PostInstalled Reinforcing Bar Guide
6.0 WHAT ’ S THE BACK STORY ?
This equation was modified in 2003 to include the confinement term , K _{tr}
, and a strength reduction factor of 0.8 as shown in equation 6 :
l _{d}
= d _{b}
where
12 f _{s}
A _{tr} f _{y}
K _{tr}
= _{1500} _{s∙n}
= contribution of confining reinforcement to increased splitting resistance , with n being the number of bars being spliced or developed along the plane of splitting ( K _{tr} may be conservatively taken as zero ).
The basic tension development length equation in ACI 318 19 is obtained from this expression by removing the constant ( 200 ), replacing 1 / 12 with 3 / 40 , replacing f _{s} in Equation [ 6 ] with the nominal yield stress f _{y}
, and taking the yield strength of the transverse reinforcement as f _{yt}
= 60000 psi .
Development length for straight deformed bars in tension is given in Section 25.4.2.4 of ACI 31819 as shown in equation 7 :
l _{d}
200
c _{b}
+ K _{tr}
d _{b}
3 f _{y} ψ _{t} ψ _{e} ψ _{s} ψ = x x g
40 λ c _{b}
+ K _{tr}
d _{b}
( in ) ( Eq . 6 )
( in ) ( Eq . 7 )
where 


K _{tr}

40A _{tr}
= s∙n

where by s is the bar spacing and n is the no . of bars being developed 
ψ _{t}

= 
1.3 
for horizontal reinforcement placed with more 



than 12 in . of fresh concrete cast below the 



bars 
= 
1.0 
for other situations ( applies to postinstalled 


bars ) 
ψ _{e}

= 
1.5 
for epoxy coated bars , zinc and epoxy dual 



coated bars with cover less than 3d _{b} , or clear 



spacing less than 6d _{b}

= 
1.2 
for all other epoxy coated bars , zinc and 


epoxy dualcoated bars 
= 
1.0 
for uncoated and zinccoated reinforcement 


( applies generally to postinstalled bars ) 
ψ _{s}
= 0.8 for no . 6 and smaller bars
d _{b}
= 1.0 for no . 7 and larger bars ψ _{g}
= 1.0 Grade 40 or 60 bars c _{b}
+ K _{tr}
d _{b}
= 1.15 Grade 80 bars = 1.3 Grade 100 bars
≤ 2.5
λ = modification factor for lightweight concrete
Note : ACI Committee 408 ( Bond and Development ) has issued a report on the current development length provisions in ACI 318 . The report , ACI 408R03 [ 1 ], makes specific recommendations for the improvement of the development length equation , including a reduction in the exponent on concrete compressive strength , and reconsideration of the small bar factor .
6.3 OTHER STRAIGHT BAR PROVISIONS IN ACI 31819 [ 2 ]
ACI 31819 contains many provisions relevant for straight bar anchorage . Selected provisions are summarized here . For further information , please consult the code .
Section 25.4.1.0 requires that the calculated tension ( or compression ) in a reinforcing bar at a given section be developed on each side of that section ; that is , that the bar be extended "... beyond all points of peak stress in the reinforcement ."
Section 25.4.10 ( Excess reinforcement ) permits reduction of development length in direct proportion to the amount of excess reinforcement provided over that required by analysis . A reduction of development length is not permitted at noncontinuous supports , at locations where anchorage or development for f _{y} is required , where bars are required to be continuous , in seismicforceresisting systems in structures assigned to SDC C , D , E , or F , and in the anchorage of concrete piles and concretefilled pipe piles to pile caps in structures assigned to SDC C , D , E , or F .
The development length requirement for straight bars in compression in Section 25.4.9 is given in equation 8 :
f _{y} ψ l r d
= MAX d _{b}
; 0.0003 f _{y} ψ _{r} d _{b}
; 8 in .
50 λ
( in ) ( Eq . 8 )
Sections 7.7.3.3 & 9.7.3.3 note that reinforcement shall extend beyond the point at which it is no longer required to resist flexure for a distance at least the greater of d and 12d _{b}
, except at supports of simplysupported spans and at free ends of cantilevers .
Sections 7.7.3.4 & 9.7.3.4 require that continuing reinforcement in a flexural member be embedded for a distance at least
l _{d} beyond the point where bent or terminated tension reinforcement is no longer required to resist flexure .
Sections 7.7.3.5 & 9.7.3.5 prohibit the termination of flexural reinforcement in a tension zone unless a ) the factored
24 2021