PostInstalled 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 postinstalled 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 noncyclic shear loading across the interface :
Surface roughness shear keys , or where f _{ext}
≥ + 0.1 f ' _{c}
0.8 mechanically roughened ( 1 / 4in . amplitude ) 0.6 not roughened 0.4 not roughened , steel formed surface ( very smooth ) 0.2
Friction contribution factor , β _{f}
, for cyclic ( seismic ) shear loading across the interface = 0.4 . Dowel action contribution factor , β _{d} for noncyclic shear loading across the interface :
Dowel embedment
For cyclic shear , use l _{e} ≥ 10d _{b} and β _{d}
= 0.75 .
Example : Shear dowels ( compare with examples provided in 2.6.1 and 6.5.1 )
Requirement : Determine the embedment requirement for postinstalled reinforcing bars used to connect a new 8inch thick shotcrete ( pneumaticallyplaced ) 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 ( cyclic shear ).
v _{u}
= 9 ksf = 63 psi
A _{c}
= 12 ‧ 16 = 192 in ^{2} f _{bu} β _{d} l _{e}
> 8d _{b}
0.75
= 1090 lb . / in2 ( characteristic bond strength in cracked concrete per ACI 355.4 )
V _{n}
= A _{c} ( β _{f}
‧ f ^{+} ^{β} d ^{‧} d ^{)} β _{f}
33 2021