Product Technical Guides : US-EN Post-Installed Rebar Guide - Page 26

Post-Installed 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 318-19 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 post-installed
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 dual-coated bars
=
1.0
for uncoated and zinc-coated reinforcement
( applies generally to post-installed 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 408R-03 [ 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 318-19 [ 2 ]
ACI 318-19 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 seismic-force-resisting systems in structures assigned to SDC C , D , E , or F , and in the anchorage of concrete piles and concrete-filled 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 simply-supported 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