The end block of a post-tensioned prestressed member is 550 mm wide and 550 mm deep. Four cables, each made up of 7 wires of 12 mm diameter strands and carrying a force of 1000 kN, are anchored by plate anchorages, 150 mm by 150 mm, located with their centres at 125 mm from the edges of the end block. The cable duct is of 50 mm diameter. The 28-day cube strength of concrete f cu is 45. N / m * m ^ 2 . The cube strength of concrete at transfer f_{d} is 25N / m * m ^ 2 Permissible bearing stresses behind anchorages should conform with IS: 1343. The characteristic yield stress in mild steel anchorage reinforcement is 260N / m * m ^ 2 . Design suitable anchorages for the end block.
Answers & Comments
Answer:
According to IS:1343 (1980):
The bursting tensile force, Fbst existing in an individual square end block loaded by symmetrically placed square anchorage or bearing plate, may be derived from the equation below
Where Fbst = Bursting tensile force, P0 = Load in tendons, yp0 = Width of concrete section, y0 = Width of end block
Calculation:
Given:
y0 = 300 mm, y01 = 100 mm, y02 = 150 mm
= 0.22
Fbst1 = P0× 0.22 -----------(1)
= 0.17
Fbst2 = 0.17×P0 ------------(2)
Reduction in bursting tensile force = P = Fbst2 - Fbst1
= 0.22× P0 - 0.17×P0