Civil Engineering Reference
In-Depth Information
(
)(
)
Max shear
:
V
max
=
0 6
.
wl
=
0 6 11 6
.
.
klf
10 77
.
ft
(
)
=
75 0
.
kip
101 7 kN
.
(
)(
)
Max reaction at girder
:
R
max
=
1 1
.
wl
=
1 1 11 6
.
.
klf
10 77
.
ft
(
)
=
137 4
.
kip
186 3
.
kN
16.3 ModelIng of IaBs
When an IAB is analyzed, 2D and 3D models using the finite element method
(FEM) can be built. Three types of soil modeling are used: (1) equivalent
cantilever finite element model, (2) soil spring finite element model, and (3) soil
continuum finite element model.
16.3.1 equivalent cantilever finite element model
For piles used in the IAB design, there are two pile design alternatives,
(1) conventional elastic design approach and (2) inelastic design approach,
which address the following three AASHTO specification design criteria
(Greimann 1989):
1. Capacity of the pile as structural member (Case A)
2. Capacity of the pile to transfer the load to the ground (Case B)
3. Capacity of the ground to support the load (Case C)
In Case A, a pile embedded in soil can be analytically modeled as an equiva-
lent beam-column structural member without transverse loads between the
member ends and with a base fixed at a specific soil depth. There can be
either a fixed or pinned head based on the rotational restraint at the pile head.
Figure 16.7 shows an idealized fixed-headed pile for both (a) an actual system
and (b) the corresponding equivalent cantilever system. The total length
l
of
the equivalent cantilever equals the sum of the length
l
u
above the ground
and the length
l
e
from the soil surface to the fixed base of the equivalent
cantilever. The pile length,
l
e
, that defined whether the pile behaves as a rigid
or flexible pile is given as (Greimann 1989)
EI
k
l
=
4
4
(16.2)
e
h
where:
E
,
I
is the modulus of elastic and moment of inertia with respect to the
plane of bending of the pile
k
h
is the horizontal stiffness of the soil
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