2. Bar Stress Near Tension Face Equal to Zero, (ε_s = f_s = 0)

Figure 3 - Strains, Forces, and Moment Arms (ε_t = f_s = 0)

Strain ε_s is zero in the extreme layer of tension steel. This case is considered when calculating an interaction diagram because it marks the change from compression lap splices being allowed on all longitudinal bars, to the more severe requirement of tensile lap splices.     ACI 318-19 (10.7.5.2.1 and 2)

For Concrete:

c = d₅ = 17.37 in.

    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:

a = Depth of equivalent rectangular stress block

    ACI 318-19 (Table 22.2.2.4.3)

(Compression)    ACI 318-19 (22.2.2.4.1)

Where:

Figure 4 - Cracked Column Section Properties (ε_t = f_s = 0)

For Reinforcement:

The area of the reinforcement in this layer is not included in the area (ab) used to compute C_c. As a result, it is NOT necessary to subtract 0.85f_c’ from f_s4 before computing F_s4:

(Compression)

The same procedure shown above can be repeated to calculate the forces in the remaining reinforcement layers, results are summarized in the following table:

Where: