Hazards of post tensioned concrete slabs safety toolbox. Demolition of posttensioned concrete structures presents the contractor with unique issues. Posttensioning manual post tensioning institute on. Construction of post tensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. Post tension slab working principle, components and. 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. Even congested tendons can be routed around obstructions. Written by structural engineers who design posttensioned concrete buildings for a living and teach how to design them at the university level, there has simply never been anything like this book. The tensioned strands are anchored at either end, resulting in compression of the concrete.
Detensioning unbonded posttension tendons amsysco post. These slabs are constructed with the help of tendons or cables that transfer the load. However, the primary focus of this course covers applications of post tensioning that are typically used in buildings and parking structures, specifically one way slabs, two way slabs, and continuous beams. Our clients are home remodeling contractors, architects, home owners and engineers. Post tension slabs are slabs used to construct high strength structures with an economical cost. Finding tension cable in foundation fine homebuilding. Structural engineers design concrete slabs with posttension cables to obtain greater span lengths between supporting columns and to allow thinner slabs.
The contract work to be performed under this section consists of furnishing all required labor, materials, equipment, implements, parts and supplies necessary for, or appurtenant to, the. The post tension cables are about 34 dia sheathed in a plastic sleeve. A post tensioned concrete court slab will have a greater thickness than asphalt 4 as opposed to 3 and also have prestressed reinforcing steel. Im basing these on how practical they are in the structural engineering design industry. The question is, in case damage in cable cause cut, how far it will goes out of edge slab.
Posttension cables are steel wires inserted into plastic sheathing laid in place while pouring the concrete slab. A post tensioned foundation is a concrete slab foundation that is reinforced with stranded steel cables that are tensioned after. In states like california, texas, nevada and arizona the use of post tension slabs have increased tremendously in the last ten years. This book is destined to become the definitive work on the design of post tensioned concrete buildings for many decades to come. Once the concrete is poured and sets, the cables are tensioned. 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.
Post tensioning tendons, which are highstrength steel cables inside plastic sheathing, are positioned in the forms before the concrete is placed. Tendons may consist of single wires, multiwire strands or threaded bars that. For residential construction, tendons at 48 inches on center are common. This book is an invaluable resource for practicing engineers, architects, students. Once the cables are reinforced and tighten, the system becomes stronger than any other surface on the market. Most precast, prestressed concrete is actually pretensioned. Post tensioning institute publishes spanish translation of its essential slab onground foundation document. Structural technologies is the exclusive manufacturer of vsl post tensioning products and construction systems in the united states. Sections are tension controlled when the tensile strain in the extreme tension. The advent of posttensioned concrete allowed longer slab spans and thinner sections. Post tensioning is a technique for reinforcing concrete.
Cables are arranged as indicated by the engineer and chaired to run through the center of the slab. Rebar slabs may 03 2016 0 comments concrete, nishkian dean 0 reinforced concrete slabs have been used in buildings from the middle of the 19 th century. Post tension slab services post tension concrete, cable. Prestressed concrete is a form of concrete used in construction. With posttensioned construction, steel cables are placed in the slab and. Post tension slab means pt cable lies within a concrete slab is stressed after concreting.
Back in the 1960 there was limited use in concrete foundations in residential construction, but very little. In post tension continuous beams 9 slab thick, in case one cable. 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 the difference between normal slab and post. The use of post tension cables has been around for many years. The manual provides the industry standard for design and construction. Posttension basics how posttensioned slabs are built the. In the case of a post tension slab, steel cables are laid out in grid fashion inside the forms. Post tensioned concrete is a term heard more and more in the construction industry today. This method is a better way to construct a slab foundation to be more resistant to cracking and deflection. Pre tensioning and posttensioning in prestressed concrete design pre tensioning in prestressed concrete.
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. Post tension cable location we specialize in locating post tension cables and rebar embedded in residential concrete slabs prior to coring or saw cutting operations. Posttensioned concrete is accomplished by tensioning high strength steel cables within the concrete mass. Post tensioned concrete slabs have been used since the 1930s, and have become commonplace in the last 30 years. The book is easy to read and is accompanied by many schematics and photographs of actual posttensioning installations. Fundamentals of posttensioned concrete design for buildings. As a result, even though post tensioning is meant to help prevent a slab from cracking, the slab can still crack if the tensioning process is done incorrectly. The two options are a cast in place concrete slab or a post tensioned slab. 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. Construction of posttensioned slabs on grade is very similar to using reinforcing steel, except for the tensioning step. Post tension slab is a combination of conventional slab reinforcement and additional protruding highstrength steel tendons, which are consequently subjected to tension after the concrete has set. The best way to ensure this doesnt happen is to educate your construction teams on the best practices for designing and constructing post tensioned slabs. A normal slab is basically a rcc reinforce cement concrete slab whereas a post tensioned slab is the psc prestressed concrete slab. University bookstores and other resellers must receive authorization from pti to return books in resellable condition.
A slab tensioned against hardened concrete after the construction of the slab is called post tension slab. Heavily loaded concrete groundslabs and pavements can be sensitive to. Generally speaking the perception is that a post tensioned sport court is more expensive than a cast in place slab. 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. A novel assemblytype concretewood hybrid structural system for tall. Posttensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. New topics include seismic design, posttensioned concrete floors, parking structures, slabonground, bridges, stay cables, storage structures, barrier cables, dynamic and fatigue, durability, inspection and maintenance, and field and plant certification. Posttensioned concrete means that the concrete is poured and then. Many times inexperienced contractors may drill or shoot column collars into concrete on top of the slab. Identifying problems with post tension concrete post tensioning is a technique for reinforcing concrete with steel cables, typically referred to as tendons. For posttensioned concrete design, the user can specify the prestressing load pt by providing the tendon profile. Top 10 biggest mistakes made in posttensioned concrete design. Posttension basics how posttensioned slabs are built.
Authorized returns in resellable condition are subject to 15% restocking fee. Cast in place concrete vs post tension slab construction. 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 tensioned foundation information for the homeowner. The foundation gains tensile strength when the cables are tightened after the slab has been cast. The default load combinations for posttensioning are defined in the following sections. After decades of building and inspecting in the posttensioning pt concrete. The assembly shown in photo 1 is the ceiling of the large. The relatively thin slab at the top contains smaller rebar or welded steel wire mesh. Post tensioning pt is one of the most advanced and efficient technologies used to reinforce concrete. Preventing cracks on posttensioned concrete slabs pro. Homeowners are getting crushed by flawed posttension. Cast in place concrete vs post tension slab construction cost. Post tensioned slabs in san antonio jwk inspections.
The tendons are usually pulled to a tension of 25,000 pounds per square inch 4503 kg per square cm. Best posttensioned pt concrete design books youtube. This location is typically congested with tendons near the top of the slab and shooting pins may cause damage to. Detensioning unbonded posttension tendons posted on july 28, 2011 by neel khosa on rare occasions, the ironworkerinstaller will need to detension an alreadystressed post tensioning. Concrete floors, parking structures, slabonground, bridges, stay cables, storage. Our manufacturing facilities in the united states are certified by ptis plant certification program to ensure the highest quality fabrication of materials. Homeowners are getting crushed by flawed posttension cable foundations the switch from steel rebar to post tension cable by houston area home builders has delivered unmistakable results post tension cable foundations are failing earlier and in. Post tension slabs answers to questions buyers ask. Thats why the reinforcement of a concrete foundation is needed by steel reinforcement rebar and or post tension cables. The tensing of the cables occurs after the concrete has mostly cured, hence the term posttension. How to create a concrete slab using the posttensioning method. Our future vision pti envisions a future in which post tensioning is the first choice for reinforcing all structures.
To create a slab using this method, plastic sleevecovered steel cables are laid in a grid running in both directions. This hybridisation helps achieve the formation of a much thinner slab with a longer span devoid of any columnfree spaces. Post tension services of texas ptst is a full service post tensioning company based in dallas. The post tensioning method is the best way to create stronger, more reliable concrete slabs. Pt slab is also called as flat slab because it doesnt contain beam like regular slab. The tricky part comes when concrete is poured into the forms. Each of the tendons in the posttension slab is pulled tight, using a hydraulic jack. Usually a sign in the garage or stamp in the slab will indicate if your home has a post tension slab. Pretensioning and posttensioning in prestressed concrete. Posttensioning is a method of reinforcing strengthening concrete or other materials with highstrength steel strands or bars, typically referred to as tendons. It is an outstanding textbook with a crystalclear presentation of indeterminate design and analysis fundamentals.
The post tensioning institute designed post tensioned foundations. Eccentricity of tensioned cables produces internal moments that act in opposition to moments. If your location is an area with expansive soils, always assume the slab is post tensioned. Posttensioning tendons, which are prestressing steel cables inside plastic ducts. One of the main differences between a post tensioned beam or slab and a typical reinforced concrete element is that the strands drape or profile inside the concrete their vertical location changes along the length of the member. The first edition of the post tensioning manual was published in 1972, and as of the time of this writing 2018, they are up to their 6th edition. Posttensioned slabs use highstrength tensioned steel strands pt cable to compress the slabs. Pre tensioning is accomplished by stressing wires or strands, called tendons, to predetermined amount by stretching them between two anchorages prior to placing concrete as shown in fig. Post tensioning is a form of prestressed concrete in which highstrength steel strands are cast into a concrete slab or beam and tensioned to a high degree of stress following curing. General overview of posttensioned concrete design instructor. Unlike those of posttensioned concrete see below, the tendons of. Posttensioned concrete is widely used in bridges, shell structures, water tanks, and folded plates.
This stronger, thinner slab also saves money on concrete. 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. Sometime after the slab is poured, the cables are stretched until they achieve a predetermined tension, and then the two end sockets are grouted to keep the cable. This method is achieved in a process where metal or plastic tubes which contain loose tensioning cables or rods are cast into the concrete. Afterwards, once the concrete has gained strength but before the service loads are applied. Once the slab cures, qualified personnel apply tension and grout the cables. The forces contained within post tensioning tendons demand that owners, designers and contractors who maintain these structures have a high level of technical knowledge and skills to ensure the safety of the structure and of individuals working on, near or in the vicinity of a post. Posttensioning methods for reinforcing concrete the.