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 a construction system known as post tensioning and it has allowed for some serious miracles in urban construction since its inception.
What is Post Tensioning? Put simply, it really is a way of Anchorage Barrel And Wedge, to ensure they are stronger and much more resistant against cracking and breaking under environmental conditions. Concrete, when created and formed, can be very strong in their 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 improves its tensile strength, making the whole more durable to extreme changes.
The main benefit to creating concrete construction panels in this fashion is that it reduces the maintenance necessary to keep your structure in general fully operational. Whether or not the finished item is a slab foundation or even a nuclear containment wall, it can hold the flexibility it must have to resist temperature and environmental changes, less material is going to be needed to cover the same area, a lighter structure weight overall as well as a more impressive range of structural integrity with a marked rise in deflection and vibration control. This process has become a boon to the people areas that are regularly plagued by earthquakes, and hurricanes.
How Will It Be Done? Tensioning strands of stainless wire, usually grouped into bundles, are stretched along the duration of an empty concrete form prior to pouring. Because the concrete hardens, the strands are tightened, “stressing” them through the entire hardening concrete. The strands are anchored by adjustable chucks, which is often loosened or tightened during installing of the finished panel.
The two main methods frequently used today in creating 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 been strung. This process adds to the stability in the whole, further reducing maintenance costs in construction. Architecture designs that need greater flexibility, like those found in earthquake zones, will use the unbonded method, simply because they require greater flexibility, instead of additional reinforcement.
Typical steel strands used in post-tensioning possess a tensile strength of 270,000 pounds/in². In comparison, an average non-prestressed part of reinforcing has a tensile strength of 60,000 psi. Strands routinely have a diameter of 1/2 in., and therefore are stressed to a force of 33,000 pounds. The stresses brought in to the concrete cancel out the expected external loads the concrete will be subjected to.
In post-tensioning the steel is held in a duct, which stops the steel and concrete from binding following the concrete solidifies. The steel can then be stressed following the concrete sets. This is usually done in two stages. The initial prestress applied depends on 50% from the final force and this is achieved when the compressive strength reaches 12-15N/mm².
The 2nd stage happens when the pre-stressing anchor occurs and this is done 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 set up with an anchoring component, which holds the force in them for your lifetime of the building. Post-tensioning allows the engineer to get all of the benefits rwkhni using prestressed concrete whilst keeping the liberty of constructing on site.
Probably the most prominent markets for concrete which has been created through post tensioning represent the majority of installations that can be found in the average 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 also have taken benefit of this flexible option to traditional concrete installations. Need to know much more about post tensioning processes and what sorts of forms can be produced for construction purposes?