shortdesc

Crack control requirements are based on equation 10-6 , z = f_s (d_cA)^1/3 . The quantity z is limited to 30,000 N/mm for interior exposure and 25,000 N/mm for exterior exposure. If epoxy-coated reinforcement is used, these values are multiplied by 1.2.

where

dc	=	the distance from the extreme tension fiber to the center of the longitudinal bar located closest thereto. This definition is considered with any bar arrangements even when they are oriented askew to neutral axis and/or tension face (see figure below)
Aeff	=	the effective tension area of concrete surrounding the flexural tension reinforcement calculated by finding the center geometric curve for the pattern of tension reinforcement. The area is formed by finding parallel lines to the neutral axis at a distance of ds on both sides of the resultant rebar tension force. The distance dc is limited to a maximum of 50 mm + the max tension bar diameter according to the Standard. This limitation considers the case of large covers which generate wider surface cracks but with minor influence on rebar duration (Ref. Shear Behavior of Large, Lightly-Reinforced Concrete Beams and One-Way Slabs, Edward G. Sherwood (PhD Thesis – Carleton University – Canada). The effective tension area of concrete surrounding the flexural tension reinforcement (A) will be calculated as Aeff/ number of bars. According to the definition of A in the Standard, the number of bars will be computed as the number of equivalent bars with the largest diameter when different bar sizes are used.
fs	=	the stress at rebar level

The former calculations assume that the user will define most of the bars at closest locations to the tension face, only using a second bar layer in the case of lack of space, which is the normal and logical practice. Avoiding doing so, may lead to un-conservative results.