Special Report

Design and Constructionof Linn Cove Viaduct

Jean M. MullerChairman of the Boardand Technical DirectorFigg and Muller Engineers, Inc.Tallahassee. Florida

James M. BarkerAssistant Vice President/Projects

Figg and Muller Engiineers, Inc.Mt. Pleasant, South Carolina

The Blue Ridge Parkway, owned bythe United States National Park Ser-

vices (NPS), is a unique transportation/recreation network. Built along the crestof the beautiful Blue Ridge Mountainsin North Carolina, the 469 mile (755 km)long highway attracts millions of vaca-tioners each year with its beautifulscenery and facilities for camping, hik-ing and picnicking.

Through the years the NPS has madeevery effort to preserve the naturalbeauty of the roadway and to provide ac-cess to adjacent areas with parking areasand nature trails. All highway construc-tion is in accordance with the "park con-cept." For instance, fill must be placedand granite clad retaining walls builtbefore the side of a mountain can be cut.All bridges are built with stone-cladcurbs and wingwalls to blend with thesurrounding mountain landscape.Bridges must also have open handrails

so visitors will have an unobstructedview as they journey through the 479mile (755 km) park.

Construction of the Parkway began in1933 and was completed in the late1950's with one exception: a 5-mile (8kin) length around privately ownedGrandfather Mountain, which is one ofthe leading tourist attractions in NorthCarolina, The National Park Service hadsettled numerous location and right-of-way problems through the years, butnone approached the magnitude of thatcentered on Grandfather Mountain,

The owner of Grandfather Mountainwas insistent that construction of theParkway must not harm or be obtrusiveto the natural scenic beauty found there.Since the owner shared the samephilosophy, the Federal Highway Ad-ministration (FHWA), which suppliesengineering services for the Parkway,studied alignments and alternate routes

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Several innovative design and constructiontechniques were used to build the Linn CoveViaduct — a 1243 ft (379 m) long, S-shaped precastprestressed segmental concrete bridge — situated inone of the most scenically beautiful regions of theUnited States.

PCI JOURNALISeptember-October 1985 39

Fig. 1. Finished view of the Linn Cove Viaduct set against the beautifully rugged BlueRidge Mountains.

for approximately 10 years.Finally, a route which could not be

seen from the mountain top was chosenaround the eastern mountainside. Tominimize construction damage to thearea, the roadway alignment was raisedabove the mountainside by use of a via-duct structure.

Since building the viaduct structureby conventional methods of bridge con-struction would have done irreparabledamage to the environmentally sensi-tive area, the search for an acceptableconstruction method became a chal-lenging engineering problem.

DESIGNThe site within the limits of the Linn

Cove Viaduct (Fig. 1) is a rugged andsteeply sloped terrain with relativelyheavy ground vegetation and boulderout-croppings. A natural stream crossesthe bridge near the northern end. Thescenic location, with its protrudingboulders and the requirement for theirprotection and preservation, was themajor factor to be considered in the de-sign. Although rock existed throughout

the site, it generally occurred belowa relatively shallow overburden ofsoil surfaced with decomposed vegeta-tion.

The structure proposed for this projectwas a precast post-tensioned segmentalconcrete box superstructure, eight spansin length with both horizontal and verti-cal curvature conforming to the naturaltopography. Progressing from south tonorth, the spans are 98.5, 163 ft (30, 48m), four at 180, 163 and 98.5 ft (55, 50and 30 m) in length. Each span is com-prised of 9 ft (2.7 rn) deep single cellboxes of 8.5 ft (2.6 m) nominal lengthlocated between 5 ft (1.5 m) long piersegments.

The Linn Cove Viaduct is probablyone of the most complex bridges everbuilt; certainly, it must be the mostcomplicated concrete segmental bridgeever constructed. Three major factorscontribute to its complexity: environ-mental constraints and inaccessibility ofthe site and the vertical and horizontalalignment.

The bridge was literally built on theside of a mountain which had to remainin its natural state. There was only one

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Fig. 2. Construction overview of Linn Cove Viaduct. This bridge is the first segmentalstructure in the United States to incorporate progressive placing erection.

way in or out, namely, over the com-pleted portion of the bridge. The hori-zontal alignment includes spiral curvesgoing into circular curves with radii assmall as 250 ft (76 m) and with curvaturein two directions, which gives thebridge its S shape (Fig. 2). A small por-tion of the bridge is on a horizontal tan-gent. The superelevation goes from afull 10 percent in one direction to a full10 percent in the other direction in 180ft (55 m) transitions and part way backagain within the length of the bridge.

No two of the 153 superstructure seg-ments have the same dimensions, andonly one of the segments in the entirebridge is straight. When the verticalcurve and tangential alignment are con-sidered, the Linn Cove Viaduct includesalmost every kind of alignmentgeometry used in highway construction.

The foundations consist of cast-in-place abutments at each end and sevenintermediate precast segmental boxpiers bearing on 20 ft (6.1 m) diameterfootings. Both the abutments and pierfootings are supported on reinforced 9in. (229 mm) diameter microshaftsdrilled into the underlying rock for-

mations.The bridge is 1243 ft (379 m) in over-

all length with a curb-to-curb roadwaywidth of 35 ft (11 m). The final roadwaysurface is a 2 in. (51 mm) bituminousoverlay with waterproofing membrane.

The structure was designed in 1979 inaccordance with the AASHTO StandardSpecifications for Highway Bridges(Twelth Edition 1977) except for thosedesign and construction techniquesparticular to post-tensioned segmentalconstruction. All superstructure andsubstructure precast segments were de-signed for a 28-day concrete strength of6000 psi (41 MPa) with 4000 psi (28MPa) specified for release of the forms.In addition to the longitudinal post-tensioning tendons, the top slab was de-signed to be transversely post-tensioned, All permanent post-tensioning was done with' in. (13 mm)diameter, 270 ksi (1863 MPa), low re-laxation strand tendons.

To minimize the environmental im-pact on the construction site, the majorportion of the bridge was to be built with-out the use of access roads. The onlypermitted construction road was from

PCI JOURNAL' September-October 1985 41

the south abutment of the second pier, adistance of approximately 260 ft (79 m).From this pier to the end of the bridge,the construction was to be from the pre

-viously completed portion of the deck.

No trees other than ones directly be-neath the bridge were allowed to be cut.Each tree had to be evaluated separatelyand approved for cutting. All foliage ad-jacent to the bridge had to be protected

li TT rTTT'T'T -FT-FIL LLILLLi LJ_LJ

Permanent Permanent__.4.f[Pier Support ^ Pier

J,LL

Fig. 3. Schematic view of the progressive placing erection method.

HALF SECTION AT TYPICAL HALF SECTION

POST-TENSIONING BLOCK THRU SEGMENT

Fig. 4. Typical cross section of precast segment. The webs and bottom stab werethickened to carry the stresses due to the extreme curvature. Both temporary andpermanent post-tensioning tendons were anchored at the intermediate stiffeners shownon the left side of the drawing.

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by a silt fence located along the entirelength of the bridge. Any constructiondebris on the outside of the silt fencehad to he immediately retrieved.

None of the boulders could be de-faced during construction, except in in-stances of rock bolting. The boulderswere covered to prevent concrete, groutor epoxy stains. Any extraneous materialon the boulders was immediatelycleaned off.

The streams flowing across the bridgealignment were protected from siltationor other contamination. Water qualitywas constantly monitored.

Because of the severe environmentalrestrictions, the bridge could not heconstructed by conventional methodsand a system was devised in the designto construct it from the top. This re-quired a progressive scheme which en-abled segments of the bridge to hetransported across the previously builtdeck and assembled into final position.

Precast concrete was chosen overcast-in-place segments because the re-gion has a relatively short constructionseason. By choosing precast concrete,production of the segments could con-tinue during the winter. Additionally,the precast segments were made underplant-controlled conditions which led tohigh quality concrete.

The progressive scheme (shown inFig. 3) is considered feasible and struc-turally satisfactory for span ranges offrom 150 to 200 ft (46 to 61 m). For thesespan lengths, a constant depth box gir-der has proven to be the most economi-cal. After visits to the site and analysis ofthe possible locations of piers and tem-porary supports, the maximum spanlength was established at 180 ft (55 m).Spans were determined after locatingpiers to avoid the natural out-croppingsof rock.

Typical box girder bridges have beenbuilt with span-to-depth ratios of 18 to25. Structural aesthetics are generallymore pleasing through the use of higherspan-to-depth ratios. Considering the

beautiful site of Linn Cove, it was de-cided to use a span-to-depth ratio of 22to provide a graceful structure. How-ever, after analysis of this cross section,it was decided to increase the depth ofthe box and the web thicknesses be-cause the shallower depth structurewould have required a significantamount of high strength post-tensioningsteel, Fig. 4 shows the final cross sectionadopted.

Cantilever construction with largeequipment weights applied at the freeend induces high compressive stressesin the bottom slab. This in combinationwith shear stresses resulting from thetorsional moment and the longitudinalshear force, results in a bottom slabthicker than the usual 12 in. (305 mm)for the typical section and a web widthof 18 in. (457 mm).

Through the use of Figg and Muller'sexclusive Bridge Construction (BC)Program, it was possible to analyze thestructure with a discrete model corre-sponding to the joints between seg-ments (153 segments). Each stage oferection was analyzed. Stresses werechecked at each segment placing, ten-don stressing or support conditionchange. In addition, certain critical eon-struction phases were analyzed, for in-stance, loads induced by trucks carryingsegments over the completed deck.

The primary advantage of the BC pro-gram was its ability to handle long-termbehavior computations. The time-dependent deformations were antici-pated to he important because of creep,shrinkage and steel relaxation.

The long-term deformations calcu-lated by the BC program have beenfound very consistent with actual mea-surements of deflections in the past. Theaccuracy was again verified with fieldmeasurements on Linn Cove. The pro-gram uses the FIP-CEB concrete creepprovisions.

The transverse analysis was per-formed by utilizing the STRUDL pro-gram to analyze a three-dimensional fi-

PCI JOURNALJSeptember-October 1985 43

Core Form j Steel Bulkhead To Storage

NewOld OlderSegmen t

(N) (N-I) (N-2)

SoffitCarriage

Fig. 5_ Schematic of short line match-casting system as used on Linn Cove Viaduct.

nite element model. It should be recalledthat Linn Cove was designed in 1978and 1979. Figg and Muller has de-veloped and now uses the much morepowerful HERCULE program forthree-dimensional finite elementanalysis.

The effects of the bridge horizontalcurvature were analyzed using two ad-ditional three-dimensional computerprograms:

• A curved beam program (ABC) toanalyze the general behavior of thestructure during construction and at ser-vice. This program allows the computa-tion of load distribution in accordancewith all element stiffness (box girder,bearings, piers and temporary supports).

• A finite element analysis program(TITUS) was used for the detailed de-sign of torsional stresses in all membersof the girder. In particular, this programwas used to design the diaphragms (atpiers and temporary supports) whichtransfer the torsional load to the bear-ings.

Torsional analysis was performed for

all critical phases, i.e., completed can-tilever with equipment loadings or deckbehavior at temporary support removal.

CONSTRUCTION

Prior to discussing the precasting op-eration and erection sequence, somemention needs to be made about thecontract administration of the project.

Contract AdministrationThe National Park Service (NPS) is

the owner of the project and assumedoverall responsibility. The NPS inspec-tion responsibility related primarily tocontrol of environmental aspects. In-spection was accomplished by periodicvisits to the construction site. NPS per-sonnel were also present at all con-struction meetings.

The Federal Highway Administration(FHWA) assumed responsibility forcontract administration. A full-time staffon the construction site perfomed all in-spection work involved with microshaft

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pile- and footing construction,Superstructure and pier stein castingand erection were inspected with theassistance of Figg and Muller En-gineers, Inc. The contractor for the proj-ect was Jasper Construction Company ofMinneapolis, Minnesota. The contrac-tor's successful bid on the project was$7.9 million.

Figg and Muller Engineers de-veloped the original concept of the con-struction method. The y also did the finaldesign and prepared all contract docu-ments. Because of the complexity of theproject and relatively short time sincethe introduction of the segmental con-cept in the United States, the FHWAengaged Figg and Muller Engineers toprovide the necessary segmental tech-nical expertise to assure successfulcompletion of the project.

The engineers served in strictly anadvisory capacity to the FHWA, with nodirect relation to either NPS or the con-tractor. All functions related to thespecialized techniques required forsegment casting and erection.

Segment CastingTo tit curvature and superelevation

variation requirements, segments werelaid out for the short cell method withmatch-cast joints. Each segment wascast in casting machines between a bulk-head and the previously cast segment.Fig. 5 shows the short cell match-castarrangement where N-1 represents thematch-cast segment and N, the segmentbeing cast.

Horizontal curves, vertical curves andsuperelevations are obtained by adjust-ing the position of the match-cast seg-ment. This procedure requires a specialcasting form designed to allow defor-mations between the bulkhead and thematch-cast segment. Curves are accom-plished by successive chords providinga slight angle change at each joint.

The precast pier segments werematch-cast in the vertical direction as

shown in Fig. 6. This method involvedcasting the new segment above the pre-viously cast segment with steel formsused for the side forms and a core formto cast the void in the box. The rein-forcing cages (including the verticaltendon ducts) were prefabricated.

The only geometry involved in cast-ing the pier segments was the determi-nation of the as-cast data and makingminor corrections for casting variances.The as-cast data were later used whenerecting the box pier segments.

The severe geometry requirements ofLinn Cove necessitated some uniqueproperties for the superstructure seg-ment casting machine. The system hadto be strong enough to support 55 tons(50 t) of concrete and steel; yet flexibleenough to seal around the edges of thecast-against segment, which in some in-

1

.r• L

PCI JOURNALJSeptember-October 1985 45

stances was severely skewed because ofthe large degree of curvature to be ob-tained.

To assist in obtaining adequate seal-ing to ensure smooth joints, the con-tractor installed a strip of rubberizedmaterial on the edge of the castingmachine. This worked very well withthe only detrimental effects being occa-sional pieces of rubber which wouldstick to the concrete. However, thepieces were easily removed. The castingmachine is shown in Fig. 7.

The extreme weather conditions onGrandfather Mountain of below zerotemperatures and winds ranging to 100miles per hr (161 krn/hr) influenced thecontractor to enclose the castingmachine and reinforcement cage fabri-cation area in a building. However, sincethe box pier segments were relativelyfew in number, they were cast outside.

Casting Geometry Control

The contractor had ultimate responsi-bility for the geometry control of thesegments during the casting operationand during erection of the cantilevers.The contractor developed theoreticalcasting curves from the contract docu-ments and submitted the data to theFHWA, which consulted Figg andMuller Engineers before giving ap-proval.

The engineers established a com-pletely independent geometry controlsystem from that used by the contractor.The primary function of this separateevaluation was to provide a system ofchecks and balances, thereby assuringcomplete and accurate geometry con-trol.

The three types of movement that canbe required of a casting machine were

Fig. 7. The casting machine was located in a building enabling segments to be castduring the winter months. The next cast-against segment can be seen in the foreground;and, behind that, the steel bulkhead can be seen. The workers are standing on the coreform which moves in to form the box girder void.

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all required on this project, and to amuch greater degree than on any previ-ous bridge. They were;

• Movement in plane to obtain acurved alignment.

• Movement in elevation to obtainthe desired vertical profile.

• A warping movement in the formsoffit to obtain the desired cross fallvariations.

The theoretical casting curves arethose curves to which the segments areassembled in the bridge so that they willconform to the geometric shape shownon the contract drawings. The theoreti-cal casting curves, therefore, have totake into account the geometric align-ment and vertical profiles and the ef-fect of the deflections in the superstruc-ture that will occur during and aftererection.

For a straight bridge, the casting curveis simply the same information on thecontract drawings. However, in the caseof Linn Cove, whenever any segmentcast basically horizontal in the castingcell had to be rotated about its longi-tudinal axis to be placed in the bridge,the geometric profile of the segmentand all its adjacent segments were verydifferent to the alignment and pro-file shown on the contract draw-ings.

Normal geometry control procedurescould not be used. The geometry ofLinn Cove with 21 segments betweencast-in-place closure joints would haveresulted in the twenty-first segmentbeing approximately 4 in. (102 mm) offline and 6 ft (1.8 m) off grade, had notthe bridge and casting cell angularchange differential been taken into ac-count

For bridges of larger radii and 3 per-cent superelevation, the effect is insig-nificant in alignment, but not profile.For this bridge, it was necessary to gen-erate "geometry" casting curves from"global" data on the contract drawingsby transformation to the local "castingcell" axis.

Fig. 8. The contractor chose to erect thesegments with this stiffleg crane attachedto the end of the cantilever. This singlepiece of equipment controlled theconstruction rate of the bridge. All materialand equipment was handled with thiscrane.

Segmental Box PierConstruction

All pier footings are 20 ft (6.1 m) indiameter and 5 ft (1.5 m) in thickness.The footings are founded on variablethickness nonreinforced subfootingsthrough which microshaft piles weredrilled.

After forming the footings and placing

PCI JOURNAUSeptember•October 1985 47

Fig. 9. Precast box pier segments werelowered over the end of the completedcantilever with the stiff leg. The workmenare ready to block the segment and applythe epoxy.

the reinforcement and post-tensioningconduits, the first of the precast seg-ments was placed. A steel frame fabri-cated from rolled sections was placed inthe footing simultaneously with thereinforcing bars. The frame providedsupport for the first box pier segments.

The initial precast segment was placedon shims and flat jacks which enabledproper alignment. The segment had tohe aligned to correct for casting varia-tions and actual superstructure position.Movements were achieved by pumpingthe flat jacks one at a time or in combi-nation. The segment was supported at

four points.The contractor was responsible for

aligning the segment and the alignmentwas subsequently verified by the en-gineers. After verification, the footingwas cast. The top of the footing ex-tended approximately 1 in. (25 mm)above the bottom of the segment and thesupport beams for the segment werelost.

After the footing concrete had hard-ened, the joint between the cast-in-place concrete and the precast segmentwas pressure grouted with epoxy. Thepurpose of the epoxy was to waterproofthe joint. The epoxy was not related tostrength. The precast box pier seg-ments were delivered over the com-pleted portion of the superstructurewhich extended to within two segmentsof the pier location. The segments werelifted over the end of the cantilever by astiffleg crane attached to the cantilever(see Fig. 8).

Fig. 9 shows a box pier segment beinglowered. The pier segments wereblocked about 6 in. (152 mm) above theprevious segment while epoxy wasapplied. The segment was then loweredto the face of its match-cast unit wherethread bar tendons were installed andstressed. Each pair of segments werestressed together with thread bars. Theprocess was repeated until all of thehollow segments were erected and thepier was ready for the cap.

The last step in the pier constructionwas to place the cap and stress eight 12-strand tendons. These tendons extendfrom the top of the pier down throughand out the side of the footings. Oncestressing was completed, the tendonswere grouted.

Superstructure SegmentErection

Superstructure segments were deliv-ered to the end of the cantilever by alow-boy tractor trailer (see Fig. 10). Be-cause of the limited access, the truck

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had to be backed up the access road antibacked out onto the completed portionof the bridge.

The crane which lifted the segmentsfrom the truck and swung them aroundto the end of the cantilever was anAmerican S-20 stiffleg crane. It wasequipped with a 70 ft (21 m) boom andprovided a 125 kip (556 kn) liftingcapacity at a 25 ft (7.6 m) boom radius.

The crane had to be moved forwardafter each segment was erected. Gener-ally, it was located two segments behindthe segment being erected. The movingoperation involved lifting the entire as-sembly, removing the steel supportbeams and lowering the assembly ontosteel rollers. Once the crane was sup-ported on rollers, it was pulled forwardby hand-operated winches. Then thelifting process was reversed. The steelsupport beams were reinstalled and thecrane was tied down.

The moving operation cycle took 4 to6 hours to complete. Moving the stifflegcrane entirely controlled the erectionrate of superstructure segments. Incor-poration of a swivel crane as detailed onthe contract drawings or modifying thestiffleg crane for faster moving wouldhave substantially increased the super-structure erection rate.

The following is a step-by-step proce-dure followed during the erection of atypical segment:

Step I — The segment was backed tothe end of the bridge by truck (see Fig.10).

Step 2 — The stressing cages werepicked up by the stiffleg and attached tothe new segment (see Fig. I U.

Step 3—The lifting spreader beamwas lifted with the stiffleg and the liftingcables attached to the new segment.

Step 4 — The segment was lifted toclear the trailer and the slope waschecked to see that it matched the de-gree of superelevation at the end of thecantilever. If necessary, it was adjusted.

Step 5 — The segment was lifted bythe stiffleg, swung around and lowered

Fig. 10. 50 ton (45 t) segments had to bebacked for distances exceeding 1 mile (1.6km) in many instances because there wasinsufficient room to turn this rig around.

Fig. 11. The first step in the erectionsequence was to remove thepost-tensioning stressing cage from theend of the cantilever. The permanenttendon live end anchors can be seen at thetop of the webs.

to within about 6 in. (152 mm) of the endofthe cantilever (see Figs. 12, 13, 14 and15).

Step 6— The segment was pulledhorizontally to the end of the cantileverwith cable winches and blocked 6 in.

PCI JOURNAUSeptember-October 1985 49

Fig. 12. The segment was lifted from the truck on the right and swung out over thecantilever end.

Fig. 13. Then the segment was lowered vertically.

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Fig. 14. Here the segment is in place ready to receive the epoxy bonding agent. Theexcellent fit of the previous joints and the curvature can be seen. Most joints were lessthan 1 mm (0.004 in.) in thickness.

(152 mm) away with wood blocks. It wasstill supported vertically by the stiffleg,

Step 7 — The temporary thread bartendons were threaded and the nutsfinger tightened.

Step B — The epoxy was mixed andapplied.

Step 9 — The wooden blocks wereremoved and the segment closed to theend of the cantilevers with the cablewinches.

Step 110 — The temporary thread barswere stressed.

Step 11 — The permanent 19-strandtendons were threaded and stressed.

Step 12 — The temporary thread bartendons were released.

Because erection of the superstruc-ture continued through the winter, pro-visions were taken to heat and insulatethe joints of the precast segments. Inparticular, measures were taken to besure the epoxy in the joints was heated Fig. 15. Erection progress (May 20, 1982).

PCI JOUPNAL/Septernber-October 1985 51

Fig. 16. Linn Cove Viaduct winding throughthe Blue Ridge Mountains.

Fig. 17. Closeup of one of the many turnsof the bridge.

to at least 40°F (4.4°C) in order for thematerial to cure properly. Prior to con-struction, an elaborate testing programwas undertaken to make sure that theheating/insulating system worked prop-erly. For more details, see the articlelisted below.*

Erection Geometry ControlFigg and Muller's responsibility for

erection geometry control was to advisethe FHWA of the bridge's relative posi-tion to the plan and profile grade lines.The responsibility included verificationof the positioning of bent segments bythe contractor prior to casting closurejoints and the positioning of the bottompier shaft segments.

During erection, the bridge wastracked using the survey control pointscast into the top slab of the segments.The expected erection grades were pre-determined at each stage of constructionfor the three leading joints of the canti-lever. These grades consisted of a sum-mation of the desired final grade, theas-cast variances and the cantilevercamber data. The actual elevations ofthe joints were plotted on graphs forcomparison with expected elevations.

It was determined early in the erec-tion that the bridge was moving toomuch to acccomplish accurate horizon-tal tracking with the instrument on thebridge. The theoretical horizontal posi-tion of the cantilever end was deter-mined by calculating coordinates fromthe base grid on the plans. The actualcoordinates of the cantilever end weredetermined by turning angles andmeasuring distances from known points.

The specified erection tolerance was±1 in. (25 mm) in both the vertical andhorizontal directions. An early decisionwas made that with the many adjust-

'Muller, lean, and Barker, James M., "Joint Heat-ing Allows Winter Construction on Linn CoveViaduct," PCI JOURNAL, V. 27, No. 5, Scptcm-ber-nctnher 1982, pp. 120-130.

52

ments available at closure joints andaligning box pier segments, there wouldbe no need to shim the segments.Shimming was only to be used when noother way out could be foreseen, andwith this type of erection there was al-ways another way out. Shims werenever used.

The 250 ft (76.2 m) radius curves, spi-ral curves, and many superelevationtransitions were negotiated without asignificant problem. The rigid controls.exercised during casting made the erec-tion process very smooth.

The last segment was placed on De-cember 22, 1982. During 1983, the con-taractor cast the curbs, completed thelast abutment, finished the grade on thenorth end of the viaduct (inaccessiblebefore the bridge was erected), installedguardrails and applied the waterproof-ing membrane and wearing surface.

The bridge was completed without asingle structural problem. There is not acrack in any of the precast superstruc-ture or substructure segments. The proj-ect is a tribute to what can be accom-plished with proper segmental designand construction techniques, Figs. 16and 17 show the completed bridge.

CONCLUDINGREMARKS

The Linn Cove Viaduct is a vital partof the missing link of the Blue RidgeParkway. Connecting roadways willcomplete that link by 1987, allowing thegeneral public access to an award win-ning example of engineering ingenuity:A truly innovative bridge by design,built under difficult conditions, and setin complete harmony with its naturalsurroundings. Attesting to its success,the project has won eight national de-sign awards including a PCI AwardsProgram winner in 1983.

CREDITSEngineer: Figg and Muller Engineers,

Inc., Tallahassee, Florida.Foundation Design/Construction Ad-

ministration: Federal Highway Ad-ministration, Eastern Division, DirectFederal Projects, Arlington, Virginia.

General Contractor: Jasper Construc-tion, Inc., Plymouth, Minnesota.

Owner: National Park Service, Denver,Colorado.

PCI JOUR€NALJSeptember-October 1985 53