ANS:D - Steel will yield first.

An under-reinforced section in reinforced concrete (RC) design refers to a situation where the amount of steel reinforcement provided in the beam or structural member is insufficient to fully utilize the tensile strength of the concrete. In more detail:

• "Steel is provided at the under side only": This statement does not accurately describe an under-reinforced section. In fact, an under-reinforced section may have steel reinforcement provided on both the tension and compression faces of the member, but the amount of reinforcement is insufficient.
• "Steel provided is insufficient": This is the correct definition. An under-reinforced section means that the amount of steel reinforcement provided is insufficient to fully resist the tensile stresses developed in the concrete under the applied loads. As a result, the concrete will start to crack and take on tensile stresses before the steel reinforcement reaches its yield point.
• "Steel provided on one face only": Again, this statement does not accurately describe an under-reinforced section. While reinforcement may be provided on one face only, an under-reinforced section can have reinforcement on both faces, albeit insufficient.
• "Steel will yield first": This statement describes a balanced or over-reinforced section, where the steel reinforcement reaches its yield point before the concrete fails in tension. In an under-reinforced section, the concrete will typically start to crack and fail in tension before the steel reinforcement yields.