Feature Report

Olympic Oval Roof StructureDesign, Production,Erection Highlights

Barry Lester, P.E.PartnerSimpson Lester Goodrich Partnership -Calgary, Alberta -

Herb Armitage, P.E.Senior Advisor, Project Partnership

Con-Force Structures LimitedCalgary, Alberta

T raditionally, the Olympic Gameshave produced a number of exciting

structural designs and have left the hostcity with a legacy of outstanding sportsfacilities. Often, this has resulted inan equally monumental debt. TheSpeed Skating Oval (see Fig. 1) forthe 1988 Winter Olympics in Calgary,Alberta, is different.

The Olympic Oval features a uniqueprecast prestressed concrete, segmentalarch roof structure which marries aworld class structure to a very austerebudget. The maximum building budgetfor the entire facility was set at $30 mil-lion (Canadian funds in 1985). The ac-

tual construction cost was $27.2 million(Canadian). The precast prestressedconcrete work (including post-tension-ing) amounted to $3 million (Canadian).

The Oval, constructed as one of thevenues for the 1988 Winter OlympicGames, will serve during the Games asthe site for speed skating and, after theGames, as a multi-functional athleticfield house. These functions and a gen-eral description of the complete build-ing have been described in a previouslypublished paper.'

This article will describe the design,manufacture and erection of the precastroof structure itself.

50

The Olympic Oval, a $27 million speed skating facility made for

the 1988 Winter Olympic Games, was built using precast pre-

stressed concrete. This report describes the concept, design,

production and erection features of the roof structure.

Fig. 1. Panoramic view of Olympic Oval with Calgary skyline in background.

PCI JOURNALJNovember-December 1987 51

CONCEPTUAL DESIGN

An initial program for the buildingwas prepared which defined the designcriteria from a functional viewpoint. Theessential aspects of the program affect-ing the structural design were the re-quirements for high quality and reason-able cost. Funding for the project wasprovided by the Government of Canadaas part of their commitment to theOlympic Games and it was the desire ofthe owners, the University of Calgary, tomaximize the use of these finds by con-structing a facility with as multi-func-tional a purpose as possible.

In addition, although the initial capi-tal cost was to be paid by the federalgovernment, the maintenance and oper-ating costs of the facility would be theresponsibility of the University of Cal-gary. The structure, therefore, had toprovide a long clear span; be economi-cal to construct; and be low mainte-nance and have a long I ife.

The architects and structural engi-neers, although independent firms,worked very closely together in devel-oping the building design. The archi-tects, working from the owner's pro-gram, defined a building "footprint" andcross section which adhered as tightly tothe program as possible. In order to min-imize both capital and operating costs,floor area and volume were reduced asmuch as possible.

The role of the structural engineerswas then to develop a roof structure withthe best possible fit to the architecturalrequirements and to use the shape ofthe building cross section to structuraladvantage.

The cross section was easy to accom-modate. To provide maximum heightover the playing surface yet low exteriorwalls, in order to minimally impact ad-jacent buildings, a very low arch stnic-ture was chosen.

The plan, however, was quite unusualhaving a long straight center section anda semicircle at each end. The traditional,

parallel arch, barrel vault obviouslywould not be appropriate for these cir-cular ends.

Three families of solutions were re-viewed at this stage:

1. A barrel vault center section with adifferent framing system at each end.The end framing alternatives includedcable suspended fabrics, steel trusses orpartial domes.

2. An intersecting arch system span-ning both the center section and theends.

3. A steel space frame system.The steel space frame system utilizing

a proprietary, pre-engineered systemwas priced and found to be beyond thecapabilities of the project's budget.

The parallel and intersecting archschemes were compared and the inter-secting system was found to have sev-eraladvantages overthe barrel vault:

— A single spanning system could ac-commodate the entire building.

— The grid provides structural re-dundancy with alternate load paths toaccommodate heavy point loads or snowdrifts.

--- The arch grid was stable duringerection without lateral bracing.

- The arch grid is flexible and canaccommodate thermal and volumechanges without any expansion joints.

— Since the grid does not depend onthe deck for stability, the deck could bedetailed to "float" on the arches. Thisallows a variety of envelopes, includinginsulated fabrics, to be considered, in-dependent of the structure.

Preliminary alternative designs werecarried out for the intersecting archesutilizing triangular steel trusses andtrapezoidal concrete box segments.While costs for the two alternatives weresimilar, the concrete option was chosendue to the simplicity of the node inter-sections, the clean appearance of thestructure, and the perceived logic ofusing concrete for a structural systemwhich is predominantly in compression.

Indeed, the economy of the entire roof

52

PLAN

Ea

N0.33 knlsq m I 18.51m

YPIC L

SECTION B-B

Fig. 2. Snow and wind loading.

0.72 kn/sq m

Case 1 - Uniform Snow

1.80 kn/sq m

mm

Case 2 - Drifted Snow

1` 80 kn/sq m

Case 3 - Drifted Snow

-1.00 kn/sq m0.44-0.78 -0.78_0.44

-0.11

Case 4 -- Wind Uplift

SECTION A-A

structure was developed by using themost logical structural materials for eachcomponent; from the preformed steeldeck, long established as the most eco-nomical noncombustible decking mate-rial, to the short span open web steeljoists spanning between the arches, tothe concrete arches themselves.

DESIGN DEVELOPMENT

LoadsThe structure was designed for dead

loads; wind and snow loads; thermal ef-fects; creep and shrinkage of the con-

crete arches; and for lateral movementof the foundations.

Each of these load effects is discussedbelow:

1. Dead Loads: These included theself weight of the arches, equivalent to auniform roof load of approximately 2.5kPa (50 psf); steel framing, metal deck,waterproofing membrane and invertedroof system, a further 0.5 kPa (10 psf); anallowance for miscellaneous loadingfrom lights, sound system, ductwork,and potential future hanging loads of 0.5kPa (10 psf).

2. Wind and Snow Loads (see Fig. 2):Since the shape of the cross section is

PC! JOURNAL/November-December 1987 53

similar to that used for a curved roof,hangar type building, a preliminary es-timate of wind and snow loads was takendirectly from the National BuildingCode of Canada commentary for thistype of building. Final Ioads were con-firmed in a wind and snow study con-ducted by Morrison Hershfield Ltd.using a 1:400 model and are shown inFig. 2. Additional drift loads, caused byfilling of the valleys between the archeswere also included and these loads wereapplied in alternate bays resulting inmaximum torsion on the arches.

3. Thermal Effects: When final de-sign first commenced there were twopossible construction schedules, onerequiring winter erection and one re-quiring summer erection. As a result,the structure was analyzed for temper-ature variations of plus 17°C or minus45° C (plus 31°F or minus 81°F) fromthe erection temperature. Since temper-ature gain produced an effect oppositeto that of creep and shrinkage, it was ig-nored in the final analysis.

4. Creep and Shrinkage: Long termcreep and shrinkage were modelled as afurther temperature reduction of 74.5°C(134°F).

5. Foundation Movements: As designwas proceeding on the roof structure,the foundation design was carried outbased on a series of lateral load tests onlarge diameter concrete piles.' Theseload tests predicted a lateral movementof approximately 10 to 15 mm (0.39 to0.59 in.) under working loads. Thestructure was analyzed for outward lat-eral displacement of 20 mm (0.79 in.) atall supports along the straight portions,where the substructure provided a stiffdiaphragm to ensure that all movementwould be similar, with reducingamounts of 15 and 10 mm (0.59 and 0.39in.) at the ends where the arch spanswere shorter. In addition, an arbitrarylateral displacement of 20 mm (0.79 in.)acting singly at the isolated pile caps atthe ends of the building was input as aseparate loading case.

Load FactorsBecause the arches are designed es-

sentially as slender beam-columns,subject to potential buckling effects; andbecause, in the event of an overload onthe roof, it was considered desirable toensure that the secondary framingwould fail prior to the arches; a higherload factor was applied to the design ofthe arches than was used in the designof the secondary steel framing.

Dead and live load factors of 1.25 and1.5, respectively, were applied in thedesign of the metal deck and steel joistswhile the factors were increased to 1.25and 2.5 for the arches. Under the effectof uniform roof load this is equivalent toan increase in load factor of approxi-mately 17 percent, a similar increase tothat used historically in the design ofslender beam-columns.

Structural Analysis

Preliminary arch designs during theconceptual development stage were car-ried out manually. The initial arch depthrequirement was estimated from theflexural moments due to snow drift loadon one-half of the span. The arch widthwas calculated from lateral buckling re-quirements assuming the arch to be lat-erally supported only at the node inter-sections.

The final analysis was carried outusing a STRESS program. Fourteendifferent loading conditions and twelvecombinations were anal yzed. In addi-tion, a unit load analysis was run inorder to provide an easy reference fordetermining the feasibility of addingfuture loads to the structure.

Based on the results of the initialcomputer runs, cracked section prop-erties were estimated for the arches inorder to review the ultimate deflectionsand check for potential buckling. Aniterative P-delta analysis was used forthis pin-pose with three cycles of itera-tion.

The preliminary design assumed that

54

the arches would be reinforced withmild steel reinforcement. The finalanalysis indicated that there was insuffi-cient dead weight in the structure toovercome the moments created by largesnow drift loads and that flexural tensionwas controlling the design of the archsegments. Conceiltric post-tensioning ofthe arches was an effective method ofincreasing the compression in the sec-tion and providing tensile reinforce-ment.

At the conclusion of the computeranalysis, interaction diagrams for thearches were prepared taking into ac-count the effects of slenderness and biax-ial bending. Two sets of curves wereprepared; one set for the hollow arch it-self and one for the solid nodes. Theaxial forces and moments due to thevarious combinations of load were plot-ted on these interaction curves to de-termine the reinforcement required.

Thermal Effects and VolumeChanges

Provision for expansion joints in largeroof structures can be a problem sincethe magnitude of movements occurringat these joints can lead to ongoingmaintenance problems and potentialroof leaks. The intersecting arch griddoes not require expansion joints sincethe grid itself is capable of flexing to ac-commodate volume change movements.

The steel structure supported on thearches was provided with a series ofclosely spaced control joints by provid-ing a guided joint at one end of each joistto slip on top of the arches. The move-ments occurring at each one of these"slip" joints is small enough to be ac-commodated simply by deforming of thesteel roof deck so that ajoint in the deckand in the roofing membrane is not re-quired.

To accommodate movements in thesubstructure, control joints were placedall around the perimeter at two or threebay spacing. The precast concrete pe-

rimeter roof beam was jointed at thesame locations as the substructure. Theroof layout and control joint locationsare shown in Fig. 3.

Because the arch forces do not alwayscoincide in direction with the but-tresses, lateral forces are placed on theperimeter building columns. To assistthe columns in resisting these forces,very stiff tension ties consisting of largehollow structural steel sections werecast inside half of the perimeter beamsand connected to the column/buttressheads with high strength threadedDywidag bars.

ROOF COMPONENTS

Typical Arch SegmentsThe typical arch segment is shown in

Fig.4.The segments consist basically of a

trapezoidal thin walled box with 150mm (5.9 in.) thick webs, a 170 mm (6.7in.) soffit and a 200 mm (7.9 in.) topflange. Concrete was specified assemi-lightweight with a 28-day com-pressive strength of 40 MPa (5800 psi)and a dry unit weight of 1770 kg/m3(2980 lb per cu yd). The typical segmentlength is approximately 24 m (79 ft) witha weight of about 48 tonnes (^3 tons).

In order to maintain constant eleva-tions for the steel joist seats on oppositesides of each arch, one side of the archwas cast higher than the other. Also,since the slope of the segments wouldvary depending on their location in thecompleted arch the offset had to be var-ied between those segments near theend of the arch and those near the cen-terline of the building. Two basic sec-tions were used, each with a "left" and a

right."The final axial reinforcing ratio was

one percent. This reinforcement was con-centrated close to the corners of the archsegments in order to be effective forbending in both the vertical and hori-zontal directions. (Horizontal bending

PCI JOURNAL/November-December 1987 55

U, 198.5 m 1651 It I43.75 m 6 BAYS at 18.5m 111 m 1364 ItI 43.75m1144 ri I (144 ft(

CAST IN PLACE CONCRETEBUTTRESSES

PRECAST CONCRETE PERIMETERROOF BEAMS

INTERSECTING PRECASTCONCRETE ARCHES

Ci c..i

C.J. / - C.J.

-. :. :: •. HSS TIE IN PERIMETERROOF BEAM

INE(UN

C.J.

E E R

CA. p---------------------------------------C.J. C.J. C.J.

Fig. 3. Roof plan of Olympic Oval showing principal structural components and major dimensions.

— N 1320

CIF-

LLJW

M04

I DUCT EA SIDET8B c!w7-I6

10 M a 250 I.F. EA WEB - 6-IOM ° [760 MPa STRANDS

10 M a 250 STIRRUPS

ti5o WEBS 5-20M O.F. EA WEBc./w 161 TIES a 250tom a 500 HOOK

ENDS 1001-IOMa 3-IOM LF. EA WEBti

3-25M EA SIDE T & B2-20M

BOO

Fig. 4. Typical arch segment.

occurs due to the tilting of the principalmember axes due to the slope in the topflange.)

To resist very high torsions occurringin the arches due to snow drifts in alter-nate bays, closely spaced stirrups and auniform distribution of longitudinal re-inforcing were provided. Because thislongitudinal reinforcing was also used toresist compressive forces, 6 mm (0.23in.) ties were provided to prevent buck-ling of these bars.

The arches are concentrically post-tensioned with seven 16 mm (0.6 in.) di-ameter strands in ducts in each corner ofthe section. Since the maximum positiveand negative moments in the archeswere found to be almost equal, thispost-tensioning layout was the most ef-fective.

Typical NodesThe arch intersections were referred

to as "nodes." Typical interior and exte-rior nodes are shown in Figs. 5 and 6,respectively.

At each node, all of the forces in thearch segment (positive and negativemoments; shear; torsion; and axial com-pression) had to he transferred from onesegment to the others. To accomplishthis, all of the axial reinforcement andpost-tensioning was fully developed byeither mechanical couplers or by lapsplicing. Because the arches change di-rection in the vertical plane at thenodes, the axial forces are not alwaysnormal to this joint and shear frictionplayed a large part in transferring theaxial forces and shear through the nodes.

To ensure good bond of the precastsegments and the cast-in-place concrete,all of the surfaces of the precast elementwere given a heavy sandblast to an am-plitude of approximately 6 mm (0.24 in.).No bonding agent was used but all sur-faces were thoroughly wetted prior toplacing the node concrete. The sectionwas then cast solid using the samesemi-lightweight concrete as used forthe segments themselves.

Because the outside webs and soffits

PCI JOURNAUNovember-December 1987 57

Fig. 5, Interior node.

of the precast elements were extendedas far as possible leaving only a 150 mm(5.9 in.) gap, a very minimal amount offormwork was required in the field foreach node.

Perimeter Roof BeamsThe perimeter roof beams support a

portion of the roof, the exterior fasciaand, along the east side of the building,a sloped glazing structure over the ad-ministrative offices and VIP lounge. In

addition, approximately half of the pe-rimeter beams enclose a steel tension tieconnecting the perimeter columns.

The beams span approximately 18.5 m(61 ft) and are a hollow box section. A 75mm (3 in.) precast fascia panel and 50mm (2 in.) of insulation were cast as asandwich panel on the lower half ofeach beam.

The typical beam is shown in Fig. 7.The beam is tilted 28 degrees from the

vertical on the building to match theslope of the cast-in-place buttresses.

58

PRECAST *1 ThARCH SEGMENTS

BUTTRESS

CIP NODE INFILL

END DIAPHRAGM IN ARCH SEGMENT

LINE OF PORCELAIN ENAMEL/ ROOF AND FACIA

I/f '22.80

..J I / \\ .

.:

:.•.

CIP BUTTRESS HEAD - --

/

1500 mm DIA. COLUMN

Fig. 6. Exterior node.

Since the beam is relatively shallow forresisting flexural moments about theweak axis the section was pretensionedto resist a combination of vertical andlateral moments.

The tension ties cast into the perim-eter beams were required to be very stiffin order to be effective in transferringloads between the equally stiff cast-in-place perimeter columns [1500 mm (59

PCI JOURNAL/November-December 1987 59

4 - IOM HOOK ENDS 200

IOM a 300 STIR.TYP.

16 - 127 d STRANDSto 1662 MPaPI • 128.6 kN /STRAND

16- 15M HOOK ENDS 250

II - IOM HOOK ENDS 200

HSS 203 x 304 IN TIE BEAMS ONLY

75 THICK FACE F NEL

Fig. 7. Typical precast concrete perimeter beam.

in.) in diameter]. To achieve this stiff-ness, the tic consisted of a 300 x 200 mm(12 x 8 in.) hollow structural section witha wall thickness of 12.7 mm (0.5 in.).Additional stiffness for the ties at theextreme ends of the Oval, where the tieforces are at a maximum, was achieved byplating the 300 mm (12 in.) sides of theHSS with 20 mm (0.79 in.) thick plates.

BearingsThe thrusts from the arches are trans-

ferred to the perimeter columns andbuttresses through very large discbearings. The typical bearing is shownin Fig. 8.

Maximum axial force in the bearingwas 8453 kN (1900 kips) [unfactored ]while the maximum vertical shear forcewas 775 kN (174 kips) and lateral shearforce was 1495 kN (336 kips). Shearforces occur due to slight variations inthe thrust line of the arches dependingon the loading condition on the roof.

The bearings are also designed for arotation of two percent to allow for de-flection of the arches.

It was originally intended that thebearings would be cast into the perim-eter buttress heads prior to erection ofthe precast arches. Unfortunately, majordelays in the manufacture of the bear-ings by the supplier resulted in a delayof approximately six months in the de-livery. Fortunately, it was possible tomodify the reinforcement of the exteriornodes to allow the bearings to be in-stalled after erection of the arch seg-ments with no overall loss of time in theconstruction schedule.

MANUFACTUREThe production aspects of the arch

roof segments are given first followed bythe perimeter beams.

Arch Roof SegmentsThe structural design of the arch root

beams using the trapezoidal shapedcross section provided a very pleasingarchitectural appearance. This crosssection also provided other advantagesin the precast concrete production of the

60

BEARING PAD

SHEARTlON PIN

ANC1-IOR PIN

Fig. 8, Bearing detail.

beams. It permitted easy beam strip-ping, eliminated basic form setup, pro-vided good "as cast" finish and per-mitted the cage, complete with plywoodvoids and end block-outs, to be preas-sembled and lowered into the form.

This procedure maximized repetitionand economy by permitting all 84 pre-cast concrete arch roof beams to be castin one basic form. Although the beamsvaried in length from 14.2 to 25.4 m(46.6 to 83.3 ft), all were cast in one steel

form which had 100 mm (3.9 in.) camberbuilt into it. This form was alsoequipped with external vibrators to pro-vide a dense smooth beam finish.

All beams had a 800 mm (31.5 in.)wide base but there were two basiccross sections each with a cross-fall onthe top of the beam. The basic form wasmade to accommodate both cross sec-tions.

For the most severe cross-fall, theform side heights were 1800 and 2019

PCI JOURNAUNovember-December 1987 61

Fig. 9. Single steel form for arch segments.

mm (71 and 79 in.). To produce girderswith the smaller cross section, a 89 mm(3.5 in.) side rail was unbolted from thehigh side to produce a form with 1800and 1930 mm (71 and 76 in.) sides.

Because weight was critical to thesubstructure design, semi-light-weight concrete was used. The beamswere also voided using 4350 mm (171in.) long plywood boxes. These boxeswere chamfered on all sides and formeda part of the cage. This preassembledreinforcing cage also included the fourpost-tensioning ducts, protruding endreinforcing bars and inserts, and the endblock form.

This end block-out form accommo-dated the variation in girder lengths andensured a proper 150 mm (5.9 in.) gapbetween girders at each node. It also ac-curately positioned the 20 and 25 mm(0.79 and 1 in.) main reinforcing barsforming a very rigid cage assemblywhich could be lowered into the form,positioned and poured. By using super-plasticizer additive in the 40 MPa (5800

psi) concrete and with adequate chamferon the box voids, the beams werepoured from the top in a one-pour se-quence using both internal and externalvibrators.

Girders were stripped and yardedwith four 15 tonne (16.5 ton) overheadcranes. Low bed trucks with 12 wheelself-steering trailers were used to trans-port the beams to the site.

Perimeter Bars

Perimeter beams were produced intwo stages. In the first stage the 75 mm(3 in.) architectural exterior claddingwas cast complete with 50 mm (2 in.)S.M. styrofoam insulation backing andprotruding anchors. These 1530 x 3750mm (60 x 141 in.) panels were then po-sitioned vertically in a steel form so thatthe structural portion of the beam couldbe poured to produce a compositesandwich structural perimeter beamwith architectural finish. The structuralportion of the beam was also loafed outusing plywood voids within the rein-forcing cage and cast using standardweight concrete.

Bulkhead variation was used to pro-duce the various beam lengths 114.7 to16.9 m (48.2 to 55.4 ft)] required to ac-commodate the non-typical units at theends of the building. Of the 28 perim-eter beams, 16 required large structuralsteel tubes complete with end connec-tion hardware which were cast withinthe beams. These were used as tensionties and ran through the loafed outstructural perimeter beams for their fulllength. The inside face of the beamscontained electrical conduits for inte-rior lights and were trowelled smooth.

PEER REVIEWDue to the magnitude of the building

and the unusual nature of the design,the structural consultants engaged otherindependent structural engineers to

62

Fig. 10. Perimeter roof beams showing steel tension ties.

Fig. 11. Typical arch segment being loaded for shipment.

PCI JOURNAL/November-December 1987 63

Fig, 12. Arch segments erected on interior scaffolding and exterior steel trusssupports.

carry out a review of the design.The peer review was carried out at

two stages: first, at the completion ofconceptual design and finally, at thecompletion of the design and drawings.The concept review was consideredvaluable in ensuring that no judgmentalerrors might have been made whichmight result in potential increases incosts arising during the final design.

The check at the completion of thefinal design was carried out by running acompletely independent computeranalysis of the structure. The softwareused for this purpose was a space frameanalysis program written by the review-ers.

Not only was the structure found to besafe, but the peer review actually savedthe owner a substantial amount ofmoney. Working from nearly completearchitectural and structural drawings,the peer review team was able to ana-lyze the structure without making as

Fig. 13. Arch erection near completionshowing temporary precast head frameson top of scaffolding towers.

64

Fig. 14. Aerial view at completion of structural framing showing nodes at variousstages of casting.

Fig. 15. Close up of typical interior node prior to placing reinforcing steel andpost-tensioning ducts.

PCI JOURNALJNovember-December 1987 65

Fig. 16. Stressing of post-tensioning inside Fig. 17. Interior of Oval after removal ofexterior nodes. shoring.

many assumptions as are often requiredduring the normal design process.

The final building configuration, di-mensions, loadings, etc. were all welldefined prior to this final analysis andthe result was that the longitudinal archreinforcing was reduced from approxi-mately 2 to 1 percent, a minor reductionin design terms, but a saving of $120,000when applied to all 84 arch segments.

The authors strongly support this pro-cess on any major project.

ERECTION ANDSCAFFOLDING

Various phases of the production,shipment and erection of the precastcomponents are shown in Figs. 9through 18.

The precast components were trans-ported to the site by truck and erected,using two cranes, by the precastsupplier.

The temporary scaffolding to supportthe segments was designed and con-structed by the general contractor. Twobasic types of temporary support wererequired: 31 towers under the interiornodes, and 26 exterior steel frames tosupport the arches at the perimeter col-umns.

Each of the interior towers was re-quired to support a load of approxi-mately 1350 kN (300 kips). Maximumtower height was approximately 22 m(72 ft). The towers consisted of modifiedstandard sectional scaffolding 2 m widex 4 m long (6.5 x 13.1 R). Each tower wassupported on four temporary timberpiles approximately 6 m (20 ft) longtopped by a cast-in-place pile cap. Ascrew jack was located under each towerleg.

The towers were guyed in the longdirection of the building. No guying wasrequired across the oval since the towerswere stabilized as erection proceededby welding of the arch components.

66

Fig. 18, End view of Oval with steel joists in place.

The contractor achieved extremelyaccurate elevation control by precastingtemporary head frames for the top ofeach tower. These head frames con-tained temporary steel bearing plates toreceive the arch segments. Invertedsteel angles were temporarily bolted tothe underside of each arch segment atthe precast plant to provide a "knifeedge" bearing on the head frames.

The arch components were supportedaround the perimeter of the oval oncustom steel trusses. Each truss sup-ports a load of approximately 50 tonnes(55 tons). To complicate matters, theload had to he supported under the enddiaphragm in the arch segments whichoccurred approximately 3 m (10 ft) awayfrom the center of the perimeter column.

To allow for temperature changes,shrinkage, and elastic shortening of thearches due to post-tensioning, the pe-rimeter trusses supported a slidinghearing seat inclined at an angle parallelto the centerline of the arch segment,

SHORING REMOVALAfter all components had been

erected and the interior nodes had beencast, the post-tensioning strands wereplaced and stressed. Stressing was car-ried out from both ends.

The bearings were then set in place inthe buttress heads and the exteriornodes cast.

The structure was now ready for re-moval of the temporary supports, a sig-nificant event for the designers andcontractor.

The first step was the removal of thetemporary steel angles supporting thesegments on the perimeter steel trusses.This was accomplished by simply burn-ing out the angles to allow the weight ofthe arches to be carried by the shear pinin the center of the hearings. Removal ofthe perimeter supports first would allowthe arches to rotate as the interior tow-ers were removed.

Although a screw jack was provided in

PCI JOURNALI November-December 1987 67

Fig. 19. Interior view of finished structure showing complete arch span.

Fig. 20. Public skating after formal opening.

68

each leg of the interior towers, it wasanticipated that friction on the threadwould be too great to allow this to beturned. Accordingly, a small bracket waswelded to the side of each leg and asmall hydraulic jack was used to lift theload off the screw while it was turned.

In order to prevent overstressing ofthe structure during lowering, eachtower was dropped incrementally only10 mm (0.39 in.) at a time. As the pre-dicted dead load deflection was be-tween 40 and 50 mm (1.6 and 2.0 in.) itwas anticipated that Four to five incre-ments would be required at each tower.This required the contractor to moveback and forth from one tower to anotheras he gradually moved from one end ofthe building to the other. The actual de-flection at the first tower to he com-pletely unloaded was approximately 43mm (1.7 in.).

While this operation seems ratherprimitive, the lowering operation easilykept ahead of the crews dismantling thetowers and, in fact, the towers werecompletely removed at the north endprior to completion of jacking at thesouth end.

CONCLUDING REMARKSConstruction began in March 1985

and the roof structure was effectivelycompleted by June 1986. Finishingtrades and interior work continued untilApril 1987.

The end result is indeed a most beau-tiful and functional structure (see Figs.19 and 20).

Historically most long span buildingshave been constructed of light materials,usually steel. Recently, tension struc-tures and fabrics have received a sub-stantial amount of both positive andnegative publicity. Except for a rela-tively small number of domes andshells, concrete long span structures

have been noticeable by their absence.The intersecting precast concrete

segmental arch system used for theOlympic Oval allows the precast pre-stressed concrete industry to compete inthe long span building market withoutany new, expensive plant or erectiontechnology. The system is economicalarchitecturally exciting; and, with theadvent of high strength concretes, capa-ble of almost any span.

The Olympic Oval was a winningproject in the 1987 PCI Professional De-sign Awards Program.

CREDITSOwner: The University of Calgary, Cal-

gary, Alberta, Canada.Architect: Graham • McCourt, Calgary,

Alberta.Structural Engineer: Simpson Lester

Goodrich Partnership, Calgary, Al-berta.

Engineering Review:Dr. Walter Dilger, University of Cal-gary.Dr. Gamil Tadros, Speco Engineer-ing, Calgary.

General Contractor: W. A. StephensonConstruction (Western) Ltd., Calgary,AIberta.

Precast Concrete Manufacturer andPost-Tensioning: Con-Force Struc-tures Ltd., Calgary, Alberta,

REFERENCESLester, W. B., "Olympic Oval — Beautyon a Budget," Concrete International, V.9, No. 8, August 1987, pp. 10-18.Clark, Jack; McKeown, Shawn; Lester,W. Barry; Eibner, Len, "The Lateral LoadCapacity of Large Diameter ConcretePiles," Proceedings 38th Canadian Geo-technical Conference, Canadian Geo-technical Society, Montreal, Canada,1985, pp. 409-418.

PCI JOURNAL'November-December 1987 69