bhavana midterm ppt

7/23/2019 Bhavana Midterm Ppt

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Bhavana Valeti

11103011

Dept of Civil Engineering

Indian Institute of Technology Kanpur

Effects of Soil Structure Interaction on

Seismic Response of an Aqueduct


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Outline .

Introduction Literature Review Aqueduct Soil Structure Interaction

Motivation Modeling AqueductNumerical ModelStructural Model

Water Model Modal Analysis Future work

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Aqueduct: A water supply channel

Types

Inverted Syphonic

Open and elevated

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Trough Type Aqueduct

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Chen and Hao (2004): Proposed a suitableaqueduct model to accurately represent aqueduct

design, water structure interaction and effects of

bearing properties

Akogul and Celik(2008): Effect of elastomeric

bearings on stiffness of bridge systems

Previous Work

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Soil Structure Interaction

Fundamental Concepts Of Earthquake Engineering , Roberto Villaverdo

Fixed base

On soft soil

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Prevalent structural design assumes base to befixed at the foundation level

Structures flexible compared to foundation

small foundation displacementscan beneglected

Stiff structural systems compared to foundation

significant foundation displacementscannotbe ignored


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Foundation movements can introduceflexibilitytothe structure and may alter the frequency and mode

shapes of the system

Inelastic behavior of foundation can providevaluable energy dissipative capability to the system

upon mobilization of load capacity

As a result

Force demands to the structure may reduce- Benefit

Excessive settlement, rotation and total drift may occur-

Consequences


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Foundation Deformation Modes

Vertical mode

Sliding mode

Rocking mode

u(t)

s(t)

Initial position

of footing top

t

Vertical mode

Sliding mode

Rocking mode

u(t)

s(t)

Initial position

of footing top

Vertical mode

Sliding mode

Rocking mode

u(t)

s(t)

Initial position

of footing top

t

D

H

Inducedearthquake

motion

Super structure

Shallow

foundation L = length of footing

B = width of footing

H = thickness of footing

D = depth of embedment

f

f

Ground surface

DH

Inducedearthquake

motion

Super structure

Shallow





f

f

DH

Inducedearthquake

motion

Super structure

Shallow





f

f

Ground surface


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Current Design Provisions

ATC-40 (1996)

FEMA-356 (2000)

NEHRP (2000)

ASCE-7 (2005) }Increased period and

damping ratio to account

for SSI of shallow foundations

Winklers springs with

stiffness suggested by

Gazetas (1991)}


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Models for non-linear soil structure

interaction analysis (Gajan et al, 2010)

Beam-on-nonlinear-Winkler

foundation (BNWF)Contact Interface model(CIM)

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Aqueduct is an important lifeline system prediction of

whose seismic response is very important Introduction of SSI can reduce force demands in

structures rigid compared to the ground

Also estimation of critical depth of water (which

causes maximum demand) for design purpose

Motivation

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Forces due to

Dead load

Traffic load

Wind load Seismic loading

Water

HydrostaticHydrodynamic

Forces Acting On An Elevated Trough Type

Aqueduct

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SuperstructureDeck

Bearings

Water Substructure

Foundation

Modeling Aqueduct

Deck

BearingsPiers

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DeckLength: 188.5m

Number of spans: 13 (14.5m each)

Width: 31.5m

Number of channels:4(6.938m wide each)

Deck wall height:3.11m

Thickness of Deck wall:0.75m

Deck slab depth:0.6m

Aqueduct Dimensions

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Elastomeric bearing dimensions:0.8mx0.4mx0.112m

Dimensions of piers: 15mx34.5mx1.73m

Number of piers: 12

Aqueduct Dimensions

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Structural model:SAP2000

4 noded rectangular shell elements of concrete are used

for modeling deck and piers

Abutments are hinged in transverse direction and roller in

longitudinal direction with Elastomeric bearings

connecting to deck

Piers are connected to the deck through elastomeric

bearingsElastomeric bearings are reinforced

Piers are fixed at the bottom

Numerical model

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Numerical model

Abutment model in SAP 2000

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Elastomeric bearings:Link element

The link element is composed of uncoupled

Lateral( KH )

Vertical( KV )

Rotational( K

) stiffness components

Numerical model

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Lateral stiffness = 2709 kN/m

Vertical stiffness =1763608.5714 kN/m Akogul and Celik(2008)

Rotational stiffness =24598 kN-m/m

where, Geff= shear modulus of elastomeric bearing

A = Elastomer gross plan area

Hr = Total elastomer thickness

Ec = Elastic modulus of elastomer

H = Elastomeric bearing height

Numerical model

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Dynamic pressure of water on

Aqueduct wall

Impulsive Convective

Water modelingHousners model(1963)

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Impulsive pressure:Equivalent to static water mass attaching to the structure

vibrating in phase with the Aqueduct wall.

Equivalent impulsive mass:

Its equivalent height:

Where, l= half width of water channel

H= height of water

M= total mass of water

Connected by rigid link to aqueduct wall

Water modelingHousners model(1963)

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Convective pressure:

Due to water vibration inside the aqueduct

Equivalent convective mass:

Equivalent height:

M1 is connected to aqueduct wall by link of uniaxial

spring stiffness

g= acceleration due to gravity

Water modeling - Housner model(1963)

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Water modelingHousners model

L(m) H(m) M(kg) Ho (m) Mo (kg) H1 (m) M1 (kg) K1(kN/m)

3.469 2.36 16374 0.885 6352.5 1.0772 10041 35540(For 1 meter length of aqueduct)

Chen and Hao(2004)25


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SAP 2000 Model

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Modes corresponding to water appear initially

Time period of water mode:3.3297s (average) Time periods of the aqueduct:

Modal Analysis

Time period(s) Longitudinal Transverse

SAP model 1.432 1.143

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Longtudinal mode: 1.432s

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Transverse mode: 1.143s

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Literature Survey Detailed 3D modeling

Modal analysis and comparison with available data

Future work

Modeling the raft foundations for Soil-structure-interactioneffects

Performing nonlinear dynamic analysis to obtain seismicresponse under scenario earthquakes.

Estimate the critical depth of water for maximum seismic

response of the structure Performing seismic fragility analysis for various damage

scenarios.

Progress

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