Post tensioned concrete is an improved version of reinforced concrete. It has a greater resistance to tensile stresses, thanks to its manufacturing method.
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Generally, the construction method used to produce post-tensioned concrete is known as prestressing, which is also used to make pre-tensioned concrete, another improved version of reinforced concrete.
Post-tensioned concrete is more complex than reinforced concrete, which is why it is used in specific structures; mainly those in which heavy loads and complicated geometry are present.
What is post tensioned concrete?
Post-tensioned concrete is a type of prestressed concrete that is subjected to compressive stress after the pouring and setting of the fresh concrete mix, that is, when the concrete is in its early stages of hardening and developing its characteristic resistance.
Source: construblogspain.files.wordpress.com//09/dsc-large.jpg?w=940&h=704The compressive stresses are caused by the tensioning of metallic reinforcement steel bars or cables, which are encapsulated in plastic or metallic &#;tubes&#; enclosed and placed during the formwork, carefully following the design specifications.
After the reinforcement cables are tensioned, they are anchored to the structure using of special components.
Post-tensioning, allows concrete to store additional compressive stresses that counteract the tensile stresses caused by heavy loads, and avoids the structural element to noticeably deform and crack.
Types of post-tensioning
Most of the post-tensioned concrete reinforcement plays an active part by creating additional mechanical stresses that interact with those caused by service loads. The remaining part of the reinforcement acts passively, anchoring or fixing the active pieces.
By the time the active post-tensioning reinforcement reaches the desired stress value, the steel cables that compose it are anchored to the structural element by the passive reinforcement. Once this is done, there are two options to finish the post-tensioning process:
Bonded post-tensioning
In this construction method, the active reinforcement conduits are filled by pressure with high-strength mortar masonry to guarantee the adherence of the reinforcement to the conduit, creating a monolithic section. This way, the active steel reinforcement is prevented from seriously deteriorating due to corrosion.
Unbonded post-tensioning
In contrast to the previous method, the active reinforcement conduits are not filled in, which means the tensioned cables are only connected to the concrete by the anchor heads.
Generally, the reinforcement cables are coated with grease and are contained in plastic conduits, to reduce the environmental impact and guarantee their useful lifespan.
Characteristics of post-tensioned concrete
Although post-tensioned concrete is not a recent construction material, since it originated during the end of the XIX century, it currently presents a high level of innovation and optimization that gives it an endless number of characteristics. Among the most relevant we highlight the following:
Use of post-tensioned concrete
As a general rule, post-tensioned concrete is used for structures that receive heavy loads and with large spans in between supports (spans). In these kinds of situations, its use is essential due to the overall cost of materials and weight of the structure, which would lead to cracking, deformation and reduction of the construction&#;s useful life.
Source: es.wikipedia.org/wiki/Archivo:Acero_postesado.jpgHowever, the prestressed construction system when using post-tensioned concrete is significantly more complicated than using standard reinforced concrete, so usually the profit by gained by saving material costs tends to be minimized by the requirement of using specialized personnel and equipment.
This type of concrete has mainly been used to build cable-stayed bridges and is also widely used to build viaducts and concrete voussoirs.
On the other hand, is also used in construction for making parking lots, industrial buildings, hotels, sports complexes, airports, auditoriums and other structures that have large spans.
Although this concrete is frequently carried out in situ, it&#;s possible to purchase precast post-tensioned concrete structural elements, usually, precast slabs and beams.
Advantages and disadvantages of post-tensioned concrete
Post-tensioned concrete stands out for its high mechanical resistance and the reduced transverse dimensions of the elements that form it. However, these technical advantages are followed by certain aspects that make the construction process difficult to carry out, due to the high level of precision and detail that is required in the design.
Thus, to obtain a complete perspective, its advantages and disadvantages are presented below:
Advantages of post-tensioned concrete
Disadvantages of post-tensioned concrete
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If you're shopping for a condo, you've likely come across units you've like in buildings with Post Tension Cables (PTC). You may have also heard concerns, warnings, and stories about them, which makes you question if they are right for you. Let's take a look at the pros and cons so you can make a confident decision on if they are right for you.
WHAT ARE THEY?
Post-tension cable concrete is a construction method used in condos, parking garages, and also office buildings, bridges, etc. It's a process by which sleeve- covered steel cables stretch along the width of a structure, anchored at either end and encased in concrete. Because the cables add strength to the slab, longer spans are possible, and fewer supports are needed. The benefits are lower construction costs and more design versatility.
Are you interested in learning more about post tension system solutions? Contact us today to secure an expert consultation!
WHAT COULD GO WRONG?
Some of the considerations for this construction method are the ongoing maintenance/costs and potential for corrosion and deterioration of the cables if exposed to water and oxygen, which can lead to expensive repairs. For these reasons, some lenders are cautious, and fewer mortgage insurers provide coverage. As of this writing, Genworth Insurance does not consider buildings with post-tensioning, and Canada Guaranty will consider an exception, a building constructed in or after. Canadian Mortgage Housing Corporation (CMHC) is the only mortgage insurer for buildings between '-'.
WHY DO MORTGAGE INSURERS MATTER?
If you have less than a 20% down payment, the mortgage will need insurance, and you are limited to only lenders that work with CMHC. This limitation can also come into play when you sell and potentially reduce the number of buyers that qualify to purchase your property.
WHY WOULD YOU CONSIDER A BUILDING WITH POST-TENSION CONCRETE OR THIS AGE?
Because some of the older buildings offer greater affordability and benefit from larger square footage, ideal locations, quality construction, and features like underground parking, etc. which can add value and increase the quality of living.
Some people may focus only on buildings without post-tension concrete; however, that does not protect you from all risks as other systems could fail (i.e., plumbing, HVAC, patios, envelope membranes, roofs, etc.). These repairs can be equally as expensive and require additional funding from owners.
If you decide to consider buildings with post-tension concrete, confirm your options and the policies with your mortgage broker or bank. And below are other resources that will help you make an informed decision.
Post-Tension Cable Report with engineer's feedback on the overall condition, if there are potential concerns and funding requirements for future repairs.
WHAT I WOULD DO
Because condos in older buildings with PTC are often larger than newer and have ideal central locations, I would consider them. Iunderstandthatonresalethat there may be fewer buyers; however, if the property itself offers a higher quality of life than that is a trade-off, I am willing to consider for the right property. I would undoubtedly have the condo documents reviewed by a specialist and get their opinion.
Defects and expensive repairs and replacements can happen in buildings of any age, so the PTC is not the only potential risk.
Give yourself the most options by doing your own research, talk to a specialist in all related areas for their feedback, and be clear about your risk tolerance and capacity. Then you can make a confident decision if condo buildings with PTC are right for you.
YYC - CONDO DOCUMENT SPECIALISTS
RoyRasmusen-ExpertCondoReview 403.383.|
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Condo Document Inspection Centre http://www.cdicinspections.com/
Condo Doc Review https://www.condodocreview.com/
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