What is development length in prestressed concrete?
1. Introduction and background. When designing prestressed concrete members, engineers must determine the development length of the prestressing strands. The development length is the sum of the transfer length and the flexural bond length.
How is the strand stress assumed to vary over the transfer length?
3 – Variation in stress in prestressing steel along the length of the girders. For each group, the stress in the prestressing strands is assumed to increase linearly from 0.0 at the point where bonding commences to f pe, over the transfer length, i.e., over 30 inches.
Which type of steel is used in prestressing?
Explanation: High tensile steel are commonly used in prestressed concrete members and ultimate strength of high tensile steel is equal to 2100n/mm2, therefore the losses of prestress due to shrinkage and creep with a stress of 200n/mm2 are restricted.
How is prestressing done without steel?
Cold working (cold drawing) is being done by rolling the bars through a series of dyes. It re-aligns the crystals and increases the strength. Stress relieving is being done by heating the strand to about 350°C and cooling slowly. This reduces the plastic deformation of the steel after the onset of yielding.
How do you find the elongation of strands?
The elongation for the first stressing is the average stress in the tendon after the first stressing, divided by the modulus of elasticity of the strand. The elongation for the second stressing is the average stress in the tendon divided by the modulus of elasticity, minus the first elongation.
What is debonding in prestressed concrete?
There are three potential options to reduce end stresses in prestressed concrete bridge girders: drape strands, debond strands, or a combination of the two. In the debonding option, a portion of the strands are debonded toward the girder ends to reduce the resultant prestress force.
What type of steel and concrete is used in prestressing?
Prestressed concrete uses high tensile strength steel that is manufactured by increasing the carbon content in steel compared to ordinary mild steel used in R.C.C. In prestressed concrete, the steel used is tensioned or prestressed.
Why mild steel is not used in prestressing?
Ordinary mild steel and deformed bars are used in RCC are not used in PSC (prestressed concrete) because their yield strength is not very high. Therefore, high tensile strength steel is used for prestressing.
What is the example of linear prestressing?
Prestressing as applied to linear structural members, such as reinforced concrete beams or columns.
What is the typical accuracy of elongation measurements?
As a rule of thumb, elongation can be taken between 5 and 7 mm/m (0.06 and 0.084 in./ft) for tendons in slab systems whether bonded or unbonded. Based on an average of 6 mm/m (0.072 in./ft) and for tendon length of 5 and 10 m (16 and 33 ft), the elongation will be 30 and 60 mm (1.2 and 2.4 in.), respectively.
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