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The early stages of the architectural process are a time to make large-scale decisions related to the building&#;s form and structure. During this time, your design team may present different structural system options, discuss benefits and drawbacks, and make recommendations.
One recommendation may be post-tensioned concrete. This method introduces tension to the concrete after curing to strengthen the structure, reduce the likelihood of cracks, and allow for thinner slabs.
While this structural system offers many advantages, it can limit flexibility and complicate future modifications. We recommend considering your long-term goals and the potential for renovations and retrofits.
To help you with your decision, this article will define post-tensioned concrete and outline its pros and cons.
What is Post-Tensioned Concrete?
Post-tensioning is a method of reinforcing concrete by introducing tension after the concrete has achieved a specified strength.
Tension is introduced through high-strength steel stands or bars, typically called tendons. During construction, these tendons are placed in forms before the concrete is poured. The tendons are then tensioned with hydraulic jacks after the concrete cures.
While concrete works best under compression, steel works best under tension. Post-tensioning maximizes the use of each material for efficiency. It can be thought of as a &#;sweet spot&#; that provides the strength of concrete and steel without overusing either one.
Often, post-tensioned concrete works well for parking structures and high-rise commercial or residential developments. We have also seen this method used for tennis courts.
In this situation, the tennis courts sat over an unstable site once occupied by a city dump. Post-tensioned concrete&#;s strength prevented cracking or vibrating that would likely occur with a more traditional concrete system.
Pros of Post-Tensioned Concrete
The most significant benefit of post-tensioned concrete is its strength. The combined performance of concrete and steel allows for thinner slabs and longer spans.
Achieving the same strength with another structural system would require more columns and deeper beams. For this reason, post-tensioned concrete best aligns with structures where longer spans are desired, like parking structures.
Post-tensioning's ability to provide longer spans works well for parking garages.
Post-tensioning also allows designers to decrease a building&#;s floor-to-floor height&#;the vertical distance between the finished floors of two consecutive levels. Other systems require deeper beams and thicker slabs, increasing the distance between floors.
As such, post-tensioning can reduce a building&#;s overall height and lower costs for components like façade treatments. In short, post-tensioned concrete improves material efficiency, minimizes waste, and allows for more open interiors. It can help solve multiple challenges&#;from cost concerns to aesthetics and performance.
Cons of Post-Tensioned Concrete
Although post-tensioned concrete offers many benefits, it can complicate future modifications to the building. Vertical penetrations must be planned during the design process due to the tendons, and after construction, you can only cut through these pre-planned areas. If you cut through the tendons, the structure loses its strength.
With these limitations, post-tensioned concrete works best for buildings with stacked layouts, like residential construction and parking garages. Buildings requiring more flexibility, like healthcare facilities, may run into problems in the future. For this reason, some organizations&#;like the General Services Administration (GSA)&#;have rules against using post-tensioned concrete.
Although post-tensioned concrete can be limiting, other structural systems present a degree of inflexibility. A more traditional concrete system requires more columns, which can also complicate modifications. You and your design team should discuss the potential for future changes to determine the right approach.
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At the same time, post-tensioned concrete can add complexity to construction. It requires precision and specialized knowledge, potentially limiting your options to a smaller set of contractors.
Is Post-Tensioned Concrete Right for Your Project?
Post-tensioned concrete is a popular structural system for large-scale developments. Depending on your project type and goals, your architect may recommend it in the early stages of the design process.
Combining concrete and steel&#;s strength, post-tensioning can reduce cracking and help achieve longer spans and lower floor-to-floor heights. It can also lower initial costs by improving efficiency and reducing building height.
Despite the benefits, post-tensioned concrete is not ideal for every project. If you desire more flexibility, a more traditional concrete or steel structural system may be a better fit.
For buildings with stacked layouts&#;like parking structures and residential developments&#;post-tensioned concrete may be the right solution. Learn more about these building types by reading about the rules of thumb for parking structure design and considerations for high-rise construction.
5 Unexpected Advantages of Post-Tensioning
Since the s, post-tensioning concrete has grown in popularity. Whether you&#;re trying to streamline the building process, reduce costs or give a structure the best chance of surviving weather hazards, there are numerous benefits of post-tension slabs.
Here&#;s a look at some hidden advantages of post-tensioning concrete and why you should consider these methods for new structures.
What Is Post-Tensioning?
Post-tensioning concrete is the process of adding steel bars (tendons) below a mixture&#;s surface. Once the concrete fully cures, tension is applied to the steel bars. These reinforcements introduce stress to the concrete, which can prevent cracks and shifting down the road.
Construction teams rely on post-tensioning methods to help concrete reach its strongest state. This process is efficient for creating surfaces that can withstand the loads required for a newly developed structure.
Benefits of Post-Tensioning
Consider these surprising advantages of post-tensioning.
1. Saving on Costs and Materials
Prestressed concrete supports larger loads compared to traditional pouring. Using post-tension methods means concrete substrates are thinner, sometimes by as much as 20%.
When a building is complete, the total height of the structure is shorter than constructing slabs without post-tension reinforcements. Smaller buildings call for teams to use less cladding, concrete, cement and shear. Extra materials can be used for future projects or returned to the manufacturer to increase your bottom line. Either way, you&#;ll save on costs and materials.
2. A Sustainable Approach to Building
When you rely on post-tensioning concrete methods, fewer materials are involved in the final structure. This includes the amount of cement used to create concrete mixtures &#; a significant source of carbon emissions.
It&#;s possible the timeline for a building project will be shorter with post-tensioning concrete, which lessens the amount of time gas-powered tools and vehicles run from the start of the assignment through completion.
3. Efficient Construction Timelines
The setup for post-tension procedures can be done quickly without the variables of traditional curing. The fact that crews spend less time laying steel supports means teams will be ready to pour mixtures and let the concrete dry on an impressive timeline. Your post-tension building project can progress consistently.
4. Crack Control
Post-tensioning results in compressive stress in concrete, which helps to reduce the effects of shrinkage and temperature changes that can cause cracking. The post-tensioning system consists of steel strands that are tensioned after the concrete has hardened, creating internal forces that resist external loads.
Post-tensioning systems are effective for crack control because the tendons act as reinforcement for the concrete and prevent it from splitting apart. The tendons are anchored at both ends of the concrete member and are usually placed in ducts or sleeves to allow them to move freely during tensioning.
The tendons are tensioned by hydraulic jacks and then locked in place by wedges or nuts at the anchorages. The tension in the tendons induces a compressive stress in the concrete, which counteracts the tensile stress caused by shrinkage or bending. This way, the concrete remains relatively crack-free and watertight throughout its service life.
Many property owners building post-tension structures find surfaces do a fantastic job of limiting unwanted vibration and sag. Inside the poured concrete, cables help to balance the load.
Rather than the center of slabs being put under immense stress where they can crack, the internal cables take care of the heavy lifting. Over time, concrete maintains its shape and refrains from dipping downward when objects are placed on top of it.
About Post-Tensioning Products and Services From STRUCTURAL TECHNOLOGIES
STRUCTURAL TECHNOLOGIES provides VSL post-tensioning products as well as construction systems in the United States. Whether you want to build or repair a commercial building, parking lot or similar structure, we will assist with design, installation and material fabrication for unbonded monostrand post-tension systems, bonded multistrand post-tension systems, shear reinforcements, barrier cables and lockable dowels.
We specialize in external and internal post-tensioning technology. STRUCTURAL TECHNOLOGIES provides you with solutions for installations outside a structural element &#; within grouted ducts &#; or within an existing member &#; via core drilling &#; to handle the scope of your project.
Get Started With Post-Tensioning Today
To learn more about post-tensioning products and our service capabilities, submit a contact form with STRUCTURAL TECHNOLOGIES.
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