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Post-Tensioned Prestressed Concrete
As a building material, concrete is strong in compression, but weak in tension. Reinforcement helps extend the life of concrete, overcoming cracking that is inherent in the material and preventing its failure. Reinforcement has been used in concrete since mid-19th century France, when iron was first embedded in concrete planters. Its use quickly spread to bridges, buildings, and other civil and commercial applications. The fact that concrete is one of the most consumed COMMODITIES on the planet owes in part to the improved performance characteristics obtained through reinforcement.
Post-Tensioning Concrete Is a Method of Active Reinforcement
Post-tensioning concrete with steel strand became a popular solution to deflection and weight in slabs in the US in the 1950s. Post-tensioning is an efficient method of concrete reinforcing that reduces mass while improving building stability and resistance to wind, gravity, and seismic forces. Used in both precast and cast in place concrete construction, post-tensioning is considered active reinforcement because it applies tension to the concrete. This distinguishes post-tension concrete from passive reinforcement, which is accomplished by rebar and mesh embedded in the post-tensoned concrete.
Prestressed vs. Post-Tensioned Concrete
Post-tensioning and pretension prestressing are similar concepts. In post-tension concrete, steel strands or cables pass through the concrete member in plastic ducts or sleeves. 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. The strand used for post-tensioning and pretensioning concrete is the same, and can be used with or without a sleeve depending on design. Corrosion-resistance and strand lubrication is achieved with grease.
Post-Tension Concrete Can Increase Strength and Prevent Cracking
Depending on design, post-tensioning concrete can strengthen it to support loading as well as control plastic shrinkage cracking while using less reinforcement and concrete material than passive reinforcement systems. Any cracks that do form will be tightly held together, minimizing the possibility of propagation. Post-tensioning can also allow for longer concrete members, and can also reduce the volume of concrete so that panels, double tees, and other members can be thinner and lighter in weight.
In What Types of Structures Is Concrete Post-Tensioned?
Prestressed and post-tensioned concrete are often used together in the construction of wall panels and parking decks. Here’s how both processes are combined:
In wall panels, vertical post-tensioning strands pass from the top of the wall to the base of the structure through plastic sleeves cast into the panel. Prestressed strand is then fed through the sleeves and then post-tensioned. Studies have shown this to be an effective way to increase structural stability, at a cost that is typically lower than conventional reinforcement methods.
In parking decks, post-tensioning can be used in combination with prestressing to provide effective lateral reinforcement. This is a desirable construction technique for designers who choose to do away with field-applied pour strips that bring the potential for corrosion of diaphragm reinforcing steel.
Post-tensioned lateral reinforcement is particularly useful in applications calling for double tees of 15’ to 16’ widths or greater. The flange portions of adjacent prestressed double tee beams may be transversely post-tensioned together, replacing traditional methods used to resist lateral loads. Pour strips and cast-in reinforcing can be eliminated, reducing costs, improving concrete quality, and shortening field erection schedules.
Other Post-Tensioning Concrete Applications
Additional applications of post-tensioned concrete include:
Summary of Post-Tension Concrete Benefits
Post-tensioning concrete offers:
Contact High Concrete for Additional Post-Tensioned Concrete Information
High Concrete has extensive experience in providing innovative and effective post-tensioning concrete construction solutions for architects and construction professionals. We have an unsurpassed reputation for helping our clients overcome their specific design challenges. For more information, give us a call at 877-844-4418 today.