Which condition is true for a Tension-Controlled Section?

Which condition is true for a Tension-Controlled Section?

• A. c ≤ 3/8 dt
• B. ρ ≤ ρbal
• C. ρ ≥ ρbal
• D. εt ≥ 0.005

Answer: (D)

Tension-controlled sections fail in a ductile way because the tension reinforcement yields before the concrete in the compression zone reaches its ultimate crushing. A practical way engineers identify this behavior is by the strain in the extreme tension steel: if the tensile strain there reaches about 0.005 or more, the steel has yielded and the section behaves in a ductile, tension-controlled manner. That is why the statement about the tensile strain being at least 0.005 best characterizes a tension-controlled section. The other ideas involve reinforcement balance or neutral axis depth, which relate to other failure regimes or design checks but do not define the tension-controlled condition as clearly as the strain criterion does.

Tension-controlled sections fail in a ductile way because the tension reinforcement yields before the concrete in the compression zone reaches its ultimate crushing. A practical way engineers identify this behavior is by the strain in the extreme tension steel: if the tensile strain there reaches about 0.005 or more, the steel has yielded and the section behaves in a ductile, tension-controlled manner. That is why the statement about the tensile strain being at least 0.005 best characterizes a tension-controlled section. The other ideas involve reinforcement balance or neutral axis depth, which relate to other failure regimes or design checks but do not define the tension-controlled condition as clearly as the strain criterion does.