DEVELOPMENT LENGTH OF REBAR

Development Length Formula

As per IS Code 456:2000, (Clause 26.2.1) Development length can be calculated using the below formula

L_d = Фσ_s/4τ_bd

Where,

Ф = diameter of the reinforcement bar

σ_s = Stress developed in a bar at section considered at load design

τ_bd = Design bond stress

Note- The formula can be used for both the Limit state and the Working stress method. It only differs in design bond stress value.

REASONS FOR PROVIDING DEVELOPMENT LENGTH:

There are the following reasons for providing this length as given below;

Between the bar surface and the concrete to develop a safe bond.
Due to slippage of bar occurring during the ultimate load conditions no failure occurs.
For transferring the stresses developed in any section to the adjacent sections the extra length of the bar provided as development length is responsible for example at column beam junction the additional length of bars provided from beam to column.

Development Length Calculation

	CHECK FOR DEVELOPMENT LENGTH
	Max Shear Force wl/2		31.75	KN		Design Bond Stress
	Grade of Concrete M		25		Greade	15	20	25	30	35	40
	Grade of Steel Fe		415		Tbd N/Sqmm	1.0	1.2	1.4	1.5	1.7	1.9
	Adopt Effective Depth d		250	mm
	Width of Fdn b		1000	mm
	Dia of Main rft		10	mm
	Area of Tension rft		512	Sqmm
	Area of One Bar		78.57	Sqmm
	Spacing of Bars		150	mm
	Assumed Development Length		200	mm
INPUT	Bond Stress Tbd		1.4	N/Sqmm

	Development Length based on Anchorage Bond
	Ld= 0.87 fy Ø/ 4Tbd
	Ld in Anchorage Bond		644	mm

	Development Length based on Flexural Bond
	Ld= 1.3 M1/V + Lo
INPUT	Assumed Development Length		140	mm

		Moment of Resistance offered by		10	mm dia bar @		300	Nos
		M1 =	4,46,47,000	Nmm
		V =	31750	N		Development Length for Single Bars
	Ld in Flexural Bond		1968	mm	fy N/Sqmm	Tension Bars		Compression Bars
	Factor of Develop Length		56			M15	M20	M15	M20
	Develop length of Single Bar		560	mm	250	55Ø	46Ø	44Ø	37Ø
					415	56Ø	47Ø	45Ø	38Ø
	Max Development Length		1968	mm	500	69Ø	58Ø	54Ø	46Ø
	Max Bar Size in Develop Length		49	mm

	Check for Development Length		OK		If NOT OK Then increase No of Bars