There are several problems that can occur with post tensioning components in balcony and garage slabs in service. A 5inch post tensioned slab can handle up to 5,000 pounds, and a typical 9inchthick slab will bear a concentrated 9,000pound load. Post tension slab construction is common in areas with expansive soils. Precast posttensioned concrete structures amazing facts about us since the 1980s, dutchland has been specializing in the design, manufac. Shrinkage and temperature reinforcement in twoway post. Post tension slab posttensioned slabs are a great choice for resisting the anticipated tensile stress that will occur as a result of expansive soil. This method makes use of embedded high strength steel cables to reinforce the concrete slab. Post tension slabs reduce settling issues this giant checker board is actually the guts of an unbonded post tension slab. Post tensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons. Cutting openings in pt slabs does require care and caution.
Brendon burley structural option post tensioned twoway slab post tensioned 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 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. Jul 28, 2007 this picture was taken after a cable was tensioned. Construction maintenance of post tensioned slab on ground. Posttensioned segmental constructed structures can be vulnerable at their construction joints during periods of high construction boom it is, unfortunately, a fact that workmanship and supervision qualities fall 50% of hks bridge stock has been constructed over the last 10 years. Notice the assumptions required for the post tensioned design fig. Solid, waffle and banded flat slab systems were analysed. Finally, an example of a flat slab floor system is presented to illustrate the practice. Hazards of post tensioned concrete slabs safety toolbox. Tendons today are seven highstrength steel wires wound together and placed inside a plastic duct. A residential post tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. Market for post tensioning tendons over 40% of all pt tendons sold in the usa are for residential foundations. Pdf modern concrete buildings increasingly rely on posttensioned pt.
Before a posttension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. Effects of slab posttensioning on supporting steel beams. 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. Nonprestressed bonded reinforcement in posttensioned building. 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. In reinforced concrete members, the prestress is commonly.
Fundamentals of post tensioned design for buildings. Posttensioned pt slabs have the added complexity in that pt. Longer spans can be achieved due to prestress, which can also be used to counteract deflections. Usually a sign in the garage or stamp in the slab will indicate if. The cable is a spiral and the tensioning is done inside the slab. This is a typical concern for those purchasing new construction who are. For economical design of similar structures a smaller slab thickness leading to values between 60% to 80% of balanced selfweight is generally selected. Post tension slabs superior foundations services jackson. Tendons are terminated and tensioned at buttress panels. Cracks in foundation slab can invite subterranean termites or other things that might invade the home through those cracks. Thus, we will algebraically combine msdl, mll, and mbal at the critical sections and.
It allows slabs and other structural members to be thinner. The purpose of this publication is to widen the understanding of post tensioned 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. The medical office building malvern, pa 17 brendon burley structural option posttensioned twoway slab figure 23 details of the twoway slab. In order to take into account longterm losses, the user would estimate these losses and simply include. When planning for point loads, a safe rule of thumb is to figure on 1,000 pounds per inch of slab thickness. Post tension slabs are particularly beneficial on expansive soils and organic soils which are found in the south and southeastern united states. Several methods exist for prestressing concrete, with posttensioning being a very common one. Pdf tests of continuous posttensioned concrete slabs under. Posttensioning institutes design of posttensioned slabsonground, pti design procedure 3rd edition.
Posttensioning in buildings foreword working party wp1. Posttension concrete slab in this example posttensioned cables are introduced on a concrete slab. The expansive, or yazoo clay soils such as those present here in mississippi, shrink and swell based on the amount of water content in the soil which makes traditional slab ongrade slabs crack and. Effective inspection and monitoring of posttensioned. The main objective of the bulletin is to point out the benefits of using posttensioning for. Concrete is poured around the tendon with the tendon being positioned within the periphery of the concrete structure to form a large central area bounded by the tendon and an exterior. Tn342 design example 2way mondada 093090 adapt corporation. A method and apparatus for posttensioning a concrete slab. Abraham assisted in various aspects of instrumentation and data acquisition. 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. Pti 1990, posttensioning manual, 5th edition, posttension ing institute. Posttensioned twoway slab pennsylvania state university.
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. Aalami a must have reference book for engineers, students, contractors, building officials, and researchers. Design of posttensioned slabs posttensioning institute. 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. Also, because aci 302 says a reasonable level of cracking is from 0% to 3%, it implies that no cracking, 0%, is a possible, reasonable level. In posttensioned floor slab construction, the placement of postten sioning tendons. Project on design and construction of post tensioning slab presenting by. A tendon member is preformed to define an enclosed area yet fit within a form. In the succeeding years numerous posttensioned slabs were designed and constructed in conjunction with the lift slab method.
A normal slab is basically a rcc reinforce cement concrete slab where as a post tentioned slab is the psc prestressed concret 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. Posttensioned concrete slabs augi the worlds largest. Posttensioned concrete haunched slab bridge users manual kdot bridge section page 4 ver 2. I steer customers towards conventional every opportunity im asked. 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. System 7000 data acquisition system was used to record all. Post tension slabs are a form of prestressed slabs which means they are compressed prior to use so that the slabs are able to bear weight or service loads beyond their own natural weight.
This book is destined to become the definitive work on the design of posttensioned concrete buildings for many decades to come. Aug 28, 2015 posttensioned slab procedure duration. There are a wide variety of reasons for utilizing post tension slabs versus conventional slabs. First model a flat slab for the entire area, then model the drop panels as separate slabs from the bottom of the flat slab. Most often the cracks extend across the entire foundation and occur prior to tensioning of the tendon cables.
We had one customer come back with the ve the slab to post tension and the cost savings was offset by the redesign fee. Three posttensioned slabs with unbounded tendons were designed figures 4 and 5. This is accomplished by prestressing cables which run throughout the slab and by compressing the. Dec 24, 2014 objectives the objective of the present report is to summarize the experience available today in the field of post tensioning 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. Creating openings in unbounded posttensioned slabs icri. Posttensioned slabs are engineered based on soil conditions and loading, and can provide cost benefits as materials are used more efficiently. 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. Schematic comparing a conventially reinforced concrete member to a post tensioned membaer. Effective inspection and monitoring of posttensioned structures. What is posttensioning introduction posttensioning is a method of producing prestressed concrete, masonry and other structural elements.
Post tensioned concrete is a term heard more and more in the construction industry today. However, the beams divide the plenum space into channels, reducing the overall utility. Interior left, exterior right deflection analysis the final consideration in the design of the twoway slabs is deflection. For commercial buildings flat slab rising up to 10 to 20 stories is quite popular. Posttension basics how posttensioned slabs are built. Anchoring ceiling grids to concrete is sometimes easier said than done. It reduces or eliminates shrinkage crackingtherefore no joints, or fewer joints, are needed. Once it is tensioned the cable excess is cut off and the hole is sealed with concrete. A square 10,000 sqft slab will require less concrete than an irregularly shaped slab of the same size. The need for improved safety under overpass structures by minimizing the number of piers and maximizing horizontal clearance in comparison to rcsh. Permanent loads include the self weight of the slab and an additional dead loadof 2.
For residential construction, tendons at 48 inches on center are common. Balcony slabs in typical post tension buildings with balconies, the balcony slab is an extension of the concrete. This is part three of a threepart course that covers the fundamentals of post tensioned concrete for building structures using unbonded tendons. This slab will be modeled as a 2delement, allowing the analysis to be run in a general xyz environment. If your location is an area with expansive soils, always assume the slab is post tensioned. Sathyanarayana10631a0147 civil engineering 4th year sri venkateswara. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by pti, the tendons are stressed. Concrete slabs are often strengthened using a process called post tensioning. Post tensioning tendon installation and grouting manual fhwa. Cables are arranged as indicated by the engineer and chaired to run through the center of the slab.
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. Construction of posttensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. Tributaries used when computing average precompression. Posttension basics how posttensioned slabs are built the. This method of reinforcing concrete enables a designer to take advantage of the considerable benefits provided by prestressed concrete while retaining the flexibility afforded by the castinplace method of building concrete structures. Twoway slab systems twoway post tensioned slab systems have been widely used in building construction for many decades. It allows us to build slabs on expansive or soft soils. Market for posttensioning tendons over 40% of all pt tendons sold in the usa are for residential foundations.
Pt slabs offer the thinnest slab type, as concrete is worked to its strengths, mostly being kept in compression. However, in the greater houston area, posttensioned residential slab foundations do not have a smooth flat bottom. A posttension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. Twoway slab systems twoway posttensioned slab systems have been widely used in building construction for many decades. Posttensioning concrete increases the many benefits associated with a concrete framed building. Posttensioning, which is a form of prestressing, has several advantages over standard reinforcing steel rebars. 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. Why post tension slabs are used in phoenix, gilbert, and the. A combination of these values will determine the slab stresses at the time of stressing and at service loads. This book is destined to become the definitive work on the design of post tensioned concrete buildings for many decades to come. Post tension slabs are used in many parts of the country continue reading why post tension slabs are used in phoenix. Utilizing less material than typical conventional methods of construction. A psc is applied with a compressive stress on the cross section in advance before the application of loading on.
Post tensioning concrete increases the many benefits associated with a concrete framed building. Posttensioned pt slabs are typically flat slabs, band beam and slabs or ribbed slabs. 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. This picture was taken after a cable was tensioned.
Post tensioned slabs are engineered based on soil conditions and loading, and can provide cost benefits as materials are used more efficiently. For most large pt slabs, we also have to model the drop panels at the column supports. Our future vision pti envisions a future in which post tensioning is the first choice for reinforcing all structures. This sliding requires that the slab have a smooth flat bottom.
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. A 5inch posttensioned slab can handle up to 5,000 pounds, and a typical 9inchthick slab will bear a concentrated 9,000pound load. Apart from the possibility of poor consolidation of con. A residential posttensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. Post tension slab post tensioned slabs are a great choice for resisting the anticipated tensile stress that will occur as a result of expansive soil. The tendon member has ends which extend past the form. The study was addressed to flat slab systems currently adopted in building designo a square interior panel, with spans between 7. The thickness of a twoway, posttensioned slab for typical hotel column patterns.
Posttensioned done properly can be better, but it is never done properly, at least for residential structures. Post tension slabs are used to create a monolithic slab that is stronger than the typical slab and foundation that is poured in stages. A post tensioned concrete slab assembly comprising a concrete slab, a tendon member, and a pair of anchor means, said tendon member being preformed in a loop to define an enclosed area within said slab, said tendon member having ends adjacent one another which extend outside said slab, the tendon member being positioned within the periphery of said slab to form said enclosed area bounded. Gabriel tower 5 posttensioned transfer slabs and beams 5. Users manual posttensioned concrete haunched slab bridges. 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 time of stressing, they. The advantages are many, when compared to non post tensioned systems, and include thinner slabs, lighter structures, lower floortofloor heights, less mild reinforcing steel, and less short and long term deflections. Sometimes experienced ironworkers can merge removal and replacement into. Why post tension slabs are used in phoenix, gilbert, and. What is the difference between normal slab and posttensioned. It is common practice to use form vibrators for concrete consolidation for many precast.
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