Post-tensioned concrete (P-T) to date has been one of the most fascinating and yet underrated construction materials. Its history dates to the late 19th century. However, its acceptance gained momentum in the s. Then in , structural engineer and P-T great T.Y. Lin substantiated the equivalent load method for the design of post-tensioned concrete. In the P-T industry&#;s view, this is considered the watershed moment in the history of post-tensioned concrete. Since then, post-tensioned concrete floors have dominated the medium-high-rise building space due to their indeterminate nature and more robust seismic-resistant diaphragm capabilities.
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A typical post-tensioned concrete job site
The ability of post-tensioned concrete to be nearly crack-free, reducing the slab thickness, story height, amount of exterior cladding, which lowers seismic weight and foundation cost, has played its part in the popularity of the material. However, despite the popularity of material in the practical engineering world, many eminent P-T experts believe the academic world&#;s response to this material has been somewhat lukewarm. Perhaps, the elective nature of the subject in civil engineering schools and universities has led to fewer specialists in the industry.
Post-tensioned concrete design is generally considered a specialist&#;s job. Structural building design offices, in general, do not carry out the detailed design of the P-T system in the Middle East. However, this may not be the case in the West. In the United Arab Emirates, where high-rise construction is prevalent, post-tensioned concrete floors are the preferred choice for owners, architects, contractors, and structural engineers. Contractors opine that P-T floor plates provide access to other trades sooner than conventional RC floors, where form stripping usually occurs in only 28 days. This may have been a significant factor in the demand for P-T floor systems, apart from its other advantages.
The Royal Atlantis features P-T floors - currently under construction at the time of writing this article
Despite all its advantages, post-tensioned concrete remains one of the most complex design topics. Today&#;s engineer has their job cut out for them to design this difficult material with tight deadlines. Perhaps a comprehensive structural solution that can design P-T efficiently and economically under tight time constraints is the need of the hour.
Bentley Systems offers such a solution &#; RAM Concept. It is a desktop software application for analyzing and designing post-tensioned slabs incorporating complex floor geometries, powerful task automation, and easily understandable output. With RAM Concept, you can model tendons in their true three-dimensional positions. Banded, distributed, or arbitrary tendons with virtually any profile can be easily modelled. RAM Concept tendon loading analyses consider full 3D hyperstatic (secondary) effects, including restraint from shear walls and stiff columns. These features facilitate a better understanding of the effects of tendons on the slab and with the PT Optimization feature the user has greater control over the design resulting in economy and efficiency. Temperature and shrinkage effects, along with all possible gravity and seismic load options, streamline the design workflow.
Realistic three-dimensional layout of the prestressing steel in the structure
Take advantage of a variety of design codes:
ACI 318
AS
Eurocode 2
BS with TR 43
CAN/CSA A23.3
IS 456
RAM Concept features that cut above the competition including:
Compatible with
Analytical iTwin format (formerly ISM), including Revit integration.
Direct integration with STAAD and RAM Structural System
Python Scripting API Capabilities.
Import and export of CAD drawings-RAM Concept&#;s importing CAD background considered to be almost seamless.
Superior Load history deflection calculations.
Finite element mesh generating capabilities-automated and most straightforward.
User-defined shear reinforcement feature.
The company is the world’s best post tension system solutions supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.
With various options ranging from banded, manual, and generated tendons, and the latest advancement, Optimize Tendon Manager, to optimize the tendon layout most efficiently, RAM Concept is your ultimate global post-tensioned concrete design tool. For all of these reasons, companies worldwide have deployed RAM Concept for PT and R-C plate design.
Dean Genner, Technical Director at Taylor Thomson Whitting, noted, &#;RAM Concept&#;s ease of use and ability to model complicated floors for both post-tensioned concrete and Reinforced concrete floors is unparalleled.&#;
WSP used RAM Concept to design floor plates and foundation of the unique geometric design of The Shard at London Bridge Quarter.
RAM saved 25% in structural design time in designing a complex basement on Waldorf Astoria Hotel in London to complete the design phase one month ahead of schedule.
Diego Padilla Phillipps, Associate Director of Structures, WSP, noted, &#;RAM Concept provides a successful platform for analysis, design, and delivery that exceeds all our expectations. We are committed to using RAM software in our concrete buildings.&#;
Learn more information about RAM Concept here.
https://www.virtuosity.com/product/ram-concept/
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The Uptown Tower Post-Tensioned Concrete Design Webinar
Join us on May 25th, , at 7:00 PM GST in a webinar where we take you behind the scenes in the post-tensioned concrete design of a mega-project - the Uptown Tower.
Watch the Virtuosity team design a brand-new building from Concept to Construction!
Join us on our Digital Construction journey in a webinar series where we take you step-by-step through the conceptual and preliminary building design processes. We will be using a variety of different software products from our collection!
To learn more about what you can accomplish with Virtuosity, you can register for the entire webinar series below or choose to just join in session 5 which is dedicated specifically to Structural Analysis!
The tools that you will see showcased in this nine-part webinar series are:
For post-tensioned (PT) concrete structures with single strand unbonded tendons, protection of the exposed stressing end of the tendons can become a significant maintenance item, sometimes within a few years after original construction. The anchorages at the stressing end of the tendons are located in recessed pockets, typically at exposed slab edges or beam ends. Encapsulated PT systems include grease caps that fit over the tendon tails at the anchorages to form a tight seal. During new construction, the pockets are typically filled with a trowel-applied non-shrink grout that is nonmetallic and chloride-free, or precast PT plugs are used. The trowel-applied patches are prone to cracking at their perimeter and debonding from the pocket.
The contributing factors to a patch failure: pocket surface contamination and lack of surface preparation; poor mixing and application techniques of patch materials; incomplete filling of pockets; and excessive shrinkage due to inappropriate curing techniques and/or use of inferior shrinkage-prone repair materials. Incomplete filling of pockets can also occur if the tendon tail is not cut sufficiently short in the pocket to properly seat the grease cap onto the tendon. As a result of these failures, the de-bonded patches can loosen and become a potential falling debris hazard. Further, there is an increased risk for tendon corrosion due to moisture leaching into the pocket, particularly if the grease cap was not fully seated or was neglected to be installed at all.
It is very important to seal the PT stressing pockets as soon as possible after the stressing records have been approved to minimize the risk of any possible corrosion. The most effective way to manage deterioration of a structure is to keep up with its maintenance. This includes practices to limit moisture and ensure adequate drainage and waterproofing by protecting expansion joints and seals. To add longevity to the stressing pockets, you could apply a waterproofing coating over and around the stressing pockets after the grout has cured to better protect the system. This would need to be done after the grout has fully cured.
Replacing deteriorated grout or PT plugs and implementing protocols to prevent mechanical damage to tendons prolongs the durability of the structure. Just like your car needs regular maintenance and oil changes, your building will need to have regular inspections and maintenance as well.
The Post-Tensioning Institute (PTI) specifies three steps in this process:
1.) Cutting the Tendon Tail
2.) Installing the Encapsulation Cap
3.1) Grouting Wedge Pockets
3.2) If Using PT Plugs Instead of Grout
Once you have identified a pocket that needs repair, typically by a visual inspection or surface sounding (tapping a hammer on the concrete and checking for voids. A void will have a hollower sound to it) you can proceed with the guidelines for repairing the stressing pockets.
Repair grouts are designed specifically for filling concrete voids in vertical and overhead applications and are suitable for filling single-strand stressing pockets of PT tendons. It is very important to follow the manufacturer&#;s mixing recommendations; adding too much or too little water will weaken the mixture, and it will not be able to withstand the elements as it was intended.
In conclusion, regular inspections and maintenance are essential to manage the deterioration of a structure. This includes practices to limit moisture and ensure adequate drainage and waterproofing by protecting expansion joints and seals. By following these guidelines, PT stressing pocket problems can be minimized.
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