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 a few serious miracles in urban construction since its beginning.
Precisely what is Post Tensioning? Put simply, this is a method for stressing anchorage, so they are stronger and much more resistant to cracking and breaking under environmental conditions. Concrete, when created and formed, could be very strong in their 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 improves its tensile strength, making the entire stronger to extreme changes.
The main advantage to creating concrete construction panels in this fashion is that it cuts down on the maintenance needed to maintain the structure in general 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 is going to be necessary to cover the identical area, a lighter structure weight overall and a higher-level of structural integrity with a marked increase in deflection and vibration control. This method has been a boon to those areas which can be regularly plagued by earthquakes, and hurricanes.
How Is It Done? Tensioning strands of stainless wire, usually grouped into bundles, are stretched along the size of an empty concrete form before pouring. Because the concrete hardens, the strands are tightened, “stressing” them throughout the hardening concrete. The strands are anchored by adjustable chucks, which may be loosened or tightened during installation of the finished panel.
There are 2 methods widely used today in making a post tensioned slab of concrete: post tension anchorage. In the bonded method, a bonding grout is added to each channel by which the tensioning wires have been strung. This technique enhances the stability in the whole, further reducing maintenance costs in construction. Architecture designs that require greater flexibility, like those used in earthquake zones, uses the unbonded method, 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 contrast, a typical non-prestressed part of reinforcing includes 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 to the concrete cancel out the expected external loads the concrete will 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 are able to be stressed right after the concrete sets. This is usually completed in two stages. The first prestress applied depends on 50% from the final force and this is accomplished if the compressive strength reaches 12-15N/mm².
The next stage occurs when the slab steel anchor occurs and this is accomplished if the concrete meets its design strength. The strands and bars are tensioned by stretching all of them with a hydraulic jack. They may be then fixed in place with the anchoring component, which supports the force inside them for your lifetime of the building. Post-tensioning allows the engineer to have each of the benefits rwkhni using prestressed concrete whilst keeping the liberty of constructing on location.
Probably the most prominent markets for concrete that has been created through post tensioning represent nearly all installations that may be found in the average city’s infrastructure. Airports, stadiums, parking garages, nuclear plants and roadways all incorporate these intricately created and sturdy slabs into their design. Within the private sector, constructions like hotels, universities, offices and condominiums have likewise taken advantage of this flexible substitute for traditional concrete installations. Want to find out a little more about post tensioning processes and what types of forms can be accomplished for construction purposes?