5. Bar Strain Near Tension Face Equal to ε_y + 0.003

Figure 6 - Strains, Forces, and Moment Arms (ε_y = 0.00576 in./in.)

In ACI 318-19 provisions, this control point corresponds to the tension-controlled strain limit of ε_y + 0.003 (used to be 0.005 in ACI 318-14). It is the strain at the tensile limit of the transition zone for ϕ, used to define a tension-controlled section.

Additional resources concerning code provision changes in ACI 318-19 can be found in “ACI 318-19 Code Revisions Impact on StructurePoint Software” technical article.

5.1. c, a, and strains in the reinforcement

    ACI 318-19 (Table 21.2.2)

    ACI 318-19 (22.2.2.1)

Where c is the distance from the fiber of maximum compressive strain to the neutral axis.    ACI 318-19 (22.2.2.4.2)

    ACI 318-19 (22.2.2.4.1)

Where:

    ACI 318-19 (Table 22.2.2.4.3)

5.2. Forces in the concrete and steel

    ACI 318-19 (22.2.2.4.1)

The area of the reinforcement in this layer has been included in the area (ab) used to compute C_c. As a result, it is necessary to subtract 0.85f_c’ from f_s’ before computing C_s:

5.3. ϕP_n and ϕM_n