Section 4.3.5.2 Design tensile stresses in flexure (Transfer)

For beams and one-way slabs, tensile stresses in concrete, based on the concrete section, are limited to:

Class 1: 1 N/mm²

Class 2: $0.36 \sqrt{f_{ci}}$ .

Class 3: $0.36 \sqrt{f_{ci}}$ .

For Class 2 and 3 beams and one-way slabs, where the stresses above are exceeded, bonded reinforcement is provided as follows [TR 43, 6.10.2/6.10.5]: A_s = F_i / (0.625f_y)

For two-way slabs without supplemental untensioned reinforcement, tensile stresses in concrete, based on the concrete section, are limited to 0 in the support region and $0.15 \sqrt{f_{ci}}$ in the span region [TR 43, 6.10.2].

For two-way slabs with supplemental untensioned reinforcement, tensile stresses in concrete, based on the concrete section, are limited to $0.45 \sqrt{f_{ci}}$ . Bonded reinforcement is provided as follows [TR 43, 6.10.2/6.10.5]:

A_s = F_i / (0.625f_y)

For sections with multiple concrete mixes, the minimum f_ci is used to determine the limit stress and the peak stress reported may be approximate.

No check is made to ensure the cross section is post-tensioned.

Two way slabs can never exceed $0.45 \sqrt{f_{ci}}$ , while there is no limit for beam and one-way slabs that are class 2 or 3.

Note: Clause 4.3.5.2 is unclear on this stress limit for Class 2, as it states that additional reinforcement should be provided "if necessary". This is interpreted as reinforcement is only necessary if the tensile stress exceeds

0.36 \sqrt{f_{ci}}

(since this stress is less than the cracking stress). Hence the stress may exceed this limit if the additional reinforcement is provided.