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.