dynamic earth pressure -myths, realities and practical ways for design

7/23/2019 Dynamic Earth Pressure -Myths, Realities and Practical Ways for Design

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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




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



Introduction and Background




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




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


compaction stresses from Duncan's method (1991 and 1993)


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


surcharge, w

water water

Hydrostatic

Uplift, U

seismic increment

traction

(front and

back walls

K0g'HK0w

gwHw

H

Hw

Building inertia

Vertical

Seismic, V




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



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



Standard Practice for Partially or FullyBuried Liquid-containing Structures




Total Base Shear and Wall Pressures




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.




Sliding or wall rotation must occur for K < K0




Hydrodynamic Pressures (ACI 350)




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




Dynamic Soil Pressures ASCE 4-98(Wood 1973)




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




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




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


surcharge, w

water water

Hydrostatic

Uplift, U

seismic increment

traction

(front and

back walls

K0g'HK0w

gwHw

H

Hw

Building inertia

Vertical

Seismic, V



Experimental Results




Recent Experimental Studies (PEER 2007/06)

Stiff and flexible model structures configuration

Centrifuge model configuration

L. Atik and N. Sitar (2007)




Representative Experimental Results


M i t t l d i




Maximum total dynamic pressuredistributions measured and estimated




Detailed Seismic Fluid Soil StructureInteraction

Fl id St t I t ti




Fluid Structure Interaction




Seismic Soil Structure Interaction

(SASSI2010 Theory Manual)

Substructuring in the Flexible Volume Method Substructuring in the Substructure Subtraction Method




Case Study: Intake Pump Station




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




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.




Finite Element Model, Showing Critical Panels




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




Comparison of Acceleration TransferFunctions

EQz

EQy

EQx




SSI Model




Sample Results




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.




Design of Walls and Slabs




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.



Thank You!

dynamic earth pressure -myths, realities and practical ways for design

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