Unbounded post tensioned concrete slab unbounded post. Prior to the development of post tensioning techniques the effectiveness of concrete was limited to short spans. Posttension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. Great care must be taken to ensure the cables remain perfectly straight during the pour. Tendons may consist of single wires, multiwire strands or threaded bars that. For residential construction, tendons at 48 inches on center are common. Wood working diy floor cleaners woodworking bookshelf how to make. Pt slabs have lesser thickness than rcc slabs as their deflection can be controlled by post tensioning. In simple span beams the primary post tensioning pt moments induced by the prestressing force are directly proportional to the eccentricity of the tendons with respect to the neutral axis of the member i. Ma n y t i m e s, re w o rk of post tensioning material is the sourc e of tensioning pro b l e m s. Post tensioning is an efficient method of concrete reinforcing that reduces mass while improving building stability and resistance to wind, gravity, and seismic forces.
Pticertified personnel involved in pt field operations are vital to ensuring the performance, serviceability, durability, and safety of pt concrete construction. In post tensioned structure, the tensioning of reinforcement is done after the concrete has been placed. Construction maintenance of post tensioned slab on ground. Post tensioned concrete slabs enable us to achieve minimum floor thicknesses thus reducing storey and overall building heights. This can help to minimize cracking and differential settlement in adverse conditions. No consensusbased, offtheshelf, floodresistant designs that fully address construction in.
Post tensioning, or pt, has become increasingly popular over the past 30 years or so as the technology has been perfected. A slab tensioned against hardened concrete after the construction of the slab is called post tension slab. A wide variety of post tension slabs options are available to you, such as graphic design, 3d model design, and others. Post tensioning provides high strength and stability, but looks just. Posttensioned twoway slab pennsylvania state university.
In continuous or indeterminate post tensioned structures the moments due to the prestressing. Fabricated of north carolina black walnut, the tables, shelving, desks, and. Our future vision pti envisions a future in which post tensioning is the first choice for reinforcing all structures. A posttensioned foundation is a concrete slab foundation that is reinforced with stranded steel cables that are tensioned after the concrete hardens.
This method makes use of embedded high strength steel cables to reinforce the concrete slab. Eruption of pt tendons caused by corrosion failure early commercially available unbonded post tensioning systems were susceptible to corrosion including paper wrapped, plastic pushthrough stuffed and heatsealed cigarette wrapped sheathing systems due to their susceptibility to the ingress of water. When the foundationconcrete has sufficiently hardenedcured, the plasticsheathing is stretchedelongated. Afterwards, once the concrete has gained strength but before the service loads are applied, the cables are pulled tight, or tensioned.
The other design consideration is to ensure an adequate number of movement joints are provided in the slab. This method is achieved in a process where metal or plastic tubes which contain loose tensioning cables or rods are cast into the concrete. Post tensioned concrete slabs in buildings have many advantages over reinforced concrete slabs and other structural systems for both single and multilevel structures. Optimising the design for both concrete and steel usage saves time and. Design fundamentals of post tensioned concrete slabs bommer, allan, aalami, bijan on. 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. A posttensioning cable system was employed, where bundles of high. Unlike those of posttensioned concrete see below, the tendons of. The foundation gains tensile strength when the cables are tightened after the slab has been cast. Cables are arranged as indicated by the engineer and chaired to run through the center of the slab.
Structural engineers design concrete slabs with posttension cables to obtain greater span lengths between supporting columns and to allow thinner slabs. For the repair and modification of post tensioning pt systems as well as post tensioned concrete structure repair and protection, structural technologies offers highly specialized products and services including investigation, repair design support, repair and replacement components, corrosion protection products, strengthening solutions as well as new or replacement post tensioning systems. The stranded cables are slid inside of plasticsheathing, which prevents the stranded steel tendons from touching the concrete. The tension is transferred to the concrete, helping hold it together even better. Posttension cables are used in concrete construction to allow thinner slabs and greater span lengths between support columns. In our newest plant, we have doubled capacity to better serve customers throughout northern california, southern california, washington, oregon and colorado. How can i control a cable been cut in post tension concrete slab. Post tension services of texas ptst is a full service post tensioning company based in dallas. Design fundamentals of posttensioned concrete slabs. Post tensioning concrete is a way to further enforce the concrete structure.
You can also choose from 1 year, 2 years post tension slabs, as well as from concrete anchor, wedge anchor post tension slabs, and whether post tension slabs is iso, or gb. The spacing of the cables is determined by the engineer who provided the certification. The tendons are usually pulled to a tension of 25,000 pounds per square inch 4503 kg per square cm. Post tensioning is a technique for reinforcing concrete. Post tensioned concrete is accomplished by tensioning high strength steel cables within the concrete mass. Very good video showing step by step post tension slab. These cables, composed of steel wires inserted into a plastic sheath, are subsequently tensioned and grouted after the concrete is poured. If your location is an area with expansive soils, always assume the slab is post tensioned. 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. I suppose this is not unusual, based on other posts ive read. We specialize in new construction post tension slab projects and post tension repair work for both commercial and residential applications in dallas, fort worth, arlington, keller, plano, mansfield and throughout the metroplex, texas, oklahoma, colorado, louisiana and new mexico.
Each of the tendons in the posttension slab is pulled tight, using a hydraulic jack. Pti currently offers 5 training and certification workshops for field personnel. Post tensioned foundation information for the homeowner. The advent of post tensioned concrete allowed longer slab spans and thinner sections. An excellent 2page reference on post tensioned concrete is available from, of all places, the post tensioning institute pti.
Perpendicular to the tendons, the banded tendons run with the columns. Post tension slab advantages and disadvantages of post. In post tension concrete, steel strands or cables pass through the concrete member in plastic ducts or sleeves. How to create a concrete slab using the posttensioning method. An analysis of the bulk cross section of each segment of slab is summarized in table 22. Posttensioning actively loads the structure one of the main differences between a posttensioned beam or slab and a typical reinforced concrete element is that the strands drape or profile inside the concretetheir vertical location changes along the length of the member. Once the concrete is poured and sets, the cables are tensioned. The reason may be due to a repair procedure or restressing due to outofrange elongation readings. Utilizing less material than typical conventional methods of construction. 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. Good quality concrete should reach 2000 psi in approximately 4 days under normal curing conditions, and certainly within 7 days.
Construction of posttensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. Prestressed concrete is a form of concrete used in construction. Firths amazing post tension floor slab timelapse video 10 hours work in 5 minutes. Once the slab cures, qualified personnel apply tension and grout the cables. Post tension slab construction is common in areas with expansive soils. For post tensioning the reinforcement is not normally in the form of a metal bar and a tendon or cable is normally used. A psc is applied with compressive stress on the crosssection in advance before the application of loading on the member so that the stresses after loading are fully or partially balanced by the prestressedstresses developed due to the tensioning of steel. Post tensioned concrete has precompression loads applied to the concrete, which ensures any deflections in the slab can be eliminated by good design practices. The reason is because post tensioning is a method of precompression, which means the concrete is put into a state of compression, which allows the concrete. Shrinkage crack considerations for post tensioned foundations june 1, 2015 shrinkage cracks in concrete slab onground foundations are a significant public relations problem to home builders.
The posttensioned slabs allowed for long spans between columns. Solar cables and wires are required to transport this electricity. Post tensioned slabs should be stressed when the concrete strength designated by the engineers plan is reached. Post tensioned concrete slab tendons are unidirectional, snaking through the concrete to provide superior tension. Post tension slabs are slabs used to construct high strength structures with an economical cost. After the concrete has gained strength, but before the service load is applied, the strand is pulled tight and then anchored against the outside of the concrete member. Pti offers certification of plants producing unbonded single strand tendons. Post tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. Marks were made on the slab and the locations were measured and charted on a diagram of the balcony. That hampers efforts to properly post tensioned the slab once the concrete is poured.
Structural technologies is the exclusive manufacturer of vsl post tensioning products and construction systems in the united states. Furthermore, large, clear internal spans provide flexibility of layout which is attractive to many potential clients. This allow for more flexible tenant spaces and better sightlines. Once the tension cables are exposed, and begin rusting, is there anything you can do to fix them or repair them and prevent them from snapping. What is the difference between normal slab and post.
Segment as in2 bars spacing in interior column strip top bot 12. Brendon burley structural option post tensioned twoway slab post tension investigation besides shear strength it is also important to consider the moment capacity of each of the sections. This also reduces structural selfweight and produces overall material efficiencies whilst controlling deflections more effectively. Post tension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab.
Contractors sometimes need to drill or cut into a post tensioned slab for repair or renovation work. What is post tensioning introduction post tensioning is a method of producing prestressed concrete, masonry and other structural elements. Posttensioned slabs are thinner and lighter, which have trickledown effects on the both the building gravity and lateralforce. Post tension slab services post tension concrete, cable.
Organic matter, such as grass, roots and leaves, will decay under the slab, causing the foundation to settle and crack. In unbonded post tension concrete flat plate slab multi story building, in case mep installation were a drill used in concrete slab make a penetration in bottom. A good source for more information is design and construction of post tensioned slabsonground post tensioning institute, phoenix, ariz 6028707540. Once a suitable concrete strength has developed, the tendonsare threaded through the ducts and stretched put into tension. Cover is determined from the requirements for corrosion protection, fire protection, and wear. Span lengths up to 30 feet are common for twoway pt slab systems. Post tension cable highest quality material conco operates two large rebar fabrication, post tensioning and stud rails facilities and have made substantial upgrades to continue to expand. We can furnish all or part of the foundation package including reinforcing materials, stressing of tendons, and system repairs. Post tension cable suppliers premium products from conco. Although this construction technique produces concrete sections with excellent structural integrity, locating hidden post tension cables and rebar or conduit for that matter in concrete is difficult. Organic soil is a type of soil that contains a high percentage of organic matter. Woodworking gifts free pattern wood working gifts for her. The alternative to pre tensioning is post tensioning.
Posttension basics how posttensioned slabs are built the. This is achieved by laying out highstrength steel cables in a crisscrossed grid pattern throughout the foundation prior to pouring 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. We can provide a fullyintegrated structural, posttensioning and facade construction. Ribbed slabs there are two basic types of post tensioned residential slabs. Since the early 1950s, post tension tendons have been used in the design of concrete structures. Gregory havel takes a look at this aspect of modern building construction. The released tension will find the path of least resistance. Crawlspace foundations typically consist of perimeter masonry or concrete. Posttensioned slabs are thinner and lighter, which have trickledown effects on the both the building gravity and lateralforceresisting systems, including columns, shear walls.
Post tension cables pt cables are drawn tight with thousands of pounds of pressure. Posttensioning methods for reinforcing concrete the. Post tension depth and cable location in concrete youtube. Detensioning unbonded posttension tendons amsysco post. Before a post tension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. This tension makes the concrete slab and foundation much stronger than concrete without reinforcement and helps reduce cracking. 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. Post tensioning also results in lesser reinforceme. Aug 14, 2012 the slab was constructed with post tensioned cable. Post tension repair schnell contractors concrete repair. Fallingwater is a composition of varied materialsstone, concrete, steel, glass, and. Post tensioning concrete with steel strand became a popular solution to deflection and weight in slabs in the us in the 1950s. Post tensioned slabs are engineered based on soil conditions and loading, and can provide cost benefits as materials are used more efficiently. Post tension concrete slab, post tension concrete slab.
For conventional rebar or post tension slabs rci is ready with the materials and support you need to complete your project on time and within budget. The tensing of the cables occurs after the concrete has mostly cured, hence the term posttension. Then concrete is poured and allowed to harden to 75% of its design strength. Significant overbalancing of the weight of the concrete with posttensioning can actually lift and crack the slab. Pretensioning and posttensioning in prestressed concrete. Twoway posttensioned design amsysco post tensioning. Post tensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons.
Posttension basics how posttensioned slabs are built. All concrete will shrink during the curing process which lasts up to a year after the time concrete. Design fundamentals of post tensioned concrete slabs. Cables are arranged as indicated by the engineer and chaired to run through the center of the. A highly unique and valuable chapter is presented on construction issues and structural observations, and finally chapters addressing two of the more exotic applications of post tensioning, post tensioned slabs onground and externally applied post tensioning for strengthening and repair. The 3celled, prestressed, posttensioned concrete box girder. Preventing cracks on posttensioned concrete slabs pro. The builder used a post tension foundation with footings.
B9472, is staffed with an experienced team of skilled professionals who undertake all aspects of structural concrete rehabilitation, restoration, repair and reinforcement for a variety of commercial and industrial buildings, parking structures and slabs. The practice of mlaw has been to apply stress when the concrete reaches 2000 psi. This book is destined to become the definitive work on the design of post tensioned concrete buildings for many decades to come. Posttensioned concrete is used more frequently today than in the past, and presents several hazards to firefighters. Oct 14, 2010 cns infra, post tension company which performs construction with a unbounded post tension technique. Our manufacturing facilities in the united states are certified by ptis plant certification program to ensure the highest quality fabrication of materials. At one time there were problems with corrosion of the cables, especially in deicingsaltladen parking structures, but better materials and construction methods plus good training and certification programs have. 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. With post tensioned construction, steel cables are placed in the slab and stretched from one end of the slab.
Post tension slabs answers to questions buyers ask. During the detensioning process, the post tensioning tendon will have to be overstressed. On the other hand, the banded and distributed tendons limit the potential forms of the slab. Hazards of post tensioned concrete slabs safety toolbox. Many people are aware of the need for rebar when building retaining walls, concrete foundations and driveways. The cables are then posttensioned or pulled by a hydraulic jack and the concrete is allowed to cure completely. This was followed by the removal of the flagstone floor from the living room and the. Post tensioned slabs are used when spans are large and normal rcc slabs become uneconomical. A wide variety of post tension concrete slab options are available to you, such as free samples. Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. If a tension cable snaps, you might as well budget for a full foundation repair. If these cables are cut, nicked or in any way compromised, they can rip through the concrete and render the slab useless, or seriously injure someone.
A combination of these values will determine the slab stresses at the time of stressing and at service loads. 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. What is posttensioning introduction post tensioning is a method of producing prestressed concrete, masonry and other structural elements. Structural engineers design the slabs with post tension cables in an effort to make the slab act monolithically to counter the point loads created by the soil. In post tensioning the concrete is cast around tubes or ducts which will contain the reinforcing tendon. Construction of post tensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. During preconstruction a sonar scan was performed which indicated the locations and depth of the post tension cables. A normal slab is basically a rcc reinforce cement concrete slab whereas a post tensioned slab is the psc prestressed concrete slab. Post tensioned slabs, however, put the slab in tension after the concrete has cured.
They are stretched both directions of the slab, and placed on chairs that hold them up in the concrete as it is poured. The cables installed are usually pulled so they each have approximately 28,500 lbs. Demolition of post tensioned concrete structures presents the contractor with unique issues. Several methods exist for prestressing concrete, with post tensioning being a very common one. And will likely cause a domino effect as other tension cables begin snapping as well. On rare occasions, the ironworkerinstaller will need to detension an alreadystressed post tensioning tendon. In the case of a post tension slab, steel cables are laid out in grid fashion inside the forms.
Oct 22, 2012 concrete scanning can locate services, post tension cables, etc. The cables are then posttensioned or pulled by a hydraulic jack and the concrete is allowed to cure. The tricky part comes when concrete is poured into the forms. A technique which is used for lowering cost of construction and strengthening the construction. Back in the 1960 there was limited use in concrete foundations in residential construction, but very little. The use of post tension cables has been around for many years. Windfarm foundations stay cable systems ground anchoring heavy lifting and. In states like california, texas, nevada and arizona the use of post tension slabs have increased tremendously in the last ten years. Posttensioned concrete corrosion mitigation posttension. Although some post tensioned slab structures had been constructed in europe quite early on, the real development. Post tension pt tendon systems are primarily used for large slab construction projects.
This concrete has cable conduits cast into it and that cable is stretched, or tensioned, hydraulically after the concrete has hardened. A post tension slab is a slab of concrete which has been prestressed using a specific method to increase the strength of the concrete. Information about how posttensioned concrete is constructed. First off, one could argue that post tensioning is superior to conventionally reinforced concrete in a pure engineering sense. Heavily loaded concrete groundslabs and pavements can be sensitive to.
Post tension v conventional cph structural engineering. Post tension concrete slabs are used to create a monolithic single pour slab that is stronger than a traditional slab without reinforcement. To create a slab using this method, plastic sleevecovered steel cables are laid in a grid running in both directions. These slabs are constructed with the help of tendons or cables that transfer the load. Post tension concrete is a method of reinforcing concrete.
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