ABSTRACT
Minimum reinforcement requirements for concrete flexural members are examined using fictitious crack models (FCM), four different crack closure stress (CCS) distributions, and the results of physical tests on slabs and beams of varying depth. It is concluded that the use of a CSS Straight-Line model with an associated GF value based on measured material properties is appropriate provided account is taken of shrinkage effects and the way those effects influence cracking. Minimum reinforcement requirements should be based on gross section properties and the condition that the yield moment be greater than the cracking moment. Fracture mechanics principles then demonstrate, as specified in Norwegian Standard NS3473-1989, that minimum ratios depend on member depth, ratios of concrete to steel strength and concrete material properties. However, steel elongation requirements must be added to those Standards if hard drawn wires are used as reinforcement.
