Table 3.2. Anchor Rod Concrete Pullout Strength, kips
Concrete Pullout Strength, ϕNp
Rod Diameter,
in.
Rod Area,
Ab, in.2
Bearing
Area, Abrg ,
in.2
s
0.307
0.689
11.6
15.4
19.3
w
0.442
0.906
15.2
20.3
25.4
d
0.601
1.22
20.5
27.3
34.1
1
0.785
1.50
25.2
33.6
42.0
18
0.994
1.81
30.4
40.5
50.7
14
1.23
2.24
37.7
50.2
62.8
12
1.77
3.13
52.6
70.1
1w
2.41
4.17
70.0
93.4
2
3.14
5.35
90.0
24
3.98
6.69
fc' = 3,000 psi
112
fc' = 4,000 psi
fc' = 5,000 psi
87.7
117
120
150
150
187
22
4.91
8.17
137
183
229
2w
5.94
9.80
165
220
274
3
7.07
11.4
191
254
318
34
8.30
13.3
223
297
372
32
9.62
15.3
257
343
429
3w
11.0
17.5
294
393
491
4
12.6
19.9
334
445
557
where
φ = 0.75 for an anchor governed by strength of a ductile steel element
Ab = nominal bolt area, in.2
Ats = tensile stress area, in.2
Futa= lesser of Fu, 1.9Fy and 125 ksi
Shown in Table 3.1 are the design and allowable strengths for
various anchor rods based on the 2005 AISC Specification.
3.2.2 Concrete Anchorage for Tensile Forces
It is presumed that ASCE 7 (ASCE, 2005) load factors are
employed in this Guide. The φ factors used herein correspond
to those in Appendix D4.4 and Section 9.3 of ACI 318-08.
Appendix D of ACI 318-08 (ACI, 2008) addresses the
anchoring to concrete of cast-in or post-installed expansion
or undercut anchors. The provisions include limit states for
Concrete Pullout, and Breakout Strength following the Concrete Capacity Design (CCD) Method.
Concrete Pullout Strength
ACI concrete pullout strength is based on the ACI 318-08,
Appendix D provisions (Section D5.3).
φNp = φψ4 Abrg 8f c '
where
φ = 0.70
ψ4 = 1.4 if the anchor is located in a region of a
concrete member where analysis indicates no
cracking at service levels, otherwise ψ4 = 1.0
f c' = specified compressive strength of concrete, psi
Abrg = net bearing area of the anchor rod head or nut,
in.2
Np = nominal pullout strength, in.
Shown in Table 3.2 are design pullout strengths for anchor
rods with heavy hex heads and nuts. The 40% increase in
strength for the no-cracking case has not been included
(ψ4 = 1.0). Notice that concrete pullout never controls for
anchor rods with Fy = 36 ksi, and concrete with f c' = 4 ksi.
For higher strength anchor rods, washer plates may be necessary to obtain the full strength of the anchors. The size of
the washers should be kept as small as possible to develop
the needed concrete strength. Unnecessarily large washers
can reduce the concrete resistance to pull out.
Hooked anchor rods can fail by straightening and pulling
out of the concrete. This failure is precipitated by a localized bearing failure of the concrete above the hook. A hook
20 / BASE PLATE AND ANCHOR ROD DESIGN / AISC DESIGN GUIDE 1, 2ND EDITION
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