Post-Installed Reinforcing Bar Guide
6.0 WHAT ’ S THE BACK STORY ?
The following formulation of the interface shear design method proposed by Palieraki [ 14 ] is a simplification based on conservative assumptions . It consists of the summation of friction and dowel action effects ( see Eq . ( 18 )) with modification terms that account for surface roughness , reinforcing quantity and grade , reinforcing embedment and bond strength , and loading type ( i . e ., static vs . cyclic ). As shown in Figure 53 , the approach proposed by Palieraki provides excellent agreement with an extensive database of test results .
V n
= A c ( β f
· f
+ β d
· d
) ( Eq . 18 )
Shear contribution from dowel action can be calculated using equation 20 :
d
2
1.3 · n · d b f l · f c y
=
where
A c
( psi ) ( Eq . 20 ) d b
= diameter of interface dowel reinforcement ( in .) n = number of dowels crossing interface
A c
= area of interface transected by n dowels ( in 2 ) where
V n
= nominal interface shear strength ( lb .) f
d
β f
β d
= nominal interface shear contribution from friction ( psi )
= nominal interface shear contribution from dowel ( psi )
= contribution factor for friction = contribution factor for dowel action
A c
= surface area of interface ( in 2 )
The shear contribution from friction can be calculated using equation 19 :
f = 0 . 33 [ ( f ' c ) 2 · ( f c , vf
+ f ext ) ] 1 / 3 where
f c , vf
f ext
f bu
= compression stress over interface due to action of dowel reinforcement , and is equal to the lesser value of the equations below .
f y
· A vf = ( psi )
|
5 · f bu
· l e
· A vf
|
|
= |
d b
· A c
|
( psi ) |
= uniform stress over interface due to externally applied normal force ( positive for compression , negative for tension ) ( psi )
= bond strength associated with the post-installed bar ( psi ) l e
= embedment length of the dowel ( in .)
A vf
= area of interface dowel reinforcement ( in 2 ) f y
= yield stress of interface dowel reinforcement ( psi ) f ' c
A c
( psi ) ( Eq . 19 )
= concrete uniaxial compressive strength ( psi )
The contribution factors have been experimentally established as follows :
Friction contribution factor , β f
, for static and seismic shear loading across the interface :
Surface roughness - friction coefficient
Dowel action contribution factor , β d for static and seismic shear loading across the interface :
Example : Shear dowels ( compare with examples provided in 2.6.1 and 6.6.1 )
Requirement : Determine the embedment requirement for post-installed reinforcing bars used to connect a new 8-inch thick shotcrete ( pneumatically-placed ) shear wall to an existing concrete wall ( Figure 9 ). Bars are # 5 at 12 in . x 16 in . over face of wall . Existing shear wall is 10 in . thick with 4 ksi normal weight concrete . Try dowels embedded the minimum of 12 diameters ( static shear ).
v u
= 9 ksf = 63 psi
A c
= 12 · 16 = 192 in 2 f bu
= 1090 lb . / in 2 ( characteristic bond strength in cracked concrete per ACI 355.4 )
V n
= A c ( β f
· f + β d · d )
Static β f
Seismic
Shear keys , or where f ext ≥ + 0.1 f ' c
0.8 0.4 Roughened with externally applied compressive stress 0.8 0.4
Mechanically roughened
Not roughened
Normal concrete < 8,000 psi ( 55 MPa ) 0.6 0.2 High strength concrete ≥ 8,000 psi ( 55 MPa ) 0.4 0.1 With external compressive stress 0.5 0.2 Without external compressive stress 0.4 0.1 Not roughened , steel formed surface ( very smooth ) 0.2 n / a *
* Not recommended
Dowel embedment Static β d
Seismic l e
> 8d b 0.7 0.35
33 November 2022