ANCHOR BOLT DESIGN (Design of Anchor Reinforcement)
Project :
Pedestal Mark : P1
Structure : Pipe Rack (Route-1)
Seismic Type : Low Seismic Risk
1. Maximum Factored Loads
Condition
Pu (kN)
Tu (kN)
Vu (kN)
① Max Tension
-299.8
34.4
② Max Shear with C
-287.1
107.0
③ Max Shear with T
-287.1
107.0
where :
Pu = Compression Force
Vu = Shear Force
Tu = Tension Force
Condition / Assumptions :
1.
Low seismic risk and ductile design is not required
2.
Tension force is distributed equally among all anchors
3.
Washers are welded to the base plate to transfer the load to the anchor. Therefore, it
is assumed that all anchors will resist the shear forces.
4.
The tension and the shear forces in the anchors are transferred to the longitudinal
rebars and shear reinforcement, respectively, which will be designed as anchor
reinforcement. Therefore, the concrete breakout strength in tension and shear (D.5.2
and D.6.2) is not checked.
Note : All equations and code section numbers referred in this example are from ACI 318-11.
2. Pedestal Data
Cross Dimension of Pedestal :
b1 =
600 mm
b2 =
600 mm
H=
1600 mm
cct =
50 mm
ccs =
75 mm
Edge Distance :
c a1 =
250 mm
c a2 =
(cct)
Anchor Spacing :
s1 =
300 mm
s2 =
g
250 mm
300 mm
Anchor Bolt Data :
(ccs)
(H)
Mark : M25
Diameter, da = 25.0 mm
2
Tensile Area, Ase = 390 mm
3. Design Parameters
f'c =
28 Mpa , cylindrical strength of concrete
futa =
fy =
413 Mpa , Tensile Strength of Anchor Bolt
390 Mpa , Yield Strength of Anchor Reinforcement
2
No. of Anchors, na =
hef =
967 mm
4
460 mm
g=
110 mm
Bearing Area, Abrg =
4. Anchor Bolt Check (Strength of Anchor), D.5.1 & D.6.1
φT*Nsag = φT * na * Ase * futa (D-2)
Steel Strength of Group of Anchor in Tension :
= 483.2 kN
> 299.8 kN, OK!
φT =
0.75 Tension Reduction Factor
Ratio = 0.62
φV*Vsag = φV * na * 0.8 * 0.6 * Ase * futa
Steel Strength of Group of Anchor in Shear :
φV =
= 201.0 kN
> 107.0 kN, OK!
Ratio = 0.53
0.65 Shear Reduction Factor
Check for Combined Tension and Shear Forces, D.7
Check Interaction Ratio : (Tu / φT*Nsag) + (Vu / φV*Vsag) < 1.20
(D-42)
Case ①
299.8 kN
483.2 kN
+
34.4 kN
201.0 kN
=
0.79
<
1.20 , OK!
Case ③
287.1 kN
483.2 kN
+
107.0 kN
201.0 kN
=
1.13
<
1.20 , OK!
5. Check the pull out resistance of anchor in tension (D.5.3)
Pull out resistance in Tension of Group of Anchor : φp*Npn= φp * na 8 Ѱc,p * 8 * Abrg * f'c
Ѱc,p =
φp =
(D-29)
(D-14)
= 866.4 kN
> 299.8 kN, OK!
Ratio = 0.35
1.0 (D.5.3.6)
1.00 Pull Out Reduction Factor
6. Check the side-face blowout resistance of anchor in tension (D.5.4)
Because of symmetry, only one side-face blowout resistance on one face of the pedestal needs to be
considered.
Tu/4 = 74.9 kN
, factored tension force per one anchor bolt
Check if the corner effect (for the corner anchor) and close spacing (for the group of anchors) have to be
considered:
ca2 < 3*ca1 ---> consider corner effect
corner effect :
corner effect factor = (1 + ca2 / ca1) /4
= 0.50
, - where 1.0 < ca2/ca1 < 3.0
0.50
φsb*Nsb = φsb * [13 * ca1* (Abrg)
] * λa * f'c * [(1+ ca2/ca1) / 4]
= 187.2 kN
> 74.9 kN
Ratio = 0.40
λa =
φsb =
(D-16)
1.0 (D.5.3.6)
0.70 Side-face blowout Reduction Factor
close spacing effect : s1 < 6ca1---> Consider close spacing effect
close spacing factor = 1 + s1 / (6 * ca1)
= 1.20
φsb*Nsbg = φsb * Nsb * [1 + s1 / (6 * ca1)], for two anchors on one face of the pedestal
= 224.6 kN
> 149.9 kN
Ratio = 0.67
(D-17)
7. Transfer of Anchor Load to Vertical Re-bars
cct
To be considered effective, pedestal main rebar shall be placed at a minimum distance of 0.50*hef
from anchor bolt.
checking : 0.50*hef =
230 mm > g, rebar is effective!
Pedestal Main Rebar Data :
diameter, db = d16
2
Area of One Rebar, Ar = 201 mm
No. of Effective Bars, n =
16
cct =
g=
hef =
L3 =
Ld'
50
110
460
570
mm
mm
mm
mm
Ld'= hef - cct - 0.68g
= 335 mm
Note : L3 is the straight bar
development length in tension
per sec. 12.2. Refer to drawing
no. 1TA-NC-XCSV2-0002 (3/6).
φTr =
0.75 Tension Reduction Factor
Tension Capacity of Anchor Reinforcement, Tur = φTr * n * Ar * fy* (Ld' / L3),
Ld' / L3 < 1.0
= 553.2 kN
> 299.8 kN, OK!
Ratio = 0.54
8. Design of Shear Reinforcement
Shear Reinforcement Data :
diameter, dtie = d12
Area of One Rebar, Arv =
113
No. of Effective Layers, n1 =
2
No. of Effective Legs Per Layer, n2 =
2
Vu
(cct)
8*da
1.5
1.0
(H)
(ccs)
Note : Typical shear reinforcement
design for columns assumes that the
shear reinforcement can be fullydeveloped when closed ties are used.
Therefore, only closed ties are
assumed to be effective.
Shear Capacity of Anchor Reinforcement, Vur = φVr * n1 * n2 * Arv * fy
φVr =
0.75 Shear Reduction Factor
= 132.2 kN
> 107.0 kN, OK!
Ratio = 0.81