Perhaps 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 known as post tensioning and it has allowed for many serious miracles in urban construction since its inception.
Precisely what is Post Tensioning? Put simply, this is a way of Anchorage Barrel And Wedge, to make them stronger and more resistant to cracking and breaking under environmental conditions. Concrete, when created and formed, could be very strong in its compressed form yet 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 entire stronger to extreme changes.
The main benefit to creating concrete construction panels in this manner is it cuts down on the maintenance necessary to keep your structure in general fully operational. Whether the finished item is a slab foundation or even a nuclear containment wall, it is going to hold the flexibility it needs to resist temperature and environmental changes, less material is going to be required to cover exactly the same area, a lighter structure weight overall and a higher level of structural integrity having a marked increase in deflection and vibration control. This method has become a boon to the people areas which are regularly plagued by earthquakes, and hurricanes.
How Could It Be Done? Tensioning strands of stainless wire, usually grouped into bundles, are stretched along the size of a vacant concrete form prior to pouring. Because the concrete hardens, the strands are tightened, “stressing” them throughout the hardening concrete. The strands are anchored by adjustable chucks, which is often loosened or tightened during setting up the finished panel.
The two main methods widely used today in making 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 technique increases the stability in the whole, further reducing maintenance costs in construction. Architecture designs that require greater flexibility, like those used in earthquake zones, will make use of the unbonded method, since they require greater flexibility, instead of additional reinforcement.
Typical steel strands utilized in post-tensioning have a tensile strength of 270,000 pounds/in². Compared, a normal non-prestressed part of reinforcing features a tensile strength of 60,000 psi. Strands typically have a diameter of 1/2 in., and are stressed to a force of 33,000 pounds. The stresses brought to the concrete offset the expected external loads the concrete is going to be put through.
In post-tensioning the steel is held in a duct, which stops the steel and concrete from binding after the concrete solidifies. The steel can then be stressed after the concrete sets. Normally, this is completed in two stages. The initial prestress applied is up to 50% from the final force and this is accomplished when the compressive strength reaches 12-15N/mm².
The next stage occurs when the slab steel anchor occurs and this is done once the concrete meets its design strength. The strands and bars are tensioned by stretching these with a hydraulic jack. They may be then fixed in place having an anchoring component, which supports the force inside them for the lifetime 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 location.
By far the most prominent markets for concrete that has been created through post tensioning represent nearly all installations that may be found in the typical city’s infrastructure. Airports, stadiums, parking garages, nuclear plants and roadways all incorporate these intricately created and durable slabs to their design. In the private sector, constructions like hotels, universities, offices and condominiums have likewise taken benefit of this flexible option to traditional concrete installations. Want to know a little more about post tensioning processes and what kinds of forms can be created for construction purposes?