Pdf prestressed and posttensioned concrete yatniel. The design of post tension slab is presented below. Post tensioning in buildings is not limited to floor slabs. Our future vision pti envisions a future in which post tensioning is the first choice for reinforcing all structures. Construction of post tensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. Five underlying features of post tensioned construction allow greater flexibility in reinforcement layout. This location is typically congested with tendons near the top of the slab and shooting pins may cause damage to.
Thanks to lift slabs us post tensioning industry owes its existence to lift slab construction first lift slab buildings in the us were built in the mid 1950s using nonprestressed slabs problems with deflections and slab weight in long 2way spans to solve deflection and weight problems, lift slab companies changed to post tensioned slabs. Posttensioned slabs fundamentals of the design process ultimate limit state serviceability limit state detailed design aspects construction procedures. Posttensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons. The examples include a twoway slab, long span beam and a twoway structural mat foundation. Pre tensioning and post tensioning both method are used under prestressing process which have few edge over the orthodox nonstressed structures like more span to depth ration, higher moment and shear capacity. Longer spans can be achieved due to prestress, which can also be used to counteract deflections.
When planning for point loads, a safe rule of thumb is to figure on 1,000 pounds per inch of slab thickness. Concrete reductions up to 25%, and rebar reductions up to 65% are typical. This shortens the construction cycle by giving faster access to. Post tensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons. Post tension slab although concrete is a strong material for construction, it is not resistant to breakdown especially where longer concrete slabs are required like in a bridge or a length of a beam. Post tensioning is a special form of prestressed concrete in which the prestressing tendons are stressed after the concrete is cast. Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. Horizontal posttensioned connections for precast concrete. The variations presented later in this paper have been. Post tensioning institutes design of posttensioned slabs onground, pti design procedure 3rd edition. Tributaries used when computing average precompression. Shortening crack mitigation crack evaluation tn451010616. The alternative to pre tensioning is post tensioning. The post tension slab is designed as per is431987 04 and twoway slab is designed as per is456.
We are dedicated to providing the construction industry with engineering expertise, responsive service and manufacturing excellence to ensure safe, timely and cost effective installations, restorations and repairs. Slab post tensioning systems page 5 38 reinforcing savings as steel and concrete increase in pricing, the savings with a post tensioned slab will increase, because the quantity of steel and concrete required for a post tensioned slab is less than for a conventionally reinforced foundation. Frequently asked questions posttensioning institute. Appleton tecbnical university, lisbon, portugal, carlos a. For this, the concrete slab is tensioned with a process called prestressing and the slab of concrete which comes out after this process is known. A post tensioned foundation is a concrete slab foundation that is reinforced with. Lightly reinforced slabs on stable soilsthese slabs may be. The extent of the restraint cracking in a post tensioned member depends on a number of factors, including the stiffness of the supports. Notice the assumptions required for the post tensioned design fig. Jurgens his article presents a set of guidelines intended to t assist designers in routine post tensioning design, beginning with a discussion of the initial decisions that must be made to design post tensioned floor members. The three examples are straight forward and highlight the. Posttensioned tennis court construction renner sports.
Cables are arranged as indicated by the engineer and chaired to run through the center of the slab. Shoring and formwork can be removed as soon as the tendons are stressed. Many times inexperienced contractors may drill or shoot column collars into concrete on top of the slab. Post tensioning tendon installation and grouting manual fhwa. Post tensioning with or without bonding of tendons 3 1. Guidelines for the design of posttensioned floors by bijan o. Precast posttensioned segmental construction is defined as a method of construction for bridges, buildings, tanks, silos, cooling towers, tunnels and other structures in which primary load carrying members are composed of precast concrete segments post tensioned together. Post tension slab working principle, components and. Serviceability limit state 11 41 crack limitation 11 42. For the specified concrete material of 40 mpa cube strength, this translates to tensile stresses exceeding 5. Post tensioned slabs use highstrength tensioned steel strands to compress the slabs, keeping the majority of the concrete in compression.
Instantly download a sample cad collection search for drawings browse s of 2d cad drawings, specifications, brochures, and more. For span lengths over 2022 feet, pt slabs are often more cost effective. A typical draped profile in an elevated concrete slab would route the post tensioned reinforcing through a high point over the slab s supports, and through a low point in between those supports. The foundation gains tensile strength when the cables are tightened after the slab has been cast. Construction maintenance of post tensioned slab on ground. General principales local zone design general zone design. In a post tensioned beam, the tendons are stressed and each end is anchored to the concrete section after the concrete has been cast and has attained sufficient strength to safely withstand the prestressing force as shown in fig. The pti design procedure is used to design a slab on grade foundation that will respond elastically to forces the foundation is exposed to including those that are the consequence of soil pressure and soil deformation. Posttension basics how posttensioned slabs are built.
Renner sports surfaces has over 27 years experience in the design and construction of posttensioned concrete tennis courts, utilizing installers trained and certified by the post tensioning. Sections are tension controlled when the tensile strain in the extreme tension. Post tensioned foundation information for the homeowner. Martins university of algarve, portugal summary the specification of maximum span to thickness ratios allows the. Scribd is the worlds largest social reading and publishing site. Until now, the post tensioned hori zontal connection, with or without a hollowcore slab, has not been ade quately examined so as to gain a thorough understanding of its shear behavior under the various limit states. While it is an integral part of all post tensioning operations, its results can be misunderstood, leading to disagreements, fingerpointing, and late nights trying to get a resolution prior to tomorrow mornings 4 a. The first edition of the post tensioning manual was published in 1972, and as of the time of this writing 2018, they are up to their 6th edition. Schematic comparing a conventially reinforced concrete member to a post tensioned membaer.
Bridges, posttensioning, tendons, grout, grouting, strands, bars, protection, ducts, inlets, outlets, tests, prestressed concrete, pretensioning, stressing. Post tension slab advantages and disadvantages of post. This spreadsheet program provides for the design and analysis of post tensioned concrete oneway beam and slab systems and twoway flat plate slab systems. The program is divided into three separate screens, which correspond to the three major areas of concern in the design of a post tensioned. Pt slabs offer the thinnest slab type, as concrete is worked to its strengths, mostly being kept in compression. As is wellknown, in this method of post tensioning the prestressing steel is placed in ducts, and after stressing is bonded to the surrounding concrete by grouting. The advantages of posttensioned structures a technique that allows long beams lengths to be achieved reduces deflections and allows highspan depth ratios improves durability by the reduction or elimination of cracking more efficient utilization of steel and concrete material. In posttensioned floor slab construction, the placement of postten sioning tendons. Effective inspection and monitoring of posttensioned. In post tensioning method, tendons are coated with grease or. Twoway posttensioned design amsysco post tensioning. In this article we study about the working principle, components, construction and advantages of post tension slab.
For residential construction, tendons at 48 inches on center are common. Post tensioning utilizes high quality high strength steel such that 1 kg of post tensioning strand may replace 3 or 4 kg of ordinary nonprestressed reinforcement. A combination of these values will determine the slab stresses at the time of stressing and at service loads. Pdf posttensioned concrete longspan slabs in projects of. A 5inch post tensioned slab can handle up to 5,000 pounds, and a typical 9inchthick slab will bear a concentrated 9,000pound load. A ccldesigned posttensioned slab can contain less concrete 20% 30%, less reinforcement and less complicated rebar shaping than conventional reinforced. In post tensioned floor slab construction, the placement of post tensioning tendons and associated nonprestressed reinforcement does not strictly follow the practice of nonprestressed slabs. Pretensioning and posttensioning in prestressed concrete. 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. This hybridisation helps achieve the formation of a much thinner slab with a longer span devoid of any columnfree spaces. In the case of a post tension slab, steel cables are laid out in grid fashion inside the forms.
Members of the institute include major post tensioning material fabricators in the u. Suncoast posttension is north americas largest unbonded post tension specialist. Post tensioned concrete is the preferred method for new tennis court construction and rebuilding of old tennis courts. In part a a post tensioned member on very flexible supports shortens under the precompression, forcing the supports to follow the members moment. Developers, architects, engineers, contractors, educators and. Download free, highquality cad drawings, blocks and details of post tensioned concrete organized by masterformat. Post tensioning of foundations, transfer beams and plates, post tensioned masonry and the combination of precast elements with castinplace concrete by means of post tensioning offer other interesting opportunities. A 2 2area 2 a c 2 2 post tensioned 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. Pdf nowadays, design of modern an architectural building structures requires the use of slender and free from numerous supports slabs. The tricky part comes when concrete is poured into the forms. Post tension slab working principle, components and construction.
The vsl post tensioned concrete slab on grade is cast in very large areas, often exceeding 2,500m 2 with no joints. Post tensioned concrete design limit is the tensile strain in the reinforcement at the balanced strain condition, which is taken as the yield strain of the reinforcement, f e aci 10. What is the difference between pretension and post tension. The post tensioning institute designed post tensioned foundations. Structural calculations for posttensioned flat slab. In certain applications, slabs in the order of 10,000m 2 have been constructed without movement joints. Post tension slab is a combination of conventional slab reinforcement and additional protruding highstrength steel tendons, which are consequently subjected to tension after the concrete has set. It is the intent of this chapter to establish the practices and specific requirements of the structure and bridge division for the design and detailing of prestressed and posttensioned concrete members.
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