http://www.domeshells.com.au/inflatable-dome-air-forms/
http://www.toughcovertent.com/Products.aspx?id=72
http://www.toughcovertent.com/Products.aspx?id=72
Tuesday, December 29, 2015
Air Forms for Building Shotcrete Domes
http://www.shotcrete.org/media/Archive/2008Sum_Ragen-Briggs.pdf
Shotcrete • Summer 2008 Air Forms for Building Shotcrete Domes by Michael E. Ragen and Laurel Briggs C oncrete domes are used for both commercial and industrial applications. For example, domes have been incorporated into schools and churches. By far, however, the majority are constructed for industrial bulk storage of materials such as cement, fly ash, coal, fertilizer, gypsum, grains, and peanuts. Some of the advantages concrete domes provide include: • Superior protection of the stored material; • Strength and durability; • Simple foundation requirements; and • Superb environmental control. Shotcrete domes today are constructed using inflatable fabric forms. The air form is an engineered fabric structure manufactured of single-ply roof membrane material. It arrives at the job site as a rolled-up single piece package. Once unrolled and spread out, it is attached to the dome’s circular footing. Large blowers are used to inflate the membrane that then serves as the formwork for the shotcrete dome. Contrary to what may seem obvious, the shotcrete is seldom applied over the air form’s exterior. Instead most domes are constructed by spraying shotcrete to the air form’s inside surface. Considering that the shotcrete will be sprayed on the inside, the air form membrane is designed to remain in place and serve as part of the dome’s finished roof. As such, it is important to select the correct fabric that will satisfy the application’s performance requirements. There are many coated fabrics to choose from. For the construction process, some of the primary issues include dimensional stability and the strength of the fabric and its seams. The owner’s long-term interests usually relate more to durability, low maintenance, and appearance, including the exposed surface’s ability to shed dirt and/or be cleaned. The fabric will remain as the roofing material. Several exterior top-coats, such as acrylic polymers or polyvinylidene fluoride (PVDF), are available to protect the base fabric from ultraviolet rays and enhance long-term weathering capabilities. Several variables such as size, intended shape, and anticipated inflation pressures are considered in the selection of a specific fabric and its design into an inflatable form. Other variables like weather and fabrication tolerances can make Bishop Nevins Academy, Sarasota, FL predicting the precise inflated shape difficult, but Air form being inflated Shotcrete application inside dome Shotcrete • Summer 2008 careful engineering and quality control of the fabrication lessen inconsistencies. Air form manufacturers gather as much information as possible, and they exercise care to produce forms within reasonable tolerances of the shape requested by the customer. Shape and size are the primary variables in air form design. The most common and simplest shapes are portions of spheres, including hemispheres. Designs may also include a vertical cylindrical section producing a shape consisting of a hemisphere on top of a cylindrical base. Less common shapes are ellipsoids, or forms with barrels. The shape of the air form affects how the designer calculates the stresses on the inflated form, whereas size will determine the severity of those stresses. Fabric selection is a major factor in the design process. Air form fabrics are chosen to meet the requirements of strength, stretch, durability, and appearance. Most of the commonly used architectural fabrics are all polyvinyl chloride (PVC)-coated polyester scrims. These fabrics provide high strengths and consistent stretch characteristics. The fabric’s stretch characteristics are essential to properly pattern the air form. Fabric suppliers provide biaxial stretch test information in various ratios for their products. The stretch test information indicates the percentage of stretch that will occur lengthwise and widthwise within the fabric based on amounts of loads applied in both directions. When designing spherical-shaped forms, stretch data from a 1:1 ratio (equal loading in both directions) test is used. Cylindrical walls require using data from 1:2 ratio testing (twice the loading in one direction compared with the other). Air forms are fabricated by heat-welding together specially patterned flat pieces of fabric that, once inflated, take on the designed curved shape. Patterning takes into account how the fabric will stretch due to stresses produced by inflation pressures. Inflation pressure is the most significant stress to be considered. Wind can also influence the inflated form’s actual shape. Once at full pressure, however, wind-related stresses are minor, and any shape deformations are temporary. Many styles of patterning can be used to create the air form. The most common for relatively large air forms is referred to as a double panel system. This consists of pairs of vertical gores that have an equal, consistent width around the dome’s base circumference and extend up to a circular piece of fabric at the form’s apex. Each pair of panels has a straight center seam and curved outer seams. This style of patterning minimizes fabric waste and therefore cost during manufacture. It also provides very few horizontal seams, giving a more aesthetically pleasing final surface appearance. Air form being rolled out Inside the inflated air form Outside the inflated air form Shotcrete • Summer 2008 Michael E. Ragen is a Senior Vice President and Partner at The Farley Group and has been active in the industrial fabric and agricultural sectors for over 40 years. Laurel Briggs has been in the dome industry assisting both the Marketing and Construction Departments of DOMTEC International for almost 13 years. Briggs works with ad layouts and design along with research and writing of articles. She also assists the Construction Department with purchase orders and subcontracts. Inflatable fabric air form Fabric on the FIAB welder Seams between panels are created by a heatwelding process using high-frequency radio waves, also called dielectric welding. This radio frequency (RF) process is recognized as the highest quality seaming method. RF welding creates durable, watertight seams with strengths exceeding that of the fabric itself. Fabrics can be obtained in virtually any color. Colors not regularly stocked, however, may involve a surcharge; and, in most cases, they require longer lead times for fabrication. Inflatable fabric air forms have come a long way over the last 30 years. By selecting a strong, high-quality fabric with a durable top coat that truly is intended as a finished roof membrane and using an experienced, reputable fabricator with the right equipment and quality control practices, air forms can serve as reliable construction forms for dome builders and provide owners with low maintenance performance for many years.
Shotcrete • Summer 2008 Air Forms for Building Shotcrete Domes by Michael E. Ragen and Laurel Briggs C oncrete domes are used for both commercial and industrial applications. For example, domes have been incorporated into schools and churches. By far, however, the majority are constructed for industrial bulk storage of materials such as cement, fly ash, coal, fertilizer, gypsum, grains, and peanuts. Some of the advantages concrete domes provide include: • Superior protection of the stored material; • Strength and durability; • Simple foundation requirements; and • Superb environmental control. Shotcrete domes today are constructed using inflatable fabric forms. The air form is an engineered fabric structure manufactured of single-ply roof membrane material. It arrives at the job site as a rolled-up single piece package. Once unrolled and spread out, it is attached to the dome’s circular footing. Large blowers are used to inflate the membrane that then serves as the formwork for the shotcrete dome. Contrary to what may seem obvious, the shotcrete is seldom applied over the air form’s exterior. Instead most domes are constructed by spraying shotcrete to the air form’s inside surface. Considering that the shotcrete will be sprayed on the inside, the air form membrane is designed to remain in place and serve as part of the dome’s finished roof. As such, it is important to select the correct fabric that will satisfy the application’s performance requirements. There are many coated fabrics to choose from. For the construction process, some of the primary issues include dimensional stability and the strength of the fabric and its seams. The owner’s long-term interests usually relate more to durability, low maintenance, and appearance, including the exposed surface’s ability to shed dirt and/or be cleaned. The fabric will remain as the roofing material. Several exterior top-coats, such as acrylic polymers or polyvinylidene fluoride (PVDF), are available to protect the base fabric from ultraviolet rays and enhance long-term weathering capabilities. Several variables such as size, intended shape, and anticipated inflation pressures are considered in the selection of a specific fabric and its design into an inflatable form. Other variables like weather and fabrication tolerances can make Bishop Nevins Academy, Sarasota, FL predicting the precise inflated shape difficult, but Air form being inflated Shotcrete application inside dome Shotcrete • Summer 2008 careful engineering and quality control of the fabrication lessen inconsistencies. Air form manufacturers gather as much information as possible, and they exercise care to produce forms within reasonable tolerances of the shape requested by the customer. Shape and size are the primary variables in air form design. The most common and simplest shapes are portions of spheres, including hemispheres. Designs may also include a vertical cylindrical section producing a shape consisting of a hemisphere on top of a cylindrical base. Less common shapes are ellipsoids, or forms with barrels. The shape of the air form affects how the designer calculates the stresses on the inflated form, whereas size will determine the severity of those stresses. Fabric selection is a major factor in the design process. Air form fabrics are chosen to meet the requirements of strength, stretch, durability, and appearance. Most of the commonly used architectural fabrics are all polyvinyl chloride (PVC)-coated polyester scrims. These fabrics provide high strengths and consistent stretch characteristics. The fabric’s stretch characteristics are essential to properly pattern the air form. Fabric suppliers provide biaxial stretch test information in various ratios for their products. The stretch test information indicates the percentage of stretch that will occur lengthwise and widthwise within the fabric based on amounts of loads applied in both directions. When designing spherical-shaped forms, stretch data from a 1:1 ratio (equal loading in both directions) test is used. Cylindrical walls require using data from 1:2 ratio testing (twice the loading in one direction compared with the other). Air forms are fabricated by heat-welding together specially patterned flat pieces of fabric that, once inflated, take on the designed curved shape. Patterning takes into account how the fabric will stretch due to stresses produced by inflation pressures. Inflation pressure is the most significant stress to be considered. Wind can also influence the inflated form’s actual shape. Once at full pressure, however, wind-related stresses are minor, and any shape deformations are temporary. Many styles of patterning can be used to create the air form. The most common for relatively large air forms is referred to as a double panel system. This consists of pairs of vertical gores that have an equal, consistent width around the dome’s base circumference and extend up to a circular piece of fabric at the form’s apex. Each pair of panels has a straight center seam and curved outer seams. This style of patterning minimizes fabric waste and therefore cost during manufacture. It also provides very few horizontal seams, giving a more aesthetically pleasing final surface appearance. Air form being rolled out Inside the inflated air form Outside the inflated air form Shotcrete • Summer 2008 Michael E. Ragen is a Senior Vice President and Partner at The Farley Group and has been active in the industrial fabric and agricultural sectors for over 40 years. Laurel Briggs has been in the dome industry assisting both the Marketing and Construction Departments of DOMTEC International for almost 13 years. Briggs works with ad layouts and design along with research and writing of articles. She also assists the Construction Department with purchase orders and subcontracts. Inflatable fabric air form Fabric on the FIAB welder Seams between panels are created by a heatwelding process using high-frequency radio waves, also called dielectric welding. This radio frequency (RF) process is recognized as the highest quality seaming method. RF welding creates durable, watertight seams with strengths exceeding that of the fabric itself. Fabrics can be obtained in virtually any color. Colors not regularly stocked, however, may involve a surcharge; and, in most cases, they require longer lead times for fabrication. Inflatable fabric air forms have come a long way over the last 30 years. By selecting a strong, high-quality fabric with a durable top coat that truly is intended as a finished roof membrane and using an experienced, reputable fabricator with the right equipment and quality control practices, air forms can serve as reliable construction forms for dome builders and provide owners with low maintenance performance for many years.
Monday, December 28, 2015
Air-Formed Concrete Domes
Air-Formed Concrete Domes
by Jonathan Zimmerman, NCARB
Throughout history, structurally efficient domes have been built from masonry, wood, concrete, and even ice. But there's still plenty of room left in dome technology for invention and construction efficiency. New ways to form, reinforce, and insulate "air-formed" concrete domes have been a primary focus of my architectural practice for about 25 years.
In the 1930s, air-formed-dome pioneers tried spraying various materials over inflated rubber bladders, but they had no effective way to reinforce or insulate the structure. In the early 1960s, California architect Lloyd Turner came up with the idea of spraying concrete on the inside of inflated forms. He also developed the use of urethane foam as an insulator and as a framework for applying the reinforcing steel and concrete.
Through years of experimentation, Turner and others have devised an effective method that that satisfies a variety of environmental and cultural needs with an economy of materials. This is the method that I use in my own residential and commercial architectural work. I continue to be fascinated by this technology as an efficient method of space enclosure and excited by the opportunity to play a part in the development of a new architectural art form.
From Idea to Form
I begin very traditionally, by sketching a design on paper. When a client approves the basic concept, I move to my computer. The shell forms I envision have no straight lines and flat planes; this makes them reproducible by hot-air balloon manufacturers. >>>
Using 2D drafting software, I can define a complex 3D form by drawing a series of arc-shaped building sections. I use these sections to further develop the building's exterior and interior elevations and to build a scale model of wire for each design. I build two models at a time, keeping one and mailing the other to the client.
The sections also define the shape of the balloon. To communicate with balloon manufacturers, I show the location of these sections in plan and define the width, height, and radius of each section. These drawings give the manufacturers an accurate document by which to further describe complex curves and generate balloon gore patterns to use in bidding and fabrication.
These balloon drawings are also sent to the structural engineers who use them, along with photographs of the models and exterior elevation drawings, to define the shapes mathematically and to build digital models. Using finite element analysis, the engineers study the 3D models of the forms and shell openings to determine shell thicknesses and steel placement patterns.
From Hot Air to Warm Space
Once at the construction site, and tied down to the foundation ring, it takes the balloons about 30 to 45 minutes to inflate for a small to medium-sized building. Then foam is sprayed onto the interior surface of the fabric. The foam serves as the form for the steel rebar armature and has an insulating value about twice that of a comparable thickness of fiberglass.
The interior surface of the foam is then covered with a 3/4-inch (19-millimeter) layer of concrete, or "preshell." Next, steel reinforcing bars are pinned in place, like latitude and longitude lines, on the inside surface, leaving openings to frame windows and doors. Finally, the steel grid is sprayed with concrete to the required thickness.
This second layer of concrete performs three functions. Along with the steel, it provides the structure of the building. Second, the concrete provides fireproofing because the urethane foam is no longer exposed to the interior of the space. Third, the insulated concrete shell serves as a thermal mass capable of storing and reradiating thermal energy.
Sometimes, balloons can be peeled off and reconditioned for subsequent reuse. More often they are left in place and covered with an exterior coating. Among the many coating choices are elastomeric paints, synthetic flexible stucco, resins used for truck-bed liners, ceramic tile, and even metal shingles.
This construction system reduces the number of components necessary to build a structure and it uses the fewer materials more efficiently. The system also produces an extremely strong and energy conserving buildings
Due to the absence of corners where stresses accumulate, the domes are earthquake resistant, and they can sustain up to 300 mile- (480-kilometer-) per-hour winds. They require about half of the energy for heating and cooling when compared to conventional construction systems. This is due to the combined effect of reduced exterior surface area, high insulation values, and insulated thermal mass.
From Experiment to Credibility
In 1985, after a national conference of the leaders in the industry, theAmerican Concrete Institute formally recognized this construction process and called it "Air Supported Forming of Thin Shell-Concrete Structures." They may have given the technology a clumsy name, but ACI recognition was a shot in the arm for those of us who work in this area.
The forming of compound and complex shapes by the inflation of balloons allows us to create building forms not feasible with other methods. Building forms can be lyrical and sinuous as well as efficient.
Moreover, the strength of the steel-reinforced concrete shells allow us to berm earth against them and to sculpt the way the building meets the land. By emulating the flowing curves and natural forms of the landscape, echoed in the shapes of the shell openings, designs can be made to appear in harmony with nature.
The future of concrete dome technology looks bright. It is scalable and has been applied to buildings from 30 feet (9 meters) up to almost 300 feet (90 meters) in diameter. Energy and materials efficiency; wind, earthquake, and fire resistance; and design flexibility and aesthetics will continue to provide compelling reasons to adopt this established design and construction technology.
Jonathan Zimmerman, NCARB, is an architect based in Marin County, California. His Web site contains more information about dome building
HOW TO BUILD A LLOYD TURNER BALLOON FORM
HOW TO BUILD A LLOYD TURNER BALLOON FORM
http://www.mortarsprayer.com/thin-shell-construction/build-a-balloon-form/
LLOYD TURNER
http://www.flyingconcrete.com/lloyd-turner.htm
Contact Lloyd at lloydsturner@sbcglobal.net
he was monolithic original airform maker
Contact Lloyd at lloydsturner@sbcglobal.net
he was monolithic original airform maker
Subscribe to:
Comments (Atom)