Longer spans can be achieved due to prestress, which can also be used to counteract deflections. Typically, savings between 10% 20% in direct cost are achieved factors contributing to direct cost reduction. Posttensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or. Hazards of post tensioned concrete slabs safety toolbox. Design floors and foundations reliably and efficiently, saving time and money, and overcoming the most common concerns you face as a designer. Post tensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons.
Posttensioned general principales local zone design general zone design examples from pratice published by vsl international ltd. Post tension slabs reduce settling issues this giant checker board is actually the guts of an unbonded post tension slab. A wide variety of post tension equipment options are available to you, such as steel, stainless steel, and iron. Written by structural engineers who design post tensioned concrete buildings for a living and teach how to design them at the university level, there has simply never been anything like this book. Several methods exist for prestressing concrete, with post tensioning being a very common one. Posttensioning offers direct cost reduction over conventionally reinforced slabs primarily by reducing concrete and rebar material quantities as well as rebar insta llation labor. A psc is applied with a compressive stress on the cross section in advance before the application of loading on. Project on design and construction of post tensioning slab presenting by. Posttension india lets presentation by t rajkiran b sashi kiran s r sai pramod r bhyrava 2. 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. 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. Post tension slabs answers to questions buyers ask.
It is a concrete slab that has steel cables running through it that have been put under lots of stress to reduce cracking of the concrete and increases the strength of the slab. Typically maximum fiber stress in tension controls design. Nov 16, 2016 the systems used to posttension concrete and masonry consist of prestressing steel that is housed inside a duct or sheath, which allows the prestressing steel to be placed inside the typical job site formwork at the same time rebar and other reinforcing is placed. The following example illustrates the design methods presented in aci 31805 and ibc 2003. Sathyanarayana10631a0147 civil engineering 4th year sri venkateswara engineering college internal guide. 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. It is an outstanding textbook with a crystalclear presentation of indeterminate design and analysis fundamentals. Post tensioned concrete is a term heard more and more in the construction industry today. In order to take into account longterm losses, the user would estimate these losses and simply include. General overview of posttensioned concrete design instructor. A residential post tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. This tension makes the concrete slab and foundation much stronger than concrete without reinforcement and helps reduce cracking. While using this method more precautions has to be made for shear and deflection criteria for the slabs.
A detailed explanation will be given of the checksto. Apr 05, 2020 a post tension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. Post tensioning with or without bonding of tendons 3 1. Conventional uses more steel less concrete, post tension uses more concrete less steel at least on all of my designed slabs in east texas where expansive soil is. 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. The vsl post tensioned concrete slab on grade is cast in very large areas, often exceeding 2,500m 2 with no joints. Prestressing is a method of reinforcing concrete, counteracting applied loads.
Pretensioning steel tendons are stressed prior to concrete placement, usually at a precast plant remote from the construction site. The medical office building malvern, pa 16 brendon burley structural option posttensioned twoway slab posttension investigation besides shear strength it is also important to consider the moment capacity of each of the sections. 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. Posttensioned 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. I steer customers towards conventional every opportunity im asked. 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. Post tensioning is a special form of prestressed concrete in which the prestressing tendons are stressed after the concrete is cast. Nov 25, 2008 post tensioned concrete is a term heard more and more in the construction industry today. Pdf analysis and design of rcc and posttensioned flat slabs. Pdf the posttensioning method is now a days increasing widely, due to its application.
Slab thicknesses as a function of span lengths recommended limis slendernesses 1. Posttensioning, which is a form of prestressing, has several advantages over standard reinforcing steel rebars. Posttension basics how posttensioned slabs are built the. Us posttensioning industry owes its existence to liftslab construction first liftslab 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, liftslab companies changed to posttensioned slabs. Twoway posttensioned design amsysco post tensioning. Park plaza post tensioned parking structure demolition. Crack free performance vsl post tensioning axially compresses the concrete slab to counteract tensile stresses which. What is post tensioning introduction post tensioning is a method of producing prestressed concrete, masonry and other structural elements.
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. Tendons today are seven highstrength steel wires wound together and placed inside a plastic duct. Posttensioned twoway slab pennsylvania state university. Posttensioning institutes design of posttensioned slabsonground, pti design procedure 3rd edition. Having met and discussed with thousands of practitioners whose work encompasses the design or construction of post tensioned projects, the author presents his observations and experience in a clear and concise format, highlighting the concepts and procedures. In continuous or indeterminate post tensioned structures the moments due to the prestressing.
Serviceability limit state 11 41 crack limitation 11 42. The soil below the foundation is expansive clay with properties determined by the soil engineer. Post tension slabs are used to create a monolithic slab that is stronger than the typical slab and foundation that is poured in stages. Before a post tension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. Construction of posttensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. An analysis of the bulk cross section of each segment of slab is summarized in table 22. Post tension slab construction is common in areas with expansive soils.
Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by pti, the tendons are stressed. The book builds on over three decades of authors observation and design of post tensioning projects in more than 35 countries worldwide. What is the difference between normal slab and post. Usually a sign in the garage or stamp in the slab will indicate if. It allows slabs and other structural members to be thinner. Contractors sometimes need to drill or cut into a posttensioned 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.
Do you say you dont know anything, or can you give them a short explanation about them and why more and more builders are using them. The term prestressing is used to describe the process of introducing internal forces or stress into a. Concrete slab design software economically design posttensioned and reinforced concrete floors including slabs, mats, and rafts, with exceptional visibility into compliance, efficiency, and practicality. 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.
Cables are arranged as indicated by the engineer and chaired to run through the center of the slab. Contractors sometimes need to drill or cut into a post tensioned slab for repair or renovation work. Posttensioning concrete increases the many benefits associated with a concrete framed building. Segment as in2 bars spacing in interior column strip top bot 12. Posttensioned pt slabs are typically flat slabs, band beam and slabs or ribbed slabs. Sections are tension controlled when the tensile strain in the extreme tension. It reduces or eliminates shrinkage crackingtherefore no joints, or fewer joints, are needed. Aalami a must have reference book for engineers, students, contractors, building officials, and researchers. And from what ive seen the cost of conventional vs post tension is about a wash.
Global post tensioning system consumption market by manufacturers is on rise. A combination of these values will determine the slab stresses at the time of stressing and at service loads. Once the slab cures, qualified personnel apply tension and grout the cables. Ppt posttensioning powerpoint presentation free to. Posttension basics how posttensioned slabs are built. Sections are tensioncontrolled when the tensile strain in the extreme tension. Pre tensioning steel tendons are stressed prior to concrete placement, usually at a precast plant remote from the construction site. In certain applications, slabs in the order of 10,000m 2 have been constructed without movement joints. Why post tension slabs are used in phoenix, gilbert, and the. Posttensioned concrete design spreadsheet program a pdh. A normal slab is basically a rcc reinforce cement concrete slab where as a post tentioned slab is the psc prestressed concret slab.
A properly designed post tension slab can design around expansive soils, high water tables, etc. Crack free performance vsl posttensioning axially compresses the concrete slab to counteract tensile stresses which. 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. A posttension slab is a slab of concrete that has been prestressed using a specific method to increase the strength of the concrete. Post tension concrete slab in this example post tensioned cables are introduced on a concrete slab. Posttension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. Why post tension slabs are used in phoenix, gilbert, and. The first posttensioned slabs were erected in the usa in 1955, already using. A residential posttensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. Opportunity capitol view corridor austin, tx it was decided to remove the top deck including columns and ramp vsl was brought in to develop a safe. Several methods exist for prestressing concrete, with posttensioning being a very common one. The first post tensioned slabs were erected in the usa in 1955, already using. General principales local zone design general zone design.
Global posttensioning system consumption market by manufacturers is on rise. If your location is an area with expansive soils, always assume the slab is post tensioned. Construction maintenance of post tensioned slab on ground. 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. For residential construction, tendons at 48 inches on center are common. We had one customer come back with the ve the slab to post tension and the cost savings was offset by the redesign fee. In addition to the slendemess of the slab, there 14 are other important parameters, namely the amount of prestress and the live. The design of posttensioned flat slab can be done by.
This slab will be modeled as a 2delement, allowing the analysis to be run in a general xyz environment. What is posttensioning introduction posttensioning is a method of producing prestressed concrete, masonry and other structural elements. The vsl posttensioned concrete slab on grade is cast in very large areas, often exceeding 2,500m 2 with no joints. Posttension concrete slab in this example posttensioned cables are introduced on a concrete slab.
It allows us to build slabs on expansive or soft soils. Unless otherwise noted, all referenced table, figure, and equation numbers are from these books. Once the concrete is poured and sets, the cables are tensioned. 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. Pt slabs offer the thinnest slab type, as concrete is worked to its strengths, mostly being kept in compression. Before a posttension slab is poured, highstrength steel strands or cables, called tendons, are laid in a tight grid. Posttensioned, reinforced concrete slab design software ram. Post tension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. Introduction prestressing types of prestressing advantages of post tensioning current situation in india applications and examples of pt constructions conclusion. Post tension slabs are used in many parts of the country continue reading why post tension slabs are used in phoenix.
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