One such construction application is the Post-Tensioning Technology. Widely used in commercial applications today, post-tensioning is a method of strengthening concrete by using high-strength steel strands or cables, typically referred to as tendons. The combination of structural integrity and thinner pads allows for many practical applications.

The post-tensioning method allows for the building of stronger, more reliable foundation slabs. Office buildings and apartment style condominium buildings can have thinner floors but retain comfortable ceiling heights to reduce the total height and weight load. Even parking garages can be made stronger, more functional, and less expensive to construct.

In many cases, post-tensioning allows construction that would otherwise be impossible due to either site constraints or architectural requirements. It allows for clear spans, fewer beams, and thinner slabs and translates into a significant reduction in the building's weight versus a conventional building with the same number of floors and thus reduces the foundation load.

The post-tensioning system can be explained by imagining a set of blocks with holes drilled though them, in which elastics have been threaded through. If one were to hold the elastics on either side, the blocks would sag, however is one were to twist the elastics until they were stretched tight, the blocks would be pushed tightly together keeping them straight. The analogy of the tightened elastic is comparable to the post-tensioning tendon that has been stretched by hydraulic jacks and held in place by anchoring devices.Concrete is very strong in compression, but it's relatively weak in tension, which means that a concrete slab can be prone to cracking when forces act to pull it apart, or bending, when the earth under the slab sinks or becomes unstable. These forces can consequently damage the structural integrity of buildings. Post-tension concrete construction creates a tight grid of steel cables that actively help support the slab.

Unlike conventional "inactive" rebar, which only helps keep the slab intact after cracking, post-tension tendons continually contribute to the structural integrity of the building. Plastic sheathing is often used to cover the cables to protect them from corrosion.

Many buildings in Calgary, both residential and commercial have been built using this technology. With that being said, it is important that condominium buildings that were built using this technology have regular inspections by qualified individuals to ensure that proper maintenance is undertaken as required. The post-tensioning system must be maintained properly and as needed or costly repairs may become necessary.Because of the complexity of post-tensioning maintenance and repairs, it is important to contract the services of a profess-ional engineer that is an expert and specializes in, and is familiar with, all elements of post-tensioning systems. The corrosion of unbonded tendons is common for post-tensioned structures exposed to aggressive environments. Insufficient cover over the tendons and lack of protection from corrosion at anchorages combined with exposure to chlorides through deicing materials and coastal air can lead to the corrosion of post-tensioning systems.Repairs to post-tensioning systems fall into two categories:

Structural Repairs: These repairs address system failures. Signs of structural post-tensioning system distress disclosed in the inspection can include the following and will require immediate repairs to restore strength and integrity to the structure:
•   Broken strands which be seen coming out of the structure
•   End anchorage which has lifted out of the concrete
•   Cracking concrete which is running parallel  to the strands
•   Excessive deflections
•   Punching shear cracks in slabs
•   Diagonal shear / flexure cracks in beams and joists

Preventative Maintenance: Regular inspection of strand systems for signs of distress is one of the best ways for condominium owners to prevent costly repairs.

Items to be considered in the inspection of post-tensioned structures can include:
•    Appropriate concrete cover over strands exposed to aggressive environments
•    Condition of protective grease and sheathing
•    Cracking near strands (P-T systems are designed to reduce or eliminate cracking, so any excess cracking may indicate a problem)
•    Condition of concrete at anchorage pockets
•    Rust staining on the concrete near strands

Condominium corporations may avoid costly repairs by conducting investigations to determine if they have post-tensioning in their construction, as not all concrete structures are built using the post-tensioning system. In some cases, a building may be constructed of wood, and its concrete parkade built as a post-tensioned structure. It is important to identify whether you do or do not have post tension construction. If you are not certain, consider contracting the services of a qualified engineer to review the construction drawings/details, which can be done in conjunction with the preparation of the condominium's Reserve Fund Study. If it is determined that your building was built using the post-tensioning technology, you should establish a program that will allow for the regular and ongoing inspection of the system by a qualified party to ensure that they are monitored and repaired as necessary.

The cost of the inspection and maintenance of these systems should be included in the condominium Reserve Fund Plan and the Annual Budget.  CL