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Section 18.8.3 Cracking Moment

  • For a cantilever span (as determined by the declaration of supports in the design strip segment), this criterion is ignored if the section location is outside of L/3 of the support.
  • For a regular span (as determined by the declaration of supports in the design strip segment), this criterion is ignored if the section location is in one of the two regions between L/6 and L/3 from a support. It is assumed that these regions will contain the peak moments and hence the first part of a span to crack;
  • This criterion is not applied to bonded two-way slabs, even though the code technically requires it.
  • The cracking is assumed to be top (negative moment) or bottom (positive moment) based on the "Min. Reinforcement Pattern" selected in the design strip segment or design section.
  • See Cracking Moment Used in Design Calculations for a theoretical discussion of the cracking moment.
  • Modulus of rupture (f cr ) is 7.5 f c times the lightweight concrete factor. The maximum f’c for the cross section is used.
  • Lightweight concrete factor is assumed to be wc / 145 pcf ≤ 1.0. The maximum wc for the cross section is used.
  • The "twice that required" criterion is not checked.