Reinforced Concrete and Steel

What 4 Components of Reinforced Concrete Resist Shear Force?

Concrete in Compression Zone

Aggregate Interlock

Dowel Action of Main Reinforcement

Shear Link Reinforcement

Aggregate Interlock

As concrete cracks, the rough surfaces of the interlock aggregates physically rub against each other. This causes friction, which transfers shear stresses from one side to another. It’s this action that provides shear resistance.

Shear Link Reinforcement

The links cross the paths of the diagonal shear cracks. These links are in tension and provide vertical forces, that stop cracks from opening further and prevent sliding motion, therefore carrying most of the shear force.

Dowel Action

Dowels are structural elements, that connect concrete sections. As the concrete on either side of the crack attempts to move vertically the bars resist the moment through bending and shear resistance, in the bar it’s self.

Concrete in Compression Zone

Top section under compression from bending, remains intact after cracks form. Resists shear by acting as compressive strut, transferring forces between where they are applied and the support.

Braced and Un-Braced Frames

Braced :

• Lateral deflections of the frame are relatively small.

• Frames relies on a stiff core or ‘shear wall’ as a bracing element to carry lateral loads.

• Floors transmit lateral forces to the bracing or shear wall, stiffer than the columns.

• Frame is less sensitive to lateral loading.

• Used for multi-storey reinforced concrete structures.

• Effective column height is always less than actual column height so less slender.

• Design bending moments are lower

Un-Braced Frames :

• Frame displacements are relatively large.

• Frame relies solely on the stiffness of the columns to resist lateral forces.

• Design bending moments are greater.

• Effective column height is always greater than actual so more slender.

• More commonly used for low to medium rise concrete structures.

• The frame is more sensitive to lateral loading.

Low Moment / Pre-Cracking / SLS or Post-Cracking / Ultimate or Failure

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