Reinforced concrete design requirements| JNTUA R20

Introduction to reinforced concrete and design methods. [ 2 ]

What is Bond strength ?

It is shear stress at the interface of reinforcement of concrete developed to resist the slippage of the bar relative to its surrounding concrete.

What is tensile strength of concrete ?

• Tensile strength of concrete is very low, usually varying from 10 to 20% of its compressive strength.
• It is measured in terms of splitting tensile strength of cylindrical specimens.

\[{f_t} = 0.7\sqrt {{f_{ck}}}\]

• Where,f_t= Tensile strength in N/mm².
• f_ck= Tensile strength in N/mm².

What is Poisson's ratio ? what are the value of poisson's ratio under different condition ?

poisson's ration is lateral strain to longitudinal strain.

Poisson ratio	Conditions
μ=0.1	High strength concrete
μ=0.2	Weak concrete
μ=0.15	Design purpose
μ=0.2	Serviceability criteria

What is shrinkage of concrete ?

• Decrease in volume, during the process of drying & hardening of concrete.
• Depends upon ingredients of concrete and environment conditions.
• Shrinkage strain is independent of stress conditions.
• If restrained, shrinkage strains can cause cracking of concrete. 0.0003 shrinkage is taken for design.

Why reinforcement is used in construction ?

Steel bars are used to reinforce the concrete to resist tensile stresses resulting from the applied loads.

What are the useful properties of steel bars ?

• it has a High strength material.
• it possess High modulus of elasticity.
• Ability to develop a good bond with concrete.
• It is widely available.

What are the different types of steels available in market ?

Types of steel bars are namely TMT or TOR steel. TMT bars thermo mechanical treatment technology prevents rust and corrosion whereas TOR steel bars contain chloride irons which makes them highly vulnerable in humid conditions.

• Mild steel (fe 250 N/mm²).
• HYSD bars (fe-450 & fe-500).
• Fe means ferrous and Number shows yield stress in N/mm²).

Why we need to provide concrete covers ?

Concrete cover protects steel bar against corrosive materials like chlorides, sulfate, etc

Exposure	Mild	Moderate	severe	Very severe	Extreme
Nominal	20	30	45	50	75
Grade of concrete	20	25	30	35	40