Precast Prestressed "Space Mountain" Highlights Walt Disney World

Precast prestressed "Space Mountain" highlights Walt Disney World

Christian J. Birkeland Vice President Erik Prestegaard Marketing Manager Doyle F. Ridenour, Jr. Senior Des?gn Engineer ABAM Engineers, Inc. Consulting Engineers Tacoma, Washington

Christian J. Birkeland Erik Prestegaard Doyle F. Ridenour, Jr. Describes the precast prestressed design/construction considerations that went into building Walt Disney Worlds monumental "Space Mountain" at Lake Buena Vista, Florida.

12 Space Mountain

recast prestressed concrete was used P effectively to build Walt Disney Conceptual Design Worlds spectacular "Space Moun- tain" at Lake Buena Vista, Florida. The size and function assigned to the structure as well as the general appear- This mammoth structure, which is in ance and style of surrounding facilities the shape of an elevated truncated in the park-like layout demanded a cone, reaches 183 ft high and has a "futuristic" design concept that would 300-ft diameter. yet be compatible with the adjoining Inside its sky-high, column-free are- structures. na, Space Mountain houses a series of WED Enterprises suggested a trun- space-age rides—combining the natural cated cone roof with external, radial thrill of weightlessness and nonlinear ribs. The interior surface of the cone motion with a brilliantly conceived il- was to be used for image projections. lusion of space travel. The facility was opened to the public °The master planning, design, and engineer- in January 1975. ing arm of Walt Disney Productions.

PCI JOURNAL/September-October 1975 13 ON CRETE

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CHANNEL CONNECTION DETAIL However several consultants pointed cated so as to provide a minimum out that such a concept was not only amount of obstruction to ride structures exceptionally difficult to realize but also inside the building. A beam grid spans structurally questionable, and a tradi- between the columns and in turn sup- tional "bubble" shaped dome should ports the ledger ring which receives the be considered. roof channels. Finally, the eventual structural engi- The overall depth of the center slab neer was consulted to render an opinion is 60 in., with an integral 8-in, slab as to the feasibility of the "bubble" spanning between grid beams. The cen- concept. This firm suggested an imagi- ter slab structure contains 700 cu yds native concept featuring the extensive of concrete and was cast-in-place on use of precast and prestressed concrete scaffolding 96 ft off the ground. components—allowing a structural con- The principal beams, B1, B2, and B3 figuration that is in close conformance (see Fig. 1), were post-tensioned in the with WED Enterprises initial design. field to balance the loads from the roof The resulting structure features a channel erection. The remaining beams cast-in-place, post-tensioned concrete and the ledger ring have only mild "waffle" center slab, elevated on cast- reinforcing steel. in-place columns, precast concrete pe- To simplify the post-tensioning op- ripheral columns, precast/prestressed erations, an erection sequence for the concrete outer ring beams, and pre- roof elements was developed so as to cast/prestressed concrete pie-shaped, provide a symmetrical load pattern for channel-type roof elements. the center slab. Roof channels Structural Components The 72 roof channels, approximately 116 ft long, span the 100-ft horizontal As was mentioned previously, the basic distance between the center slab and structure of Space Mountain is in the the ring beams. They weigh about 75 form of an elevated, truncated cone. tons apiece and are inclined at 30 deg. The conical roof surface, consisting to the horizontal. of 72 tapered channel beams with The channels were cast in a self- stems extending upward, is supported stressing steel form, capable of reacting by a center slab at its apex and a series a 700-ton initial prestressing force. The of 36 ring beam segments at its lower perimeter. The ring beams, in turn, are formwork was manufactured to very close tolerances in accordance with supported by 36 precast columns. the required closeness of fit in the final The overall diameter of the structure structure. is 300 ft at the perimeter and 100 ft at the center slab. The clear inside The upturned legs of the channel height is 35 ft at the perimeter and section are tapered for ease of form re- 100 ft at the center slab. moval, and splay in plan to cover a The following is a brief description 5-deg sector. of each individual structural compo- A 4-in, slab spans between the chan- nent. See also Figs. 1 and 2 for a plan nel legs-11 ft clear at the ring beam of the structure and details of the and 2.2 ft at the center slab. They are components. 4 ft deep, with an overall width of 13 ft 21/z in. at the bottom. Center slab One-half of the prestressing steel The center slab is supported by four is located in the 4-in, slab, the remain- 60-in, diameter columns which are lo- der divided between the two channel

16 legs and harped at the one-third points. To limit deflections to a mini- Number and mum, the prestressing moment has Dimensions of been designed to accurately balance the dead load moment imposed by the Precast Units channel weight. (see also Figs. 1 2) Channel Beams Outer ring beam 72 precast, prestressed The outer ring beam structure is a concrete channel beams, 4 ft closed, circular multi-bay frame con- deep and 116 ft 1/4 in. long. sisting of 36 piled foundations inter- Width varies from 13 ft 2 1/2 in. connected by grade beams, an equal at bottom to 4 ft 5 1/4 in. at top. number of precast concrete columns ex- Stems are 15 in. thick at base, tending from the foundation and con- tapering to 9 in. Slab nected at the top by 36 precast and thickness is 4 in. prestressed tee beams. All connections are rigid to react sidesway imposed by Tee Beams lateral loads. 36 precast, prestressed The precast, simply reinforced col- concrete tee beams, 25 ft umns are 35 ft 9 1/2 in. long with a bot- long with flange width of tom cross section of 1 ft 6 in. x 4 ft 6 8 ft. Base width of stem is in. and a 1:48 taper on the longer axis. 2 ft. Flange is 2 in. thick at The columns were cast in forms al- ends tapering to 4½ in. at ready on hand from a previous project. stem. The precast and prestressed ring Columns beams are of a tee configuration, 25 ft long with an 8-ft flange width and 36 precast concrete columns, 35 ft 9 3-ft overall depth. Stems are 2 ft wide 1 in. high. Base cross at the base, flanges are 2 in. thick at the section is 1 ft 6 in. x 4 ft 6 in., with a 1:48 taper on the ends tapering up to 41/2 in. at the stem. longer axis. Connections are facilitated by extending the column reinforcing steel a certain distance beyond the upper and lower end faces. The bottom ex- beams, produced a continuous ring tensions were placed in corrugated beam structure. After erection of the pipe "cans" cast into the pile caps, the roof channels, the final concrete clo- columns positioned and levelled on a sure is reinforced as a complete ten- set of levelling bolts and the metal sion ring and diaphragm connection cans filled with concrete upon final between precast columns. alignment. The gap between column and pile cap was later filled with low shrinkage grout. Design Considerations Similarly, the top column bar exten- sions were placed in pipe sleeves pro- The design concept developed for vided in the tee beam stems and conse- Space Mountain, resulted in a visual quently grouted in place. An in-situ appearance that is both excitingly fu- concrete placement with mild reinfor- turistic yet very compatible with the cing, providing a 6-in, topping to the surrounding structures and facilities. tee beam flanges and joints between The extensive use of precast and pre-

PCI JOURNAL/September-October 1975 17 Fig. 3. Installation of precast peripheral columns and precast prestressed peripheral tee beams in outer ring. Center slab scaffolding and formwork is in background.

Fig. 4. Aerial view of center slab. Note recesses for post-tensioning anchors. Fig. 5. Completed center slab structure temporarily guyed to outer ring foundation.

Fig. 6. Ring beam installation. Note that the ride structure is being erected simultaneously.

Fig. 9. Roof installation progress. The channel sections were placed sym- metrically (see also Fig. 8).

Fig. 10. Roof installation nearing completion.

PCI JOURNAL/September-October 1975 21 Fig. 11. Aerial view of completed roof structure.

Fig. 12. Completed structure.

22 Fig. 13. Space Mountain majestically nestled.

Fig. 14. Panoramic shot of Space Mountain and environs.

PCI JOURNAL/September-October 1975 23 stressed components accomplished movement as the channel would de- two major objectives: flect inward. The joint connection uses bolts as shear friction reinforcement in 1. WED Enterprises desire to create order to establish diaphragm action a conical roof configuration was realized necessary for lateral resistance. after such a concept had previously been advised against by other consultants. The truncated cone roof surface, Construction the interior of which is used for image-projection associated with the Figs. 3 through 14 show pictorially the rides, was given a monolithic insulat- various construction stages of Space ing/reflecting layer during channel Mountain. beam production. The material, in The central slab, elevated on four sheet form, was installed in the form cast-in-place columns, was concreted in prior to concrete placement; thus the situ and post-tensioned (see Figs. 3, beams once removed from the form 4, and 5). The center structure was were complete with interior finish. temporarily guyed to the outer ring 2. Because of a very tight construc- foundation. tion schedule, a concept had to be de- At about the same time, the precast vised that would facilitate erection of peripheral columns and precast pre- structural elements from the outside of stressed peripheral tee beams were the building while interior nonstructur- erected (see Figs. 3 and 6). al activities could proceed concurrent- ly without delay or obstruction. The When this operation was complete, roof system solution based on prefab- the 75-ton precast channel sections rication of beam sections, eminently ac- could be lifted into place (see Figs. 7 complished this objective, and the con- through 11). struction schedule was complied with. At the precasting plant, lifting loops The simplifications and innovations were cast into the channel slabs for developed through the successful com- handling and erection purposes. Ceil- pletion of the structural design are ing material was also placed in the form worthy of some mention: prior to the start of concreting opera- tions. Later on, this surface was painted The previously mentioned restric- before the members were hoisted into tions on inside activities required the place. roof elements to span from the outer ring to the center slab structure with- All of the precast prestressed ele- out intermediate shoring nor shell-type ments were manufactured near the action. Normally in a shell, circumfer- building site. ential forces would be induced during Installation of the giant-sized units superimposed loadings with compres- was done with an American Sky Horse sion within the shell and tension in the crane. A specially-designed radial der- outer ring. rick that consisted of a crane boom These forces were not introduced hinged to a T-frame helped this opera- since the channels had sufficient tion. Wheels on the frame enabled it to strength to span radially without inter- run on a radius at the edge of the core mediate supports. Therefore, a chan- slab. Powered by a three-drum hoist, nel connection detail was developed the derrick tilted the roof pieces to which would allow circumferential their final 30-deg angle.

24 Figs. 12 through 14 show various con- Owner: Walt Disney World Co., Inc., figurations of the completed structure. Lake Buena Vista, Florida. Since completion, the structure has Precast Concrete and General Contrac- performed well and, in general, has tor: Buena Vista Construction Co., confirmed the philosophy of design. Lake Buena Vista, Florida.

Note: All the photographs are copy- righted by Walt Disney Productions. Credits

Design (Conceptual/Architectural/En- gineering): WED Enterprises, Glen- Acknowledgment dale, California. Prestressed Concrete Consultants: The Prestressed Concrete Instiute ABAM Engineers, Inc., Consulting wishes to express its appreciation to Engineers, Tacoma, Washington. WED Enterprises for release of this Design (Structural): Wheeler and Gray, technical information and for their Consulting Engineers, Los Angeles, hep during the preparation of this pa- California. per.

Discussion of this paper is invited. Please forward your discussion to PCI Headquarters by February 1, 1976.

PCI JOURNAL/September-October 1975 25