The pti design procedure is used to design a slabon 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. This technical note presents the layout and profile of posttensioning. Posttension concrete slab in this example posttensioned cables are introduced on a concrete slab. However, because the continuous twoway tendons had to be placed in a draped parabolic profile near the top of.
If we take as an example a car parking, we can see that, in the case of simply reinforced concrete slab, the structure is made of a forest of pillars, with floor thickness considerably high. The advantages are many, when compared to non posttensioned systems, and include thinner slabs, lighter structures, lower floortofloor heights, less mild reinforcing steel, and less short and long term deflections. A residential posttensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by pti, the tendons are stressed. Design of posttensioned slabs posttensioning institute. A 5inch posttensioned slab can handle up to 5,000 pounds, and a typical 9inchthick slab will bear a concentrated 9,000pound load. Posttensioned concrete haunched slab xcsh design and details included in this manual are intended for the use of bridge details that can be obtained from kdot bridge section for the preparation of bridge plans. Technical notes in any specifications, contract documents, purchase orders, drawings or job details. It is based on the recommendations of aci318 as expounded in adapt technical note tn292. However, the beams divide the plenum space into channels, reducing the overall utility. Shrinkage and temperature reinforcement in twoway post. The advantages of the technique of slab posttensioning are several and clear. 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.
Do not alter the drainage pattern of the site provide a minimum of 3%. When planning for point loads, a safe rule of thumb is to figure on 1,000 pounds per inch of slab thickness. Salunke mgms college of engineering and technology, kamothe, india mgms college of engineering and technology, kamothe, india abstract the use of posttensioned flat slab is increasing day by day, due to its advantages over traditional concrete. There are several problems that can occur with post tensioning components in balcony and garage slabs in service. Part three continues with the study of twoway, posttensioned slab systems, including. 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. Fundamentals of posttensioned concrete design for buildings part one. Page 2 of slab post tensioning technical document system main features the advantages of the technique of slab post tensioning are several and clear.
In the succeeding years numerous posttensioned slabs were designed and constructed in conjunction with the lift slab method. Pretensioned concrete, bonded or unbonded posttensioned concrete. Finally, an example of a flat slab floor system is presented to illustrate the practice. Most modern browsers have builtin pdf readers if you have problems opening this file in your browser, check your browsers or computer systems. Unbonded post tensioning system technology in building. The document is part of the federal highway administrations national. A ccldesigned posttensioned slab can contain less concrete 20%. Posttension basics how posttensioned slabs are built. For economical design of similar structures a smaller slab thickness leading to values between 60% to 80% of balanced selfweight is generally selected. Fundamentals of posttensioned concrete design for buildings part one a suncam online continuing education course.
A psc is applied with a compressive stress on the cross section in advance before the application of loading on. Posttensioning, which is a form of prestressing, has several advantages over standard reinforcing steel rebars. Objectives the objective of the present report is to summarize the experience available today in the field of posttensioning in building construction and in particular to discuss the design and construction of post tensioned slab structures, especially post tensioned flat slabs a detailed explanation will be given of the checks to be carried. In post tensioned floor slab construction, the placement of postten. In any event, the maximum total length of posttensioned concrete slab bridges, without introducing a strand splice or interior span joints, is expected to be about 180 m 600. Unbonded posttensioning system technology in building construction 123 fabrication of monostrand sheathing was supplied until the early to mid1990s. This method produces a good bond between the tendon and concrete, which both protects the tendon from corrosion and allows for direct transfer of tension. Posttensioned concrete haunched slab bridge standards. The vsl post tensioned concrete slab on grade is cast in very large areas, often exceeding 2,500m 2 with no joints. Originally posttensioned, twoway slab framing systems were constructed with column and middle strips, similar to those used in conventionally reinforced twoway slabs. For most large pt slabs, we also have to model the drop panels at the column supports. A typical draped profile in an elevated concrete slab would route the posttensioned reinforcing through a high point over the slabs supports, and through a low point in between those supports. The format is similar to the existing standards available for.
Posttensioning institutes design of posttensioned slabsonground, pti design procedure 3rd edition. Posttensioning concrete increases the many benefits associated with a concrete framed building. Recommendations for acceptance and application of posttensioning systems pdf fip reports 1981. Post tension slabs answers to questions buyers ask. Pdf unbonded post tensioned concrete slabs in fire. The flat slab or post tensioned slab buildings in which slab is directly rested on columns, have been adopted in many buildings constructed recently due to the advantage of reduced floor to floor heights to meet the economical and architectural demands. It reduces or eliminates shrinkage crackingtherefore no joints, or fewer joints, are needed. These categories of cracks are caused by entirely different phenomena and have very different characteristics. Brendon burley structural option posttensioned twoway slab posttensioned twoway slab introduction the filigree beam system creates a thin lightweight floor system that leaves plenty of open plenum space for mechanical and electrical equipment. The impossibility comes from the unknown location of the tendons and anchors. There is a danger that if a nonprofessional cuts or drills into the slab, that they may sever, cut or damage the post tension cable. It allows slabs and other structural members to be thinner.
Unbonded post tensioned concrete slabs in fire part ii modelling tendon response and the consequences of localized heating september 2011 journal of structural fire engineering 23. The above spreadsheet program and users manual can be downloaded and be printed free of charge. In corrosive environments, stuffed and heatsealed tendons have the inherent shortcoming of either trapping or allowing access of corrosive substances in the oversized sheathing. Cracks caused by the restraint to axial slab shortening rts cracks. Posttensioned concrete slabs augi the worlds largest. A combination of these values will determine the slab stresses at the time of stressing and at service loads. Permanent loads include the self weight of the slab and an additional dead loadof 2. In certain applications, slabs in the order of 10,000m 2 have been constructed without movement joints. 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. Solid, waffle and banded flat slab systems were analysed. Fundamentals of post tensioned design for buildings. If your location is an area with expansive soils, always assume the slab is post tensioned.
What is the difference between normal slab and post. This may weaken the structural strength of the slab. Once the concrete is poured and sets, the cables are tensioned. Please note that some documents may have unreadable pages. Posttensioned concrete design spreadsheet program a pdh. Pretensioned concrete pretensioned concrete is cast around already tensioned tendons.
Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. 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. Post tension slab construction is common in areas with expansive soils. The study was addressed to flat slab systems currently adopted in building designo a square interior panel, with spans between 7. In reinforced concrete members, the prestress is commonly. Tendons today are seven highstrength steel wires wound together and placed inside a plastic duct. Market for posttensioning tendons over 40% of all pt tendons sold in the usa are for residential foundations. 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. 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. A normal slab is basically a rcc reinforce cement concrete slab where as a post tentioned slab is the psc prestressed concret slab. The main objective of the bulletin is to point out the benefits of using posttensioning for.
In general, as long the tendons and the concrete in front of the anchors are not damaged, drilling into a posttensioned slab is a fairly. Post tensioning tendon installation and grouting manual fhwa. Ccl posttensioned slabs can bring unique freedom over conventional building. Twoway slab systems twoway posttensioned slab systems have been widely used in building construction for many decades. However, should this happen, it can be repaired and even if not repaired, the slab may still function well. 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. The purpose of this publication is to widen the understanding of posttensioned floor construction and show the considerable benefits which include minimum storey heights, rapid construction, economy, maximum design flexibility, minimum number of columns, optimum clear spans, jointfree, crackfree. In order to take into account longterm losses, the user would estimate these losses and simply include. For commercial buildings flat slab rising up to 10 to 20 stories is quite popular. Analysis of posttensioned flat slab by using safe shriraj s.
Posttensioning in buildings foreword working party wp1. Cracks caused by applied loads flexural or shear cracks. Fundamentals of posttensioned concrete design for buildings. Effective inspection and monitoring of posttensioned. Posttensioned concrete in buildings posttensioning institute. Construction maintenance of post tensioned slab on ground. The document is intended primarily for design engineers, but we shall be very pleased if it is also of use to contractors and clients. Unbonded post tensioned concrete slabs in fire part ii modelling tendon response and the consequences of localized heating. Cracking in groundsupported post tensioned slabs on. Hazards of post tensioned concrete slabs safety toolbox. First model a flat slab for the entire area, then model the drop panels as separate slabs from the bottom of the flat slab. This slab will be modeled as a 2delement, allowing the analysis to be run in a general xyz environment.