Maybe you have watched construction crews building 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 pour concrete into a form to make the panels, so how do they do it? The trick is actually a construction system referred to as post tensioning and features allowed for some serious miracles in urban construction since its inception.
Precisely what is Post Tensioning? Put simply, this is a method for Anchorage Barrel And Wedge, to make them stronger and more resistant to cracking and breaking under environmental conditions. Concrete, when created and formed, can be quite strong in its compressed form but it is still relatively weak in other places. By bonding the concrete block during creation with stainless-steel wires or rods, it increases its tensile strength, making the whole more durable to extreme changes.
The primary advantage to creating concrete construction panels in this manner is that it decreases the maintenance needed to maintain the structure as a whole fully operational. Whether the finished product is a slab foundation or a nuclear containment wall, it will hold the flexibility it must have 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 with a marked boost in deflection and vibration control. This technique has been a boon to the people areas that are regularly plagued by earthquakes, and hurricanes.
How Is It Done? Tensioning strands of stainless wire, usually grouped into bundles, are stretched along the duration of a vacant concrete form just before pouring. As the concrete hardens, the strands are tightened, “stressing” them through the hardening concrete. The strands are anchored by adjustable chucks, which can be loosened or tightened during installing of the finished panel.
There are two methods frequently used today in developing a post tensioned slab of concrete: wedge anchor. In the bonded method, a bonding grout is included in each channel whereby the tensioning wires have been strung. This method adds to the stability in the whole, further reducing maintenance costs in construction. Architecture designs that require greater flexibility, like those found in earthquake zones, will use the unbonded method, because they require greater flexibility, rather than additional reinforcement.
Typical steel strands found in post-tensioning have a tensile strength of 270,000 pounds/in². In comparison, an average non-prestressed piece of reinforcing includes a tensile strength of 60,000 psi. Strands normally have a diameter of 1/2 in., and therefore are stressed to your force of 33,000 pounds. The stresses brought into the concrete cancel out the expected external loads the concrete is going to be subjected to.
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 are able to be stressed following the concrete sets. This is usually completed in two stages. The very first prestress applied is up to 50% from the final force and this is achieved when the compressive strength reaches 12-15N/mm².
The next stage occurs when the barrel and wedge anchor occurs and this is done once 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 position with the anchoring component, which supports the force within them for that life of the building. Post-tensioning allows the engineer to possess each of the benefits rwkhni using prestressed concrete and keep the freedom of constructing on site.
By far the most prominent markets for concrete that has been created through post tensioning represent the majority of installations that can be found in the normal city’s infrastructure. Airports, stadiums, parking garages, nuclear plants and roadways all incorporate these intricately created and sturdy slabs within their design. In the private sector, constructions like hotels, universities, office buildings and condominiums have likewise taken benefit of this flexible substitute for traditional concrete installations. Want to know more about post tensioning processes and what types of forms can be created for construction purposes?
