Detail by Design
The Art and the Elevator
Carreer center gets a new look with SCC wall
Concrete Formwork - General info
How Formwork Works
by Jeff Harder (howstuffworks.com)
Formwork is the name for the molds used to create walls, columns, slabs, staircases and other concrete structures. Freshly poured concrete -- a combination of sand, gravel, cement, and water -- is wet, so it can't support its own weight or hold its shape. Formwork supports the weight of the concrete until it has dried into a specified shape and acquired the strength to support itself. "It's like when you bake a cake," says Harry Stamaty, owner of the formwork design and consulting business Detail By Design. "The pan that you put the cake in is the form, and the cake mix is the concrete" [source: Stamaty].
The concept of formwork is nothing new. The Pantheon, a domed icon of Roman architecture built around 125 AD, was one of the earliest structures to use concrete formwork in its construction. But formwork remained a fairly uncommon tool and technique for the next several centuries – cement and concrete were rare building materials until the inventions of Portland cement and reinforced concrete in the 19th century [source: Stewart].
Today, formwork is used to build everything from office buildings to single-family homes, from driveways to sports stadiums -- basically, any structure that incorporates concrete. But formwork is rarely a part of the final design. Forms are temporary structures, a variety of construction agents that provide access and support during the creation of the project's permanent features before being removed or discarded [source: Nemati]. But as we'll see, even though formwork is intended to come and go without a trace, it's an important facet of the building process -- one that threatens grave consequences for carelessness.
Let's take a look at some of the materials used to make formwork.
Read the rest of the article at howstuffworks.com
The Art and the Elevator -
Originally published in the Ohio Concrete Newsletter
Publish Date: November 2005
Art lovers visiting the new art museum in Akron, OH will want to take a few minutes to study the elevator enclosure. It's a formed concrete work of art that will be on permanent display.
The completed elevator will provide vertical transportation to passengers going from floor to floor in the new 3-story museum, but that's not obvious when looking at the walls surrounding the elevator from a distance. Described as a structural trapezoid, the 57 ft tall elevator enclosure is a 14 in. thickness of cast-in-place reinforced concrete.
The elevator (and surrounding museum project) was designed by the architectural team of Coop Himmelb (1) au LLC, Vienna Austria and Westlake Reed Leskosky, Cleveland, OH, with structural engineering by DeSimone Consulting Engineers, San Francisco, CA. Wety Building Company, of Akron, is the construction manager for the project owner, the Akron Art Museum.
It's certainly a challenge to design an architectural structure that will satisfy the discriminating tastes of art experts. That can also be a challenge for the builders.
For this project, bringing to life the architects' elevator vision required the work of another "artistic" team, comprised of concrete contractor, Parsons Concrete, of North Canton, OH, a contractor supply company, Waco Equipment, of Akron and a form designer, Harry Stamaty, of Detail by Design, Columbus, OH. Using conventional form system components, conventional materials and skilled craftsmanship, they successfully constructed an unconventional but functional structure.
The elevator enclosure has a vertically plane axes for most of its entire 3-story height. On all four faces, the walls are battered different angles, changing angular direction at each floor. Going down the south face, for example the wall is battered 4 ft-6 inches in, on the first floor, an then in again at 4ft - 6 inches, on the third floor. The other three faces are similarly canted in their construction.
Shoring from the ground was necessary to temporarily support the elevator enclosure during its eccentric construction. Bracing for the wall forming would not have prevented the rising structure from tipping over. The wall forming system was designed such that the contractor could repeat use of gang forms at the center part of each wall. This expedited the work and reduced the cost of construction to the project. However, all four corners required custom formwork using Finn.Form plywood, steel channels and 4x4 lumber with triangular shapes, rebuilt for each floor.
From bottom to top, the elevator enclosure was designed for load bearing. The walls rest on a 30ft by 30ft by 4ft thick reinforced concrete cap on 16 auger-cast piles about 45 ft deep. The walls themselves are heavily reinforced with No. 5 and No. 11 steel bars. Another 4 ft thick reinforced concrete cap was constructed on the top of the elevator enclosure to provide support for the museum's roof structure.
Concrete for the project is being supplied by Mack Concrete, Inc., of Valle City, OH from their plant in Akron. The mix used for the walls and both 4 ft thick caps was designed to achieve a 4,000 psi compressive strength in 28 days. Concrete quality control testing is being performed by Summit Testing & Inspection Co., of Akron.
Elsewhere on the museum project concrete is also playing an important role. Elevated concrete floors, 11 in. thick, will support heavy art sculptures, minimize vibration an contribute to fire safety of the structure and it valuable contents. Approximately 3,000 to 4,000 yd3 of concrete will be used to complete the total project. The Akron Art Museum is expected to be open to the public during the Fall of 2006. Be sure to see the elevator "exhibit".
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Curvaceous wall -
Originally published in the Ohio Concrete Newsletter
Publish Date: May 2004
The reinforced concrete retaining wall for a new ramp on Northbound SR 315 has a masonry-looking decorative face made with form liner. Uncommon is the fact that the wall has a radiussed alignment, and it has octagonal columns cast above each of the wall's 3-ft diameter drilled concrete caissons that hold the wall in place.
Complete General Construction Co., Columbus, OH, built the wall in conjunction with two new bridges that will connect SR 315 with Ohio State University's hospital complex. Designed to retain earthen embankment for a new pavement ramp, the wall follows a 381-ft. radius curve for the new roadway. The wall ranges in height from 6 ft to 20 ft, and has a panel thickness of 15 in. Its octagonal columns measuring 36 in. across, are spaced about 10 ft apart along the wall.
About 250 cubic yards of Ohio Department of Transportation, Specification 499 Class C concrete, supplied by Anderson Concrete Corp., was used to complete the wall. Forms for the wall were desgined for the contractor by Ersco Corporation and Harry Stamaty of Detail by Design of Columbus Ohio.
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Career Center gets new look with SCC wall -
Originally published in the Ohio Concrete Newsletter
Publish Date: May 2003
The Eastland Career Center, in Groveport, OH is undergoing a facelift, which includes two architectural walls of self-consolidating concrete, cast-in-place, in front of the building. The two walls were constructed with radiused faces, 32-ft high, and totaling approximately 300 ft in length.
The project architect, Triad Architects, LTD, of Columbus, wanted a radius-wall that presented an excellent finished surface.
Self-consolidating concrete (SCC) was used Anderson Concrete Corporation delivers for the walls because of the ease of final loads of SCC to Eastland Career placement and the need to have a nice Center
finished surface. However, to try and resolve several issues with pouring a 32 ft high wall with SCC, test pours were conducted before going forward with the form erection.
Lithko Contracting, Inc., of Plain City OH, performed the concrete work for the general contractor, Apex M&P Construction, of Columbus. One of the unique challenges on this project was designing and constructing forms to withstand the increased liquid pressure exerted by the SCC. Another challenge was that the walls were both designed to be built on a radius. In order to overcome these challenges, Ersco Corporation and Harry Stamaty of Detail by Design, of columbus, designed and pre-built the formwork offsite and delivered it to Lithko at the jobsite. Shirk & O'Donovan Consulting Engineers Inc., of Columbus, the structural engineer on the project, was also involved in designing this complicated wall. Lithko's crew then assembled the forms and used the lessons learned from the test pours to ensure the forms would not blow out or deform during the continuous SCC pour.
Anderson Concrete Corp., of Columbus, supplied the special 4000-psi SCC mix for the project. Self-consolidation concrete uses a special admixture that allows the concrete to flow like water without segregation of the coarse aggregate particles. To achieve the optimum mix that gave the desired SCC properties for this project, the concrete mix included a well-graded blended aggregate and ground granulated blast furnace slag cement. As in this mix, proper aggregate gradation is important to quality SCC mixture.
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Formwork is the term given to either temporary or permanent moulds into which concrete or similar materials are poured. In the context of concrete construction, the falsework supports the shuttering moulds.
Formwork comes in three main types:
Traditional timber formwork. The formwork is built on site out of timber and plywood or moisture resistant particleboard. It is easy to produce but time consuming for larger structures, and the plywood facing has a relatively short lifespan. It is still used extensively where the labour costs are lower than the costs for procuring re-usable formwork. It is also the most flexible type of formwork, so even where other systems are in use, complicated sections may use it.
Engineered Formwork systems. This formwork is built out of prefabricated modules with a metal frame (usually steel) and covered on the application (concrete) side with material having the wanted surface structure (steel, timber, etc.). The two major advantages of formwork systems, compared to traditional timber formwork, are speed of construction (modular systems clip or screw together quickly) and lower life-cycle costs (barring major force, the frame is almost indestructible, while the covering may have to be replaced after a few - or a few dozen - uses, depending on the applications).
Re-usable plastic formwork. These interlocking and modular systems are used to build widely variable, but relatively simple concrete structures. The panels are lightweight and very robust. They are especially suited for low-cost, mass housing schemes moladi.
Stay-In-Place Formwork systems. This formwork is assembled on site, usually out of prefabricated insulating concrete forms. The formwork stays in place (or is simply covered with earth in case of buried structures) after the concrete has cured, and may provide thermal and acoustic insulation, space to run utilities within, or backing for finishes.
Stay-In-Place Structural Formwork systems. This formwork is assembled on site, usually out of prefabricated fibre-reinforced plastic forms. These are in the shape of hollow tubes, and are usually used for columns and piers. The formwork stays in place after the concrete has cured and acts as axial and shear reinforcement, as well as serving to confine the concrete and prevent against environmental effects, such as corrosion and freeze-thaw cycles.
Schematic sketch of traditional formwork
| Pantheon dome
Some of the earliest examples of concrete slabs were built by Roman engineers. Because concrete cannot resist tension or torsional stress, these early structures consisted of arches, vaults and domes. The most notable concrete structure from this period is the Pantheon in Rome. To mold these structure, temporary scaffolding and formwork or falsework was built in the future shape of the structure. These building techniques were not isolated to pouring concrete, but were and are widely used in Masonry. Because of the complexity and the limited production capacity of the building material, concrete’s rise as a favored building material did not occur until the invention of Portland cement and reinforced concrete.
Traditional Slab Formwork
On the dawn of the rival of concrete in slab structures, building techniques for the temporary structures were derived again from masonry and carpentry. The traditional slab formwork technique consists of supports out of lumber or young tree trunks, that support rows of stringers assembled roughly 3 to 6 feet or 1 to 2 meters apart, depending on thickness of slab. Between these stringers, joists are positioned roughly 12 inches, 30 centimeters apart upon which boards or plywood is placed. The stringers and joists are usually 4 by 4 inch or 4 by 6 inch lumber. The most common imperial plywood thickness is ¾ inch and the most common metric thickness is 21 millimeters.
Traditional timber formwork on a jetty in Bangkok.
Timber Beam Slab Formwork
Similar to the traditional method, but stringers and joist are replaced with engineered wood beams and supports are replaced with metal props. This makes this method more systematic and reusable.
Metal Beam Slab Formwork
Similar to the traditional method, but stringers and joist are replaced with aluminum or steel beams and supports are replaced with metal props. This also makes this method more systematic and reusable. to be completed
Modular Slab Formwork
Panelized ceiling slab forming system with temporary support structures on a university dorm project.
With preassembled timber modules or steel or aluminum modules. to be completed
Table or Flying Form Systems
United States Patent 4036466.
These systems consist of slab formwork “tables” that are reused on multiple stories of a building without being dismantled. The assembled sections are either lifted per elevator or “flown” by crane from one story to the next. Once in position the gabs between the tables or table and wall are filled with “fillers”. They vary in shape and size as well as their building material. The use of these systems can greatly reduce the time and manual labor involved in setting and striking the formwork. Their advantages are best utilized by large area and simple structures. It is also common for architects and engineers to design building around one of these systems.
A table is built much the same way as a beam formwork but the single parts of this system are connected together in such a way making them transportable. The most common sheathing is plywood, but steel and fiberglass are also in use. The joist are either made from timber, wood I-beams, aluminum or steel. The Stringers are sometimes made of wood I-beams but usually from steel channels. These are fastened together (screws, weld or bolted) to become a “deck”. These decks are usually rectangular but can also be other shapes.
Flying formwork tables with aluminum and timber joists. The tables are supported by shoes attached to previously poured columns and walls
All support systems have to be height adjustable to allow the formwork to be placed at the correct height and to be removed after the concrete is cured. Normally adjustable metal props similar to (or the same as) those used by beam slab formwork are used to support these systems. Some systems combine stringers and supports into steel or aluminum trusses. Yet other systems use metal frame shoring towers, which the decks are attached to. Another common method is to attach the formwork decks to previously cast walls or columns, thus eradicating the use of vertical props altogether. In this method, adjustable support shoes are bolted through holes (sometimes tie holes) or attached to cast anchors.
The size of these tables can vary from 70 sqft. to 1500 sqft. or 8m² to 150m². There are two general approaches in this system.
This approach consists of assembling or producing the tables with a large formwork area that can only be moved up a level by crane. Typical widths can be 15, 18 or 20ft. or 5 to 7 meters but their width can be limited, so that it is possible to transport them assembled, without having to pay for an oversize load. The length vary and can be up to 100ft. (or more) depending on the crane capacity. After the concrete is cured, the decks are lowered and moved with rollers or trolleys to the edge of the building. From then on the protruding side of the table is lifted by crane whiles the rest of the table is rolled out of the building. After the center of gravity is outside of the building the table reattached to another crane and flown to the next level or position. This technique is fairly common in the United States and east Asian countries. The advantages of this approach are the further reduction of manual labor time and cost per sqft. or m² of slab and a simple and systematic building technique. The disadvantages of this approach are the necessary high lifting capacity of building site cranes, additional expensive crane time, higher material costs and little flexibility.
crane fork or elevator handled
By this approach the tables are limited in size and weight. Typical widths are between 6 to 10ft. or 2 to 3 meters, typical lengths are between 12 and 20ft. or 4 to 7 meters, though table sizes may vary in size and form. The major distinction of this approach is that the tables are lifted either with a crane transport fork or by material platform elevators attached to the side of the building. They are usually transported horizontally to the elevator or crane lifting platform single handedly with shifting trolleys depending on their size and construction. Final positioning adjustments can be made by trolley. This technique enjoys popularity in the US, Europe and generally in high labor cost countries. The advantages of this approach in comparison to beam formwork or modular formwork is a further reduction of labor time and cost. Smaller tables are generally easier to customize around geometrically complicated buildings (round or non rectangular) or to form around columns in comparison to their large counterparts. The disadvantages of this approach are the higher material costs and increased crane time (if lifted with crane fork).
Formwork tables in use at a building site with more complicated structural features
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