Flexural Response of RC

17 important questions on Flexural Response of RC

How are the strain assumed to vary over depth of a bending member?

Linearly

Define flexure from the perspective of the internal axial forces

- Tension equals compression and there is not net axial force

Define curvature in terms of i) Beam deflections ii) sectional strain

- Beam deflection: Change in slope per unit length - Ratio of bending rigidity and moment
- Sectional Strain:  Rate of strain change over depth. Deformation under bending
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In a linear member. The slope of bending moment - curvature response is constant. What is the name for bending moment per unit curvature? The slope is equal to the product of which material and geometrical parameters?

Bending moment per unit curvature is flexural rigidity. Slope is a product of Modulus of rupture and flexural rigidity

Why is contribution from reinforcement towards the cracking resistance of a concrete member not accounted for in members with low percentages of reinforcement?

Calculations are complex and the contribution is small

Why is the contribution from reinforcement towards the cracking resistance of a RC not accounted for in members with high % of reinforcement?

Reinforcing steel causes a reduction in cracking load since steel restrains shrinkage and does more harm than good.

If the purpose of non-prestressed reinforcement is not to increase cracking load then what is the purpose?

To prevent crack propagation

Explain why prestressed concrete is typically precast in a factory rather than cast in place

Precast concrete needs forms to prestress the steel. Steel can be dangerous if it snaps.

What is the tensile strength of a typical 13 mm 7-wire prestressing strand?

1860 MPa, 1200 MPa is the stress in the reinforcement left after shrinkage and settlement

Why does prestressed concrete need to be constructed using a high strength steel?

Because there will be losses due to concrete shrinkage and creep

Give an example of a common precast pretensioned prestressed concrete member

I-girder

Give an example of a common cast-in-place post-tensioned prestressed concrete member

Concrete slab

How does prestressing increase cracking strength?

By putting concrete into compression before loads applied

What is the physical meaning of EcIcr

Concrete response when it is fully cracked.

For a both-ends continuous slab, what is minimum depth of slab to avoid having to calculate dispacements?

Ln/28

Why is an equivalent rectangular stress block used for the flexural compression stressed?

Easier to find area

Why does Mr increase after reinforcement yields in tension and curvature is increased?

Increased curvature - top strain increases. Lever arm becomes longer as equivalent stress block becomes shallower (less depth resisting force).

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