Post-Installed Reinforcing Bar Guide
2.0 HOW ARE THEY DESIGNED ?
2.6.2 DESIGN EXAMPLE — LAP SPLICE
Requirement : Provide post-installed reinforcing for a new balcony extension on an existing concrete structure as shown in Figure 11 .
( E ) slab reinforcing
( N ) bars installed in drilled holes
( E ) slab ( N ) slab extension
Positive moment reinforcement : try # 8 @ 12 in . o . c . 0.79 ρ = = 0.0082 12 x 8
K n ρf y
0.0082 ( 60000 )
= 1 - ρfy = 1 -
1.7λf l c
1.7 ( 0.85 ) ( 5000 )
0.0082 ( 60000 ) = 458 psi
12 ( 8 ) 2 x 458 ϕM n
= ϕb ∙ d 2 K n = 0.9
= 26.3 ft-k / ft > 25 .. · ok
12 x 1000
Use # 8 @ 12 in . on center for top bars
( E ) wall mechanically roughened surface , 1 / 4 in . amplitude
Required area of reinforcement per 22.9.4.2 , Eq . ( R22.9.4.2 ) ACI 318-19
V
A vf
= u
V
= u
6000 = = 0.18 in 2 / ft ϕf y μ ϕf y 1.0λ 0.75 x 60000 x 1.0 x 0.75
Figure 11 — Section through balcony .
Step 1 : Determine area of flexural reinforcing for cantilever moment . Existing construction : ( E ) slab , 10 in . thick , 4 ksi normal weight concrete , top bars # 9 @ 8 in . on center , bottom bars # 8 @ 12 in . on center , transverse bars # 5 @ 16 in . on center top and bottom
New construction : ( N ) tapered slab as shown , 5000 psi sand lightweight concrete , ASTM A615 Gr . 60 reinforcement Factored moment and shear at face of cantilever :
M u
= 25 ft-k / ft
V u
= 6k / ft d = 8 inches ( Figure 12 )
Note : Although this is sand-lightweight concrete , the value of λ for use with the shear friction equation is taken conservatively as 0.75 in the absence of specific information to support a higher value — see Table 19.2.4.1 ( b ) of ACI 318-19 .
Shear reinforcement : use # 5 at 16 in . on center for bottom bars
Step 2 : Set design conditions .
• Drilling method : Rotary-hammer drilling
• Orientation of connection : Horizontal / wall position
• Installation and in-service temperature : 90˚F
• Type of concrete : Normal weight , 4 ksi
• Condition of concrete : Dry
• Choice of adhesive based on condition : HIT-RE 500 V3
• Type and location of bars : As shown on drawings , position to avoid existing reinforcing , but no further than 4 inches from existing flexural reinforcing . b
( N ) bars installed in drilled holes
Step 3 : Calculate the required embedment ( splice length ) fro the new top and bottom bars . Top bars :
( E ) wall d = 8 in .
Note : Since the new # 8 bars are being spliced with existing # 9 bars , the required splice length per ACI 318-19 25.5.2.2 is the larger of the development length of the larger bar (# 9 ) and the tension lap splice length of the smaller bar (# 8 ).
Figure 12 — Placement of new positive moment reinforcement .
8 November 2022