure at about

$170 per sq ft ($1935 per m 2). A break-

down of the bid is as follows:Common Items (mobilization,

utilities, etc.) .........$3.3 millionSubstructure (steel pipe piles,

foundation and reinforced concretepier columns) ........$9.1 million

Superstructure (post-tensionedstructure) ...........$11.4 million

I Construction ModificationsBasically, the bridge was built in ac-

cordance with the conforming cast-in-place design. However, the followingmodifications were furnished by thecontractor:

1. Instead of casting the two box gird-ers separately, the contractor elected topour the complete bridge section all at

once. This was accomplished by tyingtwo parallel form travellers togetherduring concrete casting. This modifica-tion eliminated the need for leaving alongitudinal closure between the twobox girders. Since all transverse tendonswere made continuous, any possiblemisalignment of the transverse tendonducts was avoided. This simplified theconstruction but required a more inten-sive labor force, reducing flexibility of

manpower allocation.Fig. 10 indicates the construction se-

quence selected by the contractor. Thegirder cross section was kept the same asthat shown in Fig. 3. The segmentallength of 16 ft 6 in. (5 m) specified by the

designer was used in construction.2. As permitted in the specifications,

the contractor had the option of select-ing any post-tensioning systems pro-viding they met the requirementsspecified in the special provisions.

Table 3 compares the designed systemswith the contractor's choices.

Although the contractor replaced the12 x 0.6 in. (15 mm) diameter strandswith 19 x 0.5 in. (13 mm) diameterstrands for the longitudinal tendons, thepattern, distribution, and anchorage lo-cation of the tendons remain the same asshown in the design drawings. Thespacings of vertical and transverse ten-dons were adjusted to provide theminimum effective forces required by

the designer.

3. As described previously in the con-struction sequence (Fig. 5), the designerrecommended that the unbalanced partsof the side spans be built segmentally bythe form travellers, with the help oftemporary supports. However, the con-tractor elected to construct that portionof the side span totally on falsework(Fig. 10). To allow room for adjustingmisalignment, a 3-ft (0.91 m) wide clo-sure was provided between the end ofthe side span cantilever and thefalsework-supported portion. Since thecontractor dismantled the form travel-lers in the proximity of the east end clo-sure prior to making the closure pour,clamping the ends together proved to bedifficult, and concrete block counter-weights were placed on the higher sideof the two free cantilevers to achievevertical alignment.

PCI JOURNALIJuly-August 1984 65

Concluding RemarksThe construction went smoothly with

only a few delays at the beginning of thejob. The first two segments took about 2months to complete. Once the crews be-came familiar with the repetitive opera-tions of advancing the form travellers,

Fig. 11. West Seattle Bridge, halfwaythrough construction.

placing reinforcing bars and tendonducts, concreting, stressing the tendons

and grouting the ducts, their pro-ductivity dramatically improved. Nearthe end of construction of each balancedcantilever, it was not uncommon for twosegments to be completed within aweek.

A special feature of this project wasthe close involvement of the consultantsin nearly all aspects of the construction.Continuous review of construction prog-ress and daily field inspection were pro-vided by the design engineers. This ap-proach proved to be effective in ensur-ing that the construction met the intentof the contract documents.

There was one incident whichexemplifies the importance of carefulfield inspection. Inspectors noticed thatthe brownish color of a freshly cast seg-ment appeared to be abnormal. It waslater discovered that an undue amountof fly ash had been accidentally mixedinto the concrete by the supplierthrough a mechanical failure in themixing process, reducing the concretestrength considerably.

Fortunately, the mistake was caughtbefore any forward segments were castand corrected by jackhammering off the

Fig. 12. West Seattle Bridge, nearing completion.

66

Fig. 13. West Seattle Bridge, completed and in-service.

defective segment. Had additional seg-ments been poured without the correc-tion, devastating consequences could

have resulted.Figs. 11 through 13 show various

views of the bridge during constructionand after completion. The bridge wasopened for traffic in November, 1983.During the last 8 months the structurehas performed with total satisfaction.

I AcknowledgmentsThe following are those chiefly re-

sponsible for the realization of the WestSeattle Bridge, and their areas of re-sponsibility:

Owner: The City of Seattle,Washington; Bruce Wasler, ProjectManager.

Prime Consultant: West SeattleBridge Team, composed of: Anderson-Bjornstad-Kane-Jacobs, Inc., Kramer,Chin & Mayo, Inc., Parson Brinckerhoff,and Tudor Engineering Co.; Thomas A.Kane, Project Manager.

Contractor: Kiewit-Grice.Superstructure Subconsultant: Con-

tech Consultants, Inc.; M. C. Tang and J.B. Louie, Principal Designers; PaulBrallier, Construction Inspector.

REFERENCES1. Kane, T. A., Carpenter, J. E., and Clark,

J. H., "Concrete Answer to Urban Trans-portation Problems," Concrete Interna-tional, August, 1981, pp. 85-92.

2. Kane, T. A., Carpenter, J. E., and Clark,J. H., "Approach Spans to the West Seat-tle Bridge," PCI JOURNAL, V. 28, No. 6,November-December 1983, pp. 58-67.

3. Standard Specifications for HighwayBridges, 12th Edition, American Associ-ation of State Highway and Transporta-tion Officials (AASHTO), Washington,D.C., 1977 (with 1978 and 1979 InterimSupplements).

4. ACI Committee 318, "Building CodeRequirements for Reinforced Concrete(ACI 318-77)," American Concrete In-stitute, Detroit, Michigan, 1977.

5. CEB/FIP Joint Committee, Interna-tional Recommendations for the Designand Construction of Concrete Struc-tures, Comit6 Europeen du BE ton/Federation Internationale de la Pr6con-trainte, Cement and Concrete Associa-tion, London, 1970.

6. Post-Tensioning Manual, Third Edition,Post-Tensioning Institute, Phoenix,Arizona, 1981.

7. Homberg, Hellmut, Fahrbahnplattenmit Veraenderlicher Dicke, Springer-Verlag, New York, N.Y., 1968.

8. Post-Tensioned Box Girder Bridge Man-ual, Post-Tensioning Institute, Phoenix,Arizona, 1978.

9. Jungwirth and Baumann, "Shear Designwith Dywidag Prestressing System," In:Finsterwalder Festschrift, Verlag G.Braun, Karlsruhe, 1973.

10. ATC-6 Seismic Design Guidelines forHighway Bridges, Applied TechnologyCouncil, Berkeley, California, 1981.

11. Mahoney, T. F., and Clark, J. H., "Seis-mic Design — West Seattle Bridge,"Paper Presented at the Northwest BridgeEngineers' Seminar, Olympia, Wash-ington, October 4, 1983.