or more than twenty years now the Olympic Stadium in Montreal has been widely cited as an example to be avoided. Long a rival to Montreal, Toronto proposed to build itself a major league stadium, with a movable roof. Hatch's initial involvement with movable roofs was largely an accident of geography, since the company headquarters is in the Toronto area, site of the retractable roof stadium which came to be called Skydome. It may be asked why two Canadian cities, opted for facilities which were so novel and risky at the time. The answer lies in the weather - Canada is a cold country and outdoor spectator sports in spring and late summer can be spoiled by unpleasantly cold days. As far as the technical challenge was concerned, Canadian engineers proceeded with confidence based on a long history of heavy engineering in the resource sector, and felt little need to look beyond their own engineering heritage for reassurance. 

The lessons of Montreal were carefully noted and great stress was placed on due diligence. The members of the consortium which eventually executed the design/ build contract, collectively called the RAN group, were all well established and respected companies, equipped with the technical and construction skills needed for the project. The Owner, on the other hand, which was first a government appointed entity and later a private corporation, did not have technical personnel - no Owner's engineer - to monitor the activities of the supplier. 

Thus the TEC, (Technical Evaluation Committee), was brought into being, with a wide-ranging mandate and an adequate budget. The assembled group contained specialists in all aspects of the stadium design, who were charged with the task of closely evaluating RAN's engineering solutions and proposed equipment. For areas, which were termed high-risk, principally the movable roof and its associated equipment, the review included the making of a complete set of "parallel" calculations. The engineer who reviewed the roof structure in detail was Peter Sheffield Associates. 

For the roof mechanical, electrical and control systems, the reviewing engineer was Hatch. The work carried out by Hatch began just as RAN finished basic engineering, and continued until commissioning of the roof was completed. All drawings, including shop drawings, were reviewed and a complete, independent set of calculations was made. Regular meetings were held, during which differences were clarified and settled. Hatch lays no claim to authorship of the design, but its participation did result in a number of changes and improvements. 

Beyond Skydome 
The most important lesson of Skydome is that the discontinuous work processes of North American construction should not be applied to the design, manufacture, installation and commissioning of movable roof machinery. A better approach is to follow the practices of manufacture and procurement used in industries where such systems are the norm. This is characterised by integration of tasks, rather than dis-integration, so that the number of responsible parties is reduced to the lowest number. 

A second lesson learned is that the equipment design must be simplified, not only in accordance with its function but, just as importantly, in accordance with the abilities and training of the available operating and maintenance personnel. A movable roof has a low duty cycle compared to industrial machinery, and its designers should strive for reliable low-tech solutions that require only one maintenance intervention annually. 

 
Three of the lower bogies with BankOne Stadium roof in open position.

Following the Skydome project Hatch participated in the Ellerbe-Beckett team which was successful in the competition to design the new BankOne ballpark in Phoenix, Arizona. Four significant requirements of the competition were as follows: 

• The facility to be for baseball only.

• The playing surface to be natural grass.

• A retractable roof to be included.

• The facility to be air-conditioned.

The winning design featured a roof with eight panels, two being fixed, and six being movable. Three movable panels open eastwards from the centre of the building and three open westward. The leading edges of the movable panels consist of a truss fitted with multi-wheeled (lower) bogies at each end. The trailing edge of each panel is supported on the panel below by multiple (upper) bogies spaced across the span. 

The drive requirements arising from the roof design are as follows: 

• The lowest moving panel travels approximately its own length, the middle one twice its own length, and the upper panel travels three times its length.

• If all panels are to stop and start together, then their respective travel distances determine their speeds.

• Since the maximum distance travelled by the uppermost panel is equal to one half of the total roof opening, the time to open and close is intrinsically short.

• The drive should maintain the "squareness" of all panels as they move along the track.

The drive chosen consists of two wire rope winches, one on the east end, and one on the west end. Each winch has three grooved drums, geared together to provide a panel speed ratio of 3:2:1, and each provided with grooves sufficient to accommodate the length of steel wire rope (cable) needed for the travel distance of each panel. Its weight is approximately 60 tons and its dimensions are 44 ft. long x 8 ft. wide. 

This design was chosen because of the following benefits: 

• All panels move together at a speed appropriate to their travel distance.

• The rope system ensures that all panels remain "squared" during travel.

• The positive nature of the winch drive eliminates the effects of operating wind loads (40 mph), since uplift due to wind cannot reduce roof traction.

• The winch-mounted brakes are of sufficient capacity to permit the roof to be stopped in open, closed or intermediate positions, and yet resist the maximum wind load without requiring additional locking devices.

The alternative to the rope drive described above was to drive the roof panels through the wheels, as on Skydome. This has the following drawbacks: 

• Wind and weather can affect adhesion of the wheels.

• Squaring of the panels is not assured and must be constantly confirmed by position transducers working in conjunction with a PLC.

• Security of the panels under high wind conditions requires additional locking devices

• Multiple electric motors and brakes create maintenance problems insofar as the failure of one or more motors cannot be readily detected without additional diagnostic aids.

• Six cable reels are required for electric power and control cables.

In general, a wheel drive system requires more complex electric/control/computer systems - the maintenance requirements of these systems are unlikely to be matched by the skills of maintenance personnel in sports complexes. 

At the time of writing, the BankOne roof drive has just been commissioned. Its operating reliability cannot yet be compared to that of Skydome. It can be said, however, that its commissioning was trouble-free and much faster than at Skydome. The BankOne design features twelve large doors, which are located in the north wall of the building. 

These doors will be opened to provide a panoramic view out of the stadium and to increase the sense of openness of the facility. The doors are approximately 64ft high x 32ft wide and are hinged to open inwards. The engineering of the doors and their opening mechanisms was carried out in a similar manner to the roof and represented about one-quarter of the total engineering effort expended by Hatch. 

Driving Seat 
Three methods of delivering the engineering services related to the roof drive are now discussed. 

METHOD ONE: Drive consultant provides complete engineering services, including shop drawings. This method places full responsibility on the consultant - but provides him with the control to match that responsibility. 

The equipment supplier's responsibilities are confined to fabricating and installing the equipment in accordance with the consultant's drawings. It should be noted that the cost of detailed engineering, normally 15-20% of the selling price of custom-designed equipment, should be transferred from the capital cost budget to the engineering budget. 

METHOD TWO: Drive consultant provides general arrangement drawings and a specification only. Qualified contractors then issue this for competitive bidding. The principal advantage of this method is familiarity to the construction industry. The disadvantages are more significant and include the following: 

• The design responsibility is split between the consultant and the supplier.

• The drive supplier is involved in competitive bidding and has an incentive to interpret the specification in a manner, which reduces quality.

• It is difficult to evaluate competing bids since they will likely be short on detail and incorporated into a larger bid package.

Hatch considers that the split responsibility inherent in this method raises the consultant's risk to an unacceptable level, and we would not participate in such an arrangement without substantial legal release. 

  Roof-drive winch during installation at BankOne Stadium.

 
METHOD THREE: Drive consultant forms a partnership with an equipment supplier/ installer to provide a turnkey drive. This method is simple and compact, but would likely be in conflict with the procurement policies of public agencies. 

For BankOne Ballpark the first method was chosen. The Owner and Project Manager considered and understood the differences between the different methods, and concluded that the clear responsibilities inherent in the first method were in the best interests of the project. Their choice was a good one and the roof drive has been implemented in a harmonious and successful manner. The scope of work performed by Hatch consisted of the following: 

• Conceptual design

• Basic engineering

• Detailed engineering, including 100% shop drawings

• Equipment procurement and expediting assistance

• Shop inspections

• Shop testing attendance and verification

• Field assistance during construction

• Field commissioning assistance

• Preparation of maintenance manual

• Training of Owner's operating and maintenance personnel

Overdrive 
In looking to the future of stadiums, the challenge is to find ways of making them profitable. Sports and recreation complexes will become profitable only by attracting patrons almost every day, and this can best be achieved through multi-use/multi-configuration technology. Hatch has developed a number of patented systems, which permit multiple uses and short conversion times. These provide two full-size surfaces, one inside the building and one outside, each of which may be converted to natural grass, smooth concrete, or water. In addition, conversion from full-size stadium mode to a more intimate arena mode is featured. 

Such a facility creates the promise of providing medium-size cities with a single venue, which can facilitate all professional sports, as well as conventions, trade shows, concerts and community events. It is hoped that the architectural and logistical problems can be solved and that such facilities may begin to emerge early in the next century.