Post-Installed Reinforcing Bar Guide
6.0 WHAT ’ S THE BACK STORY ?
6.1 ESTABLISHING THE REQUIRED BAR EMBEDMENT
Systems qualified under AC308 are required to demonstrate bond resistance and stiffness characteristics that are compatible with cast-in reinforcement . Therefore , postinstalled reinforcing bars installed with qualified systems can be designed and detailed using the same provisions that are applicable to the development of straight cast-in-place bars .
6.2 OVERVIEW OF ACI 318-19 15 DEVELOPMENT LENGTH PROVISIONS FOR STRAIGHT REINFORCING BARS
The ACI concept of development length is based on the attainable average bond stress over the length of embedment of the reinforcement . Development length can be defined as the shortest length in which the bar stress increases from zero to the nominal yield strength . This definition incorporates two very important concepts — bar stress and nominal yield strength . Bar stress is the force per unit area of the bar cross section . The nominal yield strength is the minimum bar stress at which permanent ( inelastic ) deformation occurs . Structural reinforced concrete design is based on the assumption that the reinforcing bar will develop its yield strength before premature failure occurs due to inadequate bond . Development length is intended to ensure that the nominal yield strength of the bar can be developed under structure loading .
Orangun , et al . [ 13 ] proposed an expression for determining the development length l d of deformed reinforcing bars in tension as shown in equation 5 :
where , f s
-50 |
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4 |
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l d
=
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c b
|
A tr f yt
|
d b
|
( in ) |
( Eq . 5 ) |
1.2 + 3 |
d b
|
+
500 s · d b
|
A tr
The total cross-sectional area of all transverse reinforcement within spacing that crosses the potential plane of splitting through the reinforcement being developed c b
Smaller of : ( a ) center of bar to nearest concrete surface , and ( b ) one-half the center-to-center spacing of bars being developed d b
Diameter of bar being developed f΄c Specified 28-day compressive strength of concrete
f s
The maximum stress in the bar
f yt
Specified yield strength f y of transverse reinforcement
U . S . reinforcing bar size
Imperial bar size
" Soft " metric size
Mass per unit |
|
|
length |
Nominal diameter |
Nominal area |
lb / ft ( kg / m ) ( in ) ( mm ) ( in 2 ) ( mm 2 ) # 2 # 6 0.167 0.249 0.250 = 1 / 4 6.35 0.05 32 # 3 # 10 0.376 0.561 0.375 = 3 / 8 9.525 0.11 71 # 4 # 13 0.668 0.996 0.500 = 4 / 8 12.7 0.20 129 # 5 # 16 1.043 1.556 0.625 = 5 / 8 15.875 0.31 200 # 6 # 19 1.502 2.24 0.750 = 6 / 8 19.05 0.44 284 # 7 # 22 2.044 3.049 0.875 = 7 / 8 22.225 0.60 387 # 8 # 25 2.670 3.982 1.000 25.4 0.79 509 # 9 # 29 3.400 5.071 1.128 28.65 1.00 845 # 10 # 32 4.303 6.418 1.270 32.26 1.27 819 # 11 # 36 5.313 7.924 1.410 35.81 1.56 1006 # 14 # 43 7.650 11.41 1.693 43 2.25 1452 # 18 # 47 13.60 20.257 2.257 57.3 4.00 2581 # 18J 14.60 21.775 2337 59.4 4.29 2679
Canadian reinforcing bar size
Metric bar size
Mass per unit length ( kg / m )
Nominal diameter ( mm )
Cross-sectional area ( mm 2 )
10 M 0.785 11.3 100 15 M 1.570 16.0 200 20 M 2.355 19.5 300 25 M 3.925 25.2 500 30 M 5.495 29.9 700 35 M 7.850 35.7 1000 45 M 11.775 43.7 1500 55 M 19.625 56.4 2500
Figure 42 — North American reinforcing bars .
15 ) American Concrete Institute , “ Building Code Requirements for Structural Concrete ( ACI 318-19 ) and Commentary ,” Farmington Hills , MI , 2011 [ 2 ].
23 November 2022