Advantages & Applications of Post-Tensioning

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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
• It allows us to build slabs on expansive or soft soils
• It lets us design longer spans in elevated members, like floors or beams

Common Applications for PT

Post-tensioning, or PT, has become increasingly popular over the past 30 years or so as the technology has been perfected. At one time there were problems with corrosion of the cables, especially in deicing-salt-laden parking structures, but better materials and construction methods (plus good training and certification programs) have eliminated most problems.

External post-tensioning is a good method for strengthening or retrofitting concrete structures. www.vsl.net

The applications for post-tensioning are almost endless, but what holds it back is the lack of experience among designers and builders. In an article in Structure magazine (PDF), Gerard Feldman noted that "Most engineers have only a cursory overview of post tensioning in college...this unfamiliarity creates a bias towards conventional reinforced concrete structures."

Some of the more common applications are:

• Slabs on ground: Today, PT is used extensively for slabs on grade where soils are likely to move (expansive soils)-especially in the American southwest. Jim Rogers, editor and publisher of Post Tension Magazine, says that until housing construction ground to a halt last year, about half of all post-tensioning work was slabs-on-ground for homes. Residential Concrete magazine had a good review of this in its September issue.
• Another good application for PT slabs is producing crack-free tennis courts.
• A recently developed application of PT is external post-tensioning for strengthening of existing structures, especially as an upgrade to resist seismic forces. The best review of this is available from the International Concrete Repair Institute, "Guideline for the Selection of Strengthening Systems for Concrete Structures."

Water tanks can be post-tensioned. DYK in El Cajon, CA

Contact us to discuss your requirements of post tensioning system services. Our experienced sales team can help you identify the options that best suit your needs.

• Bridge designers have used PT both for cast-in-place concrete and for precast segmental construction. PT allows longer spans and keeps cracks tight.
• Concrete water tanks are often post-tensioned to reduce crack width and leakage. The companies that make prestressed concrete tanks are Crom, DYK, Natgun, and Preload.
• Masonry walls can be post-tensioned-this is usually done with a solid steel bar fastened to the foundation and stressed with a nut at the wall's top. A good article on PT for masonry is available on Masonry Construction magazine.
• One interesting application is for a concrete countertop that needed to span 6 feet and carry a heavy load.

Architects, Structural Engineers, General Contractors, Real Estate Developers, and Owners incorporate post-tensioning systems on their projects in order to achieve economy, efficiency, quicker construction and lower lifetime cost of the structure. Why? Because Post-Tensioning enhances concrete strength under both compressive and tensile stresses.

Post-tensioning tendons are installed in a parabolic profile prior to placing the concrete and later stressed to a specified concrete strength. This process introduces both compressive forces in the concrete and stresses that counterbalance service loads. The benefits are substantial.

Post-tensioning frequently solves design and construction challenges that other construction methods simply cannot. Some key advantages include:

MATERIAL SAVINGS

• Thinner concrete member sizes; reduction in concrete is approximately 20%
• Rebar in floor elements is reduced by 60% to 75%
• Decreased dead load reduces rebar and concrete in columns and foundations
• Reduction in building height decreases the cost of building cladding, vertical mechanical/service elements, and rebar and concrete in shear walls

QUICKER CONSTRUCTION

• Potential pour cycle of 3-4 days
• Reduced re-shoring requirements
• Coordination with embeds and MEP openings

INCREASED PERFORMANCE

• Improved seismic behavior
• Reduced deflection and vibration
• Improved crack control and waterproofing properties&#;especially beneficial for parking garages and balconies
• Longer spans and fewer columns give greater flexibility in floor layouts in office/residential buildings and better lighting in parking garages which enhances personal safety.

REDUCED LIFETIME COSTS

• Lower overall maintenance and lifecycle costs of the structure
• Reduced building height also results in energy savings, especially for office buildings
• Potential LEED® credits for Green building design and construction

AMSYSCO provides cost-effective post-tensioning solutions across a wide range of structures and applications such as condominiums and apartments, office buildings, parking garages, hospitals, schools, slab-on-ground, storage tanks, stadiums, repair and restoration, barrier cable, special structures and applications.

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