R.C.C. beam detailing: Which statement about the behavior/placement of tensile reinforcement in a rectangular beam is INCORRECT?

Introduction / Context:
Proper reinforcement detailing ensures that reinforced concrete beams safely resist flexure and shear. Traditional detailing may use bent-up bars and stirrups for shear; however, the direction and purpose of bending must be correct and consistent with the flow of tensile forces in the member.

Given Data / Assumptions:

• Rectangular, singly reinforced beam under gravity loading.
• Working stress or limit state concepts for anchorage, curtailment, and shear resistance apply.
• Standard code-based bond and anchorage provisions are observed.

Concept / Approach:

Tension reinforcement is placed near the tension face (bottom for sagging midspan). When bending moment decreases toward supports, bars may be curtailed subject to anchorage and shear checks. Bent-up bars are traditionally “bent up” toward the compression zone to intersect potential shear cracks, contributing to shear resistance along with stirrups. The phrase “bent down” for shear is incorrect in this context.

Step-by-Step Solution:

Verification / Alternative check:

Historic detailing practice and many codes illustrate bent-up bars sloping upward toward supports; modern design often relies primarily on vertical stirrups with continuous bottom bars for ductility and constructability.

Why Other Options Are Wrong:

(a), (b), and (d) reflect correct practice; (e) is an acceptable added note that negative moments at supports can require top bars. The incorrect statement is (c) because “bent down” contradicts the established detailing direction for shear.

Common Pitfalls:

Premature bar curtailment without sufficient anchorage length; inadequate stirrups; misinterpreting diagrams and bending directions.

Final Answer:

Tensile bars are bent down at selected locations to act as shear reinforcement