Recreation Centers Are Unique: Some Issues to Plan For
The design and construction process for buildings of any type is complicated, to say the least, and filled with opportunity for missteps. The recreation center, though, is more complex than might be expected, involving close tolerances on flooring, concrete flatness and dryness, humidity control in the HVAC systems, and much more. Hopefully the project team will have had prior experience with similar building types and be able to avoid problems by understanding the special features of recreation centers and anticipating the issues.
Recreation center gyms may have wood floors or poured sports floors; either way the balls don’t bounce properly if the floors aren’t flat. So, how flat is flat? Flooring manufacturers and the subcontractors who install the flooring require the substrate to be of acceptable flatness (and dryness) before the flooring installation begins. The architect specifies in the design documents how flat the concrete slabs must be.
FF/FL is the construction shorthand for the flatness and levelness measurement of a flooring surface and is the American Concrete Institute (ACI) standard. FF, or Flatness F-Number, is a numeric value that defines the maximum floor bumpiness allowed over a 2 ft (0.6 m) distance; FL, or Levelness F-Number, defines the tilt or pitch of a floor over a 10 ft (3 m) distance. The higher the F-Number value, the more level or flat the slab. For example, an FF/FL of 40 30 may be acceptable flatness and levelness (the first number is always the flatness). For gym floors in recreation centers, a 50 FF is not uncommon.
If an F-Number is specified for flatness, it must be at least the equivalent of the Maple Flooring Manufacturers Association (MFMA) standard 1/8 in. (0.3 cm) in 10 ft (3 m) radius tolerance, which is roughly a 40 FF. Flatness measurements are taken within 72 h of the slab placement, because slab flatness can change over time as the concrete cures, or dries out. Preferably, measurements are taken as soon as each day’s placement is dry enough to bear foot traffic; the results can then be used to make corrections in any construction problems before placement is repeated the next day.
Flatness and levelness are more readily achievable for "slab-on-grade" concrete than for "elevated slabs," or concrete slabs poured on a prepared surface on the ground (as opposed to upper floors). Accordingly, elevated slabs typically are measured only for the single FF number.
Concrete floor slabs above grade are either (1) composite construction, consisting of light gauge corrugated metal deck, reinforcing steel mesh and concrete, or (2) poured-in-place concrete. The wet concrete is heavy, and when poured the weight causes the metal deck on which it rests to deflect, or sag slightly. When the elevated slab cures, or dries out enough to take weight, or load, other than itself, it is a little lower in the middle of the span.
To counteract some of the deflection and keep the slab as flat as possible, shoring can be placed under the midpoint of the span of the metal deck, as shown in figure 11.4 for the Cleveland State University Recreation Center project. These measures typically are supplemented by filling in low spots on top of the slab if necessary.
Prior to flooring installation, the installer measures the substrate flatness before accepting the conditions as satisfactory for the final surface. The FF readings can be taken in 1 ft (0.3 m) intervals in 11 ft (3.4 m) sections using equipment specialized for that purpose; however, many installers may rely on the basic straightedge method.
Concrete and Flooring: The Dryness Chase
The concrete under gym floors not only has to be really flat, it has to be really dry. If it’s not dry enough, the flooring that goes on top of it may have serious problems, such as debonding, blistering, buckling, or adhesive failure caused by water vapor.
On the recreation center construction site, the race is on to dry out the concrete slab in time for the flooring installation, whether the floors are wood, synthetic sports floor, or vinyl tile. Each flooring material has an industry standard for how dry the concrete substrate has to be before it is acceptable, and each product manufacturer may have its own requirement.
Although concrete looks monolithic and impenetrable, it is actually quite porous to water vapor. The water that is added to the concrete mix to make it fluid enough to easily pour into place eventually evaporates, leaving tiny voids throughout the slab. Water vapor migrates through these voids, moving from areas of higher relative humidity to areas of lower humidity, such as from the ground below the slab on grade to inside the building.
The properties of the concrete are affected by a wide range of factors, such as weather; amount of water in the mix of the cement, water, sand, lime, and aggregate (stone) that concrete is made of; the mix design; and the amount of time between mixing and placement. Some or all of these factors can conspire to cause a floor slab to be too moist to accept the flooring material.
So, what do you do about this problem if you are the CM? You dry the slab out until the numbers are right. The numbers are the measurement of the concrete dryness, and low numbers are needed for flooring material adhesion and performance. Typically, testing is conducted with either surface moisture meters or standard test kits that collect the moisture in a 1 square foot (SF) (0.09 m2) area over a 24 h period. The moisture emitted by the slab is absorbed by a measured amount of calcium chloride and weighed. The weight is expressed in pounds per 1,000 square feet (SF); the lower the number, the drier the slab. Sensors embedded in the body of the concrete are the most accurate moisture measurement method but are less commonly employed for this building type.
The drying-out process can take a long time, but the flooring installation has to wait for the moisture emission levels to be low enough, or else the flooring will fail in some way. For example, wood floors may require results to be 3.5 lb (1.6 kg) or less to be right for the flooring installer. For rubber and vinyl floors, 3.0 lb (1.4 kg) or less is generally the standard. Moisture testing is conducted by a trained and certified independent testing agent. The test results are reviewed by the architect or a knowledgeable consultant to determine whether or not the surface is ready for the flooring installation.
Drying out the concrete is mostly a matter of time, but the process can be accelerated by methods employed immediately after the slab is poured and other methods after the building is enclosed. Floor tests must be made after the air-conditioning system is operating and has been at service conditions for at least 48 h, allowing time for water vapor to migrate and humidity to stabilize inside the building.
A dry slab starts with a dry construction site and continues with a vapor barrier properly placed under the slab on grade. The vapor barrier is a sheet of plastic at least 6 mm thick that typically is placed between the stone or sand base and the concrete. The product is protected during construction because punctures in the barrier allow the water vapor through and may make the moisture content of the slab hard to overcome.
After the slab is poured, the concrete is kept moist to improve the hydration process, or curing. Moisture-retaining blankets facilitate the curing better than wet curing compounds. After some months of drying while other construction activities proceed, the slabs still may not test out. If so, isolation of the slab area-plus dehumidifiers and fans-usually does the job.
Steel Erection: The Race Is On
In the structural steel business, speed is king. The overall project schedule depends on getting the skeleton of the building erected as soon as possible. Everything else to be built depends on having the frame in place on time. In order for the steel to get topped out quickly, the individual pieces that make up the frame have to fit together precisely.
Structural steel shop drawings are used for the very specific purpose of getting the pieces to fit. Every bolt-hole location and size is planned, every dimension shown, and every connection between pieces designed and drawn before any steel beam or column is made. The shop drawings are submitted to the project structural engineer for review and approval and in the sequence in which the steel will be placed. Due to their effect on the critical path of the construction schedule, the structural shop drawing submittals are carefully planned to facilitate a steady flow through the engineer’s office, avoiding review bottlenecks.
The precision of fit requirements extends to the levelness of the frame and its vertical and horizontal elements. After erection, the structural steel is surveyed with precision instruments for plumb, alignment, and elevation. This as-built survey is conducted by a third party to provide documentation of quality and evidence of suitability for work of the trade contractors that will follow, such as the masonry and glazing.
Long Structural Spans: Gravity Is Not Your Friend
Recreation centers have several types of courts, each with its own dimensional requirements. The largest are basketball courts, which can vary in length but are nominally 90 ft (27 m) long by two or more courts side by side. A long clear distance is needed inside the building, without support columns. This is economically achieved through use of structural steel trusses or truss joists.
A truss is a structural element constructed of angled and vertical steel members connecting a top and bottom cord; it looks like a steel bridge. The truss is specially designed and constructed specifically for each job. Truss joists are similar, but off-the-shelf sizes are selected for each length of span.
Erecting trusses is a tricky business; they are very long (typically more than 100 ft [30.4 m] in length) and very heavy. Specialty contractors with specialized equipment and experience are employed to do this work, because one slip can be a disaster (see figure 11.5). On a construction site, gravity is not a friend.
Trusses and other long-span structural members are built with camber, or upward bowing, to compensate for the sag caused by the weight of the truss itself plus the weight of the roof and other loads such as snow. This sag is known as deflection, and the longer the truss, the greater the deflection and offsetting camber.
Truss deflection is not fully predictable in the field for a variety of reasons, and it affects other building systems that may be designed such that they come into contact with the truss, like window frames and plumbing. In such cases the contractors provide for flexible connections, or spacers, to allow for the movement of the structure.
Cranes are a vital part of any construction operation. To ensure that they properly handle the loads safely and with great efficiency, very precise procedures are necessary for setup and ground stability. The crane operator is responsible for the proper placement of the crane in relation to the load to be handled and the landing area so as to obtain the optimum rated lifting capacity.
Leveling the crane and the proper placement and use of outriggers for all lifts are essential for crane safety, as well as crane swing radius protection. The determination of stable or unstable ground is also the individual crane operator’s responsibility. Often additional floats, cribbing, timbers, or other structural members are needed to ensure solid footing.
Many recreation centers have swimming pools as a part of the program of requirements. Natatoria and indoor aquatic centers are complex structures, with unique construction issues that are covered in detail in chapter 8, "Aquatic Facilities."
Indoor Running Tracks
Many recreation centers are designed to accommodate indoor running-walking tracks, which are often suspended from the roof structure. These types of tracks are elevated above and along the perimeter of the gymnasium floor to use a portion of the large volume of space that comes with high ceilings (see figure 11.6). The long span structures that are required to support the roof are typically custom steel trusses. These roof structure trusses normally contain some variance in the elevation of the bottom chords of the truss that carries the track framework, and the frame is lightweight, so construction crews may find it difficult to get the final track subfloor as flat and level as is required for use.
Uniformity of the track running-walking surface is the goal. Tolerances are specified by the manufacturer and achieved by the installer, starting with the floor flatness. Ways to achieve uniformity in the field include grinding off the concrete floor slab high spots and filling in low spots. Durability of the track surface is an important issue for users and owners. To achieve the critical uniform thickness of a poured synthetic rubber surface, specialized equipment and experienced, certified subcontractors are required, and they will ensure that the subsurface is properly prepared.
Recreation centers may have many different types of sports flooring surfaces, depending on the flooring’s intended use. Basketball courts, racquetball courts, and aerobics rooms may have wood floors; multipurpose courts may have poured urethane sports flooring, vinyl composition tile, or other types of resilient flooring. Strength training or weight rooms may have a composite, energy-absorbent fitness floor or solid rubber. Whatever the flooring system, each is selected by the designer and owner according to playability, cost, and maintenance considerations. Each system has its own construction considerations as well. Every manufacturer of each playing surface system has its own set of installation requirements, and failure to precisely adhere to the requirements may void the warranty.
The durability of the floor is one of the first considerations in its selection and is a factor in acceptance of the construction of the facility. The durability of a floor is largely determined by its ability to withstand loads and abrasion. Floors experience both athletic and nonathletic loads; typical nonathletic loads may include the movement of portable equipment, such as basketball backstops, scissor lifts, and mat carts, as well as substantial loads of retractable bleachers. Even the placement of chairs on the surface can result in significant point loads. The start-and-stop nature of athletic movements on a floor will result in wear of the floor surface, and roller skating will increase wear of the floor, as will ordinary foot traffic in nonathletic shoes.
Criteria for the performance of an athletic floor are defined at the start, and performance is measured following installation. The criteria include requirements for resistance to impacts, static loads, rolling loads, and wear, as well as dimensional stability. Standards from the American Sports Builders Association (ASBA) include performance criteria for evaluating sports flooring, such as shock absorption, energy restitution, vertical deformation, slip resistance, and ball bounce. Mechanical criteria for evaluating sports flooring include resistance to indentation and heavy moving loads, impact absorption, abrasion resistance, light reflection, and surface uniformity.
There are many options for wood floors and several levels of quality, measured by grades of wood and type of system selected. Wood floors will be specified by the designer, bought by the CM, installed by the contractor, warranted by the manufacturer, inspected and accepted by the owner, and hopefully appreciated by the user. Ideally, communication about the details of the design and selection of the wood floor system occurs early and often.
Wood floors are specified in several species of hardwoods, but the desired floor often is maple because of the hardness, durability, and appearance of the finished product. Maple flooring types include random length, finger jointed, and parquet. Quality levels are expressed in five grades as described by the MFMA, from first down to utility level, according to the published grading rules set by the association. Of course, the lower grades cost less.
Random length northern hard maple flooring is commonly provided in 2 1/4 in. (5.7 cm) wide strips, continuous tongue-and-grooved and end matched, and the product is shipped in graded bundles. The maple flooring strips are placed on subfloor cushioning systems, commonly over plywood on top of "sleepers," or padded support board spacers, which provide the unique ball bounce and cushioning characteristics of wood floors. The sleeper system provides an air space below the floor system. Standard thickness of the flooring is 25/32 in. or about 3/4 in. (2 cm), although higher-traffic floors might require the greater thickness, 33/32 in. or about 1 in. (2.5 cm).
Finger-jointed maple flooring comprises one or more individual board segments attached end to end using a series of interlocking fingers and adhesive. The number of segments varies by grade. The finger-jointed product is the same basic assembly as the random length flooring and is similar in appearance. The parquet floor appearance is very different, consisting of individual slats or pickets 1 1/8 in. (about 3 cm) wide that fasten together in mesh-backed panels ranging from 6 to 12 in. (15-30 cm) with a minimum thickness of 5/16 in. (0.8 cm).
Wood warps, buckles, and cups if it gets wet or if moisture conditions are not right. Wood flooring is made from lumber that has been kiln dried to the proper moisture content (6% to 9% moisture content), then cooled and cut into strips, milled, graded, bundled, and stored in an environmentally controlled warehouse. Once it is shipped, care in handling and transport is taken to maintain dryness; and when delivered to the job site, it is off-loaded to a dry, well-protected and ventilated space where the relative humidity is low.
The wood floors will go down last: after the concrete subfloor has been dried, its moisture content has been tested and accepted, and all masonry work and overhead mechanical work in the building have been completed and tested. The permanent heat, light, and ventilation for the building is working and maintaining between 55° and 75° F and between 35% and 50% relative humidity. The flooring is delivered a minimum of seven days before installation and is placed in the area where it is to be installed to ensure proper acclimation to the environmental conditions of the room.
After final installation of the floor and finishes, some minor movement is to be expected. Sleeves and cover plates for equipment inserts such as volleyball posts need just a little room for movement of the floor, both in the center and at the edges. The wood floor playing surface is not fixed to the subfloor for that reason: It will need to expand and contract as environmental conditions change.
If a mechanical room is adjacent to the gymnasium and at the same level, consider installing an 8 in. (20 cm) or higher integral curb to contain water releases from plumbing accidents. Otherwise, someone may end up buying a new floor. Consider buying extended warranties for all fitness flooring and wood floors.
Fitness Center Equipment
In a new facility, the fitness equipment can take a while to install and check out. During the installation period, the subcontractors are finishing the interior construction of the building and generating lots of dust, which settles on the new equipment if it’s not protected. When the building’s HVAC systems are started up and the construction filters are in place to catch it, the dust is less of an issue. All equipment, whether new or relocated, should be protected and covered until the building is nearly ready to open.
Much of the active fitness equipment today is motor driven, and the motors can be rather large, such that a single piece of equipment has its own dedicated electrical circuit (for example, one wire in a conduit that goes all the way to the breaker at the distribution panel). The placement of the electrical outlets for the equipment plugs is a coordination issue to be resolved in the design process-not after the floor outlets are roughed in and concrete has been poured around the electrical boxes. Often, each item of equipment has a dedicated television as well, and the coordination of the wiring for that system can be involved and take several weeks to complete and test. Start early and test often.
Climbing and bouldering are popular activities and key features of modern recreation and fitness centers. The construction issues involved in climbing walls are detailed in chapter 9.