PRE-STRESSED CONCRETE MUHAMMAD SHAHRON NIZAM MUHAMMAD SHABERY ZULHELMI ROSZITA KARTINA NURUL NAZIRA NUR ZANAH
Introduction A prestressed concrete structure isdifferent from a conventional reinforcedconcrete structure due to the applicationof an initial load on the structure prior toits use. The initial load or ‘prestress’ isapplied to enable the structure tocounteract the stresses arising during itsservice period. The prestressing of astructure is not the only instance ofprestressing. The concept of prestressingexisted before the applications inconcrete.
Pre stressed concrete is a methodfor overcoming concretes naturalweakness in tension It can be used to produce beams,floors or bridges with a longer spanthan is practical with ordinaryreinforced concrete
Pre stressing tendons (generally of hightensile steel cable or rods) are used to providea clamping load which produces acompressive stress that balances the tensilestress that the concrete compression memberwould otherwise experience due to a bendingload Traditional reinforced concrete is based onthe use of steel reinforcement bars, re bars,inside poured concrete.
Pre – tensioned concrete In pre – tensioning system, the high- strengthsteel tendons are pulled between two end abutments(also called bulkheads) prior to the casting ofconcrete. The abutments are fixed at the end prestressing bed Once the concrete attains the desires strength forpre stressing, the tendon are cut loose from theabutments. The pre stress is transferred to theconcrete from the tendons, due the bond betweenthem During the transfer of pre stress, the memberundergoes elastic shortening. If the tendons arelocated eccentrically, the member is likely to bendand deflect (camber)
The various stages of the pre-tensioning operation are summarized as follows : Anchoring of tendons Placing of against the end jacks abutmentsCutting of the Applying tension tendons to the tendons Casting of concrete
Post – tensioned concrete Post-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands or bars, typically referred to as tendons Post-tensioning applications include office and apartment buildings, parking structures, slabs-on-ground, bridges, sports stadiums, rock and soil anchors, and water-tanks
Pre-tensioned Concrete Improving the performance of the building under various service condition. Allow to carry a greater load or span a greater distance then ordinary reinforce concrete. It permits steel to be used at stresses several times larger than those permitted for reinforcing bars
Post-tensioned Concrete Large reduction in traditional reinforcement requirements as tendons cannot distress in accidents Tendons can be easily "woven" allowing a more efficient design approach Higher ultimate strength due to bond generated between the strand and concrete Strong against compression