1 9 th – 11 th September th International Benchmark Workshop on Analysis of Dams Theme A: Seismic Safety Evaluation of Concrete Dam Based on Guidelines Seismic safety evaluation of an arch dam with Akantu FE code developed at EPFL M. Corrado (1), G. Anciaux (1), D. Scantamburlo (1), S. Laffely (1), M. Chambart (2), T. Menouillard (2), J-F Molinari (1) (1) LSMS (2)

2 9 th – 11 th September 2015 Outline  Introduction  Stucky  LSMS – EPFL and code AKANTU  Swiss guideline  Modeling  Hydrodynamic pressure  Damping  Results  Displacements  Stresses  Conclusion

3 9 th – 11 th September 2015 Stucky Ltd - Renens Switzerland Multidisciplinary competence:  Civil engineering  Mechanical engineering  electrical engineering  Project management  Geotechnics, rock mechanics  Hydrology  Applied hydraulics  Environmental studies  Economical and financial studies  Project development Ilisu Dam and HEPP - Turkey

4 9 th – 11 th September 2015 FE Modeling of dams and seismic safety evaluation

5 9 th – 11 th September 2015 Luzzone Dam  Luzzone: 225 m and 101 Mio m 3 According to the Swiss guidelines : Class I dam (h>60m)

6 9 th – 11 th September 2015 Class I dam seismic evaluation  Swiss guidelines requirements:  3D FE Model including foundation  Time-History analysis ( 3 accelerogramms, one for each direction)  Dynamics effect of the reservoir : Distributed mass (Westergaard approach - incompressible)  Linear elastic model with visco-damping  Stiffness increase in dynamics (without experimental data, consider Ed = 1.25 Es)  Construction phases and joint grouting to be considered  Soil-structure interaction to be carefully addressed  Model calibration based on static results

7 9 th – 11 th September 2015 LSMS - EPFL Computational Solid Mechanics Laboratory EPFL – ENAC – Civil Engineering Institute Head: Prof. J.F. Molinari Research Contact mechanics Damage and fracture mechanics Particles methods Multiscale methods Dynamic fragmentation of a brittle shell (colors represent processors) 3D Damage evolution in concrete (dark=hard inclusions; white=voids)

8 9 th – 11 th September 2015 Luzzone Dam  Luzzone: 225 m and 101 Mio m 3 According to the Swiss guidelines : Class I dam (h>60m)

9 9 th – 11 th September 2015 Class I dam seismic evaluation  Swiss guidelines requirements:  3D FE Model including foundation  Time-History analysis ( 3 accelerogramms, one for each direction)  Dynamics effect of the reservoir : Distributed mass (Westergaard approach - incompressible)  Linear elastic model with visco-damping  Stiffness increase in dynamics (without experimental data, consider Ed = 1.25 Es)  Construction phases and joint grouting to be considered  Soil-structure interaction to be carefully addressed  Model calibration based on static results

10 9 th – 11 th September 2015 General Finite-Element library Solid mechanics Structural mechanics Heat transfer Open Source C++ Object/Vector approach Python Interface Open-source : A stance against “black box” codes

11 9 th – 11 th September 2015 Fracture modeling (Cohesive elements/Damage modeling)

12 9 th – 11 th September 2015 Local Non-local

13 9 th – 11 th September 2015 Numerical Modeling with Akantu  Pre-processing : o GMSH (GNU – GPL licence) o  FE Library o Akantu (GNU LGPL Licence) o  Post-Processing o Paraview (BSD Licence) o o Python (MatPlotlib, Scipy) o o

14 9 th – 11 th September 2015 Numerical Modeling with Akantu  Question 1 - What are the actual analysis and pre/post- processing capabilities of AKANTU and how is the development from possible multiple-users/developers managed?  Akantu is a multi-purpose Finite-Element library  The newly added Python interface, simplifies pre/post- processing  Akantu has already a communauty of users and developpers  Sources can be gotten from a tarball or from an access to our GIT repository  Contributions are welcome

15 9 th – 11 th September 2015 Mesh & Materials properties  Mesh (foundation included) : 3100 quadratic elements and nodes  Concrete material properties (old and new concrete) PropertiesValues Density2.5 and 2.4 t/m 3 Static Young’s modulus20 and 18 GPa Dynamic Young’s modulus25 and 22.5 GPa Poisson ratio0.18 Coefficient of thermal expansion10 -5 /°C Static compressive strength38 and 32 MPa Dynamic compressive strength57 and 48 MPa Static tensile strength3 and 2.3 MPa Dynamic tensile strength4 and 3.5 MPa

16 9 th – 11 th September 2015 Loads  Self weight applied by stages (6) o No displacements due to self weight, but stresses remain)  Hydrostatic pressure o Dynamic effect introduced through added masses (Westergaard approach)  Silt pressure o No dynamic effect  Thermal gradients o Thermal transcient analysis over 3 years  Earthquake o 3 accelerogramms(x,y,z) applied to the foundation boundaries

17 9 th – 11 th September 2015 Modeling  Added masses:  Westergaard o Westargaard (1931) calculated the additional hydrodynamic pressures during a seismic event in the case of a rigid dam with a vertical face. o Chopra (1968) concluded that if the fundamental frequency of the dam (without water) is less that the half of the fundamental frequency of the reservoir, then the water may be treated as incompressible. f r =c w /(3.4 H)=1451/(3.4x210)=2.03 Hz > f 1 =1.98 Hz OFEN: ->Westergaard added mass modeling accepted.

18 9 th – 11 th September 2015 Remark: Westergaard  Westergaard theory deals with a rigid dam body and an incompressible fluid. Therefore the compressibility of the fluid and the flexibility of the dam introduces added damping (reservoir boundary absorption models). So adding mass is conservative for stability analysis. o [3] “The added mass approach neglecting water compressibility substantially overestimate the significance of hydrodynamic effect, which results in an increase of the stress response of the dam.” o [4] “Westergaard was found to be very conservative with results 15% greater than Chopra, while the fluid element results were within 6% of the Chopra results.” o [5]: Navigation lock walls (Housner, 1957): [1] Loads and Loading Conditions, EM , 1 Dec [2] Earthquake Hydrodynamic Pressure on Dams, C-H Zww and R Zee, Journal of Hydraulic Engineering, ASCE, p , November [3] A novel procedure for determination of hydrodynamic pressure along upstream face of dams due to Earthquake, I Gogoi and D Maity, 14 th World Conference on Earthquake Engineering, 2008, China. [4] Numerical Model Validation for Large Concrete Gravity Dams, F Scheulen et al., Collaborated Management of Integrated Watersheds. [5] Time history Dynamic Analysis of Concrete Hydraulic Structures, EM , US Army Corps of Engineers, 22 December 2002.

19 9 th – 11 th September 2015 Loads combinations

20 9 th – 11 th September 2015 Rayleigh damping & eigen modes Rayleigh Damping (5 %) First eigen modes

21 9 th – 11 th September 2015 First eigen modes Full reservoir

22 9 th – 11 th September 2015

23 9 th – 11 th September 2015 Results  Displacements Radial directionVertical direction

24 9 th – 11 th September 2015 Results  Stresses: Envelopes  Maximum principal stress on upstream and down faces  Minimum principal stress on upstream and down faces

25 9 th – 11 th September 2015 Results  Stresses: Static and envelopes Vertical stressHoop stressPrincipal stress Downstream face Upstream face

26 9 th – 11 th September 2015 Conclusions  Swiss guideline provides a clear and precise methodology for dam safety seismic evaluation.  Hypothesis done are on the safe side.  All numerical tools needed to lead a seismic evaluation following the swiss guideline are availabe in Akantu.  Further developments are in progress to improve modeling and deal with more critical cases TRY IT !

27 9 th – 11 th September 2015 Perspectives Soil-structure Cohesive elements Cohesive law Damage (non-)local damage law Pre/Post treatment GUI Application métier INTRINSIC EXTRINSIC