Feature Report

Olympic Oval Roof Structure Design, Production, Erection Highlights

Barry Lester, P.E. Partner Simpson Lester Goodrich Partnership - Calgary, Alberta -

Herb Armitage, P.E. Senior Advisor, Project Partnership Con-Force Structures Limited Calgary, Alberta

raditionally, the Olympic Games tual construction cost was $27.2 million Thave produced a number of exciting (Canadian). The precast prestressed structural designs and have left the host concrete work (including post-tension- city with a legacy of outstanding sports ing) amounted to $3 million (Canadian). facilities. Often, this has resulted in The Oval, constructed as one of the an equally monumental debt. The venues for the 1988 Winter Olympic Speed Skating Oval (see Fig. 1) for Games, will serve during the Games as the 1988 Winter Olympics in Calgary, the site for speed skating and, after the Alberta, is different. Games, as a multi-functional athletic The Olympic Oval features a unique field house. These functions and a gen- precast prestressed concrete, segmental eral description of the complete build- arch roof structure which marries a ing have been described in a previously world class structure to a very austere published paper.' budget. The maximum building budget This article will describe the design, for the entire facility was set at $30 mil- manufacture and erection of the precast lion (Canadian funds in 1985). The ac- roof 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 parallel arch, barrel vault obviously would not be appropriate for these cir- An initial program for the building cular ends. was prepared which defined the design Three families of solutions were re- criteria from a functional viewpoint. The viewed at this stage: essential aspects of the program affect- 1. A barrel vault center section with a ing the structural design were the re- different framing system at each end. quirements for high quality and reason- The end framing alternatives included able cost. Funding for the project was cable suspended fabrics, steel trusses or provided by the Government of Canada partial domes. as part of their commitment to the 2. An intersecting arch system span- Olympic Games and it was the desire of ning both the center section and the the owners, the University of Calgary, to ends. maximize the use of these finds by con- 3. A steel space frame system. structing a facility with as multi-func- The steel space frame system utilizing tional a purpose as possible. a proprietary, pre-engineered system In addition, although the initial capi- was priced and found to be beyond the tal cost was to be paid by the federal capabilities of the project's budget. government, the maintenance and oper- The parallel and intersecting arch ating costs of the facility would be the schemes were compared and the inter- responsibility of the University of Cal- secting system was found to have sev- gary. The structure, therefore, had to eraladvantages overthe barrel vault: provide a long clear span; be economi- — A single spanning system could ac- cal to construct; and be low mainte- commodate the entire building. nance and have a long I ife. — The grid provides structural re- The architects and structural engi- dundancy with alternate load paths to neers, although independent firms, accommodate heavy point loads or snow worked very closely together in devel- drifts. oping the building design. The archi- --- The arch grid was stable during tects, working from the owner's pro- erection without lateral bracing. gram, defined a building "footprint" and - The arch grid is flexible and can cross section which adhered as tightly to accommodate thermal and volume the program as possible. In order to min- changes without any expansion joints. imize both capital and operating costs, — Since the grid does not depend on floor area and volume were reduced as the deck for stability, the deck could be much as possible. detailed to "float" on the arches. This The role of the structural engineers allows a variety of envelopes, including was then to develop a roof structure with insulated fabrics, to be considered, in- the best possible fit to the architectural dependent of the structure. requirements and to use the shape of Preliminary alternative designs were the building cross section to structural carried out for the intersecting arches advantage. utilizing triangular steel trusses and The cross section was easy to accom- trapezoidal concrete box segments. modate. To provide maximum height While costs for the two alternatives were over the playing surface yet low exterior similar, the concrete option was chosen walls, in order to minimally impact ad- due to the simplicity of the node inter- jacent buildings, a very low arch stnic- sections, the clean appearance of the ture was chosen. structure, and the perceived logic of The plan, however, was quite unusual using concrete for a structural system having a long straight center section and which is predominantly in compression. a semicircle at each end. The traditional, Indeed, the economy of the entire roof

52 0.72 kn/sq m

Case 1 - Uniform Snow

1.80 kn/sq m mm

Case 2 - Drifted Snow

` 801 kn/sq m

PLAN Case 3 - Drifted Snow

E -1.00 kn/sq m a -0.78_0.44 -0.11 0.44-0.78

N 0.33 knlsq m I 18.51m YPIC L Case 4 -- Wind Uplift

SECTION B-B SECTION A-A

Fig. 2. Snow and wind loading.

structure was developed by using the crete arches; and for lateral movement most logical structural materials for each of the foundations. component; from the preformed steel Each of these load effects is discussed deck, long established as the most eco- below: nomical noncombustible decking mate- 1. Dead Loads: These included the rial, to the short span open web steel self weight of the arches, equivalent to a joists spanning between the arches, to uniform roof load of approximately 2.5 the concrete arches themselves. kPa (50 psf); steel framing, metal deck, waterproofing membrane and inverted roof system, a further 0.5 kPa (10 psf); an DESIGN DEVELOPMENT allowance for miscellaneous loading from lights, sound system, ductwork, Loads and potential future hanging loads of 0.5 The structure was designed for dead kPa (10 psf). loads; wind and snow loads; thermal ef- 2. Wind and Snow Loads (see Fig. 2): fects; creep and shrinkage of the con- Since the shape of the cross section is

PC! JOURNAL/November-December 1987 53 similar to that used for a curved roof, Load Factors hangar type building, a preliminary es- Because the arches are designed es- timate of wind and snow loads was taken sentially as slender beam-columns, directly from the National Building subject to potential buckling effects; and Code of Canada commentary for this because, in the event of an overload on type of building. Final Ioads were con- the roof, it was considered desirable to firmed in a wind and snow study con- ensure that the secondary framing ducted by Morrison Hershfield Ltd. would fail prior to the arches; a higher using a 1:400 model and are shown in load factor was applied to the design of Fig. 2. Additional drift loads, caused by the arches than was used in the design filling of the valleys between the arches of the secondary steel framing. were also included and these loads were Dead and live load factors of 1.25 and applied in alternate bays resulting in 1.5, respectively, were applied in the maximum torsion on the arches. design of the metal deck and steel joists 3. Thermal Effects: When final de- while the factors were increased to 1.25 sign first commenced there were two and 2.5 for the arches. Under the effect possible construction schedules, one of uniform roof load this is equivalent to requiring winter erection and one re- an increase in load factor of approxi- quiring summer erection. As a result, mately 17 percent, a similar increase to the structure was analyzed for temper- that used historically in the design of ature variations of plus 17°C or minus slender beam-columns. 45° C (plus 31°F or minus 81°F) from the erection temperature. Since temper- ature gain produced an effect opposite Structural Analysis to that of creep and shrinkage, it was ig- Preliminary arch designs during the nored in the final analysis. conceptual development stage were car- 4. Creep and Shrinkage: Long term ried out manually. The initial arch depth creep and shrinkage were modelled as a requirement was estimated from the further temperature reduction of 74.5°C flexural moments due to snow drift load (134°F). on one-half of the span. The arch width 5. Foundation Movements: As design was calculated from lateral buckling re- was proceeding on the roof structure, quirements assuming the arch to be lat- the foundation design was carried out erally supported only at the node inter- based on a series of lateral load tests on sections. large diameter concrete piles.' These The final analysis was carried out load tests predicted a lateral movement using a STRESS program. Fourteen of approximately 10 to 15 mm (0.39 to different loading conditions and twelve 0.59 in.) under working loads. The combinations were anal yzed. In addi- structure was analyzed for outward lat- tion, a unit load analysis was run in eral displacement of 20 mm (0.79 in.) at order to provide an easy reference for all supports along the straight portions, determining the feasibility of adding where the substructure provided a stiff future loads to the structure. diaphragm to ensure that all movement Based on the results of the initial would be similar, with reducing computer runs, cracked section prop- amounts of 15 and 10 mm (0.59 and 0.39 erties were estimated for the arches in in.) at the ends where the arch spans order to review the ultimate deflections were shorter. In addition, an arbitrary and check for potential buckling. An lateral displacement of 20 mm (0.79 in.) iterative P-delta analysis was used for acting singly at the isolated pile caps at this pin-pose with three cycles of itera- the ends of the building was input as a tion. separate loading case. The preliminary design assumed that

54 the arches would be reinforced with rimeter roof beam was jointed at the mild steel reinforcement. The final same locations as the substructure. The analysis indicated that there was insuffi- roof layout and control joint locations cient dead weight in the structure to are shown in Fig. 3. overcome the moments created by large Because the arch forces do not always snow drift loads and that flexural tension coincide in direction with the but- was controlling the design of the arch tresses, lateral forces are placed on the segments. Conceiltric post-tensioning of perimeter building columns. To assist the arches was an effective method of the columns in resisting these forces, increasing the compression in the sec- very stiff tension ties consisting of large tion and providing tensile reinforce- hollow structural steel sections were ment. cast inside half of the perimeter beams At the conclusion of the computer and connected to the column/buttress analysis, interaction diagrams for the heads with high strength threaded arches were prepared taking into ac- Dywidag bars. count the effects of slenderness and biax- ial bending. Two sets of curves were prepared; one set for the hollow arch it- ROOF COMPONENTS self and one for the solid nodes. The axial forces and moments due to the Typical Arch Segments various combinations of load were plot- The typical arch segment is shown in ted on these interaction curves to de- Fig.4. termine the reinforcement required. The segments consist basically of a trapezoidal thin walled box with 150 mm (5.9 in.) thick webs, a 170 mm (6.7 Thermal Effects and Volume in.) soffit and a 200 mm (7.9 in.) top Changes flange. Concrete was specified as Provision for expansion joints in large semi-lightweight with a 28-day com- roof structures can be a problem since pressive strength of 40 MPa (5800 psi) the magnitude of movements occurring and a dry unit weight of 1770 kg/m3 at these joints can lead to ongoing (2980 lb per cu yd). The typical segment maintenance problems and potential length is approximately 24 m (79 ft) with roof leaks. The intersecting arch grid a weight of about 48 tonnes (^3 tons). does not require expansion joints since In order to maintain constant eleva- the grid itself is capable of flexing to ac- tions for the steel joist seats on opposite commodate volume change movements. sides of each arch, one side of the arch The steel structure supported on the was cast higher than the other. Also, arches was provided with a series of since the slope of the segments would closely spaced control joints by provid- vary depending on their location in the ing a guided joint at one end of each joist completed arch the offset had to be var- to slip on top of the arches. The move- ied between those segments near the ments occurring at each one of these end of the arch and those near the cen- "slip" joints is small enough to be ac- terline of the building. Two basic sec- commodated simply by deforming of the tions were used, each with a "left" and a steel roof deck so that ajoint in the deck right." and in the roofing membrane is not re- The final axial reinforcing ratio was quired. one percent. This reinforcement was con- To accommodate movements in the centrated close to the corners of the arch substructure, control joints were placed segments in order to be effective for all around the perimeter at two or three bending in both the vertical and hori- bay spacing. The precast concrete pe- zontal directions. (Horizontal bending

PCI JOURNAL/November-December 1987 55 U, 198.5 m 1651 It I 43.75 m 6 BAYS at 18.5m 111 m 1364 ItI 43.75m 1144 ri I (144 ft( CAST IN PLACE CONCRETE BUTTRESSES PRECAST CONCRETE PERIMETER ROOF BEAMS

INTERSECTING PRECAST CONCRETE ARCHES Ci c..i

C.J. / - C.J.

: -. . :: •. HSS TIE IN PERIMETER ROOF 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 LLJW

CIF-

M04

I DUCT EA SIDE T8B 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 WEB c./w 161 TIES a 250 tom a 500 HOOK ENDS 100 1-IOM a 3-IOM LF. EA WEB ti

3-25M EA SIDE T B 2-20M BOO

Fig. 4. Typical arch segment.

occurs due to the tilting of the principal At each node, all of the forces in the member axes due to the slope in the top arch segment (positive and negative flange.) moments; shear; torsion; and axial com- To resist very high torsions occurring pression) had to he transferred from one in the arches due to snow drifts in alter- segment to the others. To accomplish nate bays, closely spaced stirrups and a this, all of the axial reinforcement and uniform distribution of longitudinal re- post-tensioning was fully developed by inforcing were provided. Because this either mechanical couplers or by lap longitudinal reinforcing was also used to splicing. Because the arches change di- resist compressive forces, 6 mm (0.23 rection in the vertical plane at the in.) ties were provided to prevent buck- nodes, the axial forces are not always ling of these bars. normal to this joint and shear friction The arches are concentrically post- played a large part in transferring the tensioned with seven 16 mm (0.6 in.) di- axial forces and shear through the nodes. ameter strands in ducts in each corner of To ensure good bond of the precast the section. Since the maximum positive segments and the cast-in-place concrete, and negative moments in the arches all of the surfaces of the precast element were found to be almost equal, this were given a heavy sandblast to an am- post-tensioning layout was the most ef- plitude of approximately 6 mm (0.24 in.). fective. No bonding agent was used but all sur- faces were thoroughly wetted prior to Typical Nodes placing the node concrete. The section The arch intersections were referred was then cast solid using the same to as "nodes." Typical interior and exte- semi-lightweight concrete as used for rior nodes are shown in Figs. 5 and 6, the segments themselves. respectively. Because the outside webs and soffits

PCI JOURNAUNovember-December 1987 57 Fig. 5, Interior node. of the precast elements were extended addition, approximately half of the pe- as far as possible leaving only a 150 mm rimeter beams enclose a steel tension tie (5.9 in.) gap, a very minimal amount of connecting the perimeter columns. formwork was required in the field for The beams span approximately 18.5 m each node. (61 ft) and are a hollow box section. A 75 mm (3 in.) precast fascia panel and 50 mm (2 in.) of insulation were cast as a Perimeter Roof Beams sandwich panel on the lower half of The perimeter roof beams support a each beam. portion of the roof, the exterior fascia The typical beam is shown in Fig. 7. and, along the east side of the building, The beam is tilted 28 degrees from the a sloped glazing structure over the ad- vertical on the building to match the ministrative offices and VIP lounge. In slope of the cast-in-place buttresses.

58

PRECAST 1 Th ARCH 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 for The tension ties cast into the perim- resisting flexural moments about the eter beams were required to be very stiff weak axis the section was pretensioned in order to be effective in transferring to resist a combination of vertical and loads between the equally stiff cast-in- lateral moments. 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 STRANDS to 1662 MPa PI • 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- It was originally intended that the ness, the tic consisted of a 300 x 200 mm bearings would be cast into the perim- (12 x 8 in.) hollow structural section with eter buttress heads prior to erection of a wall thickness of 12.7 mm (0.5 in.). the precast arches. Unfortunately, major Additional stiffness for the ties at the delays in the manufacture of the bear- extreme ends of the Oval, where the tie ings by the supplier resulted in a delay forces are at a maximum, was achieved by of approximately six months in the de- plating the 300 mm (12 in.) sides of the livery. Fortunately, it was possible to HSS with 20 mm (0.79 in.) thick plates. modify the reinforcement of the exterior nodes to allow the bearings to be in- stalled after erection of the arch seg- Bearings ments with no overall loss of time in the The thrusts from the arches are trans- construction schedule. ferred to the perimeter columns and buttresses through very large disc bearings. The typical bearing is shown MANUFACTURE in Fig. 8. The production aspects of the arch Maximum axial force in the bearing roof segments are given first followed by was 8453 kN (1900 kips) [unfactored ] the perimeter beams. while the maximum vertical shear force was 775 kN (174 kips) and lateral shear force was 1495 kN (336 kips). Shear Arch Roof Segments forces occur due to slight variations in The structural design of the arch root the thrust line of the arches depending beams using the trapezoidal shaped on the loading condition on the roof. cross section provided a very pleasing The bearings are also designed for a architectural appearance. This cross rotation of two percent to allow for de- section also provided other advantages flection of the arches. in the precast concrete production of the

60 BEARING PAD

SHEAR TlON PIN

ANC1-IOR PIN

Fig. 8, Bearing detail.

beams. It permitted easy beam strip- form which had 100 mm (3.9 in.) camber ping, eliminated basic form setup, pro- built into it. This form was also vided good "as cast" finish and per- equipped with external vibrators to pro- mitted the cage, complete with plywood vide a dense smooth beam finish. voids and end block-outs, to be preas- All beams had a 800 mm (31.5 in.) sembled and lowered into the form. wide base but there were two basic This procedure maximized repetition cross sections each with a cross-fall on and economy by permitting all 84 pre- the top of the beam. The basic form was cast concrete arch roof beams to be cast made to accommodate both cross sec- in one basic form. Although the beams tions. varied in length from 14.2 to 25.4 m For the most severe cross-fall, the (46.6 to 83.3 ft), all were cast in one steel form side heights were 1800 and 2019

PCI JOURNAUNovember-December 1987 61 psi) concrete and with adequate chamfer on the box voids, the beams were poured from the top in a one-pour se- quence using both internal and external vibrators. Girders were stripped and yarded with four 15 tonne (16.5 ton) overhead cranes. Low bed trucks with 12 wheel self-steering trailers were used to trans- port the beams to the site.

Perimeter Bars Perimeter beams were produced in two stages. In the first stage the 75 mm (3 in.) architectural exterior cladding was cast complete with 50 mm (2 in.) S.M. styrofoam insulation backing and protruding anchors. These 1530 x 3750 mm (60 x 141 in.) panels were then po- sitioned vertically in a steel form so that Fig. 9. Single steel form for arch segments. the structural portion of the beam could be poured to produce a composite sandwich structural perimeter beam with architectural finish. The structural mm (71 and 79 in.). To produce girders portion of the beam was also loafed out with the smaller cross section, a 89 mm using plywood voids within the rein- (3.5 in.) side rail was unbolted from the forcing cage and cast using standard high side to produce a form with 1800 weight concrete. and 1930 mm (71 and 76 in.) sides. Bulkhead variation was used to pro- Because weight was critical to the duce the various beam lengths 114.7 to substructure design, semi-light- 16.9 m (48.2 to 55.4 ft)] required to ac- weight concrete was used. The beams commodate the non-typical units at the were also voided using 4350 mm (171 ends of the building. Of the 28 perim- in.) long plywood boxes. These boxes eter beams, 16 required large structural were chamfered on all sides and formed steel tubes complete with end connec- a part of the cage. This preassembled tion hardware which were cast within reinforcing cage also included the four the beams. These were used as tension post-tensioning ducts, protruding end ties and ran through the loafed out reinforcing bars and inserts, and the end structural perimeter beams for their full block form. length. The inside face of the beams This end block-out form accommo- contained electrical conduits for inte- dated the variation in girder lengths and rior lights and were trowelled smooth. ensured a proper 150 mm (5.9 in.) gap between girders at each node. It also ac- curately positioned the 20 and 25 mm PEER REVIEW (0.79 and 1 in.) main reinforcing bars forming a very rigid cage assembly Due to the magnitude of the building which could be lowered into the form, and the unusual nature of the design, positioned and poured. By using super- the structural consultants engaged other plasticizer additive in the 40 MPa (5800 independent 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 truss supports. carry out a review of the design. The peer review was carried out at two stages: first, at the completion of conceptual design and finally, at the completion of the design and drawings. The concept review was considered valuable in ensuring that no judgmental errors might have been made which might result in potential increases in costs arising during the final design. The check at the completion of the final design was carried out by running a completely independent computer analysis of the structure. The software used for this purpose was a space frame analysis program written by the review- ers. Not only was the structure found to be safe, but the peer review actually saved the owner a substantial amount of money. Working from nearly complete architectural and structural drawings, Fig. 13. Arch erection near completion the peer review team was able to ana- showing temporary precast head frames lyze the structure without making as on top of scaffolding towers.

64 Fig. 14. Aerial view at completion of structural framing showing nodes at various stages of casting.

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

PCI JOURNALJNovember-December 1987 65 Fig. 16. Stressing of post-tensioning inside Fig. 17. Interior of Oval after removal of exterior nodes. shoring.

many assumptions as are often required The temporary scaffolding to support during the normal design process. the segments was designed and con- The final building configuration, di- structed by the general contractor. Two mensions, loadings, etc. were all well basic types of temporary support were defined prior to this final analysis and required: 31 towers under the interior the result was that the longitudinal arch nodes, and 26 exterior steel frames to reinforcing was reduced from approxi- support the arches at the perimeter col- mately 2 to 1 percent, a minor reduction umns. in design terms, but a saving of $120,000 Each of the interior towers was re- when applied to all 84 arch segments. quired to support a load of approxi- The authors strongly support this pro- mately 1350 kN (300 kips). Maximum cess on any major project. tower height was approximately 22 m (72 ft). The towers consisted of modified standard sectional scaffolding 2 m wide ERECTION AND x 4 m long (6.5 x 13.1 R). Each tower was SCAFFOLDING supported on four temporary timber piles approximately 6 m (20 ft) long Various phases of the production, topped by a cast-in-place pile cap. A shipment and erection of the precast screw jack was located under each tower components are shown in Figs. 9 leg. through 18. The towers were guyed in the long The precast components were trans- direction of the building. No guying was ported to the site by truck and erected, required across the oval since the towers using two cranes, by the precast were stabilized as erection proceeded supplier. by welding of the arch components.

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

The contractor achieved extremely SHORING REMOVAL accurate elevation control by precasting temporary head frames for the top of After all components had been each tower. These head frames con- erected and the interior nodes had been tained temporary steel bearing plates to cast, the post-tensioning strands were receive the arch segments. Inverted placed and stressed. Stressing was car- steel angles were temporarily bolted to ried out from both ends. the underside of each arch segment at The bearings were then set in place in the precast plant to provide a "knife the buttress heads and the exterior edge" bearing on the head frames. nodes cast. The arch components were supported The structure was now ready for re- around the perimeter of the oval on moval of the temporary supports, a sig- custom steel trusses. Each truss sup- nificant event for the designers and ports a load of approximately 50 tonnes contractor. (55 tons). To complicate matters, the The first step was the removal of the load had to he supported under the end temporary steel angles supporting the diaphragm in the arch segments which segments on the perimeter steel trusses. occurred approximately 3 m (10 ft) away This was accomplished by simply burn- from the center of the perimeter column. ing out the angles to allow the weight of To allow for temperature changes, the arches to be carried by the shear pin shrinkage, and elastic shortening of the in the center of the hearings. Removal of arches due to post-tensioning, the pe- the perimeter supports first would allow rimeter trusses supported a sliding the arches to rotate as the interior tow- hearing seat inclined at an angle parallel ers were removed. to the centerline of the arch segment, Although a screw jack was provided in

PCI JOURNALINovember-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 was have been noticeable by their absence. anticipated that friction on the thread The intersecting precast concrete would be too great to allow this to be segmental arch system used for the turned. Accordingly, a small bracket was Olympic Oval allows the precast pre- welded to the side of each leg and a stressed concrete industry to compete in small hydraulic jack was used to lift the the long span building market without load off the screw while it was turned. any new, expensive plant or erection In order to prevent overstressing of technology. The system is economical the structure during lowering, each architecturally exciting; and, with the tower was dropped incrementally only advent of high strength concretes, capa- 10 mm (0.39 in.) at a time. As the pre- ble of almost any span. dicted dead load deflection was be- The Olympic Oval was a winning tween 40 and 50 mm (1.6 and 2.0 in.) it project in the 1987 PCI Professional De- was anticipated that Four to five incre- sign Awards Program. ments would be required at each tower. This required the contractor to move back and forth from one tower to another CREDITS as he gradually moved from one end of the building to the other. The actual de- Owner: The University of Calgary, Cal- flection at the first tower to he com- gary, Alberta, Canada. pletely unloaded was approximately 43 Architect: Graham• McCourt, Calgary, mm (1.7 in.). Alberta. While this operation seems rather Structural Engineer: Simpson Lester primitive, the lowering operation easily Goodrich Partnership, Calgary, Al- kept ahead of the crews dismantling the berta. towers and, in fact, the towers were Engineering Review: completely removed at the north end Dr. Walter Dilger, University of Cal- prior to completion of jacking at the gary. south end. Dr. Gamil Tadros, Speco Engineer- ing, Calgary. General Contractor: W. A. Stephenson CONCLUDING REMARKS Construction (Western) Ltd., Calgary, AIberta. Construction began in March 1985 Precast Concrete Manufacturer and and the roof structure was effectively Post-Tensioning: Con-Force Struc- completed by June 1986. Finishing tures Ltd., Calgary, Alberta, trades and interior work continued until April 1987. The end result is indeed a most beau- REFERENCES tiful and functional structure (see Figs. 19 and 20). Lester, W. B., "Olympic Oval — Beauty Historically most long span buildings on a Budget," Concrete International, V. 9, No. 8, August 1987, pp. 10-18. have been constructed of light materials, Clark, Jack; McKeown, Shawn; Lester, usually steel. Recently, tension struc- W. Barry; Eibner, Len, "The Lateral Load tures and fabrics have received a sub- Capacity of Large Diameter Concrete stantial amount of both positive and Piles," Proceedings 38th Canadian Geo- negative publicity. Except for a rela- technical Conference, Canadian Geo- tively small number of domes and technical Society, Montreal, Canada, shells, concrete long span structures 1985, pp. 409-418.

PCI JOURNALNovember-December 1987 69