Development Length, Hooks and Splices & Design of Short Column

Reinforced Concrete Lesson 1

Bond between the steel and concrete after the concrete hardens

Joint behavior of Steen and concrete in a reinforced Concrete member

It requires a considerable forced to pull out the concrete

Straight bar of round section is embedded then

The steel bar may yield leaving some length of the bar in the concrete

Embedded length of the bar is long enough, then

Friction

Bonding force of concrete and steel is depend on its

Roughness of the surface area of the steel

Concrete mix

Shrinkage

Cover of the Concrete

Factors influencing the friction between the steel and concrete

Roughness of the surface area of steel

Deformed bar is referred due to its ridges formed than the plain bar

Concrete mix

Rich mixes have a great adhesion

Shrinkage

Frictional resistance

Cover of the concrete

Increase on it can improve the ultimate bon stress of a steel bar

Bond failure

Mechanism by which failure occurs when the provided development length is inadequate

Bond stress

Occurs the moment bending change

Max Moment in RC Formula

Theoretical Cutoff Locations for a simple span beam

Diagram for theorical cutoff location for a simple span beam

Development Length general formula for tension reinforcement

Transverse reinforcement index

Transverse reinforcement index

It is used to account for the contribution of confining reinforcing (stirrups/ties) across possible splitting planes

Provision of cover and transverse reinforcement terms

1.3

Value of Location Coefficient when 300 mm or above is placed1.0

1.5

Value of coating factor when it is coated with epoxy-coated or zinc with cover less 3d_b and spacing less than 6d_b

1.2

Value of coating factor when it is coated with epoxy-coated or zinc with cover more than 3d_b and spacing more than 6d_b

1.0

Value of coating factor when it is uncoated

1.0

Value of size of bar with 22-diameter or up

0.8

Value of size of bar factor when 19-diameter and below

1.0

Value of concrete weight factor when it is stated normalweight

0.85

Value of concrete weight factor when it is stated sand light0.weight

0.75

Value of concrete weight factor when it is stated lightweight

1.7

reinforcement location factor and epoxy coat factor shall not be greater than

300

Minimum length of development length in tension reinforcement

Simplified Version of Development length in Tension reinforcement

Do not have the cracks that develop in tension concrete members that cause a reduction in the bond between bars and the surrounding concrete

Why development length of deformed bars in compression is generally smaller?

Formula for Development Length in Compression Reinforcement

200 mm

Minimum length in compression reinforcement

a. Spiral

b. Circular continuously wound tie with d_b greater than or equal to 6 mm with a pitch of 100 mm

c. No 13 wire ties spaced less than or equal to 100 mm

d. Hoops spaced less than or equal to 100 mm

Confining factor provisions0

0.75

Value of confining reinforcement factor1.

1.0

value of confining reinforcement without confining reinforcement

additional length in 90-degree hook

additional length in 180-degree hooked bar

hooks formula

Modification factors for development of hooked bars in tension

Splices at tension reinforcement

Splices in compression reinforcement

Axial Compression

0.65

Safety factor of Tied Columns0.

0.75

Safety factor of Spiral column

1%-8%

steel reinforcement ratio (min-max)

200-250 mm

minimum diameter of column

10-12 mm diameter

Size of Ties and Spiral

Center-to-center spacing of ties

formula for tied column

Formula for spiral column

gross reinforcement formula

25 mm

minimum pitch at spiral column

75 mm

maximum pitch at spiral column

Steel reinforcement ratio