Alternative Support Systems for Cantilever - National Transportation ...

The maximum length for le is limited to 8da as delineated in ACI 318-08 D6.2.2. The
constant 7 from Equation 3-1 was determined from a 5% fractile with cracked concrete. The
constant 7 becomes a constant 13 for the mean breakout strength of a single anchor in uncracked
concrete loaded in shear perpendicular to the edge. The mean breakout strength is described in
Equation 3-2, as shown below (12).
( ) 5 . 1
0.
2 ⎛
e
V ⎜ ⎛ l ⎞
b = 13
⎜ ⎜
d ⎟
a ⎝ ⎝ ⎠
⎞
d ⎟
a λ
⎟
⎠
f ′ c ca1
(3-2)
ACI 318-08 (5) describes the nominal breakout strength of an anchor loaded in shear
perpendicular to the edge in Equation D-21 and is described below as Equation 3-3. Figure 3-4
depicts the projected concrete failure area of a single anchor in rectangular concrete. Figure 3-5
depicts the projected concrete failure area of a single anchor in cylindrical concrete. An
important distinction to note between the failure area of a single anchor in rectangular concrete
and cylindrical concrete is the edge distance ca1. Equation 3-4 details how to calculate the value
of ca1 for an anchor adjacent to a circular edge.
A
= ψ ψ ψ V
(3-3)
Vc
V c b
ed , V c,
V h,
V
AVco
Where
Vcb
AVc
AVco
ψed,V
ψc,,V
ψh,V
b
= The nominal concrete breakout strength in shear of a single anchor (lb.)
= The projected area of the failure surface for a single or group of anchors,
used to determine the shear strength (in 2 )
= The projected concrete failure area of a single anchor, for calculation of
strength in shear, if not limited by corner influences, spacing, or member
thickness (in. 2 )
= 4.5(ca1) 2 , based on an ≈35° failure cone (Figure 2-16)
= The factor used to modify shear strength of anchors for edge effects, ACI
318-08 Section D.6.2.6
= The factor used to modify shear strength of anchors based on presence or
absence of cracks in concrete and presence or absence of supplementary
reinforcement, ACI 318-08 Section D.6.2.7, accounted for in Equation 2-2
= The factor used to modify shear strength of anchors based on anchor location
and effective length of anchor, ACI 318-08 Section D.6.2.8
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