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NB 35047-2015: Code for seismic design of hydraulic structures of hydropower project
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 exceed...