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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Dynamic Earth pressure - Myths, Realitiesand Practical Ways for Design
Carlos Coronado and Javeed Munshi
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Presentation Outline
Introduction and Background
Standard Practice
Simplified Determination of Lateral Earth Pressures
Hydrodynamic Fluid Pressures
Review of Lateral Soil Pressure Theories
Recent Experimental Results
Detailed Seismic Fluid Soil Structure Interaction
Detailed fluid-structure interaction
Simplified fluid modeling
Seismic soil structure interaction
Case Study Intake Pump Station
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Introduction and Background
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Force Diagram of Subsurface Walls - StaticConditions
ground surface
groundwater
Applicable loads
at-rest earth pressure
surcharge stress from surface loading
compaction stresses from Duncan's method (1991 and 1993)
U = buoyancy due to water table
N = normal stress along basemat
N = W - U
STATIC
Building Weight, W
at-restat-rest
surchargesurcharge
compaction compaction
surcharge, w
water water Hydrostatic
Uplift, U
K0g'HK0w
gwHw
H
Hw
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Force Diagram of Subsurface Walls – SeismicWithout Movement
ground surface
groundwater
Base Friction = N , where N = W - U - V
+ Base adhesion
Applicable loads
at-rest earth pressure
surcharge stress from surface loading
compaction stresses from Duncan's method (1991 and 1993)
U = buoyancy due to water table
V = vertical seismic force
N = normal stress along basemat
base friction using interface coefficient, m
traction = friction along building sides = at-rest pressure x msides
msides = friction coefficient along sidewalls of structure
seismic increment = horizontal base forces from SASSI output include all driving forces,
composed of those from seismic, at-rest, and building inertia
Sliding check Compare SASSI basemat horizontal forces (Demand = D)
against basemat frictional/adhesional resistance (Capacity = C).
If FS = C/D 1.1, then building is stable against sliding
SEISMIC - NO MOVEMENT
Building Weight, W
at-restat-rest
surchargesurcharge
compaction compaction
surcharge, w
water water
Hydrostatic
Uplift, U
seismic increment
traction
(front and
back walls
K0g'HK0w
gwHw
H
Hw
Building inertia
Vertical
Seismic, V
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Force Diagram of Subsurface Walls – SeismicWith Movement
ground surface
groundwater
Base Friction = N ( reduced 25%)
where N = W - U - V
+ Base adhesion
Applicable loads
resisting earth pressure is dependent on amount of movement
surcharge stress from surface loading
U = buoyancy due to water table
V = vertical seismic force
N = normal stress along basematreduced base friction using interface coefficient, mred
reduced traction = friction along building sides = at-rest pressure x msides_red
msides_red = reduced friction coefficient along sidewalls of structure
seismic increment = horizontal base forces from SASSI output include all driving forces,
composed of those from seismic, at-rest, and building inertia
Sliding check Compare SASSI basemat horizontal driving forces (Demand = D)
against basemat friction/adhesion + side friction + passive resistance (Capacity = C)
using reduced resistance coefficients for frictional/adhesional components
If FS = C/D 1.1, then building is stable against further sliding
SEISMIC - WITH MOVEMENT
Building Weight, W
active
surcharge, w
Building inertia
K = at-rest
increasing to
passive with
movement
seismic
increment
Hydrostatic
Uplift, U
Kag'H
H
Hw
Kg'H
raction
(front and
back walls)
Vertical
Seismic, V
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Standard Practice for Partially or FullyBuried Liquid-containing Structures
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Total Base Shear and Wall Pressures
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Practical Earth Pressure Analysis
Select all potential critical interface combinations at the
base and sides of the structure on which to determine theminimum base frictional resistance.
Compare base and side frictional resistance to seismic at-rest demand. If C/D > 1.0, then use seismic at-rest
demand to design walls. If the C/D < FS, then sliding will occur. Then reduce base
and side friction coefficients by 25%. loading side of thestructure will be subject to the active earth pressure, theseismic lateral active earth pressure increment, and the
building inertia. Increase resisting load on the passiveside, until C/D ≥ 1.0.
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Sliding or wall rotation must occur for K < K0
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Hydrodynamic Pressures (ACI 350)
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Seismic Active and At-Rest Lateral EarthPressure
=2( )
cos cos2cos( + + ) 1 + sin + sin( )cos( + + ) ∗ cos( )
= tan− ℎ
1
P AE = 0.5gH2(K A+DK AE) p AD = DK AE·g·(H-z) p0D = 2DK AE·g·(H-z)
NCHRP 611
DK AE~0.75kh
D i S il P ASCE 4 98
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Dynamic Soil Pressures ASCE 4-98(Wood 1973)
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Soil Pressures Sample Calculation
EL 0’
EL -5’
EL -20’
= 320
= 120 pcf
Kh = 0.25
249 (498) psf
147 (294) psf
0 psf
0 psf
186 (300) psf
454 (732) psf 936 psf 1390 (1668) psf
249 (498) psf
333 (594) psf
0’
-5’
-20’
Static Earth Pressure Seismic Earth Pressure Hydrostatic Pressure Total Pressure
H = 20 ft.
q
= tan-1(0.25) = 14o
KAE = = 0.48
KA = 0.31
KAE = 0.48-0.31 = 0.17
KAE ~ 3/4·0.25 = 0.1875, use 0.17
moist = 120 pcf
sub = 120-62.4 = 57.6 pcf
K0S = 1-sin(32o) = 0.47, use K0S = 0.5
K0E = 2
KAE = 2·0.17 = 0.34
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Ground Water Considerations
if the backfill is well drained, seismic ground waterpressures need not be considered. In this case,only hydrostatic pressures are taken intoconsideration:
pW
= gWz
Whitman, RV (1990) suggests that the seismic groundwater thrust exceeds 35% of the hydrostatic thrust for
kh>0.3g.
I fl f W ll M t I t it f
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Influence of Wall Movement on Intensity ofEarth Pressures in Cohesionless Materials
ground surface
groundwater
Base Friction = N ( reduced 25%)
where N = W - U - V
+ Base adhesion
SEISMIC - WITH MOVEMENT
Building Weight, W
active
surcharge, w
Building inertia
K = at-rest
increasing to
passive with
movement
seismic
increment
Hydrostatic
Uplift, U
Kag'H
H
Hw
Kg'H
traction
(front and
back walls
Vertical
Seismic, V
ground surface
groundwater
Base Friction = N , where N = W - U - V
+ Base adhesion
SEISMIC - NO MOVEMENT
Building Weight, W
at-restat-rest
surchargesurcharge
compaction compaction
surcharge, w
water water
Hydrostatic
Uplift, U
seismic increment
traction
(front and
back walls
K0g'HK0w
gwHw
H
Hw
Building inertia
Vertical
Seismic, V
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Experimental Results
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Recent Experimental Studies (PEER 2007/06)
Stiff and flexible model structures configuration
Centrifuge model configuration
L. Atik and N. Sitar (2007)
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Representative Experimental Results
L. Atik and N. Sitar (2007)
M i t t l d i
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Maximum total dynamic pressuredistributions measured and estimated
L. Atik and N. Sitar (2007)
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Detailed Seismic Fluid Soil StructureInteraction
Fl id St t I t ti
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Fluid Structure Interaction
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Seismic Soil Structure Interaction
(SASSI2010 Theory Manual)
Substructuring in the Flexible Volume Method Substructuring in the Substructure Subtraction Method
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Case Study: Intake Pump Station
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Structure Geometry
EL. +0'-0" (MaximumOperating Level in Forebay)
EL. (-) 22'-6"
EL. + 26'-6"EL. + 11'-6"(Operating Deck)
EL. + 11'-6"
(Operating Deck)EL. + 10'-0" EL. + 10'-6"
EL. (-) 5'-6"
Circulating Water
Intake StructureForebay Structure
UHS Intake Structure
UHS ElectricalBuilding
EL. (-) 10'-0" EL. (-) 10'-0"EL. (-) 11'-0" EL. (-) 8'-0"
EL. + 3'-0" (GWT)
Pump house Enclosure
3'-0" 3'-0"
5'-0"
Baffle Wall
Slanting/
Skimmer Wall
Slanting/
Skimmer Wall
Baffle
Wall
5'-0"
2'-0"
Bar Screens
Y
X
2'-0"
ExpansionJoint
EL. + 20'-6"
Traveling Screen
Enclosure
Pump Room
Staircase
Enclosure
8 0 ' - 0 " ( c l e a r
d i m e n s i o n )
100'-0" (clear
dimension) 59'-0" 33'-0"
3 6 ' - 6 "
6 0 ' - 0 "
7 4 ' - 0 "
CWS Makeup WaterIntake Structure Forebay Structure UHS Makeup Water
Intake Structure
UHS Electrical
Building
CCNPP
Unit 3
NORTH 1 8 ' - 6 "
105'-11" (including
slab on grade portion)
26'-6"
Pump HouseEnclosure
ElectricalRoom Slab
Pump House EnclosureSlab on grade
X
Z
ExpansionJoint
7'-0"
60" dia.
Intake Pipe (TYP)
Debris BasinSlab
Debris BasinSlab
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Overall Analysis/Design Approach
The finite element model of the structures is developed
using GT STRUDL Version 29.1.
Lumped Mass is used to model the Hydrodynamic Load.
The SSI analysis is performed using Site-Specific InputGround Motion and three soil cases (UB, BE and LB).
The FE model used for the SSI analysis is modified toobtain the static response of the structure, using GTSTRUDL.
Only critical panels are designed. Microsoft Excel
Workbook is used to combine element forces andmoments from static and SSI analyses, for these criticalpanels.
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Finite Element Model, Showing Critical Panels
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Hydrodynamic loads
(a) Actual distribution (b) Idealized distribution
CCNPP Unit 3 NORTH
2 0 8 ,
1 4 5 4
2 0 8 ,
1 4 5 4
2 0 8 ,
1 4 5 4
2 0 8 ,
1 4 5 4
207, 1449
207, 1449
Equivalent weights of accelerating liquid
W i.ew
tanh 0.866
Lew
H L
0.866
Lew
H L
W L
Impulsive Weight Distributions
W iy.ew y( )
W i.ew
2
4 H L 6 hi.ew 6 H L 12 hi.ew y
H L
H L2
Height to centers of gravity EBP
hi.ew 0.5 0.09375
Lew
H L
H L
Lew
H L
1.333if
0.375( ) H L otherwise
Comparison of Acceleration Transfer
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Comparison of Acceleration TransferFunctions
EQz
EQy
EQx
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
SSI Model
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Sample Results
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Design of Walls and Slabs
a. Design for In-plane shear using full section cuts.
b. Design vertical and horizontal sections for out-of-planemoments and axial forces using a P-M interactionanalysis.
c. Conservatively add the reinforcement from steps a and b
d. Check out-of-plane shear for the whole wall, or wholesegments on either side of openings, based on averageshear.
e. Check for punching shear where required.
Forces and moments computed after combination of seismic
and static results are used for the design of each criticalpanel, using a Microsoft Excel Workbook, as outlined nextand described in detail later.
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Design of Walls and Slabs
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Dynamic Earth pressures - Myths, Realities and Practical Ways for Design : October 2012
Conclusions
Simplified and detailed approached for the dynamic
analysis of embedded liquid containing structureswhere presented. Conclusions and recommendationsare as follows:
Additional guidelines are required for the calculations
of dynamic earth pressures. In particular regardingthe use of active or at rest dynamic soil pressures.
Detailed soil structure interaction analyses canprovide additional inside regarding the behavior of
embedded liquid containing structures. However theyare only warranted for critical structures.