In reinforced concrete (R.C.C.) beam detailing, which statements about bent-up bars near supports are correct with respect to resisting negative bending moment, sharing (shear) force, and the typical bend angle?

Introduction / Context:
Bent-up bars (also called cranked bars) are a classic detailing feature in reinforced concrete beams. Near the supports, beams face high shear and negative bending moments (hogging). Understanding what bent-up bars actually do—and the typical bend angle used—helps students connect structural behavior with practical detailing provisions used on site and in design drawings.

Given Data / Assumptions:

• We are discussing simply supported or continuous R.C.C. beams under typical gravity loads.
• Options refer to negative bending resistance at supports, shear resistance, and the bend angle (commonly 45°).
• Standard limit-state design practice and conventional detailing rules apply.

Concept / Approach:
At supports, the top fiber of a continuous or partially fixed beam is in tension due to negative (hogging) moment. Bent-up bars, originally placed in the tension zone at mid-span, are cranked up toward the support to provide tension steel where needed for negative moment. Additionally, because these bars are inclined, they contribute to shear resistance by providing an inclined tensile tie, working with stirrups to carry diagonal tension (web shear). Traditional detailing often uses a 45° crank (or sometimes 30° to 45° depending on code and bar diameter), which is easy to fabricate and provides an effective vector component toward the support.

Step-by-Step Solution:
Check statement about negative bending: Bent-up bars at supports place steel in the correct (top) zone to resist hogging tension — correct.Check statement about shear: Inclined bars add to shear capacity by intersecting potential diagonal cracks — correct.Check statement about bend angle: Typical practice uses about 45° (some codes permit 30°–45°) — correct as a general rule.Therefore, the comprehensive choice that captures all truths is “All the above”.

Verification / Alternative check:
Design texts show that inclined reinforcement contributes to V_resist through its vertical component. Crack patterns near supports align with diagonal tension, so cranked bars plus stirrups form a truss-like mechanism to resist shear and negative moment together.

Why Other Options Are Wrong:

• Any single statement alone is incomplete; the full behavior involves negative moment resistance, shear contribution, and conventional bend angles.
• “None of these” contradicts well-established detailing practice.

Common Pitfalls:
Assuming stirrups alone resist shear; forgetting that support regions need top steel; thinking crank angle has to be exactly one value without code-permitted ranges.

Final Answer:
All the above.