fb multipier v.4 single pile · pdf filesanglerat (silty clay) sowers (high pi) 12 next, we...
TRANSCRIPT
FB Multipier v.4
Single Pile Example
Professor’s Driven Pile Institute
Utah State University – June 26, 2013
J. Brian Anderson ([email protected])
Department of Civil Engineering Auburn University
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Deep Foundations – FB-MultiPier
Example 1a: Single Pile Axial Load
40 ft
Soil:
N = 15
= 32o
k = 100 pci
= 120 pcf
G = 7.5 ksi
= 0.33
f = 570 psf (from SPT97)
Qtip = 384 kips (from SPT 97
Pile:
Standard FDOT
24” Prestressed
Square Section
Default properties
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Start “FB-MultiPier” by selecting the
shortcut on your desktop, or find “BSI >
FB –MultiPier> FB – MultiPier” under
the Start Menu.
Select File>New from the menu at the
top to create a new file.
Fill in the appropriate project
information. Select, for this case,
choose Structure Type “Single Pile”
Finally set Units to “English (mixed
units)”. Click OK to continue.
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The editor windows will now appear.
The top left window is the Model Data
window where most info is entered. The
top right window is the Pile Edit window
shows the pile group in plan. The
bottom left window is the Soil Edit
window where the soil stratigraphy is
shown. A 3-D view of the pile group is
shown in the bottom right pane.
A default problem is automatically
loaded which you will need to change
Select “Pile” on the menu along the left
side of the Model Data pane.
Choose “Edit” under Cross Section Type
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Under “Database Section Selection,”
click on “Retrieve Section” and selection
Rectangular > 24” Square FDOT
Standard prestressed
Change the length of the pile to 40 ft.
Click OK to continue.
Select “Soil” from the Model Data pane.
Note that the “Soil Layer” drop down
box contains the layers shown in the Soil
Edit pane below.
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Since we will be using a single soil layer
for this example, select layer 2 then hit
the delete button to remove the layer.
Set the Soil Type, for Layer 1, to
“cohesionless.” Enter Total Unit Weight
equal to 110 pcf. Enter a friction angle
of 32o. Set the top of the layer at 0ft and
the bottom at –60ft (for proper
embedment). Since there is no water
table in this problem, use water table
depth of –100ft.
Under Soil Layer Models, use the drop
down box by “Lateral” to choose the
lateral soil type, in this case, Sand
(O’Neill).
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Click “Edit.” The unit weight and
friction angle will be copied from
before. Enter the value for subgrade
modulus, 100 pci. Click “OK” to
continue.
Under Soil Layer Models, use the drop
down box by “Axial” to choose the axial
soil type, in this case, Driven Pile.
Click “Edit.” The unit weight and
friction angle will be copied from
before. Enter the value for shear
modulus, 7.5ksi, Poisson’s Ratio, 0.3,
Vertical Failure Shear, 570psf. Click
“OK” to continue.
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Under Soil Layer Models, use the drop
down box by “Tip” to choose the end
bearing type, in this case, Driven Pile.
Click “Edit.” Enter the value for shear
modulus, 7.5ksi, Poisson’s Ratio, 0.3,
Axial Bearing Failure, 384kips. Click
“OK” to continue.
Soil properties can also be input in table
form. Click on the table button to bring
up the soil properties table.
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Soil Properties Input Table
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Lateral Properties for Sand:
Friction Angle,
Ne *0147.0*6034.27881.53
(Peck, Hanson, Thornburn, 1974)
(Gibbs and Holtz, 1967)
(Robertson and Campanella 1983)
Subgrade Modulus, rK
(Meyer and Reese, 1979)
(Terzaghi, 1955)
(Reese and Wang, 1993)
Lateral Properties for Clay:
Undrained Shear Strength, Su
VOUKC SNq
where: qc is cone tip resistance,
Nk is a factor ~17,
Su is undrained shear
strength,
and vo is the total
overburden stress. qc, Su
and vo are all in identical
units.
0
50
100
150
200
250
300
0 20 40 60 80 100
Dr (%)
k (
lb
/ i
nc
h 3
)
V ER Y
LOOS ELOOS E
M ED IU M
D EN S E
V ER YD EN S E
D EN S E
S A N D B ELOW
THE WA TER
TA B LE
S A N D A B OV E
THE WA TER
TA B LE
Relative Density of Sand
Parameters Loose Medium Dense
Blows/ft, N 4 to 10 10 to 30 30 to 50
, degrees 30 34 39
Dry or moist sand k lb/in3
8.1 24.3 64.8
Submerged sand k lb/in3
4.6 16.2 39.4
Relative Density of Sand
Loose Medium Dense
Dry or moist sand k lb/in3
25 90 225
Submerged sand k lb/in3
20 60 125
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Lateral Properties for Clay:
Undrained Shear Strength, Su
(EPRI Manual, 1990)
Subgrade Modulus, k
(Reese and Wang, 1993)
Strain at 50 % of the Failure Stress in
an Unconfined Compression Test, 50
(Reese and Wang, 1993)
(Reese and Wang, 1993)
Axial Properties for Sand and Clay
Unit Skin Friction, f
Plastic Clay: 6.4006
110**0.2)(
NNtsff
Clay-Silt-Sand:3.4583
110**0.2)(
NNtsff
Clean Sand: Ntsff *019.0)(
Limestone: Ntsff *01.0)(
(SPT97 Users Guide)
Shear Modulus, G
Sand/Sand with Fines
G(psi)= 500N [N<40]
G(psi) = 20000 [N>40]
Silt G(psi) = 500N [N<10]
G(psi) = 5000+175(N-10) [N>10]
Clay G(psi) = 500N [N<10]
G(psi) = 5000+100(N-10) [N>10]
(PLAID)
Ultimate Tip Resistance, QTIP
Plastic Clay: Ntsfq *73.0)(
Clay-Silt-Sand: Ntsfq *6.1)(
Clean Sand: Ntsfq *2.3)(
Limestone: Ntsfq *6.3)(
(SPT97 Users Guide)
0
5
10
15
20
25
0.0 0.5 1.0 1.5 2.0
Su / Pa
SP
T N
Va
lue
Sowers (low PI)
Terzaghi & Peck, Sanglerat (sandy clay)
Sowers (medium PI)
U.S.B.R (Houston clay-Trend line)
Schmertmann (Chicago clay)
Sanglerat (silty clay)
Sowers (high PI)
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Next, we need to specify the loads on the
pile. Now, choose “Load” menu in the
model data window. Two default load
cases will be displayed.
Highlight “Load Case 2”, then click in
“Del” to delete it.
For this case, we will edit load case 1.
Click on “Node 1” under “Node
Applied.” Node 1 in this case is the top
of the pile. Make sure that the only load
listed is 310k in the Z direction.
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Alternately, you can edit load cases using the load table
You should see an arrow representing
this load in the “3dView” box.
This concludes the data input.
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Use the “save as..” command to save
your problem before the analysis.
The next step will be to perform the
analysis. Click on the lightning bolt icon
to run the analysis. You will get a
warning that you will force a file save,
accept and continue.
The iterative process of FB-MultiPier
will be shown while the analysis
progresses.
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Once the analysis is complete, click on
the 3D Results icon to see a graphical
depiction if the analysis.
In the tool bar area, you can select the
load case to view, in this problem there
is only load case 1. In the 3D Display
Control pane, you can select which node
to display displacements or rotations, as
well as the nodal coordinates. A 3
Dimensional representation of the results
is shown in the 3D View pane. The
deflection of node 1 (top of the pile
should be approximately 0.5 inches)
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Example 1b: Single Pile Lateral Load
Use same input as for axial loading presented above:
In the Model Data window, select
“Analysis” from the menu, click “user
defined” Phi ( ) factor and set = 1.0.
This removes AASHTO phi factors from
moment interaction diagram. Only use
this for hand calculation verifications.
In the “Load” Tab: click node # 1 and
set Z = 0.0, and X = 30kips.
Lat = 30 k
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Click on the lightning bolt icon to run
the analysis. You will get a warning that
you will force a file save, accept and
continue.
Click “Pile Results” (icon next to
lightning bolt) and see results below:
a. X deflection = 0.176”, soil lateral
load = 13.7 kips
b. Max moment = 136 ft-kips and
Ratio = 0.172
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Moment details: Click “Pile Interaction” and “Biaxial moment” and “component selection”
a. Maximum moment for 24” x 24” PSC pile is 795.4 to 795.6 ft-kips
b. 33
3
3 333.16
2
12
)(
()( ft
b
b
bh
axisneutralfromdistC
inertiaofmomentIftS
c. kipsftconcreteksiftMomentstressyield
MomentS 152,11446333.1; 3
max
d. However, more correctly is moment interaction shown by FB-Pier, where due to
prestressing Mmax ≈ 654 ft-kips
e. Moving up and down the segment selection finds “element #4 giving highest moment
(see on moment interaction diagram) Demand Ratio = 0.208 (4b above) = 136 ft-kips /
654 ft-kips
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Example 1c: Single Pile - Lateral Pushover Analysis
Return to “Edit” icon and then select
“Load” from the Menu. Add Load Case
# 2 and set X = 5 kips.
Click “Pushover” tab. Pushover will
increment lateral load in 5kip increments
until “failure”, either soil or maximum
moment.
Results of Pushover show: Lateral load producing “failure” = 120 kips (18 x 5 kips = 90 kips + original
30 kips load case #1 = 135 kips) Deflection = 2.17”, Max moment = 648 ft-kips, Ratio = 648 / 654 =
0.99
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