Prestressed Concrete Design
PRE-STRESSED CONCRETE
R.C.C is formed by the combination of concrete and steel. Steel is basically used to withstand tension. This can also be used to with stand compression if need be. While concrete is used to withstand compression only because concrete cannot withstand tension, These forces of compression and tension are produced by the external Applied Load.
According to the new research. If stress is produced opposite in nature to the stress induced due to external load in any component of R.C.C .the the resisting capacity of the component .The action of producing stress opposite to he expected stress in member in the design is called pre-stressing .this making the size of structure less. This makes the structure cheap and safe By this action compression in the tension part and tension in the compression part are produced .This action can only be applied by stretching steel bars. This stretching action is done in two ways . In the first type the steel bars are tension ed before casting concrete which is called pre-tensioning. In the second type plastic or steel pipes are placed in the beam instead of bars before casting concrete. Then steel bars are inserted in the pipes or holes after hardening the concrete. This method is post-tensioning. Jacks are used in both of these desired tension. And the ends are anchored properly .High strength concrete is prepared or the construction of such structures .Also the steel of high strength is used .The concrete of at least 420 kg/cm (6000lbs/in) is used .Such steel in the form of cold drawn and alloy steel is used .The structure prepared form pre-stressing action are used in big bridges and other such projects one of the advantage of pre-stressing is that there are no cracks in the tension zone of the structure. This
enlarges the life of the structure.
Material for Prestressed Concrete Design
The members prepared form pre stressing involves the use of concrete and steel .Since high stress are created in the method there for materials of high qualities are required .These materials should contain he following qualities .Concrete .Strong concrete is used in pre stressing .Taking this into consideration. it is also taken into account that members should be light weight . For the construction of then sections certainly strong concrete is needed .For this purpose rich concrete is prepared therefore quick setting cement is used if the ordinary Portland cement be used then it is to be used more in quantity organic acids should be used for more strength .While chlorides are never used . The modulus of elasticity of such concrete is more which is an important quality of such concrete members .Such materials are needed in pre stressing whose shrinkage and creep is minimum because in this case the created stressed in prestressing decrease . This quality can be achieved by preparing concrete of optimum water-cement ratio. In addition to this the other materials used are of high standard . The ultimate strength of such concrete should not be less than 420 kg/cm square (600 lb/in square) .Slump should be minimum in this concrete which should not be more than 10 cm (4 inch) in any case .By using stem curing better results could be achieved.
STEEL In Prestressed Concrete Design .
In pre-stressing steel is generally used in the form of strained wires . These are called tendon. These are prepared form high Tensile steel .The diameter of Hard Drawn steel wires is 15 mm (1/16 in.) to 8 mm(3/8inch.).Their ultimate strength is 5600 kg/cm square (80000 lb/inch square ). In addition to this the tendon made by joining 7 or 8 wires are also used . All these are prepared form High Tensile Steel. These bares are not prepared by mild steel because in such bars the stresses created from pre stressing in being wasted on account of different causes. Of these the creation of shrinkage and creep important stress in wasted in mild steel due to creep where as this stress in sot wasted in High Tensile Steel.Related Posts With Prestressed Concrete
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