What is the definition of post tensioned concrete?
What Does Post-tensioned Concrete Mean? Post-tensioned concrete is a type of prestressed concrete where the concrete is strengthened via an arrangement of reinforcement held in tension. Steel cables, called post-tensioning tendons, are placed in plastic sleeves and positioned inside the concrete formwork before the concrete is poured.
What is post tension in concrete?
What is Post-tensioning?
- The engineering-best friend of developers, architects, engineers and contractors – post-tensioning enables the construction and refurbishment of concrete structures; improving structural performance while also reducing construction time, costs, materials and ...
- Post-tensioning uses. ...
- Structural repair. ...
What is post tension?
What is Post-Tensioning. Post tensioning is a technique for reinforcing concrete. Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed.
What is post tension construction?
What is Post-Tensioning Introduction Post-tensioning is a method of producing prestressed concrete, masonry and other structural elements. 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
How is post tensioned concrete made?
A typical process, called post-tensioned prestressing, involves casting concrete beams with longitudinal holes for steel tendons—cables or bars—like reinforced concrete, but the holes for the tendons are curved upward from end to end, and the tendons, once fitted inside, are stretched and then anchored at the ends.
How does a post tensioned slab work?
Post-tensioned slabs use high-strength tensioned steel strands to compress the slabs, keeping the majority of the concrete in compression. This gives a very efficient structure which minimises material usages and decreases the economic span range when compared to reinforced concrete.
How can you tell if concrete is post tensioned?
How to tell if you have a post tension slab. Most homes that have post tension slabs have a sign that is stamped into a concrete garage floor, often near the edge of the garage door right in plain sight. Older homes with post tension slabs may have a plastic or paper sign fastened to the wall.
How do you post tension?
0:294:03Post-tensioned slab procedure - YouTubeYouTubeStart of suggested clipEnd of suggested clipStep one installing slab formwork step to installing side formwork step 3 placing lowerMoreStep one installing slab formwork step to installing side formwork step 3 placing lower reinforcement.
What are the disadvantages of Post-Tensioning?
DisadvantagesSince many tendons or steel cables are used in a Post-tensioned structure, there are high chances of corrosion,Skilled labour is required.If the post-tensioned structure is not laid as per the standards, it may cause accidents due to poor workmanship.
Is post tension better than rebar?
Post-tensioning, which is a form of prestressing, has several advantages over standard reinforcing steel (rebars): It reduces or eliminates shrinkage cracking-therefore no joints, or fewer joints, are needed. Cracks that do form are held tightly together. It allows slabs and other structural members to be thinner.
Can a post tension slab be repaired?
0:583:09What's the fix for a broken post tension slab cable? - YouTubeYouTubeStart of suggested clipEnd of suggested clipWell the best fix is to call a post-tension repair company and they'll re-cable. It because there'sMoreWell the best fix is to call a post-tension repair company and they'll re-cable. It because there's a sleeve.
Does post tension slab crack?
Errors that lead to cracks in post-tensioned slabs 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.
How long does post tension slab last?
about 15-20 yearsPost-tension slabs are lasting about 15-20 years and are failing at a much higher rate. Post-tension slabs are created with concrete trenches around the perimeter of the house where the external walls will be placed.
How thick is a post tension slab?
Basic Overview of Post Tension Foundations A post tension slab foundation can range anywhere from 4 to 12 inches thick.
How deep are the cables in a post tension slab?
8"The plan maps show the rebar at 3" depth, and the post-tension cables at 8" depth. Discerning a post-tension cable from rebar generally requires scanning a larger area to properly understand the layout of structural elements in a slab.
What is the difference between prestressed and post tensioned concrete?
Most precast, prestressed concrete is actually pre-tensioned-the steel is pulled before the concrete is poured. Post-tensioned concrete means that the concrete is poured and then the tension is applied-but it is still stressed before the loads are applied so it is still prestressed.
How far can a post tension slab span?
12- to 14-inch post-tensioned slabs are used to accommodate the 28- to 30-foot spans for parking, with 3 to 4 story structures above. The post-tensioning is designed to balance the podium slab's dead load, thereby providing “zero” deflection on the first floor from which to erect the balance of the structure.
How long does post tension slab last?
about 15-20 yearsPost-tension slabs are lasting about 15-20 years and are failing at a much higher rate. Post-tension slabs are created with concrete trenches around the perimeter of the house where the external walls will be placed.
Do post tension slabs have footings?
Now, what makes them different from your conventional slab foundation system is that post tension slab foundations typically don't have standard footings at all. They don't have deep footings around the perimeter of the home or under load-bearing walls within the structure.
Does post tension slab crack?
Errors that lead to cracks in post-tensioned slabs 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.
What is Post-tensioning and How is it Implemented in a Concrete Structure?
Post-tensioning was first patented by P.H. Jackson in the 1800s in San Francisco and refined to its contemporary form in the 1920s by Eugene Freyssinet in France. This technique gained popularity in North America in the 1960s and has been rapidly increasing in popularity over the past 30 years.
How does post tensioning work?
The post-tensioning process works as follows: First, you must install steel tendons into the formwork and position them before the concrete is placed. Steel tendons are pre stressing steel cables inside plastic protective ducts or sleeves, each one with anchors on each end to transmit the forces into the structure.
How strong are steel tendons?
Once the tendons are tensioned, it creates a force that counteracts the weight that is subsequently applied to the hardened concrete structure, preventing cracking and increasing its service life. Steel tendons used for post-tensioning typically have a tensile strength of 270,000 pounds per square inch (psi), are about 1/2 inch in diameter, ...
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What is the benefit of tensioning or pulling the tendon-filled sleeves after the concrete is placed?
What’s the benefit of tensioning or pulling the tendon-filled sleeves after the concrete is placed? Doing so allows them to be readily formed into the desired shape such as incorporating vertical and/or horizontal curvature. Once the tendons are tensioned, it creates a force that counteracts the weight that is subsequently applied to the hardened concrete structure, preventing cracking and increasing its service life.
How does SmartRock work?
The high-tech and rugged SmartRock TM wireless sensors provide accurate real-time calculations based on the maturity method. More specifically, it allows you to collect the concrete’s temperature history, which is used to calculate the maturity index of concrete, enabling you to predict its early-age compressive strength. Keep in mind that the standard level of strength for post-tensioning is 75% and in some cases, your concrete can reach this level of strength sooner than expected. By employing the maturity method, you’ll be able to closely monitor when your concrete reaches the necessary level of strength so you can move forward post-tensioning as soon as possible.
What is concrete tensile strength?
Ensuring your concrete is durable and stable isn’t just about achieving an acceptable level of compressive strength, which is the concrete’s ability to withstand loads that crush or squeeze it. You also need to consider its tensile strength, the concrete’s ability to withstand loads that will likely elongate or stretch it.
What is post tensioning?
Post tensioning is a technique for reinforcing concrete. Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed.
Is precast concrete pretensioned?
Most precast, prestressed concrete is actually pre-tensioned-the steel is pulled before the concrete is poured. Post-tensioned concrete means that the concrete is poured and then the tension is applied-but it is still stressed before the loads are applied so it is still prestressed.
How does post tensioning work?
Designers use post-tensioning as a way to reinforce concrete by prestressing it. In prestressed members, compressive stresses are introduced into the concrete to reduce tensile stresses resulting from applied loads including the self weight of the member (dead load). Prestressing steel, such as strands, bars or wires, is used to impart compressive stresses to the concrete. Pre-tensioning is a method of prestressing in which the tendons are tensioned before concrete is placed and the prestressing force is primarily transferred to the concrete through bond. Post-tensioning is a method of prestressing in which the tendons are tensioned after the concrete has hardened and the prestressing force is primarily transferred to the concrete through the end anchorages.
What is pretensioning steel?
Prestressing steel, such as strands, bars or wires, is used to impart compressive stresses to the concrete. Pre-tensioning is a method of prestressing in which the tendons are tensioned before concrete is placed and the prestressing force is primarily transferred to the concrete through bond. Post-tensioning is a method ...
Why do designers use post tensioning?
Designers use post-tensioning as a way to reinforce concrete by prestressing it. In prestressed members, compressive stresses are introduced into the concrete to reduce tensile stresses resulting from applied loads including the self weight of the member (dead load).
What is the strength of steel strands?
Steel strands used for post-tensioning typically have a tensile strength of 270,000 pounds per square inch (psi), are about 1/2 inch in diameter, and are stressed to a force ...
Is concrete strong in compression?
Benefits. While concrete is strong in compression, it is weak in tension. Steel is strong under forces of tension, so combining the two elements results in the creation of very strong concrete components.
Can I Drill into a Post Tension Slab?
Bonded post tensioning simply means that after stressing of the cables has occurred, the PT ducts are fully grouted, this allows for a progressive transfer of the force from the cables to the slab. For this type of post tensioning, it is generally OK to drill or cut into the slab, provided necessary investigation works have been undertaken and advice from a qualified structural engineer is given (see below for more on this).
What is post tensioning?
Post Tensioning: The assembly of the post tensioning cables ducts and embedment systems. This system provides the compressive force to the slab.
What is PT concrete?
A post tensioned (PT) concrete slab uses the compressive force of post tensioning cables to reduce the tension within the slabs cross-section allowing it to span further and have a thinner profile compared with a conventionally reinforced concrete slab.
What happens when you post tension a slab?
The introduction of post tensioning within the slab can result in the full cross section of the slab remaining in compression when it is bending. Taking the simple example from the previous image, we can cut a cross section through a portion of slab to see the stress distribution across the section with and without post-tensioning.
How long after concrete is poured can you use a stressing jack?
24 Hours after the concrete has been poured around 25% stress load is applied to the cables using the stressing jack. This is to control shrinkage cracking.
How does self weight of concrete affect the building?
Therefore reducing the slab thickness can allow reduction in column sizes as well as depth and volume of foundations.
Why add a compressive force to a toilet roll?
Adding a compressive force at either end of the toilet roll system ensures that no net tension exists while it is bending. Tension capacity has not been added to the system but rather the need for tension capacity has been removed.
What is post tensioning in concrete?
Larger structural concrete members may also be post-tensioned, especially in bridges and floors and beams in parking structures. The process is very similar to that used for slabs, except on a bigger scale. One interesting difference is that the tendons will often be "draped" so that they are low at the midpoint of a beam and high at the supports—this places the steel at the point of highest tension where it can keep the concrete held together tightly. With structural members the duct is often grouted full following stressing to bond the strand to the concrete along its entire length—these are called bonded tendons. Unbonded tendons, used in residential slabs, remain free to move within the duct and are protected from corrosion by grease.
What is PTI certification?
Post Tensioning Institute: PTI has certification programs for manufacturing plants and for individuals:#N#Manufacturing is certified for Unbonded Single Strand Tendon Fabrication Facilities (about 95% of U.S. production is certified under this program) and Prestressed Concrete Strand manufacturing (this is afairly new program--only 6 plants are certified, all in China).#N#Individuals must first be certified as Level 1 (fundamentals), then can go for Level 2 (either as an inspector or as an ironworker for bonded post tensioning installation). A new certification for slab-on-ground installer/stressor is in the planning stages.#N#More information on PTI certification programs. 1 Manufacturing is certified for Unbonded Single Strand Tendon Fabrication Facilities (about 95% of U.S. production is certified under this program) and Prestressed Concrete Strand manufacturing (this is afairly new program--only 6 plants are certified, all in China). 2 Individuals must first be certified as Level 1 (fundamentals), then can go for Level 2 (either as an inspector or as an ironworker for bonded post tensioning installation). A new certification for slab-on-ground installer/stressor is in the planning stages. 3 More information on PTI certification programs.
What is PT tendon?
Unbonded tendons, used in residential slabs, remain free to move within the duct and are protected from corrosion by grease. PT tendon placement and stressing is usually done by companies with certified workers who specialize in this work.
How thick is a post tensioned concrete slab?
Tendons can be easily routed around obstructions. Tendon (cable) tails after tensioning. The cables are pulled to 33,000 pounds, resulting in 8 inches of elongation in a 100-foot cable. www.avalonstructural.com. A residential post-tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete.
How much pressure is needed to post tension a concrete slab?
A residential post-tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed.
Where are PT anchors located?
At each end a PT anchor is located and these are located in pockets embedded into the slab edge. When the strands are stressed, the wires will stretch—about 4 inches for a 50 foot strand—to apply 33,000 pounds of load. Stressing should only be done by qualified workers.
Can you use PT on concrete?
Since PT is simply reinforcement, there really aren't any specific decorative applications related to post tensioning. The advantages of PT as noted in the opening page are the lack of cracking (or at least very narrow cracks) and the ability to span farther. PT slabs on ground can be placed and stamped just like with any other concrete slab. Surfaces can be stained or overlaid. The only concern is to always remember not to cut or drill into post-tensioned concrete slabs, since once a tendon has been cut, it is very difficult to repair. Many post-tensioned slabs will be stamped to alert the owner and any renovation contractors that the slab is post tensioned.
What Does Post-tensioned Concrete Mean?
Post-tensioned concrete is a type of prestressed concrete where the concrete is strengthened via an arrangement of reinforcement held in tension. Steel cables, called post-tensioning tendons, are placed in plastic sleeves and positioned inside the concrete formwork before the concrete is poured. Once the concrete is poured and gained sufficient strength, the cables are pulled at either end (tensioned) and anchored on the outer edges of the concrete. The steel cables, like any steel object, may be subject to corrosion.
What is the effect of compression on concrete?
This constant compression increases the concrete’s flexural and shear strength, thus giving post-tensioned concrete several advantages over standard reinforced concrete, including:
What is the ACI 318 code?
Reality: ACI 318 code states that the size of the drop panel has to be ⅙ of the span in each direction for conventionally reinforced concrete only. This size limitation does not apply to PT slabs. The engineer has tremendous flexibility to size relatively small and efficient drop panels that are effective in shear and flexure.
What does it mean when a steel wedge cracks?
Cracks indicate that the wedges are conforming more tightly and getting a better grip on the steel strands as they hold the prestress force in place. It is common to see cracks in 2-part wedges after stressing. It is less common in 3-part wedges.
How does posttensioning work?
Reality: Okay, this one is true. However, the use of post-tensioning also results in many other cost savings to the owner that are often overlooked. The following is a list of additional cost-savings to the owner: 1 Overall building height is reduced. This can be used to add more leasable space within the same building height, it can be used to increase ceiling height, or it can be a cost savings. 2 Because the building height is reduced, there is a reduction in all building services that are tied to building height such as mechanical, electrical, plumbing, elevators, etc. 3 Because the building height is reduced, there is a savings in the cost of the building façade. 4 Because the building height is reduced, operating costs such as heating and cooling costs are reduced for the life of the building. 5 When used in below-grade applications, excavation costs are reduced. 6 Formwork and reshoring costs are reduced.
Why is there not enough room for PT?
There is a common misconception that there is not enough room to stress the PT in a below-grade situation because of the confines of the surrounding walls. There is also the fear that the surrounding walls will result in restraint to shortening cracking.
Why is there a reduction in the cost of the building façade?
Because the building height is reduced, there is a savings in the cost of the building façade.
Why is building height reduced?
Because the building height is reduced, there is a savings in the cost of the building façade. Because the building height is reduced, operating costs such as heating and cooling costs are reduced for the life of the building. When used in below-grade applications, excavation costs are reduced.
What is general zone?
The general zone encompasses a larger zone around the local zone and is inclusive of the local zone. The design of the general zone is influenced by not only the local zone but also by the overall geometry of the member and the reinforcement that exists in the member.
