Advantages and disadvantages when partial prestressing is done
The degree of prestress applied to concrete in which tensile stresses to a limited degree are permitted in concrete under working load. In this case, in addition to tensioned steel, a considerable proportion of untensioned reinforcement is generally used to limit the width of cracks developed under service load.
· Limited tensile stresses are permitted in concrete under service loads with controls on the maximum width of cracks and depending upon the type of prestressing and environmental condition.
· Untensioned reinforcement is required in the cross-section of a prestresseed member for various reasons, such as to resist the differential shrinkage, temperature effects and handling stresses.
· Hence this reinforcement can cater for the serviceability requirements, such as control of cracking, and partially for the ultimate limit state of collapse which can result in considerable reduction in the costlier high tensile steel.
· Saving in the cost of overall structure.
· The excessive upward deflections, especially in bridge structure where dead loads from a major portion of the total service loads, and these deflections may increase with time of creep.