Chapter 16 discusses the challenging application of posttensioningexternal post. Cables are arranged as indicated by the engineer and chaired to run through the center of the slab. In the 1960s, as the higher strength steel developed, there was very good attachment hardware, construction techniques, and simplified design methods, which made the use of post tension reinforce structures more popular. A square 10,000 sqft slab will require less concrete than an irregularly shaped slab of the same size. In typical post tension buildings with balconies, the balcony slab is an extension of the concrete floor slab and usually cantilevered with a guardrail or parapet on the outer edge. The balcony slabs are exterior building components and are subjected to weather, temperature fluctuations, uv exposure, air pollutants and foot traffic. Post tension repair schnell contractors concrete repair. This course is intended to be an introductory course for structural engineers new to posttensioned concrete design, and is a good refresher for experienced structural engineers.
Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. Park plaza post tensioned parking structure demolition. Before a posttension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. Back in the 1960 there was limited use in concrete foundations in residential construction, but very little.
Posttension cables are used in concrete construction to allow thinner slabs and greater span lengths between support columns. Sections are tension controlled when the tensile strain in the extreme tension reinforcement is equal to or greater than 0. A residential post tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. What is post tensioning introduction post tensioning is a method of producing prestressed concrete, masonry and other structural elements. This tension makes the concrete slab and foundation much stronger than concrete without reinforcement and helps reduce cracking. Post tension ed concrete slabs there is document post tension ed concrete slabs available here for reading and downloading. Analysis and design of concrete and posttensioned floor and foundation systems. Advantages and disadvantages of each of these slab designs are provided, including the ability of some slab designs to minimize cracking and curling more than others. If your location is an area with expansive soils, always assume the slab is post tensioned. Posttensioned concrete in buildings posttensioning institute.
The foundation in question was a posttension cable reinforced foundation as opposed to a foundation which is reinforced with steel rebar see the typical photograph in this article. Chapter 15 covers the slab on grade industry, which represents more sales of posttensioning tendons than all other posttensioning applications combined. About us we believe everything in the internet must be free. What is the difference between normal slab and post. What is posttensioning introduction posttensioning is a method of producing prestressed concrete, masonry and other structural elements. This knowledge was obtained over many years of working on our own projects and listening and learning from the the pioneers of posttensioned concrete. Hazards of post tensioned concrete slabs safety toolbox. Using a ridingtrowel specifically designed for working over large areas of concrete, the slab is finished ensuring planarity and a uniform texture across the entirety of the courts. Prestressed concrete is basically concrete in which internal stresses of a suitable magnitude and distribution are introduced so that the stresses resulting from external loads are counteracted to a desired degree. Post tensioning concrete is a way to further enforce the concrete structure. It is of fundamental importance to evaluate the stress losses that might occur in this kind of connector due to.
Post tension slab construction is common in areas with expansive soils. Post tension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. Posttension concrete slab in this example posttensioned cables are introduced on a concrete slab. A 2 2area 2 a c 2 2 posttensioned concrete design table 11 list of symbols used in the aci 31808 code cp area enclosed by the outside perimeter of the section, in a g gross area of concrete, in a 2 l total area of longitudinal reinforcement to resist torsion, in a o area enclosed by the shear flow path, sqin a oh area enclosed by the centerline of the outermost closed. These cables, composed of steel wires inserted into a plastic sheath, are subsequently tensioned and grouted after the concrete is poured. Several methods exist for prestressing concrete, with posttensioning being a very common one.
Posttension basics how posttensioned slabs are built. Post tension design of slab there is document post tension design of slab available here for reading and downloading. An analysis of the bulk cross section of each segment of slab is summarized in table 22. A combination of these values will determine the slab stresses at the time of stressing and at service loads. Reinforced and posttensioned concrete slab design software. Many people are aware of the need for rebar when building retaining walls, concrete foundations and driveways. By using posttensioned tendons to compress the concrete, the formation of visible shrinkage cracks can be greatly. Brendon burley structural option posttensioned twoway slab posttension investigation besides shear strength it is also important to consider the moment capacity of each of the sections.
Posttensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are. Figure 12 iv at the strength limit state, the failure of a slab. Plans having prestressed concrete members shall include a table with top of slab elevations at the following points along centerline of beams. Load balancing is used, a portion of the load on slab is balanced by the transverse forces imposed by the draped tendons in each direction. A posttension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. A residential posttensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. The hazard exists when workers cut into the slab and rupture the. First model a flat slab for the entire area, then model the drop panels as separate slabs from the bottom of the flat slab.
Sections with between the two limits are considered to be in a transition re. Novel application of posttensioning solves highrise. Chapters 14 cover the art of detailing and observing the construction of posttensioned concrete. Posttensioned concrete slabs for buildings youtube. Contractors sometimes need to drill or cut into a post tensioned slab for repair or renovation work. In the case of a post tension slab, steel cables are laid out in grid fashion inside the forms. Since the early 1950s, post tension tendons have been used in the design of concrete structures. A post tension slab is a concrete slab or foundation that contains high tension cables running through the concrete to increase strength and reduce cracking typically in areas with poor soil conditions.
General overview of posttensioned concrete design instructor. Very good video showing step by step post tension slab duration. A psc is applied with a compressive stress on the cross section in advance before the application of loading on. Concrete grade beams span from column pile cap to pile cap and support the exterior walls of the building. Typically maximum fiber stress in tension controls design. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design. Whatever the posttensioning requirement tensioned concrete has the. Once the concrete is poured and sets, the cables are tensioned. Posttension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. Adaptfloor pro software for advanced reinforced and posttensioned concrete slab design. For this reason, the maximum tendon spacing for tendons is several times larger than that for reinforcement in nonprestressed floors. Pretensioned tendons are stressed prior to casting of concrete. Posttensioned twoway slab pennsylvania state university.
This slab will be modeled as a 2delement, allowing the analysis to be run in a general xyz environment. The parametric study of the posttensioned flat slab by varying the span by 0. For most large pt slabs, we also have to model the drop panels at the column supports. Posttensioned concrete slabs augi the worlds largest.
Download tr 43 post tensioned concrete floorsdesign handbook. Although some posttensioned slab structures had been constructed in europe quite early on, the real development. Tendons today are seven highstrength steel wires wound together and placed inside a plastic duct. Most modern browsers have builtin pdf readers if you have problems opening this file in your browser, check your browsers or computer systems settings.
I had a call this morning from a prospective client who was concerned about cracks in the concrete foundation of the home they were building. Under the balanced load, the slab remains plane without curvature and is subjected only to the resultant. The tendons change their vertical location in the beam to follow the tensile moment diagram. Part two of the course was exampleintensive, and key concepts were introduced along the way. Timber concrete composite floors with prefabricated fiber. In posttensioned floor slab construction, the placement of postten. Although some post tensioned slab structures had been constructed in europe quite early on, the real development. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by pti, the tendons are stressed. Posttension concrete slabs are used to create a monolithic single pour slab that is stronger than a traditional slab without. Post tensioning is a technique for reinforcing concrete.
The balcony slabs are exterior building components and are subjected to weather, temperature fluctuations, uv exposure, air. Post tension concrete slab in this example post tensioned cables are introduced on a concrete slab. Posttensioned concrete design spreadsheet program a pdh. This reduced the floortofloor height, allowing the required office space to be. Posttensioning methods for reinforcing concrete the. Mean value of the youngs modulus for tension of timber in the grain. When moment is drawn on the tension side, the diagram matches the general drape of the tendons.
A posttension slab is a slab of concrete which has been prestressed using a specific method to increase the strength of the concrete. The tensile face indicates what portion of the beam requires reinforcing for strength. Now in many areas they are the builders choice for reinforcing a concrete slab. Use the download button below or simple online reader. A concrete slab is susceptible to soil expansion and contraction, which can lead to cracking. Post tension slabs answers to questions buyers ask.
Post tensioned concrete slabs in buildings have many advantages over reinforced concrete slabs and other structural systems for both single and multilevel structures. Pdf tr 43 posttensioned concrete floorsdesign handbook. Do not alter the drainage pattern of the site provide a minimum of 3%. The use of posttensioning can reduce the depth of slabs and story height, as well as improve the installations of heating and electrical ducts. Several methods exist for prestressing concrete, with post tensioning being a very common one. Advantages and disadvantages of each of these slab designs are provided, including the ability of some slab designs to. So this tool was designed for free download documents from the internet. However, not many know about the value of post tensioning concrete for a much stronger structure.
Posttensioning is a form of prestressing concrete to provide reinforcement and overcome concretes weaknesses. Jun 16, 2014 posttensioned concrete slabs for buildings. Concrete rebar concrete 25% reduction rebar 65% reduction pt system total savings 10% 20% 100% of material cost in a typical slab with spans over 7 meters, the net savings in material cost can range between 10% 20% of original rc alternative 4 improved construction efficiency since post tensioned slabs are designed to carry their own weight at. The parametric study of the post tensioned flat slab by varying the span by 0. For prestressed concrete voided slabs and box beams, all reinforcement. The concrete is cast around a plastic, steel or aluminium curved duct, to follow the area where otherwise tension would occur in the concrete element. Prestressed concrete principle using high tensile strength steel alloys producing permanent pre compression in areas subjected to tension. The contract work to be performed under this section consists of furnishing all required labor, materials, equipment, implements, parts and supplies necessary for, or appurtenant to, the. Usually this is done by using hollow core slabs or other types of allconcrete solutions. Post tension pt tendon systems are primarily used for large slab construction projects.
This is part three of a threepart course that covers the fundamentals of post tensioned concrete for building structures using unbonded tendons. This means the foundation is reinforced by cables laid in a grid arrangement and tensioned after the concrete cures sufficiently with the intent to create compression in the foundation concrete to resist cracking. The foundation gains tensile strength when the cables are tightened after the slab has been cast. Bonded posttensioned concrete is the descriptive term for a method of applying compression after pouring concrete and the curing process in situ. A portion of tensile stress is counteracted thereby reducing the crosssectional area of the steel reinforcement. Fundamentals of post tensioned design for buildings. Construction of post tensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. The file extension pdf and ranks to the documents category. Construction maintenance of post tensioned slab on ground. Evaluation of timber concrete composite floors lund university.
Once the slab cures, qualified personnel apply tension and grout the cables. In order to take into account longterm losses, the user would estimate these losses and simply include. Using posttensioned flat slab construction with lightweight concrete allowed floor spans of up to 45 ft. Applying tension as the concrete is curing, the slab is partially stressed, with a final stress to 33,000 psi to follow. Posttensioned concrete slabs in buildings have many advantages over reinforced concrete slabs and other structural systems for both single and multilevel structures.
Contractors sometimes need to drill or cut into a posttensioned slab for repair or renovation work. Concrete rebar concrete 25% reduction rebar 65% reduction pt system total savings 10% 20% 100% of material cost in a typical slab with spans over 7 meters, the net savings in material cost can range between 10% 20% of original rc alternative 4 improved construction efficiency since posttensioned slabs are designed to carry their own weight at. Most often the cracks extend across the entire foundation and occur prior to tensioning of the tendon cables. Posttensioning is used for many reasons, including economy and building efficiency as well as the reduction of deflection and cracking it provides. Posttensioning is simply a way to reinforce in a more active way. Posttensioning tensioned concrete offers a wide range of posttensioning solutions from mono strand systems typically used in house slabs where the ground is highly reactive, slab systems 12. This is part three of a threepart course that covers the fundamentals of posttensioned concrete for building structures using unbonded tendons. The condominium building floors will have 8 inch thick post tensioned concrete slabs. Conventional and make sure to prepare the subgrade correctly, expansive clays are verboten. A normal slab is basically a rcc reinforce cement concrete slab where as a post tentioned slab is the psc prestressed concret slab. Streamline modeling process by importing dwgdxf files and intelligently. This course is intended to be an introductory course for structural engineers new to post tensioned concrete design, and is a good refresher for experienced structural engineers.
Segment as in2 bars spacing in interior column strip top bot 12. In states like california, texas, nevada and arizona the use of post tension slabs have increased tremendously in the last ten years. Footfall analysis of concrete floor system pdf report. For residential construction, tendons at 48 inches on center are common. The term prestressing is used to describe the process of introducing internal forces or stress into a concrete or masonry element during the construction process in order to. Before a post tension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. If the concrete is not well vibrated, penetrations are located in front of the anchors figure 7, or congested rebar prevents a uniform bearing surface, a concrete blow out is likely figure 8. The tricky part comes when concrete is poured into the forms. In slabs on ground, the friction between the slab and the ground acts to resist this shrinkage and results in what are commonly referred to as shrinkage cracks. Aug 28, 2015 posttensioned slab procedure duration. Nov 03, 2017 a normal slab is basically a rcc reinforce cement concrete slab where as a post tentioned slab is the psc prestressed concret slab. Apr 05, 2020 a post tension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. The use of post tension tendons allows the engineer to design for larger slab construction spans typically used in parking structures or high rise. Two way posttensioned slabs with bonded tendons pdf.
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