Instruments for measuring loss of prestress in prestressed concrete: The initial pre-stressing force applied to the concrete element reduces due to elastic shortening of the concrete, anchorage losses, frictional losses etc. The pre-stressing force further reduces with the passage of time due to creep, shrinkage, temperature effect and relaxation of steel. The loss of pre-stressing(…)
Prestressed Concrete Design
MIX DESIGN OF HIGH STRENGTH CONCRETE
The properties of a high-strength concrete-mix with a compressive strength of more than 40 MPa is greatly influenced by the properties of aggregates in addition to that of the water-cement ratio. To achieve high strength, it is necessary to use lowest possible water-cement ratio, which invariably affects the workability of the mix and necessitates the(…)
SPECIFICATIONS OF PRESTRESSING STEEL
Specification of Prestressing Steel For prestressed concrete members, the high-tensile steel, used generally, consists of wires, bars or strands. The high tensile strength of steel is generally achieved by marginally increasing the carbon content in steel in comparison to mild steel. High-tensile steel usually contains 0.6 to 0.85% carbon, 0.7 to 1 % manganese, 0.05%(…)
Materials for Prestressed Concrete
High strength concrete mix: Pre-stressed concrete requires concrete which has a high compressive strength, with comparatively higher tensile strength. Low shrinkage, minimum creep characteristics and a high value of Young’s modulus are generally deemed necessary for concrete used for concrete used for pre-stressed members. A minimum cement content of 300 to 360 kg/m3 is prescribed(…)
Classification of Prestressed Concrete
There are many ways of classifying pre-stress concrete members based of the member of design, construction and application of pre-stress, some of them are as follows:- External or internal pre-stressing Linear or circular pre-stressing Pre-tensioning and post tensioning Pre-tensioning system (fully bonded constructions) Post –tensioning system (end anchored constructions) 4. Full pre-stressing or partial pre-stressing(…)
PRESTRESSED CONCRETE- MERITS AND DEMERITS
Prestressed concrete has the following merits: Since the technique of prestressing eliminates cracking of concrete under all stage of loading, the entire section of the structures takes part in resisting the external load. In contrast to this, in the reinforced concrete, only portion of the concrete above neutral axis is effective. Since concrete does not(…)
PRESTRESSING SYSTEMS AND ANCHORAGES
In concrete structures, prestress is introduced by stretching steel wire and anchoring them against concrete. Therefore, the prestressing systems should comprise essentially a method of stretching the steel and a method of anchoring it to the concrete. Different systems are adopted for pre-tensioning and post tensioning. PRE-TENSIONING SYSTEM: Hoyer system or long line method is(…)
PRE-TENSIONING AND POST-TENSIONING
PRE-TENSIONING AND POST-TENSIONING IN PRESTRESSED CONCRETE DESIGN The prestress in a structure is influenced by either of the two processes: Pre-tensioning, and Post-tensioning Pre-tensioning can be further classified into two categories: Linear pre-tensioning Circular pre-tensioning PRE-TENSIONING Pre-tensioning is accomplished by stressing wires or strands, called tendons, to predetermined amount by stretching them between two anchorages(…)
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