Civil Engineering Reference
In-Depth Information
the angle between the plane of the tension ties and the diagonal strut of 28.4°,
the principal strain e
1
can be determined using the following:
2
ε
=
0 002
0 691 10
ε
+
(
ε
+
.
)
cot
α
1
s
s
s
.
−
3
( .
0 691 10
−
3
0 002
.
)
cot
2
28
.
4
=
×
+
×
+
°
9 9 10
3
−
=
.
×
and the limiting compressive stress
f
cu
, the nominal resistance
P
n
, and then
the factored resistance
P
r
, in the strut are
′
f
3
0 8 170 9 90 10
c
f
=
=
=
1 21
.
ksi
≤
0 85 3
.
×
cu
−
3
0 8 170
.
+
ε
.
+
×
.
×
1
=
2 55
.
ksi (
17 58
.
MPa)
P
f A
1 21 161 6 195 5
.
.
.
kip (
869 63
.
kN)
=
=
×
=
n
cu
cs
P
P
0 7 195 5 137
.
.
kips (
609 4
.
kN)
=
φ
=
×
=
r
n
As this is less than the factored load in the strut of 305 kip (1356.7 kN), the
strut capacity is inadequate. To meet the strength requirement of the strut, the
depth of the footing would need to be increased by approximately 355.6 mm
(14″). This increase in depth would decrease the load in the strut and increase
the area of the strut due to the change in the geometry of the STM.
13.2.2.3
Check nodal zone stress limits
The CCC nodal zone at the column-cap interface has a stress of
9 145
42 42
×
f
c
=
=
0 74
.
ksi( Mpa)
5 1
.
×
This value is below the nodal stress limit for a CCC node of
φ
′
0 85
.
f
c
=
0 85 0 70 3 1 78
.
×
.
× =
.
ksi(
12 27
.
MPa)
The stress in the CTT nodal zone immediately above the piles is
145
14 14
f
c
=
=
0 74
.
ksi( MPa)
5 1
.
×
As the CTT nodal zones immediately above the piles have tension ties in at
least two directions, the nodal zone stress limit is
φ
′
0 65
.
f
c
=
0 65 0 70 3 1 36
.
×
.
× =
.
ksi(
9 38
.
Mpa)
>
0 74
.
ksi( MPa)
5 1
.
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