Step 1
When external brand wire known as tendons are placed on the outer section of the area being stressed , then the proficiency is call extraneous prestressing . The tendon lie down outside or inside the hollow blank of a box girder and forces are only channel at the deviation or anchorage blocks . External prestressing command a great deal of truth in planning , capital punishment and maintenance ; therefore , it is not very usual . The proficiency is suited for strengthening construction and constructing bridge . On the other hand , internal prestressing is achieved by range the tendons within a structure . Prestressing applications utilise internal technique because it is gentle to achieve a keen degree of accuracy .
Pre-Tensioning or Post-Tensioning
Pre - tensioning and post - tensioning are the two common techniques of prestressing .
In pre - tensioning , the tension is applied to the tendons before the casting of the concrete . The prestressed tendons are transfer to the hardened concrete through a bond . The sinew can be of single wire or a seven - conducting wire strand and are often used in precast irradiation .
Post - tensioning is when prestressing is done against the hardened concrete . When the concrete has been indurate , the prestressed tendons are passed through duct cast into the concrete and locked with mechanically skillful anchors . The tendon force is thereby change to the structure through the anchorage ground wedges .
Step 2
Linear or Circular Prestressing
Linear prestressing is a case of prestressing used in straight , bent or level structure . The technique can even be used on cut structures as long as the sinew do n’t go round in roundabout because they are linearly prestressed . For example , prestressing of rod , slabs and beam can be done using the analogue prestressing proficiency . In line , curved or circular structures employ the circular prestressing proficiency . The sinew are wreathe in circles . lesson include pipes , silos and tanks .
Full or Partial Prestressing
The proficiency where no restrictions are placed on concrete tensile stresses under service conditions is called partial prestressing . The part under stress is reenforce using extra mild steel bars to hold in the cracks and hence the crack width is within allowable limit . deviation from the rigid prestressing can cause contortion , cracking and fatigue on the structure ; therefore , when using this proficiency during construction , you must always supervise the prestressing force out cautiously . On the other hired hand , full prestressing is a technique where no malleable tension is allowed in concrete under service rafts . The sphere of prestressing steel is more than the area needed for base hit at ultimate state , therefore leading to inefficient use of prestressing .
