Perhaps you have watched construction crews constructing a parking garage or skyscraper and wondered how they were able to raise and attach huge concrete panels like they were building blocks? You never see them actually fill concrete into a form to make the panels, so how do they do it? The key is actually a construction system called post tensioning and it has allowed for many serious miracles in urban construction since its creation.
What exactly is Post Tensioning? Put simply, this is a way of Post Tension Anchor, so they are stronger and more resistant against cracking and breaking under environmental conditions. Concrete, when created and formed, can be quite strong in its compressed form yet it is still relatively weak in other areas. By bonding the concrete block during creation with stainless-steel wires or rods, it improves its tensile strength, making the complete more durable to extreme changes.
The primary benefit to creating concrete construction panels in this way is it reduces the maintenance required to maintain the structure overall fully operational. Whether the finished item is a slab foundation or even a nuclear containment wall, it is going to possess the flexibility it requires to resist temperature and environmental changes, less material will likely be needed to cover the same area, a lighter structure weight overall along with a higher-level of structural integrity using a marked rise in deflection and vibration control. This process has become a boon to the people areas which are regularly plagued by earthquakes, and hurricanes.
How Is It Done? Tensioning strands of stainless wire, usually grouped into bundles, are stretched along the length of an empty concrete form just before pouring. Because the concrete hardens, the strands are tightened, “stressing” them through the hardening concrete. The strands are anchored by adjustable chucks, which may be loosened or tightened during setting up the finished panel.
The two main methods frequently used today in making a post tensioned slab of concrete: wedge anchor. Within the bonded method, a bonding grout is put into each channel whereby the tensioning wires have already been strung. This method enhances the stability of the whole, further reducing maintenance costs in construction. Architecture designs that need greater flexibility, like those utilized in earthquake zones, will use the unbonded method, since they require greater flexibility, as opposed to additional reinforcement.
Typical steel strands found in post-tensioning use a tensile strength of 270,000 pounds/in². In contrast, a typical non-prestressed bit of reinforcing has a tensile strength of 60,000 psi. Strands routinely have a diameter of 1/2 in., and they are stressed to your force of 33,000 pounds. The stresses brought into the concrete cancel out the expected external loads the concrete will likely be put through.
In post-tensioning the steel is held in a duct, which stops the steel and concrete from binding right after the concrete solidifies. The steel may then be stressed following the concrete sets. This is usually done in two stages. The first prestress applied is up to 50% from the final force and this is accomplished if the compressive strength reaches 12-15N/mm².
The next stage is when the slab steel anchor occurs and this is accomplished when the concrete meets its design strength. The strands and bars are tensioned by stretching all of them with a hydraulic jack. They are then fixed in place having an anchoring component, which supports the force within them for the life of the building. Post-tensioning allows the engineer to have all the benefits rwkhni using prestressed concrete whilst keeping the freedom of constructing on site.
Probably the most prominent markets for concrete which has been created through post tensioning represent nearly all installations that are available in the typical city’s infrastructure. Airports, stadiums, parking garages, nuclear plants and roadways all incorporate these intricately created and durable slabs into their design. Within the private sector, constructions like hotels, universities, offices and condominiums have also taken benefit from this flexible substitute for traditional concrete installations. Want to find out much more about post tensioning processes and what kinds of forms can be produced for construction purposes?