Do not alter the drainage pattern of the site provide a minimum of 3%. Hazards of post tensioned concrete slabs safety toolbox. Posttension concrete slab in this example posttensioned cables are introduced on a concrete slab. This may weaken the structural strength of the slab. 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. However, the beams divide the plenum space into channels, reducing the overall utility. For commercial buildings flat slab rising up to 10 to 20 stories is quite popular. Ccl posttensioned slabs can bring unique freedom over conventional building. Finally, an example of a flat slab floor system is presented to illustrate the practice. The document is part of the federal highway administrations national. 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. Posttensioned concrete in buildings posttensioning institute. Posttensioned concrete slabs augi the worlds largest. 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.
A psc is applied with a compressive stress on the cross section in advance before the application of loading on. Post tension slab construction is common in areas with expansive soils. Recommendations for acceptance and application of posttensioning systems pdf fip reports 1981. The study was addressed to flat slab systems currently adopted in building designo a square interior panel, with spans between 7. Solid, waffle and banded flat slab systems were analysed. It allows slabs and other structural members to be thinner. The format is similar to the existing standards available for. 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. Technical notes in any specifications, contract documents, purchase orders, drawings or job details. 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. For economical design of similar structures a smaller slab thickness leading to values between 60% to 80% of balanced selfweight is generally selected. 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. Fundamentals of posttensioned concrete design for buildings part one. Fundamentals of posttensioned concrete design for buildings.
Posttensioning institutes design of posttensioned slabsonground, pti design procedure 3rd edition. Posttension basics how posttensioned slabs are built. 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.
Design of posttensioned slabs posttensioning institute. 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. These categories of cracks are caused by entirely different phenomena and have very different characteristics. In post tensioned floor slab construction, the placement of postten. A normal slab is basically a rcc reinforce cement concrete slab where as a post tentioned slab is the psc prestressed concret slab. Fundamentals of posttensioned concrete design for buildings part one a suncam online continuing education course. Cracking in groundsupported post tensioned slabs on. Posttensioned concrete haunched slab bridge standards. Once the concrete is poured and sets, the cables are tensioned.
Part three continues with the study of twoway, posttensioned slab systems, including. Shrinkage and temperature reinforcement in twoway post. In order to take into account longterm losses, the user would estimate these losses and simply include. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by pti, the tendons are stressed. Analysis of posttensioned flat slab by using safe shriraj s.
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. For most large pt slabs, we also have to model the drop panels at the column supports. The main objective of the bulletin is to point out the benefits of using posttensioning for. However, because the continuous twoway tendons had to be placed in a draped parabolic profile near the top of. Unbonded post tensioned concrete slabs in fire part ii modelling tendon response and the consequences of localized heating. Originally posttensioned, twoway slab framing systems were constructed with column and middle strips, similar to those used in conventionally reinforced twoway slabs. 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.
What is the difference between normal slab and post. Fundamentals of post tensioned design for buildings. A 5inch posttensioned slab can handle up to 5,000 pounds, and a typical 9inchthick slab will bear a concentrated 9,000pound load. Post tension slabs answers to questions buyers ask. Page 2 of slab post tensioning technical document system main features the advantages of the technique of slab post tensioning are several and clear. 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. 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. First model a flat slab for the entire area, then model the drop panels as separate slabs from the bottom of the flat slab. Tendons today are seven highstrength steel wires wound together and placed inside a plastic duct.
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. Unbonded posttensioning system technology in building construction 123 fabrication of monostrand sheathing was supplied until the early to mid1990s. A combination of these values will determine the slab stresses at the time of stressing and at service loads. Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab.
A ccldesigned posttensioned slab can contain less concrete 20%. 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. Pretensioned concrete pretensioned concrete is cast around already tensioned tendons. Please note that some documents may have unreadable pages. In certain applications, slabs in the order of 10,000m 2 have been constructed without movement joints. The impossibility comes from the unknown location of the tendons and anchors. It is based on the recommendations of aci318 as expounded in adapt technical note tn292. Construction maintenance of post tensioned slab on ground. Two broad categories of cracking can occur in groundsupported posttensioned slabs. 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. The vsl post tensioned concrete slab on grade is cast in very large areas, often exceeding 2,500m 2 with no joints. The document is intended primarily for design engineers, but we shall be very pleased if it is also of use to contractors and clients.
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. Balcony slabs in typical post tension buildings with balconies, the balcony slab is an extension of the concrete. 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. 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. This slab will be modeled as a 2delement, allowing the analysis to be run in a general xyz environment. A residential posttensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. The advantages of the technique of slab posttensioning are several and clear. Posttensioned twoway slab pennsylvania state university. Posttensioning concrete increases the many benefits associated with a concrete framed building.
It reduces or eliminates shrinkage crackingtherefore no joints, or fewer joints, are needed. Posttensioning, which is a form of prestressing, has several advantages over standard reinforcing steel rebars. The above spreadsheet program and users manual can be downloaded and be printed free of charge. Unbonded post tensioning system technology in building. Cracks caused by applied loads flexural or shear cracks. 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. If your location is an area with expansive soils, always assume the slab is post tensioned. This technical note presents the layout and profile of posttensioning. When planning for point loads, a safe rule of thumb is to figure on 1,000 pounds per inch of slab thickness. In the succeeding years numerous posttensioned slabs were designed and constructed in conjunction with the lift slab method. 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. Allowable deflection limits refer to table 1 of the appendix.
Permanent loads include the self weight of the slab and an additional dead loadof 2. Effective inspection and monitoring of posttensioned. Most modern browsers have builtin pdf readers if you have problems opening this file in your browser, check your browsers or computer systems. Posttensioned concrete design spreadsheet program a pdh. Pretensioned concrete, bonded or unbonded posttensioned concrete.
Posttensioning in buildings foreword working party wp1. Twoway slab systems twoway posttensioned slab systems have been widely used in building construction for many decades. 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. In reinforced concrete members, the prestress is commonly. Post tensioning tendon installation and grouting manual fhwa. There are several problems that can occur with post tensioning components in balcony and garage slabs in service. 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. Pdf unbonded post tensioned concrete slabs in fire. 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. However, should this happen, it can be repaired and even if not repaired, the slab may still function well. Market for posttensioning tendons over 40% of all pt tendons sold in the usa are for residential foundations.
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