Limit state of cracking

No check is required at transfer since beam is totally in compression.

Design crack width for post-tensioned member under frequent load combinations ww = 0.2 mm

Table 4.10

The method adopted to determine the minimum reinforcement required is to

carry out a rigorous calculation of the crack width where the flexural tensile stress

under rare loads exceeds 3 N/mm2. If the calculated crack width under frequent loads does not exceed 0.2 mm then further bonded reinforcement is not required.

From Table 9.4 the stress at support 2 under the rare load combination is -4.19 N/mm2 and hence a more detailed calculation is required. As this example is a beam, at least two longitudinal bars at the top and bottom are required to hold the links in place.

For this analysis include 2T16s in the top of the beam.

0 =1.7 for load induced cracking The value of srm can be conservatively calculated as srm = h — x The value of esm can be conservatively calculated as esm = ^ Eqn 4.81

The values of as and x, the neutral axis depth, for this example were determined from computer analysis assuming linear stress/strain relationships and no tension from the concrete.

Applied moment = -377.6 kNm (frequent load case) x = 213 mm

0 0

Post a comment