The SuperStructure

"Bent-up bars," also commonly referred to as cranked bars, are reinforcement steel bars that are bent at an angle (typically 45°) within a reinforced concrete beam or slab. They transition from the bottom of the member near the mid-span to the top of the member near the supports.

Primary Purposes

Resisting Shear Forces: Shear forces in a beam are typically highest near the supports. The inclined portion of the bent-up bar helps resist these diagonal tension forces effectively.

Resisting Negative Bending Moments: At the supports, concrete beams experience "hogging" (negative bending), where the tension zone shifts to the top of the beam. Bending the bottom bars up allows them to provide tensile reinforcement in this top zone.

Economization: By utilizing the existing bottom reinforcement to serve both as tension steel at the mid-span and as shear/negative moment reinforcement near the supports, the overall amount of steel required can be reduced, making the design more cost-effective.

Crack Control: They help in controlling the width and propagation of cracks, particularly diagonal tension cracks that occur near supports.

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