Tilt slab
Encyclopedia
Building
In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...
and a construction
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...
technique using concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
. It is a cost-effective building technique and efficient construction method.
In this method concrete elements (i.e. walls, columns, structural supports, etc.) are formed on a concrete slab
Concrete slab
A concrete slab is a common structural element of modern buildings. Horizontal slabs of steel reinforced concrete, typically between 10 and 50 centimeters thick, are most often used to construct floors and ceilings, while thinner slabs are also used for exterior paving.In many domestic and...
; usually the building floor, but sometimes a temporary concrete casting surface near the building footprint. After the concrete has cured, the elements are tilted from horizontal to vertical with a crane and braced into position until the remaining building structural components (roofs, intermediate floors and walls) are secured.
Tilt-up construction is a dominant method of construction throughout North America, several Caribbean nations, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. It is not significantly used in Europe or the northern two thirds of Asia. It is gaining popularity in southern Asia, the Middle East, parts of Africa, Central and South America.
Concrete elements can also be formed at factories away from the building site. Tilt-up differs from prefabrication
Prefabrication
Prefabrication is the practice of assembling components of a structure in a factory or other manufacturing site, and transporting complete assemblies or sub-assemblies to the construction site where the structure is to be located...
, or plant cast construction, in that all elements are constructed on the job site. This eliminates the size limitation imposed by transporting elements from a factory to the project site.
Construction
Carpenter
A carpenter is a skilled craftsperson who works with timber to construct, install and maintain buildings, furniture, and other objects. The work, known as carpentry, may involve manual labor and work outdoors....
s work off engineered drawings designed for each panel or element to construct on site. They incorporate all door and window openings, as well as architectural features and other desired shapes that can be molded into the concrete. Studs
Wall stud
A wall stud is a vertical member in the light frame construction techniques called balloon framing and platform framing of a building's wall.-Purpose:...
, gussets and attachment plates are located within the form for embedding in the concrete. The forms are usually anchored to the casting surface with masonry nails or otherwise adhered to prevent damage to the floor slab.
Next, a chemically reactive bondbreaker is sprayed on the form's surfaces to prevent the cast concrete from bonding with the slab. This allows the cast element to separate from the casting surface once it has cured. This is a critical step, as improper chemical selection or application will prevent the lifting of the panels, and will entail costly demolition and rework.
A rebar
Rebar
A rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...
grid is constructed inside the forms, after the form release is applied, spaced off the casting surface the desired distance with plastic "chairs". The rebar size and spacing is generally specified by the engineer of record.
Concrete is then placed, filling the desired thickness and surrounding all steel inserts, embedded features and rebar. The forms are removed when the concrete is cured, rigging is attached and a crane tilts the panel or lifts the element into place. In circumstances when space is at a premium, concrete elements can be cast one on top of the other, or stack cast. Quite often a separate casting pad is poured for this purpose and is removed when the panels are erected.
Cranes are used to tilt the concrete elements from the casting slab to a vertical position. The slabs are then most often set onto a foundation and secured with braces until the structural steel and the roof diaphragm is in place.
Structure
Concrete tilt-up walls can be very heavy, as much as 300,000 pounds or more. Most tilt-up wall panels are engineered to work with the roof structure and/or floor structures to resist all forces; that is, to function as load-bearing walls. The connections to the roof and floors are usually steel plates with headed studs that were secured into the forms prior to concrete placement. These attachment points are bolted or welded. The upper attachment points are made to the roof trusses. Interior walls may be present for additional stiffness in the building structure as necessary, known as shear walls.Insulation can be applied to either side of the panels or cast as an integral part of the panel between two layers of concrete to create sandwich
Sandwich
A sandwich is a food item, typically consisting of two or more slices of :bread with one or more fillings between them, or one slice of bread with a topping or toppings, commonly called an open sandwich. Sandwiches are a widely popular type of lunch food, typically taken to work or school, or...
panels. Concrete has the ability to absorb and store energy and is high mass, which regulates interior temperature (thermal mass
Thermal mass
Thermal mass is a concept in building design which describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect...
) and provides soundproofing
Soundproofing
Soundproofing is any means of reducing the sound pressure with respect to a specified sound source and receptor. There are several basic approaches to reducing sound: increasing the distance between source and receiver, using noise barriers to reflect or absorb the energy of the sound waves, using...
and durability.
Like all concrete construction, tilt-up buildings are fire-resistant
Fire-resistance rating
A fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test. This can be quantified simply as a measure of time, or it may entail a host of other criteria, involving other evidence of functionality or fitness for...
. In addition, wall panels can be designed to sag inward when damaged, which minimizes collapse (this can also be done with prefabricated
Prefabrication
Prefabrication is the practice of assembling components of a structure in a factory or other manufacturing site, and transporting complete assemblies or sub-assemblies to the construction site where the structure is to be located...
panels).
Uses
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Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....
or the ancient Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
. Modern tilt-up, made with reinforced concrete
Reinforced concrete
Reinforced concrete is concrete in which reinforcement bars , reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. It was invented by French gardener Joseph Monier in 1849 and patented in 1867. The term Ferro Concrete refers only to concrete that is...
, was first used in America circa 1905. Early erection was done using tilt tables, but the development of the mobile crane and truck mixers allowed tilt-up construction to grow. Tilt-up gained widespread popularity in the post World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
construction boom. Tilt-up was not used successfully in Australia until 1969.
Most early tilt-up buildings were warehouses. Today the method is used in nearly every type of building from schools to office structures, houses to hotels. They range from single story to more than seven and can be more than 96 feet in height.
An early example of this method is found in the innovative Schindler House, built in 1922 in West Hollywood, California
West Hollywood, California
West Hollywood, a city of Los Angeles County, California, was incorporated on November 29, 1984, with a population of 34,399 at the 2010 census. 41% of the city's population is made up of gay men according to a 2002 demographic analysis by Sara Kocher Consulting for the City of West Hollywood...
. Architect Rudolf Schindler
Rudolf Schindler
Rudolph Michael Schindler Rudolph Michael Schindler Rudolph Michael Schindler (born Rudolf Michael Schindler (1887 Vienna - 1953 Los Angeles) was an American, born in Austria, architect whose most important works were built in or near Los Angeles during the early to mid-twentieth century....
claimed that with the assistance of a small hand-operated crane, just two workmen were needed to raise and attach the tilt-up walls.
Appearance
Early tilt-up architecture was very minimalist and boxy. Recent techniques have expanded the range of appearance and shape.Many finish options are available to the tilt-up contractor, from paints and stains to pigmented concrete, cast-in features like brick and stone to aggressive erosion finishes like sandblasting and acid-etching. Shapes are also a feature that have become dominant in the tilt-up market, with many panels configured with circular or elliptical openings, panel tops that are pedimented or curved, facades that are curved or segmented and featured with significant areas of glazing or other materials.
Association
The Tilt-Up Concrete Association (TCA) is the international trade association for tilt-up concrete construction. TCA is a membership-based association, with nearly 500 members worldwide. TCA members can be contractors (general contractors or tilt-up subcontractors), engineers, architects, developers, consultants, suppliers, specialty trade firms, educators and students.TCA offers primarily educational, networking and exposure benefits to its members. TCA also offers an Achievement Awards program annually, recognizing the best examples of tilt-up construction over a variety of end uses.
Risks
In the wake of the 2011 Joplin tornado2011 Joplin tornado
The 2011 Joplin tornado was a devastating EF5 multiple-vortex tornado that struck Joplin, Missouri, USA late in the afternoon of Sunday, May 22, 2011. It was part of a larger late-May tornado outbreak sequence and reached a maximum width of in excess of during its path through the southern part of...
in which seven people were killed in a Home Depot when the 100,000 pound panel walls collapsed after the store was hit by an EF5 tornado
Enhanced Fujita Scale
The Enhanced Fujita Scale rates the strength of tornadoes in the United States based on the damage they cause.Implemented in place of the Fujita scale introduced in 1971 by Ted Fujita, it began operational use on February 1, 2007. The scale has the same basic design as the original Fujita scale:...
, engineers in an article published in The Kansas City Star
The Kansas City Star
The Kansas City Star is a McClatchy newspaper based in Kansas City, Missouri, in the United States. Published since 1880, the paper is the recipient of eight Pulitzer Prizes...
criticized the practice. They said that once one wall falls, it creates a domino effect
Domino effect
The domino effect is a chain reaction that occurs when a small change causes a similar change nearby, which then will cause another similar change, and so on in linear sequence. The term is best known as a mechanical effect, and is used as an analogy to a falling row of dominoes...
. 28 people in an un-reinforced training room in the back of the building survived. According to a study of the collapse, the tornado hit the south corner of the store and lifted the roof up causing the west walls to collapse into the store. The walls on the east side (where the people survived) collapsed out. Only two walls remained standing. Engineers said that stronger roof-to-wall connections might have tempered the collapse. Two other big box stores at the corner that had concrete block construction (an Academy Sports and Walmart) lost their roofs but the walls remained intact. Three people died in the Walmart, but 200 survived. The engineers told the Star that when concrete blocks fail they usually break apart, and do not come down in the huge slabs. Home Depot, which has hundreds of stores built with tilt-up, said it disagreed with the finding and that it would use tilt-up when it rebuilt the Joplin store.