This section applies to post-tensioned beams, one-way slabs, and two-way slabs. This section of TR43 defines hypothetical stress limits for comparison with gross section stresses.

The design strip segment or design section property "Environment" is used to determine the exposure category of members as follows:

• Protected: X0, XC1
• Normal: XC2, XC3, XC4
• Corrosive, Very Corrosive: XD1, XD2, XS1, XS2, XS3

For bonded beams and one way slabs, it is assumed that the hypothetical tensile stresses in Table 3 exist at the limiting crack width values given in Eurocode 2. For exposure class XD or XS, a limiting crack width value of 0.1mm is assumed for the determination of hypothetical tensile stresses. The recommended design strip property setting "PT Service Design Type" is either "Stress" or "Stress and Crack Width". "Crack Width" only is not explicitly permitted by TR43.

The supplemental reinforcement for bonded beams and one way slabs in accordance with TR43 5.8.1 is calculated as follows:

Stress Difference = Actual Stress - Supplemental Reinforcement Limit Stress

A_s = A_ct [(Stress Difference) / (400 N/mm²)]

where A_ct = cross-sectional area of the concrete in the tension zone

User defined reinforcement that is at an angle to the cross section will only have the component perpendicular to the cross section considered.

For unbonded beam and one way slabs, for members with tension stresses supplemental reinforcement is always provided in accordance with TR43 5.8.7. TR43 does not provide an absolute tensile stress limit for exceeding the Table 3 values. As such, RAM Concept uses the Table 3 values as absolute limits and therefore does not permit enhancing the stresses by adding un-tensioned reinforcement. The recommended design strip property setting"PT Service Design Type" is either "Stress" or "Stress and Crack Width". "Crack Width" only is not explicitly permitted by TR43.

For two way slabs, for members with tension stresses supplemental reinforcement is always provided in accordance with TR43 5.8.7. Table 4 or Table 5 values are used depending upon whether or not full panel width strips are used (average stresses) or column/middle strips are used (‘design strip’ stresses). In determination of using ‘with bonded reinforcement’ limits the average spacing of the bonded reinforcement on the tension face is checked (using bonded tendons in the tension zone). If the bonded reinforcement spacing limit is greater than 500 mm at the time when the limits are being determined, the ‘without bonded reinforcement’ limits are used. Since the reinforcement in the service design is left in the cross section from force envelope to envelope, it is possible that an envelope will use the ‘without bonded reinforcement’ limits while the subsequent envelope will use ‘with bonded reinforcement’ limits due to the reinforcement added in the previous envelope. Where full panel width strips are used, the recommended design strip property setting "PT Service Design Type" is either "Stress" or "Stress and Crack Width". "Crack Width" only is not explicitly permitted by TR43. In the case where column/middle strips are used the recommended setting is "Stress" or "Stress and Crack Width" or "Crack Width" as TR43 explicitly permits the stress limits in Table 5 to be exceeded where explicit crack width checks are performed.