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NB 35047-2015**NB 35047-2015: PDF in English **

NB 35047-2015

NB

ENERGY INDUSTRY STANDARD OF

THE PEOPLE’S REPUBLIC OF CHINA

ICS 27.140

P 59

Registration number. J2042-2015

P NB 35047-2015

Replacing DL 5073-2000

Code for seismic design of

hydraulic structures of hydropower project

ISSUED ON. APRIL 02, 2015

IMPLEMENTED ON. SEPTEMBER 01, 2015

Issued by. National Energy Administration

Table of Contents

Foreword ... 4

1 General ... 9

2 Terms and symbols ... 11

2.1 Terms ... 11

2.2 Symbols ... 14

3 Basic requirements ... 16

4 Site, foundation and slope ... 19

4.1 Site ... 19

4.2 Foundation ... 21

4.3 Slope ... 22

5 General in earthquake action and seismic analysis ... 24

5.1 Seismic action components and its combination ... 24

5.2 Seismic action types ... 25

5.3 Design seismic acceleration and standard design response spectrum ... 25

5.4 Earthquake action and combination with other actions ... 26

5.5 Structural modeling and calculation method ... 27

5.6 Dynamic properties of concrete and foundation rock for hydraulic structures

... 29

5.7 Seismic design ultimate limit state with partial factors ... 30

5.8 Seismic calculation for subsidiary structure ... 31

5.9 Seismic earth pressure ... 32

6 Embankment dam ... 33

6.1 Seismic calculation ... 33

6.2 Seismic measure ... 36

7 Gravity dam ... 39

7.1 Seismic calculation ... 39

7.2 Seismic measure ... 43

8 Arch dam ... 44

8.1 Seismic calculation ... 44

8.2 Seismic measure ... 47

9 Sluice ... 49

9.1 Seismic calculation ... 49

9.2 Seismic measure ... 51

10 Underground hydraulic structure ... 53

10.1 Seismic calculation ... 53

10.2 Seismic measure ... 55

11 Intake tower ... 56

11.1 Seismic calculation ... 56

11.2 Seismic measure ... 61

12 Penstock of hydropower station and ground powerhouse ... 63

12.1 Penstock... 63

12.2 Ground powerhouse ... 64

13 Aqueduct ... 65

13.1 Seismic calculation ... 65

13.2 Seismic measure ... 66

14 Shiplift ... 67

14.1 Seismic calculation ... 67

14.2 Seismic measure ... 67

Appendix A Seismic stability calculation of embankment dam with quasi-static

method ... 69

Appendix B Calculation of aqueduct dynamic water pressure ... 72

Explanation of wording in the Code ... 76

List of normative standards ... 77

2 Terms and symbols

2.1 Terms

2.1.1 Seismic design

Special design for the engineering structure of the strong earthquake zone. It

generally includes two aspects. seismic calculation and seismic measure.

2.1.2 Basic intensity

Within the 50-year period, under general site conditions, it may encounter the

seismic intensity of which the exceeding probability P50 is 0.10. Generally, the

corresponding seismic intensity value is determined in accordance with the

Appendix [in GB 18306], in accordance with the seismic peak acceleration

value as indicated in GB 18306 for the site.

2.1.3 Design intensity

The seismic intensity determined as the basis for engineering fortification based

on the basic intensity.

2.1.4 Reservoir earthquake

Earthquakes associated with reservoir impoundment that generally occur within

10 km of the reservoir bank.

2.1.5 Maximum credible earthquake

Earthquakes with the greatest ground motion that may occur at sites which are

evaluated in accordance with the seismic geological conditions of the project

site.

2.1.6 Scenario earthquake

Among the potential sources that may generate peak acceleration of ground

motion at the site, the earthquake with the magnitude and epicentral distance

that is determined along the main fault location in accordance with the principle

of the maximum probability of occurrence.

2.1.7 Seismic ground motion

Geotechnical movement caused by earthquakes.

2.1.8 Seismic action

The dynamic action of ground motion on the structure.

time history.

2.1.18 Mode decomposition method

The method of firstly solving the seismic effect of the structure corresponding

to its various modes at each stage and then combining them into the structure

total seismic effect. The direct superimposing of the mode effects of each stage

obtained by time-history analytical method is called mode decomposition time-

history analytical method, whilst the combination of those obtained by reaction

spectrum is called mode decomposition reaction spectrum method.

2.1.19 Square root of the sum of the squares (SRSS) method

The mode combination method of taking the square root of the sum of squared

seismic effects of various modes as the total seismic action.

2.1.20 Complete quadratic combination (CQC) method

The mode combination method of taking the square of the seismic effect of

each mode and the square root of the sum of the coupling items of different

vibration modes as total seismic effect.

2.1.21 Seismic hydrodynamic pressure

The dynamic pressure exerted by the water body on the structure due to

seismic effect.

2.1.22 Seismic earth pressure

The dynamic pressure exerted by the soil on the structure caused by the

earthquake.

2.1.23 Quasi static method

The static analytical method of using the product of gravity action, the ratio of

design seismic acceleration to gravity acceleration, and the given dynamic

distribution factor as the designed seismic force.

2.1.24 Seismic effect reduction factor

A factor that is introduced to reduce the seismic effects due to the simplification

of the calculation method of the seismic effect.

2.1.25 Natural vibration period

The time required for the structure to complete a free vibration in accordance

with a certain mode. The natural vibration period corresponding to the first mode

is called the basic natural vibration period.

years is 0.10 for the hydraulic structures of categories other than

category A, but it shall also not be less than the corresponding

seismic horizontal acceleration divisional value in the divisional map.

3 For the hydraulic structures, of which the engineering seismic

fortification is category A, which requires specific site seismic safety

evaluation, in addition to performing seismic design based on the

design seismic peak acceleration, it shall make specific

demonstration for the safety margin of avoiding uncontrolled

drainage catastrophe of reservoir water when it is subject to the

maximum credible earthquake of the site, and propose the seismic

safety theme report it is based on, wherein. the horizontal peak

acceleration representative value of the “maximum credible

earthquake” shall be determined in accordance with the seismic

geological conditions of the site, using the deterministic method or

the result of the probability method of which the exceeding

probability P100 within 100 years is 0.01.

4 When the backwater structure is upgraded from grade 2 to grade 1 due to

dam height and seismic geological conditions, in addition to performing

seismic design based on the horizontal design seismic peak acceleration

of which the exceeding probability P50 within 50 years is 0.10, it shall also

be based on the horizontal design seismic peak acceleration of which the

exceeding probability P100 within 100 years is 0.05 to perform specific

demonstration for the safety margin of avoiding uncontrolled drainage

catastrophe of reservoir water.

5 In the special report on seismic safety, the site-related design response

spectrum should be determined in accordance with the scenario

earthquake corresponding to the horizontal design seismic peak

acceleration, and produce the manually simulated seismic acceleration

time-history based on this; for the strong nonlinearity analysis of the

structural seismic effect, it should study the influence of the non-stationary

frequency of ground motion; when the seismic fault is less than 30 km

from the site and the inclination angle is less than 70°, it should be

included in the influence of the hanging wall effect; when the distance from

the site is less than 10 km and the magnitude is greater than 7.0, it should

study the process that, in the near-field large earthquake, the seismogenic

fault acts as the surface source rupturing, to directly generate the random

seismic acceleration time-history of the site, and take-use the time-history

of which the asymptotic spectrum peak period is most approaching to the

basic period of the structure.

6 The short-term condition during the construction period can be exempted

from combining with the seismic action.

4.2 Foundation

4.2.1 The seismic design of the foundation of a hydraulic structure shall take

into account the type, load, hydraulic and operating conditions of the upper

structures, as well as the engineering geological and hydrogeological

conditions of the foundation and bank slope.

4.2.2 For foundations and bank slopes of dams, sluices, and other backwater

structures, it shall meet the requirements for no failure of strength instability

(including sand liquefaction, soft cohesive soil subsidence, etc.) and seepage

deformation under the seismic action of design intensity, to avoid harmful

deformation that affects the use of the structures.

4.2.3 The weak structural planes such as ruptures, fracture zones and interlayer

displacements in the foundations and bank slopes of hydraulic structures,

especially the gently inclined angled mud layers and rock layers that may be

muddy, shall be subject to demonstration that it does not cause instability or

unallowed deformation under the seismic action based on their occurrence and

burial depth, boundary conditions, seepage conditions, physical and

mechanical properties, and it shall take seismic measures if necessary.

4.2.4 The anti-seepage structure of the foundation and bank slope of the

hydraulic structure and its connection parts, as well as the drainage filtration

structure shall take effective measures to prevent harmful cracks or osmotic

damage during the earthquake.

4.2.5 For the uneven foundations with large changes in the horizontal direction

such as geotechnical properties and thicknesses, it shall take measures to

avoid large uneven settlement, slippage and concentrated leakage during

earthquakes, and take measures to improve the upper structure’s ability to

adapt to the uneven settlement of the foundation.

4.2.6 The determination of soil liquefaction category in the foundation shall be

carried out in accordance with the relevant provisions of GB 50287 Code for

hydropower engineering geological investigation.

4.2.7 For the liquefiable soil layer in the foundation, it can be based on the

project type and actual conditions to select the following seismic measures.

1 Excavate the liquefied soil layer and replace it with non-liquefied soil;

2 Artificial densification such as vibrating densification and strong blow

compaction;

3 Ballasting and drainage;

5 General in earthquake action and seismic analysis

5.1 Seismic action components and its combination

5.1.1 In general, hydraulic structures other than aqueducts may only consider

horizontal seismic action.

5.1.2 The following grade 1 and 2 hydraulic structures of which the design

intensity is VIII and IX. the backwater structures such as embankment dams

and gravity dams, long cantilever, large-span or towering hydraulic concrete

structures shall take into account the horizontal and vertical seismic action

simultaneously. The representative value of the vertical design seismic

acceleration can generally take 2/3 of the representative value of the horizontal

design seismic acceleration. For the near-site earthquake, it shall take the

representative value of the horizontal design seismic acceleration.

5.1.3 For special types of arch dams with severe asymmetry and void, as well

as the grade 1 and 2 double-curved arch dam of which the design intensity is

VIII and IX, it should perform specific study for its vertical seismic effect.

5.1.4 For horizontal seismic action, in general, in the seismic design of

embankment dams and concrete gravity dams, it may only take into account of

the horizontal seismic action along the river flowing direction. For the gravity

dam section on the steep slope of the two banks, it should take into account of

the horizontal seismic action perpendicular to the river flowing direction; for

important embankment dams, it should make special study for the horizontal

seismic action perpendicular to the river flowing direction.

5.1.5 For the concrete arch dam and sluice, it shall consider the horizontal

seismic action along the river flowing direction and that perpendicular to the

river flowing direction.

5.1.6 For the hydraulic concrete structure with the similar lateral stiffness along

the two main axial directions, such as the intake tower and the sluice top frame,

it shall consider the horizontal seismic action of the structure along the two main

axial directions.

5.1.7 When the mode decomposition method is used to simultaneously

calculate the seismic effects in mutually orthogonal directions, the total seismic

effect may take the square root value of the sum of the squares of the seismic

effects in mutually orthogonal directions.

6 Embankment dam

6.1 Seismic calculation

6.1.1 Seismic calculation shall include seismic stability calculation, permanent

deformation calculation, anti-seepage safety evaluation and liquefaction

determination, etc., the comprehensive evaluation of seismic safety is

performed combined with seismic measures.

6.1.2 For the seismic stability calculation of embankment dams, the quasi-static

method is generally used to calculate the seismic effects. When one of the

following conditions is met, the finite element method shall be used

simultaneously to perform the dynamic analysis for the seismic effect of the

dam body and the dam foundation, to judge comprehensively its seismic

stability.

1 Design intensity VII and dam height of 150 m or more;

2 Design intensity VIII, IX and dam height of 70 m or more;

3 When the thickness of the cover layer exceeds 40 m or there is a liquefiable

soil layer in the dam foundation.

6.1.3 When the quasi-static method is used to calculate the seismic effect and

the seismic stability calculation is carried out for the embankment dam, it should

be based on the slip-arc method based on the force between the strips to make

verification in accordance with clause 5.7.1 of this Code, the calculation formula

is as shown in Appendix A. For foundations with thin soft clay interlayers, as

well as thin inclined wall dams and thin core wall dams, it may use the slip

wedge method for calculation.

6.1.4 When the quasi-static method is used to calculate the seismic effect and

the seismic stability calculation is carried out for the embankment dam, the

dynamic distribution factor of the seismic inertia force of the particle i shall be

adopted in accordance with the provisions of Table 6.1.4. In the table, the αm is

taken as 3.0, 2.5, and 2.0 when the design intensity is VII, VIII, and IX.

6.1.5 When the embankment dam uses the quasi-static method to calculate the

seismic effect and the seismic stability calculation is carried out, for the grade

1 and 2 embankment dam, it should use the dynamic test to determine the

dynamic shear strength of the soil body. When the dynamic strength given by

the dynamic test is higher than the corresponding static strength, it shall take

the static strength value.

For non-liquefied soils such as cohesive soil and compact sand gravel, when

6.2 Seismic measure

6.2.1 For the construction of embankment dams in strong earthquake areas, it

should use the dam axis that is curved straight or upstream. It should not adopt

a dam axis that is curved downstream, folded or S-shaped.

6.2.2 When the design intensity is VIlI and IX, it should select the rockfill dam,

the anti-seepage body should not adopt the type of rigid core wall. When using

a homogeneous dam, it shall set an internal drainage system to lower the

immersion line.

6.2.3 The safety freeboard of embankment dams in strong earthquake areas

shall include earthquake surge height and earthquake subsidence, which can

be determined in accordance with the following principles.

1 In accordance with the design intensity and the water depth in front of the

dam, the earthquake surge height is taken as 0.5 m ~ 1.5 m.

2 When the design intensity is VII, VIII, IX, the safety freeboard shall take

into account of the seismic subsidence of the dam and foundation.

3 For the surges that may be formed by large-scale collapse and landslides

in the reservoir area due to earthquakes, it shall perform special research.

6.2.4 When the design intensity is VIII or IX, it should widen the dam crest and

slow down the upper dam slope. The foot of the slope can be covered or

ballasted, the upper dam slope can be protected by a masonry block stone, the

upper dam slope can be reinforced with reinforcing steel, geosynthetic

materials or concrete frame.

6.2.5 It shall appropriately improve the seismic indicators of the embankment

dam anti-seepage body in the strong earthquake area, especially the top of the

dam which may crack during earthquake and the connection part between the

dam body and the bank slope or concrete structure. The joint surface of the

anti-seepage body and the bank slope or concrete structure shall not be too

steep, the slope changing angle should not be too large, there shall be no anti-

slope and sudden slope change; it shall appropriately thicken the anti-seepage

body and its anti-filter layer and transition layer upstream and downstream of it.

6.2.6 It shall select the earth and rock materials with good seismic performance

and permeability stability and good grading for dam construction. Uniform

medium sand, fine sand, grit and silt should not be used as dam materials in

strong earthquake areas.

6.2.7 For the compaction function and compaction of cohesive soils and the

filling dry density or porosity of the rockfill, it shall be carried out in accordance

7 Gravity dam

7.1 Seismic calculation

7.1.1 For the seismic calculation of gravity dams, it shall perform the dam

strength and the overall anti-sliding stability analysis along the construction

base plane. For roller compacted concrete gravity dams, it shall also perform

the anti-sliding stability analysis along the rolling layer.

7.1.2 For the seismic analysis of gravity dams, generally the highest dam

section of different types of dam sections can be taken, which is carried out in

accordance with a single dam section. For gravity dams with significant overall

actions, it should perform the comprehensive analysis for the entire dam section.

7.1.3 The seismic calculation of gravity dam can be performed by dynamic

method or quasi-static method. the seismic effects of the gravity dam of the

engineering seismic fortification category A, or that of the engineering seismic

fortification category B and C but the design intensity VIII and above or the dam

height higher above 70 m shall be calculated by the dynamic method.

7.1.4 The overall anti-sliding stability analysis of the gravity dam along the

foundation base plane and the anti-sliding stability analysis along the rolling

compaction layer shall be calculated in accordance with the shear strength

formula in the rigid body limit equilibrium method. For the deep anti-sliding

stability problem, the rigid body limit equilibrium method based on the equal

safety factor method (also known as the equal-K method) shall be taken as the

basic analysis method. For gravity dams with complex geological conditions, it

should supplement nonlinear finite element analysis.

7.1.5 For gravity dams with a dam height greater than 70 m, the strength safety

shall subject to the finite element method analysis in addition to the material

mechanical calculation of dynamic and static force. For the gravity dam of the

engineering seismic fortification category A or with complex structure or with

complex geological conditions, it shall consider the nonlinear influence such as

materials when performing finite element analysis. For gravity dams that shall

be subjected to seismic calculation under the maximum credible earthquake,

special studies shall be carried out using the finite element method that

accounts for the nonlinear characteristics of the dam and foundation.

7.1.6 The dynamic analysis method of gravity dam shall adopt the mode

decomposition method. For the gravity dam of which the seismic fortification

category A, it shall increase the calculation evaluation of nonlinear finite

element method.

7.1.7 Under the design earthquake, the dynamic method is used to check the

the rock mass shall take the static mean value, the partial factor shall be 1.0,

the structural factor of anti-sliding stability shall not be less than 1.40; or

otherwise it shall use the time-history analysis method to perform

comprehensive analysis judgement of the seismic stability of the potential

sliding rock mass of the abutment.

8.1.10 When using the time-history analysis method to comprehensively

analyze and evaluate the seismic stability of the potential sliding rock of the

abutment, the following steps shall be taken.

1 Under the action of the three components of the design ground motion, the

time-history analysis method is used to calculate the combined time-

history of static and dynamic integration of the arch end, and it acts on the

potential sliding rock mass together with the inertial force of the rock mass

without the power amplification effect.

2 In each time step, the structural factor of the stability of the abutment rock

mass is calculated in accordance with the rigid body limit equilibrium

method, to provide the time-history of the structural factor changes with

time in the whole seismic process, and the minimum value of the structural

factor in the time-history is used to evaluate the abutment seismic stability.

3 If the minimum value of the structural factor time-history does not meet the

requirements specified in clause 8.1.9, it shall be based on the duration

and extent of the stability index overrun, to comprehensively evaluate the

anti-sliding stability of the potential sliding rock of the abutment as well as

its impact onto the integral safety of the dam.

8.1.11 In the seismic calculation analysis of important arch dams fortified with

the maximum credible earthquakes, it shall take into account of the impacts of

dam transverse joint and the contact nonlinearities forming the controlled

slipping plane in the dam foundation, the material nonlinearities of the main

weak belts in the near-site bedrock, and the radiation damping effect of the far-

site foundation. For important arch dams within the scope of clause 3.0.6, it

shall be based on the calculation analysis and model test, combined with the

engineering comparison, in accordance with the fortification requirements of the

catastrophic failure of the reservoir water out of control, to perform the

comprehensive evaluation.

8.1.12 When the seismic analysis and evaluation of the dam is carried out in

accordance with the provisions of clause 8.1.11, the inflection point on the curve

of the typical deformation of the dam or bedrock changed with the increase of

the seismic action may be used as the evaluation index for the overall safety of

the dam foundation system, at this time, the ratio of the seismic acceleration

value to the design seismic acceleration is used as the safety margin for the

dam to avoid uncontrolled drainage catastrophe of reservoir water.

by the formula (7.1.14) can be converted into the waterfront additional mass

corresponding to the unit seismic acceleration for consideration.

9.1.8 The representative value of the seismic active earth pressure acting on

the sluice side pier or side wall and wing wall may be calculated in accordance

with the provisions of clause 5.9.1.

9.1.9 The structural strength of each component of the sluice structure shall be

subject to seismic verification in accordance with clause 5.7.4 and comply with

other relevant provisions of the SL 265 Design specification for sluice. It shall

check the influence of the structural deformation of each part of the sluice during

earthquake on the operation of the hoisting equipment.

9.1.10 The anti-sliding stability along the bottom surface of the sluice foundation

shall determine the seismic effect in accordance with this Code and comply with

other relevant provisions of SL 265. When the dynamic method is used to

calculate the seismic stability of the sluice, it shall use the seismic effect

consistent with the strength verification.

9.1.11 For the sluice on the rock foundation, when using the dynamic method

or quasi-static method to check the anti-sliding stability along the foundation

bottom surface or the shallow layer of sluice foundation, it can make reference

to the provisions of 7.1.7 or 7.1.15, respectively; for the sluice on the soil

foundation, when using the quasi-static method to verify the anti-sliding stability

along the foundation bottom surface or the shallow layer of sluice foundation,

the structural factor shall be taken as 1.2.

9.2 Seismic measure

9.2.1 When the pile foundation is used for the sluice foundation, the connection

between the pile foundation and the sluice bottom plate and the anti-seepage

measures shall be taken. The bottom plate may be provided with measures

such as anti-seepage wall, tooth wall and tail sill, to prevent the foundation from

being separated from the sluice bottom plate due to seismic action, thus

causing piping or concentrated seepage.

9.2.2 The arrangement of the sluice chamber structure shall be symmetrical

and enhance the integrity. The sluice chamber shall adopt a reinforced concrete

integral structure. The water-stop structure of the split joint shall be of a type

and material that is durable and adaptable to large deformations, and the water-

stop measures for the split joint of key parts shall be strengthened.

9.2.3 It should reduce the height of the rack bridge and reduce the weight of the

top of the rack from the selection and arrangement of the sluice and hoist.

9.2.4 The frame bridge should adopt the frame structure, it shall strengthen the

11 Intake tower

11.1 Seismic calculation

11.1.1 The seismic calculation of the intake tower shall include the verification

of the tower body stress or internal force, the overall anti-sliding and anti-

overturning stability, and the bearing capacity of the foundation at the bottom of

the tower. The non-structural components, the auxiliary electromechanical

equipment and the joints with the structural body shall be subject to seismic

design.

11.1.2 The dynamic method or quasi-static method shall be used to calculate

the seismic effect of the intake tower. For the non-reinforced concrete structure

intake tower of which the engineering seismic fortification is category A or the

design intensity VIII and above or tower height greater than 40 m, it should use

the dynamic method to calculate the seismic effects.

11.1.3 The dynamic analysis of the seismic effect of the intake tower shall

consider the influence of the water body inside and outside the tower and the

foundation, and it should use the mode decomposition method.

11.1.4 The seismic calculation model of the intake tower body can be

considered as the variable section cantilever beam using the material

mechanics method or the finite element method, but it shall be the same as the

calculation mode used in the basic load combination analysis.

11.1.5 When quasi-static method is used to calculate the seismic effect of the

intake tower, the representative values of the horizontal seismic inertial force of

each particle shall be calculated in accordance with the provisions of clause

5.5.9, where GEi is the gravity action representative value of the tower body,

framed bent and its subsidiary equipment which is concentrated at the particle

i, the dynamic distribution factor αi of seismic inertial force shall be adopted in

accordance with Table 11.1.5. When the height of the building is H = 10 m ~ 30

m, αm = 3.0, when H > 30 m, αm = 2.0.

11.1.6 When using the dynamic method to calculate the seismic effect of the

intake tower, the hydrodynamic pressure inside and outside the tower can be

considered as the additional mass of the inner and outer surfaces of the tower,

respectively, calculated in accordance with the formula (11.1.6).

calculated in accordance with the shear strength formula.<......

Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.