Better ideas for warehouse construction
Tuesday, February 17, 2015
A quiet revolution has been growing in the construction of warehouse buildings. While the price of other products and services has steadily escalated, the cost of warehouse construction has remained relatively stable. As you look at new construction, consider where the priorities for controlling quality should be placed.
The most important component in any warehouse building is the floor. If extremely bad, a defective floor can result in the need to tear down the building. In less extreme cases, bad floors typically stay bad for the whole life of the building.
Second in priority is the framing and roof system. However, if the structure and the roof are done badly, they can be repaired — although such repairs are difficult and expensive.
Next in importance are docks and dock doors, which are the key points for flow of material in and out of the building. If the doors are poorly placed, the material flow will be difficult and expensive.
Least in importance is the part of the building that gets the most attention from the uninitiated — the walls. Many warehouse buildings have walls that do not bear any load, with the entire roof supported by the upright columns.
When the walls are not load-bearing, it matters little whether they are made of granite or cardboard, as long as they are accompanied by a perimeter alarm system and insulation to protect toward products.
The goal for the end product is a floor that requires minimal maintenance and has durable wear surfaces. The floor cannot be stronger than the earth beneath it. If the ground is not properly prepared and compacted, a void in the earth beneath the floor will inevitably cause the floor itself to fail.
To reduce maintenance, the floor should be poured in a manner that minimizes curling, which is the development of concave patterns in the floor as the concrete cures. The joints must be created in a way that minimizes spalling or failure of the surface at the joint. In order to create the strongest wear surface, it is important that the concrete itself be dense and nonporous.
In one warehouse, the floor was poured with a series of butt joints. Under this system, a strip of concrete is poured, with an adjacent area of similar size left vacant, followed by another strip of concrete. The void between each strip is poured after the first strips have already cured. The builder uses this method to create a higher-quality floor.
Another builder places prime reliance on controlling the installation environment. The floor is not poured until the walls and roof are nearly complete in order to reduce temperature variance and wind flow over the curing floor. Direct exposure to the sun can cause concrete to dry too quickly. In the controlled installation environment, relative humidity remains as high as possible to slow the drying process.
Strength of the concrete is controlled by reducing the amount of water mixed with cement and carefully managing the amount of water used in the mixture. Dowel joints in the concrete are used at high-traffic areas, and the thickness of the floor in high-traffic areas may also be increased. A surface hardener is always installed, and when budget permits, a plasticizer may also be added to produce a mirror finish.
A flatness test is utilized as the concrete is finished to assure that the floor will be level as possible. A floor process called FACE uses statistical analysis to define variances in flatness. Each pour of concrete is larger as it is easier to control flatness.
A laser screed allows larger amounts of concrete to be finished at one time, thus reducing the number of construction joints that are needed. The laser-screeded floor reduces flatness variance from .75 inches down to .25 inches over a length of 50 feet. Most damage to concrete appears at the joints, and the best floors are the ones with the least number of joints.
Since the sub base is of critical importance, a laser bulldozer and vibrator roller are used to assure a solid and level base. That base is then surfaced with 46D, a gravel compound that possesses concrete properties. The concrete is poured in the same direction in which traffic will move in the warehouse. The wet-cure process should take four weeks in order to achieve maximum strength.
Structural system and roof
The expectation for the end product of the roof and framing system is to achieve the longest possible life with minimum maintenance and no leaks. Outside of the Sun Belt, it is also important for the roof to be able to handle significant temperature changes during its useful life and weather hazards.
For most of the United States, the best option is a pre-engineered metal roofing system. However, in some parts of the western U.S., some or all of the structural support systems use wood rather than steel beams. Wood systems are used primarily when they are acquired at a more favorable cost. But for most structures in the U.S., metal is both best and most economical.
Current technology allows a slope that is so gentle that the building does not appear to have a pitched roof. The gentle slope also makes it safer to walk on the roof when maintenance and cleaning is performed.
In contrast to the heavier and more complicated roof systems that use several plies of felt roofing and asphalt, the middle system is simpler, lighter and easier to maintain and repair. Because the framing and roof system is significantly lighter than the older systems used, there is less risk of settlement as the building ages.
Docks and drive areas
Because docks are the heart of the material flow in and out of the building, they must be designed for low maintenance and maximum life.
The exterior drive area is one that is frequently neglected in warehouse construction. It should be constructed to eliminate any ponding by maintaining positive drainage both above and below the wear surface. Proper preparation of the subbase soil is just as critical for the drive areas as it is for the warehouse floor. Yet this process is neglected in the construction of some warehouses.
The dock apron is prepared to specifications that exceed those of the warehouse. It should be of 8-inch thick concrete with reinforcing steel mesh. The steel is not required for the warehouse floor, but it should be used for the dock to handle the stress of truck trailers. That apron extends at least 50 feet from the face of the dock doors.
The dock doors should be designed to minimize maintenance. Metal and plastic have replaced wood for many of the overhead doors, and the best of them today have a channel that brings the door straight up rather than to make a 90-degree turn like those found in a residential garage.
Mechanical dock levelers are an investment that pays back in reduced operating cost for any busy truck dock. Dock lights are another investment which enhances productivity and safety.
Illumination and heating
Approaches to warehouse lighting have made revolutionary changes in the past two decades.
Skylights have been used to provide available sunlight and reduce electrical cost. However, as more warehouses are used on a second- and third-shift schedule, the importance of sunlight is reduced.
Furthermore, skylights have poor insulating value and are a source of heat loss. They can also be a source of roof leaks. Design improvement and lighting systems provide maximum flexibility at an economical cost.
The best way to heat a warehouse is the use of an air rotation system. This type of heating allows a single unit to heat over 100,000 square feet of space. However, if the building is designed for partitioning into several rooms, then several smaller air rotation units will be necessary to provide heat in all areas.
Foundations and building heights
Foundation walls are precast or cast in place. One builder uses precast wall panels that are load-bearing, and they are erected with the foundation to reduce costs and increase construction speed.
The amount of interior backfill is minimized to reduce cost and increase speed. Building height today is dictated by the specification of ESFR sprinkler systems, which are the most effective fire protection available.
One builder uses hollow or prestressed concrete wall panels that have foam insulation in the cores. Similar wall construction is used for both foundations and dock walls.
Other builders argue that a metal wall is less expensive. However, the insulated concrete wall is durable and abuse-resistant, and it has more eye appeal to the bankers who finance the building and the brokers who lease it.
Wall panels should be designed to allow additional dock doors to be installed later, since changing uses of the building will frequently require new doors.
Bright white paint is the most economical way to make the building attractive to workers and visitors. Columns that contain fire extinguishers usually are indicated with red paint, and other color coding may be used at certain places in the warehouse.
The use of a maximum amount of white finish will improve light levels and general appearance.
While the warehouse purist would maintain that the exterior of the building has little to do with operating efficiency, it has a great deal to do with the impressions left on visitors, sources of financing and customers.
Landscaping is one of the most cost-effective ways to improve the appearance of a warehouse exterior. Just as good housekeeping is an important symbol of warehouse management, similar attention to the appearance of exterior and grounds will greatly influence the impression of those who observe the warehouse from the street.
Perhaps the best argument for the use of concrete wall panels is that they appear to be more durable and more attractive than concrete block or metal walls. While the durability of walls may be unimportant to the physical function of the warehouse, it is important to the casual observer.
A trashy or poorly-kept exterior may not necessarily signify a bad warehouse operation, but many observers will immediately downgrade management if the exterior of the building presents an eye sore.
Carelessness on the part of warehouse operators is frequently the primary cause for deterioration of the building. Perhaps the most vulnerable area is the walls, particularly if they are fragile metal panels.
A forklift operator who continues to move forward until he hits something can batter and seriously damage building walls. Similar abuse can come from outside the building by those who park automobiles too close to the walls or those who strike the building with trucks. Warehouse walls should be protected from abuse by barriers on both sides.
Certain material-handling practices can also cause grave damage to floors. Among the worst of these is the practice of "freight training" a row of pallets.
Some lift-truck operators will move several pallets at a time by pushing them ahead of the lift truck in a long train. This practice should be stopped for several reasons. The most important one is the fact that pushing pallets over the floor causes damage to the concrete.
Of nearly equal importance is the fact that the practice is inherently unsafe because the operator cannot get a clear view of what is happening ahead of the front pallet. Finally, the practice causes damage to the pallets themselves.
Given reasonable care, a good warehouse building should last for many years. If abused, the building will start to deteriorate relatively early in its life.
New construction techniques have caused warehouses to be more economical and of higher quality than ever before. With a flexible design and proper maintenance, such a building should have a useful life of many decades.
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