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Retractable roof structures in the US have had a rocky introduction in terms of adherence to budget, schedule and meeting owner expectations. How well will they fare on the operational and maintenance side in the first years after opening day?Two experts in retractable roof design - Bart Riberich of Uni-Systems, Inc. and Lawrence G. Griffis of Walter P. Moore, USA - offer some insight. |
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What now? Well, somebody has to operate and maintain the retractable roof and its systems, and this may well be the biggest challenge of all. That is, unless this part of the project has been properly planned and implemented. Successful operation and maintenance of retractable roof facilities
begins in the early stages of conceptual design. Initial programming and
schematic design decisions ultimately have a significant effect on the
safety, reliability, convenience, and cost of operating and maintaining
a retractable roof system. Some of the structural and mechanism
considerations critical to operation and maintenance follow. |
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Consider These PROTECTION OF THE STRUCTURE: Water penetration and corrosion are problems for any exposed structure - and retractable roof buildings are no exception. Proper planning in the design stage can reduce problems on the operation and maintenance side. For the structure, this means avoidance of water build-up and penetration by good drainage details. Selection of high-quality paint systems for the structural steel will reduce corrosion of steel members and joints. Paying close attention to the seals between moving and fixed roof portions is also important to protecting the structure and the mechanized system. PERSONNEL & MATERIAL ACCESS: Retractable roof mechanisms and their associated subsystems are most generally located high in the structure, at remote locations that would not otherwise require convenient access. However, for retractable roof facilities, provision for safe and convenient personnel and material access to these remote areas should be a high priority for the design team because this is one of the most significant factors affecting safety and cost of operation and maintenance. For safe and convenient personnel and material access, elevators should be provided to the highest elevation practical. Above the level to which elevator service is provided, standard stairs should be made available for vertical personnel access to mechanisms. Standard, fixed ladders and ship's ladders should be avoided as the only vertical access to mechanisms, if at all possible. Designers should ensure that they provide ample, safe, horizontal access to all areas requiring maintenance as well. Catwalks may be adequate access to areas that are likely to require only visual inspection or to small components such as sensors. SAFETY: In addition to the many structural design challenges offered by a moving structure, retractable roof facility designers must consider operating safety issues. In other words, the design team must focus on some safety-related design issues that would normally be the domain of machine designers. Consideration must be given to guarding pinch points and rotating equipment. Video surveillance of the travel path may be deemed to be important to the safe operation of the system. Visual and audio warning signals prior to operation of the mechanism may be appropriate. Collision avoidance systems such as sonic sensors may be used to shut down the system in the event that an obstruction is inadvertently left in the travel path. Design redundancy of critical motion control systems is an important design consideration. Physical end of travel stops and bumpers to stop motion of the system in the event of a control system failure are an important design feature. CONTROL SYSTEM: The operating controls are the interface between the operator and the mechanism. This interface and its associated control system can be as simple as a push button or as complicated as a sophisticated interactive touch screen connected to multiple computers and programmable logic controllers (PLCs). In almost all cases, the more sophisticated systems have an operational advantage and are worth a slightly higher initial cost. Optimally, these systems provide a Human Machine Interface (HMI) in the form of a PC screen and mouse. The control screens should be custom designed for easy operation and presentation of the maximum amount of operating information. The best control systems include weather monitoring and reporting, operating status indications of all major drive components, system speed and position feedback, system diagnostics, and on-screen trouble shooting support. For optimum operator support, these sophisticated systems can be connected directly to the system manufactures facility via DSL so that real-time troubleshooting and guidance is available for the operator from a remotely located expert. Most of the retractable roof systems currently in service are expansive systems with drive motors and sensors spread out over several acres. The design team should give significant consideration to the most safe and convenient location for the operator control station. The operator control station can be located on-board or at a remote location. Ideally, the operator control station should be located where there is very easy access and where the operator has a line of sight to the roof and its movement. Operation and Maintenance WATER PENETRATION & CORROSION: One of the unique features of a retractable roof building is the fact that it is both an open and enclosed structure. The roof can be fully open, fully closed or oftentimes anywhere in between. This means that water from rain or snow must be removed from the large roof areas in a variety of configurations. Without proper planning for good positive drainage, water can spill onto structural steel joints or sensitive mechanization parts and cause damage or corrosion if left unchecked. Seals between roof sections are always vulnerable and should be routinely inspected for possible damage. Periodic inspections should be performed for unexpected water infiltration into the building. PAINT SYSTEMS: A good coating system for all exposed structural steel is a must for a retractable roof building. The steel should be inspected periodically for signs of corrosion and breaches to the paint system. EXCESSIVE WEAR: Most retractable roof structures ride on steel rails. These rails need to be regularly inspected for signs of wear or excessive noise indicating wear. Wear or noise at the rail can be a sign of misalignment in the system. The key is preventive maintenance to ensure there is never down-time for an event. PREPARATION FOR SEVERE WIND STORMS: Because of the multiple roof positions required for retractable roof buildings, these structures are usually designed for several wind levels. There will be a limit to the maximum winds that can occur for the roof to open or close. For severe winds, such as hurricane storms, there may be a requirement that the roof be fully closed and battened down in some fashion. It is critical for the safety of the roof system that the owner understands the structural requirements for different wind events and the building personnel prepared to respond to the situation. If on-site weather stations are part of the monitoring for wind speeds, the equipment must be kept in working order and the building personnel trained to perform the required steps. OPERATIONS & MAINTENANCE MANUALS & TRAINING: One of the most
critical elements of a smooth transition from the design/ construction
team to the team responsible for operation and maintenance of a
retractable roof system is the provision for effective training and
quality operation and maintenance reference materials. In order for
operation and maintenance activities to commence safely and effectively,
the owner must commit to having his operations and maintenance team in
place well before opening day. The operation and maintenance staff must
be available prior to opening day to set up parts inventories, plan
maintenance programs, plan operation logistics, participate in the
turnover of the system, and participate in a single training session
provided by the mechanism supplier. |
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Enron Field, Houston, Texas - hydraulics inspection
on the Carrier Beam. |
Electrical control panel inspection on carrier beam. |
Maintenance of Wheel Box assembly for Carrier Beam. |
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WARRANTY ISSUES: Unless special provisions are made, most roof mechanization systems would be provided with a standard one-year construction warranty with all operation and maintenance being the responsibility of the owner. Many owners have a desire to have an extended warranty period on the roof mechanism. However, if the owner chooses to split responsibilities by having several different parties responsible for warranty, maintenance, and operation of the system, he may not achieve the desired result of minimizing his risk and management burden. If an owner desires to minimize his risk and system management effort, he should consider an extended service agreement with one contractor to cover maintenance, operation, and unscheduled repairs. An owner should evaluate his warranty, maintenance, and operation needs very early in the contracting process. SPARE PARTS INVENTORY: An appropriate spare parts inventory must be maintained in order to ensure the most reliable operation of the roof and short down-times in the event that the repair and replacement of parts is required. Typically, many components of the mechanism are very large custom machined components. Other components are standard manufactured parts but require custom configuration or finishing. These custom manufactured components can take up to twelve weeks for delivery after placement of an order. For these reasons, it is beneficial for the design team to develop a recommended spare parts list and for the owner to purchase the spare parts inventory as part of the original mechanism supply contract or as a separate purchase at the time of production of the original mechanism components. OPERATION & MAINTENANCE TOOLS & MATERIALS: The maintenance staff will need to maintain a significant array of both common and very specialized tools for maintenance and repairs. Many maintenance and repair activities are likely to involve jacking roof loads off wheels, partial disassembly of the mechanism/structure and manipulation of large heavy objects. These operations can require large equipment for hoisting and moving parts as well as high capacity hydraulic tools for moving and supporting loads. In addition to tools and equipment, there are consumables used to maintain and repair systems. OPERATION & MAINTENANCE STAFF: Operation and maintenance activities include a wide variety of tasks that require a range of skill sets. Many of the routine maintenance operations are lubrication and inspection tasks that are suitable for mechanics or millwrights. Many of the scheduled maintenance, inspection, troubleshooting and repair tasks require the skills of a highly trained electrical controls technician. Inspection and testing requirements, such as surveys, material testing, used lubricant analysis, surface hardness testing, etc., are best suited to be performed by testing laboratories, surveyors, structural engineers, mechanical engineers and electrical engineers. Generally, any responsible employee with modest computer and technical skills could be trained to be an effective member of the operating crew. These operation and maintenance activities should be planned and managed by a skilled professional. The quality of the work performed by the maintenance and operating staff has a great effect on the life cycle costs of the roof system. BUDGETING FOR OPERATION & MAINTENANCE: The operation and maintenance of retractable roofs is a relatively new challenge faced by sports venue owners and managers. Therefore, there is not a wealth of historical cost data for these activities that can be used as a basis for budgeting and planning. Although costs can vary widely with a variety of system designs and contract terms, some general cost guidelines are presented below based on experience. These figures are provided primarily as a framework for owners to begin budget planning. The construction costs for the retractable roof systems currently in service in North America range from about US$35 million to about US$70 million.
Enron Field,
These construction cost figures are for the moving portion of the roof, the roof mechanism, the roof control system and the rail on which the roofs travel. The cost of the drive mechanism, its associated control system and the roof rail ranges from about US$7 million to US$14 million of the total roof costs listed above.
Generally, if maintenance and operation responsibilities are shared by one group, an efficiency is realized which is beneficial to the owner. Extended service agreements that cover all spare parts, tools, maintenance, and repair costs associated with the mechanism for the term of the agreement minimize the owner's risk but can have an annual cost of two to four percent of the roof mechanism construction cost. For example, a ten-year service agreement to cover a mechanism that cost US$10 million to design, manufacture and install could have a total contract value of about US$2 million to US$4 million. These agreements can be drafted to include operation for only a modest cost increase. These types of extended service agreements can ultimately be the best value for the owner. Final Analysis Although the costs listed above may not be accurate for every facility, the most important point for owners to remember is that these costs exist in one form or another, and they should be defined and planned for as early as possible. It is critical that owners, designers and operators of retractable
roof facilities address all of these issues to ensure the long-term
successful performance of the building. After all, for that
all-important critical event, when the operator hits the "GO"
button, everyone will expect the roof to respond - long after the first
game is over! Bart Riberich, P.E., CWI, M.S. Civil Engineering, is Vice President of Engineering at Uni-Systems, Inc. He has designed, patented, manufactured, installed and maintained many unique and innovative mechanized structures, including mechanisms for retractable roofs, operable walls and mechanized entertainment features for stadia. Lawrence G. Griffis, P.E., M.s. Structural Engineering, is President of the Structures Division at Walter P. Moore. |
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onstruction
is substantially complete (or at least as complete as it gets these
days), the punch list has but a few remaining items, the political
opening day speeches are over, and the first game hoopla has finally
come and gone.
