Kathmandu University, Dhulikhel, Kavre

Ground motion characterization and seismic performance

evaluation of powerhouse: A case study
Nilgiri II Khola Hydropower project
Pre final Thesis Defense for the Degree of ME in Structural Engineering
Presented By:
Suraj Kisi (Regd No.: 026625-19)
Supervisor:
Dr. Prachand Man Pradhan
Associate Professor
Dept of Civil Engineering, KU
Dean, School of Engineering
Manmohan Technical University

Department of Civil Engineering

Contents
1. Introduction
2. Objectives
3. Scope and limitations
4. Literature review
5. Methodology
6. Result and Discussion
7. Conclusion
8. Recommendations

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1. Introduction
• Case study of Nilgiri II khola hydropower
powerhouse structure has been
considered.
• The powerhouse has installed capacity of
70 MW.
• Run off river project and is located in
Myagdi district.

Figure 1: Project Location of Nilgiri II cascade

project (Source: Nilgiri HPP, E.I.A.)

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1. Introduction contd.
• Natural calamities mainly earthquake has been major challenge for the
development of infrastructure.
• 115 MW out of the total installed capacity of 787 MW in the country
(on-grid and off-grid) were severely damaged, and 60 MW combined
capacity were partially damaged (Shrestha et al., 2016).
• In this thesis, seismic hazard analysis (SHA) is carried out for the
specific site hydropower powerhouse site.
• Seismic performance evaluation is carried out.

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2. Objectives
 To determine the PGA value for Nilgiri II khola powerhouse, and
develop response spectra site specific.

 To evaluate response behavior of powerhouse structure using site

specific response spectra.

 To compare the results (base shear and displacement) from site

specific response spectrum analysis with that from NBC 105: 2020
and IS 1893:2016 using FEM software (SAP 2000 V21).
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3. Scope and Limitations
Scope Limitations
• Various geological and Seismological • Fault seismicity and its recurrence
data from different available literature parameters data were limited and not
considering seismic source up to considered.
300km within site. • Machine foundation is not considered in
• MATLAB computer programing the analysis and design of structure is
software is used. not done.
• SAP2000 V20.2 finite element • The effects of temperature, creep,
software is used for the analysis shrinkage, fatigue and soil structure
purpose. interaction is not considered in this
work

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4. Literature review
Table 1: Literature review and results
Study Conducted by Result
Pradhan et al., 2020 PHA ranged from 0.09g to 0.5g

Moklesur Rahman & Bai, 2018 PHA ranged from 0.21g to 0.64g
0.21-0.62g for 10% probability of
Thapa & Wang, 2013
exceedance in 50 years
500 gals near Kathmandu, 400 gals in
Parajuli et al., 2010 western part and 300 gals in remaining
part of country

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4. Literature review contd.
• Study conducted were basically from incomplete catalog of
earthquake data.
• New method from Monte-carlo simulations showed that method of
moments (MM) and Maximum likelihood (ML) were effective.
• For complete catalog MM and ML method takes the form of classic
Aki and Utsu (1965) solutions for b value.
• Probabilistic seismic hazard analysis (PSHA) for the development of
Seismic hazard curve was done in this study.

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 Literature Review

5. Methodology Selection of Case Studies

Geological data
Seismic data
Data Collection Structure location

Numerical Modelling Developing Seismic

Hazard curve

Response Spectra, NBC 105: 2020, IS 1893:2016

Site Specific value Response Spectra Response Spectra

Seismic performance evaluation

Result and Discussion

Conclusion and Recommendation

End

Figure 2: Flow Chart of Methodology

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5. Methodology contd.
Steps for development of Seismic Hazard Curve:
• Data collection and processing (National Seismological Center (NSC),
• Earthquake declustering
• Seismic source zones
• Seismicity parameters
• Attenuation relationship
• Probability distribution for source to site distance
• Probability distribution for magnitude
• Seismic hazard curve

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5. Methodology contd.
Steps for Seismic performance evaluation:
• Development of response spectrum using Two-point method as described in FEMA
273 guidelines.
 Result of PGA obtained using hazard curve of different period of ground motion
were used.
 The response spectra was developed for 5% damping with design earthquake
(return period 475 years).
• NBC 105:2020 and IS 1893:2016 response spectra are predefined from codal
provision and were used as input.
• FEM modelling developed using the civil drawing and loading conditions and
combination as per codal provision.
• Analysis result were compared for base shear and top storey displacements using FEA
software SAP 2000 V21.
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5. Methodology contd.

Figure 3: Plan view of powerhouse in FE Figure 4: Longitudinal view of powerhouse in

modelling FE modelling

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5. Methodology contd.

Figure 5: Transverse view of powerhouse in Figure 6: 3D view of powerhouse in FE

FE modelling modelling

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6. Result and Discussion
• Seismic Hazard curve

Figure 7: Seismic hazard curve at Powerhouse site (from all sources combined)
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6. Result and Discussion contd.
Table 2 : PHA values in different Table 3: Comparison of PGA value with different
hazard level earthquakes literature

PHA (g) Literature PGA value in g

Return
Thapa & Wang, 2013 0.425 - 0.475
Period (Tr) ML MM
Moklesur Rahman & Bai, 2018 0.38 - 0.47
years Method Method
Pradhan et al., 2020 0.41
75  0.14  0.13 NBC 105:2020 0.34
475  0.42   0.40 IS 1893:2016 0.36
1000  0.60  0.57 ML method 0.42
MM method 0.40

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 6. Result and Discussion contd.
SA_0 SA_0.075 SA_0.1 SA_0.2 SA_0.3 SA_0.4 SA_0.5
SA_0.75 SA_1 SA_1.5 SA_2 SA_3 DBE
1.00E+00
MEAN ANNUAL RATE OF EXCEEdaNCE

1.00E-02 DE

1.00E-04

1.00E-06

1.00E-08

1.00E-10

0 0.5 1 1.5 2 2.5 3

1.00E-12

spectral acceleration, sa(G)

Figure 8: Seismic hazard curve at Powerhouse site for different period of ground motion
(from all sources combined) using ML method
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 6. Result and Discussion contd.
SA_0 SA_0.075 SA_0.1 SA_0.2 SA_0.3 SA_0.4
SA_0.5 SA_0.75 SA_1 SA_1.5 SA_2 SA_3
DBE
1.00E+00
Mean annual rate of exceedence

1.00E-02 DE

1.00E-04

1.00E-06

1.00E-08

1.00E-10

0 0.5 1 1.5 2 2.5 3

1.00E-12
spectral acceleration, sa(G)

Figure 9: Seismic hazard curve at Powerhouse site for different period of ground motion
(from all sources combined) using MM method
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6. Result and Discussion contd.
2.75

2.50

2.25
ML_method_Two_point_Metho
d
Spectral Acceleration (Sa/g)

2.00
MM_method_Two_point_Meth
1.75 od
1.50
IS 1893:2016
1.25
NBC 105:2020
1.00

0.75

0.50

0.25

0.00
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3
Time Period (Sec)

Figure 10: Comparison of Response Spectrum for 5% damping

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6. Result and Discussion contd.
Table 4: Base Shear comparison table
Model 1 Model 2 Model 3 Model 4
Input Parameters
(ML with 2 point) (MM with 2 point) (NBC 105:2020) (IS 1893:2016)
Seismic Zone Factor (Z) 0.42 0.4 0.34 0.36
Importance factor (I) 1.5 1.5 1.5 1.5
Soil Type I I I I
Ductility Factor (Rμ) 4 4 4 5
Over-strength factor (Ωu) 1.5 1.5 1.5
Time period (sec) (X-dir) 0.190 0.226 0.221 0.343
Time period (sec) (Y-dir) 0.350 0.414 0.405 0.476
Spectral acceleration (Sa/g) (X-dir) 2.200 2.300 2.500 2.500
Spectral acceleration (Sa/g) (Y-dir) 1.200 1.250 2.500 2.200
Design Seismic Horizontal Coefficient (Ah) X-dir 0.231 0.230 0.213 0.135
Design Seismic Horizontal Coefficient (Ah) Y-dir 0.126 0.125 0.213 0.119
Seismic Weight Used (kN) 19742.001 19742.001 19742.001 19185.016
Base Shear (kN) in X-dir 4560.40 4540.66 4195.18 2589.977
Base Shear (kN) in Y-dir 2487.49 2467.75 4195.18 2279.18
% increase w. r. t NBC 105:2020(X direction) 8.71 8.24 -  -38.26
% increase w. r. t NBC 105:2020(Y direction) -40.71 -41.18 -  -45.67

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6. Result and Discussion contd.
Base shear
6000.00 X- Direction
Y- Direction
5000.00 4560.40 4540.66
4195.18 4195.18
Base Shear (kN)

4000.00

3000.00 2589.98
2487.49 2467.75 2279.18
2000.00

1000.00

0.00
Model 1 Model 2 Model 3 Model 4
(ML with 2 point) (MM with 2 point) (NBC 105:2020) (IS 1893:2016)

Models

Figure 11: Comparative chart showing base shear in different models

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6. Result and Discussion contd.
ML_Two_point_method_RS X-dir ML_Two_point_method_RS Y-dir

3 475.876 3 274.911

Storey
Storey

2 1517.926 2 446.578

1 4560.357 1 2487.516

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 500 1000 1500 2000 2500 3000
Storey Shear (kN) Storey Shear (kN)

MM_Two_point _method_RS X-dir MM_Two_point_method_RS Y-dir

3 561.678 3 292.15
Storey

2 1816.473

Storey
2 546.119

1 4540.675 1 2467.745

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 500 1000 1500 2000 2500 3000
Storey Shear (kN) Storey Shear (kN)

Figure 12: Comparative chart showing storey shear force distribution in different models
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6. Result and Discussion contd.
NBC 105:2020 RS X-dir NBC 105:2020 RS Y-dir

3 668.357 3 787.86

2 2190.301 2 2078.36
Storey

Storey
1 4195.174 1 4195.174

0 500 1000 1500 2000 2500 3000 3500 4000 4500 0 500 1000 1500 2000 2500 3000 3500 4000 4500
Storey Shear (kN) Storey Shear (kN)

IS 1893:2016 RS X-dir IS 1893:2016 RS Y-dir

3 357.381 3 332.298
Storey

2 1337.181

Storey
2 1019.619

1 2589.974 1 2176.452

0 500 1000 1500 2000 2500 3000 0 500 1000 1500 2000 2500
Storey Shear (kN) Storey Shear (kN)

Figure 13: Comparative chart showing storey shear force distribution in different models
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 6. Result and Discussion contd.
3 3
Rsy IS
RSx IS 1893:2016
1893:2016
2 2 RSy NBC
RSx 105:2020
NBC105:2020
Storey

Storey
RSy
RSx ML ML_Two_po
Two_point int
1 1
RSx
MM_Two_poi RSy
nt MM_Two_p
oint
0 0
0 1 2 3 4 5 6 7 8 0 2 4 6 8 10 12 14 16 18 20 22 24 26
Displacement (mm) Displacement (mm)

Figure 14: Deformation in X-direction using Response spectrum Figure 15: Deformation in Y-direction using Response
for different models spectrum for different models

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6. Result and Discussion contd.
Table 5: Top storey displacement using Response spectrum method

Top Storey Displacement (mm) % Variation

Model 1 X direction 4.40 -30.37

  Y direction 5.34 -77.33
Model 2 X direction 5.26 -16.63
  Y direction 6.47 -72.52
Model 3 X direction 6.37  
  Y direction 24.22  
Model 4 X direction 3.86 -38.81
  Y direction 11.62 -50.67
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 6. Result and Discussion contd.
3 3

RSx IS RSy IS
1893:2016 1893:2016
2 2
RSx NBC RSy NBC
105:2020 105:2020
Storey

Storey
RSx RSy
ML_Two_poi ML_Two_poi
1 nt 1 nt
RSx RSy
MM_Two_poi MM_Two_poi
nt nt

0 0
0 0.0002 0.0004 0.0006 0.0008 0 0.0005 0.001 0.0015 0.002 0.0025
Drift Drift

Figure 16: Inter-storey drift in X-direction using Figure 17: Inter-storey drift in Y-direction using
Response spectrum for different models Response spectrum for different models

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7. Conclusion
• PSHA was carried out for Nilgiri II Khola HPP powerhouse using
MATLAB programming for the development of final seismic hazard curve.
• Different hazard level were accessed and for design earthquake (475 years
return period) were compared.
• ML method gave highest PGA for DE with value of 0.42g and MM method
slightly lower with 0.4g.
• Two-point method was used as per FEMA 273 guidelines and site specific
data to develop site specific response spectra.

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7. Conclusion contd.
• Comparison of base shear showed highest base shear value of 4560.40 kN
for ML method in X direction and NBC 105:2020 showed 4195.18 kN base
shear in Y direction.
• Top storey displacement of NBC 105:2020 to provide maximum
displacement of 6.37mm and 24.22mm in X and Y direction respectively.
• Inter-storey drift also illustrated the similar result of drift with NBC
105:2020 value as maximum value and is within permissible limit.
• Higher deflection in structure undergoes higher tensile stress and thus to
accommodate that more reinforcement is required.

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8. Recommendation
• Current study was conducted based on many assumptions and simplified in
many aspects.
• Crane load and machine loads in machine floor actual data from
electromechanical vendor could be used for actual interpretation of loads.
• For the powerhouse of this scale the machine foundation can also be
incorporated for the analysis through solid modelling.
• Non-linear analysis can be performed for the performance based design as
well.

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 Thank you!

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