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Dam Modelling with LUSAS

LUSAS Marketing Department

Overview of main dam types

• Arch – Concrete

• Buttress– Concrete or masonry

• Gravity– Concrete or masonry or both

• Embankment – Earth fill or rock fill

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Model with LUSAS?

Concrete dam analysis

KEY REQUIREMENTS• Staged construction analysis

– Birth and death (element activation / deactivation)• Heat of Hydration modelling• Creep

– CEB-FIB, Chinese creep code, General• Contact / rock interface modelling

– Slidelines, interface elements• Thermo-mechanical coupled analysis• Concrete cracking material model• Comprehensive results viewing facilities

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Results viewing / processing

KEY BENEFITS• Diagram, stress contour,

vector and discrete values• Load combinations• Results plotting on slice

sections through model• Graphing of nodal results• Animations of loadcases /

construction sequences

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LUSAS Concrete Material Model

• Is a Plastic-Damage-Contact Model constitutive model based on– Directional damage – Continuum plasticity– Rough contact theories

• Was developed at Cardiff University in collaboration with LUSAS..

• Underwent extensive validations using experimental test data

• Has now been implemented in LUSAS

LUSAS CMM 5

Key Features of the Concrete Model

Similar form to traditional non-orthogonal crack model … But

• Models cracking and crushing in the same model

• Fully coupled Planes of Damage

• Thermodynamically valid

• Includes shear contact (aggregate interlock and crack closure)

LUSAS CMM 6

Heat of Hydration modelling with LUSAS

• Cement types I, II, III and V can be modelled• Effects of fly ash and ground granulated blast furnace

slag can also be taken into account • Concrete properties that are appropriate for the time

when the greatest temperature differential occurs can be specified to assess any possibility of cracking

• User input of chemical composition for any cement type is possible.

• Results have been validated against data provided by Professor Schindler and also against a standalone heat of hydration program

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Example Projects

• Muela Dam, Lesotho– Concrete arch dam– Mott MacDonald and LUSAS

Consultancy Services• Seismic analysis of the Tannur

Dam, Jordan – Concrete gravity dam– LUSAS Consultancy Services

• Cine Dam, Turkey– Concrete gravity dam – Jacobs Engineering Group

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Muela Dam, Lesotho

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Research uses

• Use by one of the project partners on the EU-sponsored NW-IALAD project “Integrity Assessment of Large Concrete Dams”– CIGB/ICOLD (1999)

benchmark dam– (also used for work on

Koyna Dam, India)– (also used for work on

Schlegeis Dam, Austria

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CIGB/ICOLD (1999) benchmark

• Research on the CIGB/ICOLD (1999) benchmark

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CIGB/ICOLD (1999) benchmark (cont)

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Thermo-mechanical coupled testcase

• Simplistic QA example but proves the facility • Test cube of concrete modelled with HF8/HX8

elements. • Curing process is simulated and temperatures

due to the heat of hydration are transferred to the structural analysis.

• In the structural analysis the concrete cracking model is used and cracks can be observed when differential expansion is enough to cause principal stresses that lead to material failure.

• The external thermal boundary conditions were chosen to emphasize the heat gradient across the concrete block, and in the structural analysis the block is free to expand unrestrained.

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Test cube example

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Thermal / Structural results

• In the structural analysis the concrete cracking model is used and cracks can be observed when differential expansion is enough to cause principal stresses that lead to material failure

• External thermal boundary conditions were chosen to emphasize the heat gradient across the concrete block, and in the structural analysis the block is free to expand unrestrained

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Test Cube Animation

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Simplistic dam example

3 stages of construction:

Stage 1 Stage 2 Stage 3

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Heat of Hydration analysis

Section slice through the model showing maximum temperature differential at each casting stage

Stage 1 Stage 2 Stage 3

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Heat of Hydration analysis: Animation

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Semi-Coupled analysis with creep

Maximum surface stresses in dam for each casting stage

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Semi-Coupled analysis: Animation

Embankment dams

Coupled pore/fluid diffusion/stress analysis:

• Model partially saturated fluid flow through porous medium where the position of the phreatic surface (the boundary between fully saturated and partially saturated soil) is of interest.

• Include the influence of the pore fluid weight on the solid skeleton only (excess pore pressure solution) or on both the solid skeleton and fluid (total pore pressure solution)

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Coupled pore/fluid diffusion/stress analysis

• Use a default analytical capillary pressure relationship or define a piece-wise relationship in a tabular form...

• Specify different filling (or absorption) and draining (or exsorption) capillary (or pore water) pressure–effective saturation curves, as well as a scanning curve for transition between absorption and exsorption.

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Coupled pore/fluid diffusion/stress analysis

• In addition to prescribed head (pressure) and impervious (closed) boundary conditions, inflow/outflow over a boundary can be considered

• It is also possible to control the boundary condition automatically when a phreatic surface meets a boundary surface using lift-off supports

• The initial equilibrium state can be established via a geostatic analysis step

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Embankment Dams

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• Groundwater flow

Embankment Dams

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Embankment Dams

• Trapezoidal earth dam with drainage toe

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Selected LUSAS users

plus many more...

Dam details• Details of Schlegeis dam from Zenz, Aigner &

Perner (1999)• Double curvature concrete arch-gravity dam• Height 131m, Crest length 725m• Crest width 5m, • Maximum thickness 34m• Constructed 1969 to 1971. • Full storage level reached in 1973• Foundation material Granite-Gneiss rock

Schlegeis Dam, Austria

Loadcases

• Self weight• Hydrostatic • Uplift• Temperature

(excluded here)

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Modifications to Dams

Adding spillways and fish holes using boolean operations

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Analysis with Nonlinear Concrete and Rock

• New nonlinear material model applied to concrete and rock– Craft Plastic Damage contact model in LUSAS– Consistent formulation

• Fully bonded interface• Dead, hydrostatic and uplift loads (as per previous problem)• Solution using full Newton with arc-length procedure with

automatic step selection features in LUSAS• Load factored until load reduces or convergence not achieved

– This produce gives unreal hydro loading but does give indication of FOS

• Tighter tolerances than previous analyses 0.0001 for force and 0.000001 for displacement norm

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Results

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Minor principal stresses on u/s face

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Major principal strains u/s face

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Summary

• LUSAS provides you with advanced material models, analysis facilities and general modelling tools including:– Heat of Hydration modelling– Creep, – A state-of-the-art concrete cracking material model

• With LUSAS you can carry out stability assessment and new design of most/all (?) types of concrete and masonry arch, buttress and gravity dams