OPG Proprietary
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GENERATION
Document
Number:
HYDRO
Revision:
Page:
R08
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DS-STD-03
Title:
Effective Date:
Standards
for Design Review of Concrete
Gravity
December
Dams
31,2011
Sci #: DSP 08200.012
.
- -
II
Review Period:
3 years
- - 0019
.• ""rr"-
:'.{F.·-.
Standard
ms in the Ontario Power Generation Dam Safety
AUTHORIZATION
This governing document has been created and reviewed against the principles and criteria outlined in the OPG
Dam Safety Program Management Document (DS-PGM-01).
~~-_._
Revised by: ~
...
--====-
~~
Date: .~~
Recommended
262120/(
I
Brent Craig
Senior Engineer, Civil Engineering Department
by:
Date:
Approved by:
Tony Bennett
afety & Emergency Preparedness
PRESENTATION
Based on the impact assessment does this document
determined In consultation with approval authority)?
~
NONE
0
DS Team
Printed on 22 December, 2011.
Power Generation Intranet.
0
This document
HMT
0
require presentation
to any of the following teams (to be
OTHER:
may have been revised since it was printed.
The approved current version is posted on the Ontario
OPG Proprietary
HYDRO
Document
Number:
Revision:
Page:
R08
1 of 30
DS-STD-03
Title:
Effective Date:
Standards for Design Review of Concrete Gravity Dams
December 31, 2011
3 years
Sci #: DSP 08200.012 - - 0019
Review Period:
Standard
PURPOSE
Document prepared for use in the safety assessments of dams in the Ontario Power Generation Dam Safety
Program
AUTHORIZATION
This governing document has been created and reviewed against the principles and criteria outlined in the OPG
Dam Safety Program Management Document (DS-PGM-01).
Revised by:
Original signed by
Date:
Dec.22/2011
Date:
Dec.22/2011
Date:
Dec.22/2011
Brent Craig
Senior Engineer, Civil Engineering Department
Recommended by:
Original signed by
Jim Wagner
Section Manager, Civil Engineering Department
Approved by:
Original signed by
Tony Bennett
Director-Dam Safety & Emergency Preparedness
PRESENTATION
Based on the impact assessment does this document require presentation to any of the following teams (to be
determined in consultation with approval authority)?
NONE
DS Team
HMT
OTHER:
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CREATION
Impact assessment:
Has a “track changes” copy of previous revision been provided?
Yes
No
HMT Members for Implementation:
The following Hydro Management Team members need to take action to implement this new or revised procedure:
HMT Members for Awareness:
Dam Safety Team Members for Awareness:
Hydro Engineering Division
Civil Engineering Dept.
Asset Managers
DOCUMENT REVIEWERS
Document Reviewers: the following individuals were invited to provide comment:
P. Chan – Director, Engineering
ACKNOWLEDGEMENT – COMPLIANCE
If this document cannot be implemented within a reasonable time period please provide a brief explanation by email
to the approval authority.
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REVISION HISTORY
Rev
R4
Date
January
2000
December
2000
September
2002
February
2006
December
2011
R5
R6
R7
R8
Revision
Revisions to meet CDA Dam Safety Guidelines (January 1999 Edition)
Approved By
M. Bechai
Revised to incorporate the Scope of Structural Assessment based on ICC
(section 4.1)
Document was revised to reflect new OPG organization and minor editorial
changes
Document was revised to reflect new OPG organization and minor editorial
changes
Document revised to include updated 2011 MNR Guidelines, 2007 CDA
guidelines, Quebec Dam Safety Regulations and Parks Canada Dam
Safety Directive
M. Bechai
CONTENT AUTHORITY
T. Bennett
T. Bennett
T. Bennett
ACCOUNTABLE DEPARTMENT/DIVISION
Name:
Jim Wagner, Section Manager, Civil
Engineering Department
Location:
ND2
Telephone Number:
(905) 357-0322 x7415
Dam Safety & Emergency Preparedness
NOTE: PLEASE DIRECT INQUIRIES ABOUT THE DOCUMENT TO THE CONTENT AUTHORITY
COPY DISTRIBUTION
Copy
Copy Location
Accountable
1
Original signed copy – Filed in Hydro Records
Director Dam Safety & Emergency
Preparedness
2
Electronic Copy – available on DSP intranet website
Director Dam Safety & Emergency
Preparedness
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TABLE OF CONTENTS
Page
1.0
Purpose ............................................................................................................................ 5
2.0
Structures ......................................................................................................................... 5
2.1
3.0
3.1
3.2
3.3
3.4
3.5
CONDITION OF STRUCTURE ...........................................................................................................................5
Loads and Load Combinations ....................................................................................... 5
ICE LOADS ....................................................................................................................................................6
HYDROSTATIC UPLIFT ..................................................................................................................................6
SEISMIC LOADS .............................................................................................................................................7
SOIL LOADS ..................................................................................................................................................8
OTHER LOADS ..............................................................................................................................................9
4.0
Inflow Design Flood (IDF) and Classification of Dams .................................................. 9
5.0
Stability Analysis ............................................................................................................. 9
5.1
5.2
5.3
5.4
6.0
6.1
6.2
7.0
GENERAL ......................................................................................................................................................9
GRAVITY METHOD OF ANALYSIS ................................................................................................................ 10
SEISMIC ANALYSIS ..................................................................................................................................... 11
ICE LOAD ANALYSIS ................................................................................................................................... 13
Acceptance Criteria ....................................................................................................... 13
GENERAL .................................................................................................................................................... 13
ACCEPTABLE CRITERIA .............................................................................................................................. 13
Additional Considerations ............................................................................................ 15
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1.0
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Purpose
The purpose of this document is to provide the requirements and the minimum
acceptance criteria for the design review of the structural integrity and safety of new and
existing concrete gravity dams related to hydraulic generating stations and control dams.
2.0
Structures
Concrete gravity dam structures may include the following:
(a)
Water retaining structures such as Headworks, Sluices, Bulkheads, Log Chutes,
etc.
(b)
Earth retaining structures such as Retaining Walls and Wingwalls.
These standards are applicable to structures founded on rock foundations, as is the
case for most of Ontario Power Generation’s concrete dams.
For structures built on other foundation materials, special methods and criteria shall be
established in accordance with accepted engineering principles and practice as required.
2.1
Condition of Structure
The strength and condition of the existing structure shall be determined to the extent
necessary by review of design, construction records, historic behaviour and visual
inspection. Sampling and testing may be required to assess the present condition.
3.0
Loads and Load Combinations
For the purpose of evaluating the safety of concrete gravity dams, combinations of loads
are categorized by nature of their likelihood of occurrence. Permanent and operating
loads are considered under normal or, usual load cases, while loads due to flood and
earthquake events are included in the unusual (flood) and extreme (earthquake) cases.
The various load combinations are shown on Table 1 and Figure 1.
For new or modified structures, consideration should also be given for construction load
cases.
In general, certain loads have to be considered in most loading cases. They include
dead, live, wind, drag, thermal loads, water pressures, hydrostatic uplift and the effects
of soil and silt deposits, where applicable. In addition, loads reflecting winter operating
condition, especially snow and ice loads, have to be taken into account in the
appropriate load combinations. Among these loads, the effects of ice loads, hydrostatic
uplift, seismic and soil loadings are discussed below in more detail.
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3.1
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Ice Loads
For dam structures located in areas with severe winters like Ontario, the predominant
mechanism of the thermally-induced ice load is the expansive force which occurs in the
ice sheet during a rapid warming trend. A second significant component of the ice load
that must be considered is the ice jacking force which is related to the fluctuations in
headpond water elevation. In general, the overall magnitude of the ice load is governed
by a number of controlling factors such as the initial temperature, rate of temperature
rise, ice thickness, snow and slush cover, headpond configurations, shoreline
confinement, water velocity, water level fluctuation, ice buckling and hinging effects, ice
creep and relative stiffness of the various hydraulic structures.
The design ice loads used in the design review are to be derived in accordance with
OPG procedure DS-PRO-08, Procedure for Determining Ice Loads in the Assessment of
Concrete Dams. The ice loads are generated using the CEATI model and are based on
a 100 year return period with a 95% confidence level. Two magnitudes of ice load shall
be derived for the site under consideration. The first accounts for purely thermal loading,
while the second accounts for thermal with ice jacking (if applicable). Winter headpond
fluctuation characteristics must be analyzed to determine the ice jacking loads.
The full thermal ice load shall be applied as a normal case and have a minimum value of
75 kN/m. The thermal with ice jacking load shall be adopted as an unusual load case.
The application of the ice load shall be 0.3 m below the winter headwater level. Ice
bridging should be considered between piers.
3.2
Hydrostatic Uplift
Hydrostatic pressures from the headwater and tailwater act, not only on the faces of the
dam, but also occur within the dam and foundation as internal pressures, generally
referred to as hydrostatic uplift.
The distribution of uplift pressures at any elevation will generally depend on the following
factors:
(1)
the upstream and downstream water levels at the dam,
(2)
the effectiveness of drainage and/or pressure relief systems, and grout
curtains, if present,
(3)
the global permeability and geological structure of the bedrock
foundation,
(4)
the condition of the concrete and bedrock contact – open or tight, and
(5)
time effects.
For the design review purpose hydrostatic uplift shall be taken into account under all
load cases. For dams with no foundation drains or pressure relief systems, full uplift
varying linearly from 100% headwater pressure at the upstream face to 100% of the
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tailwater pressure at the downstream face, shall be assumed to act on the entire base
area of the dam.
For dams equipped with an effective drainage and/or pressure relief system (based on
field investigations and/or monitoring data), reduced uplift can be used in the evaluation
process. The uplift distribution can be considered to vary from 67% of upstream
headwater pressure in Normal, Unusual and Extreme load combinations, to 100%
tailwater pressure. Proposed uplift distributions, as discussed above, are shown in
Figures 2, 3 and 4. Alternative methods for calculating the reduced uplift such as the
recommended practices provided in Technical bulletin 9 of the 2007 CDA dam safety
guidelines can be approved. For all load cases, the reduced uplift should not be less
than the actual recorded uplift.
The uplift pressure considered for each case of loading is the uplift corresponding to
water elevations for that case, i.e. “locked in” pressures are not to be considered.
Where tension acting on a plane exceeds the allowable limits, it is assumed to cause
cracking which might result in significant changes to the uplift pressures. Except for a
cracked condition caused during an earthquake in which the uplift pressure assumed
prior to the seismic event is maintained, all other analysis shall consider the following
adjustment to the uplift distribution:
(a)
On cracked planes not intersected by drains, the uplift is assumed to be full
headwater pressure over the length of the crack and then to vary as a straight
line from this pressure at the end of the crack to tailwater pressure at the toe
(Figure 5-a).
(b)
On cracked planes intersected by drains where the crack does not penetrate as
far as the drains, the uplift is assumed to be at a the reduced headwater pressure
over the length of the crack, then to vary linearly from this pressure to tailwater
pressure at the toe (Figure 5-b).
(c)
On cracked planes intersected by drains where the crack extends beyond the
drain location, the drains are assumed to be no longer effective. The uplift is
assumed to be at full headwater pressure over the length of the crack then vary
linearly to tailwater pressure at the toe (Figure 5-c).
Additional sensitivity analysis must be performed for dams with effective drainage
systems to evaluate the stability of the dam in the event that the drains no longer function
(e.g. plugged drains). In effect, the drain efficiency shall be reduced to 0. This analysis
shall be done in conjunction with all normal and unusual load cases. Result of this
analysis shall be treated as a sensitivity case with no associated acceptance criteria.
3.3
Seismic Loads
Two levels of seismic events are to be considered for the design review. They are:
(a)
the Maximum Design Earthquake (MDE), which shall have a probability of annual
exceedence as specified in Tables 4(a) and 4(b) with the worst case value
governing the analysis. It is recommended that all new structures be analyzed
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for a MDE with a minimum return period of 1:2500. The MDE shall have a
minimum Peak Ground Acceleration of 5 %g.
(b)
the Design Earthquake event used in conjunction with Ice Loading (DEice), which
shall have a probability of annual exceedence of 1 in 200 or a Peak Ground
Acceleration of 2 %g, whichever is greater.
The seismic loading, which is the input for the dynamic analysis, is to be derived for
each specific dam site based on the appropriate probability of annual exceedence and
geological studies if necessary. The Procedure for Determination of Design Seismic
Ground Motion Parameters is given in OPG Dam Safety Program Document DS-PRO01, Procedure for Determination of Design Seismic Ground Motion Parameters.
According to the method selected for the analysis, the required loading may consist of a
set of either Ground Response Spectra or Acceleration Time Histories.
3.4
Soil Loads
Vertical and horizontal loading, due to soil or rock backfill, must be considered where
applicable.
Soil data, i.e. soil type, unit weight, shear strength parameters (undrained & drained
parameters) and any other pertinent soil data used in the original design shall be
evaluated in consultation with the Geotechnical Engineer before being adopted for the
design review.
In cases where soil data are unavailable, a granular backfill may be assumed for the
design review, with the following properties:
Moist Unit Weight (bulk),
Submerged Unit Weight,
= 2163 kg/m3 [135 lb/ft3]
= 1249 kg/m3 [78 lb/ft3]
Angle of Internal Friction (),
= 33º
Cohesion (C),
=0
Since all concrete structures to be evaluated are expected to be founded on competent
rock and mostly bonded to it, under the normal and unusual loading combination the
magnitude of displacements of these structures are expected to be insignificant.
Therefore, the soil loading used in the design review should be based on soil pressure at
“rest”.
The soil coefficient at rest, K0, can be calculated from the formula,
K0 = 1-sin 
Where  is the internal angle of friction for the soil.
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However, if occurrence of significant structural deformation is likely (e.g. due to structural
flexibility or to lack of bonding at the foundation) and therefore active/passive pressure
could be mobilized, Rankine or Coulomb theory can be used.
To complete the active and passive dynamic lateral soil pressures during an earthquake,
the Monomobe-Okabe method based on Coulomb’s theory may be adopted.
Angle of wall friction δ = /2 is to be considered satisfactory for active pressure. For
passive, pressure, a wall friction δ = 0º is to be assumed.
The additional soil loading due to the seismic event (i.e., the difference between total
static and dynamic load, and the static soil load) shall be assumed to be acting at 2/3 of
the soil height above the base of the structure.
The design vertical seismic coefficient, Kv, for soil and concrete structures can be
assumed to be two thirds of the design horizontal seismic coefficient, Kh:
Kv = 2/3 Kh
3.5
Other Loads
In general, loads induced by other factors such as dynamic thrust of ice sheets and
temperature induced loads are not significant in OPG dam structures. However, they
may be considered where found necessary. Forces such as Wave and Drag should be
assessed for various structures and applied to appropriate load cases. Other loads to
be considered in all cases where applicable are indicated in Section 3.0.
4.0
Inflow Design Flood (IDF) and Classification of Dams
The inflow design flood (IDF) shall be determined based on the selection criteria and the
classification of the specific dam as given in the OPG Dam Safety Standards titled
Classification of Dams and Inflow Design Flood Selection, Documents No. DS-STD-06.
All the applicable loads and load combinations shall be considered as per Section 3.0
and stability analysis shall be carried out using the methods and acceptance criteria
described in Sections 5.0 and 6.0, respectively.
5.0
Stability Analysis
5.1
General
Stability analysis for the structures shall be carried out. The “Gravity Method” of analysis
may be used.
For the Extreme Load Combination, a linear elastic dynamic analysis may be carried out
to determine the seismic response. A nonlinear dynamic analysis might also be used to
determine the displacements during an earthquake if necessary. The different types of
dynamic analyses are briefly described in Section 5.3 “Seismic Analysis”.
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5.2
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Gravity Method of Analysis
The Gravity Method of analysis includes the determination of factors of safety against
sliding, location of the resultant force, and stresses along any horizontal plane
considered for the analysis (see Figure 6).
(a)
Sliding
The Factor of Safety against Sliding (FSS) along any horizontal plane shall be
determined based on the shear-friction factor.
  V  CA c
FSS =
H
where
∑V
=
total vertical load acting on the plane
μ
=
coefficient of friction at the plane considered.
∑H
=
total net horizontal load acting on the plane.
C
=
cohesion of the material on the plane.
Ac
=
area of the plane under compression. See Figure 6.
=
Bc x W
Bc
=
length of base under compression
W
=
width of the base
Previous assessments under OPG guidelines have allowed the incorporation of the
bonded tension zone to be used to enhance the sliding resistance.
(b)
Location of Resultant & Stresses
The location of the resultant acting on the plane under consideration is
determined as follows:
a=
 M  M
V
st
ov
where
a
=
location of resultant from Toe (see Figure 6).
∑Mst
=
sum of stabilizing moments about Toe.
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Standards for Design Review of Concrete Gravity Dams
∑Mov =
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sum of overturning moments about Toe.
The stresses may be computed by the following equations:
f1= -
V
f2 = -
A
V
A
(1 
6e
)
B
(1 
6e
)
B
where
f1 & f2 =
stresses acting on the plane (section) considered at the
Heel and the Toe of the structure, respectively.
A
=
area of the plane (section).
=
W x B.
=
eccentricity.
=
B
a
2
=
length of base.
e
B
Note: During the analysis if tensile strength is considered to exist across the plane
(section), the resultant could fall outside the middle third of the base.
5.3
Seismic Analysis
Since the seismic loading is time-dependent, a dynamic analysis is generally required to
evaluate the structural stability. However, to minimize the analytical efforts, the
procedures for the seismic analysis may be divided in five stages as illustrated in
Figure 8. These are described as follows:
(a)
Linear Elastic Dynamic Analysis
This analysis is generally carried out for the specific requirements of the pseudostatic analysis. Its analytical complexity may range from a simplified first mode
response to a detailed finite elements dynamic formulation based on the
response spectra or time history method.
The seismic response is generally expressed in terms of peak instantaneous
forces and bending moments acting at elevations where stability calculations are
to be carried out.
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(b)
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Pseudo-Static Stability Analysis
In this stage, the seismic response is added to the static components of the
Extreme Load Combinations. Stability calculations are then carried out based on
the Gravity Method.
It is recognized that for a safety assessment based on static material strength
values, such as the Gravity Method, using the instantaneous peak response
forces is too conservative. Therefore, to account for the higher failure stresses
when the loads are applied rapidly, the seismic forces used in the pseudo-static
stability evaluation shall be obtained by multiplying the seismic response by a
factor of 2/3.
The required factors of safety under the Extreme Load Combination, which are
applicable only to the pseudo-static analysis method, are used as a simplified
screening test. It must be noted that failing this screening test does not
necessarily imply that the structure (dam) is unstable. If this is the case, the
following additional analyses are required.
(c)
Post-Seismic Stability Test
The most common result of exceeding the allowable tensile stresses during the
seismic event is the loss of bond and development of a cracked plane at the
concrete-rock interface or any weak section. The lateral stability is not
necessarily lost due to the loss of bond, but is reduced to frictional resistance
and, where available, keying in the rock foundation or along construction joints.
A stability analysis should be carried out to see whether the dam, in its postearthquake condition, may still be capable of containing the reservoir.
The analysis should be carried out according to the Gravity Method, taking into
account the loss of bond due to cracking during the seismic event. Where
complete cracking is identified, the uplift pressure used (Reference 6) should be
based on straight line distribution as shown in Figure 7.
(d)
Non-Linear Dynamic Analysis
If the results of the post-seismic stability test are satisfactory, it is recommended
that a nonlinear dynamic analysis shall be carried out to evaluate the slip and
uplift movements along the failure planes.
The analytical complexity may range from using simple empirical formulae,
based on the sliding block concept, to detailed finite element formulations based
on step-by-step numerical integration of the dynamic response.
(e)
Post-Seismic Condition Assessment
The cracked failure planes along which the slip occurs are not likely to be smooth
surfaces. Geometric irregularities may be present prior to cracking, either
concrete-to-concrete along the construction joints or concrete-to-rock at the
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Standards for Design Review of Concrete Gravity Dams
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base. Consequently, the slip movements will cause a gap opening along the
cracked surfaces as well.
The structural integrity and the functionality of the dam should be assessed in
light of the slip and gap opening movements identified between the concrete
monoliths and rock foundation, along the vertical and, where applicable,
horizontal construction joints and other structures, such as penstocks, sluice
gates, etc.
The potential reservoir discharge through this gap and the effects of the flow on
the concrete and rock surfaces should be assessed as well.
5.4
Ice Load Analysis
The magnitude of the design ice load is governed by a number of controlling factors as
described in Section 3.1. If the design review determines that the structure does not
meet engineering standards for ice loads, then additional analysis shall be carried out to
determine the critical ice loads and water level combinations. This information shall be
used to define the scope and priority of the recommended remedial action.
6.0
Acceptance Criteria
6.1
General
The acceptance criteria depends on the method of analysis used. In the case of the
gravity method of analysis, the factors of safety against sliding, the stresses, and the
location of the resultant force are the main criteria used to evaluate the integrity of the
concrete dam. For the Extreme Load Combinations, the magnitude of deformations
induced by the earthquake and their effects on the structure are the main factors to be
assessed.
In addition, the acceptable factors of safety are closely related to the reliability of the
design parameters and the hazard potential classification. The minimum acceptable
factors of safety against sliding are provided in Table 2. The higher factors of safety are
applied where consideration of cohesion is taken into account in the analysis. Extensive
foundation investigations, using state-of-art techniques, are required to justify the use of
cohesion.
6.2
Acceptable Criteria
A summary of acceptance criteria is provided in Tables 2 and 3. In order to meet this
standard, the structure under review should satisfy the following criteria:
(a)
Sliding
The computed Factor of Safety against Sliding (FSS) shall be equal to or greater
than the values given in Table 2.
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(b)
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Stresses
The allowable unit stresses shall not be exceeded. The allowable stresses for the
foundation shall be determined by dividing the ultimate strength of the foundation
materials by the appropriate safety factors on Table 2. The allowable normal
compressive stress for concrete is provided in Table 3. The lower stress
threshold between the concrete and foundation stress shall govern the analysis.
(c)
Location of the Resultant
Acceptable limits for the location of the resultant are summarized in Table 3.
The resultant shall fall within the middle third of the plane being analyzed for the
Normal Load combinations. Some cracking might be permitted for existing
structures given that all other acceptance criteria are met.
The resultant shall fall within the middle half of the plane being analyzed for the
Unusual Load combinations.
The resultant shall fall within the plane being analyzed for the Extreme Load
Combinations.
(d)
Cracked Plane Approach
Cracking shall be assumed to occur if the tensile stress at the upstream face
exceeds the allowable tensile stress.
Cracking, if allowed, requires that the potential crack stabilizes within the plane
under investigation, and an adequate Factor of Safety against Sliding is attained
using the uncracked portion of the plane.
(e)
Post-Seismic Condition
The dam shall be able to contain the reservoir for a sufficient period of time to
allow for strengthening of the structure, if required. The acceptability of the
potential structural and functional damage to the dam in its post-earthquake
condition shall be decided from case to case based on environmental safety and
economic considerations. Post–Seismic case shall consider any cracking along
the analysis plane that would have been generated through the relevant
earthquake event.
(f)
Seismic Deformations
For most parts of Ontario, seismicity studies suggest that potential deformations
induced by earthquakes even under the most conservative assumptions are most
likely to be very small.
The computed seismic deformation shall be evaluated from case to case and the
safety of the dam structure shall be decided based on engineering judgment and
other available relevant site information.
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7.0
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Additional Considerations
All dam should be checked for stability in accordance with OPG guidelines. The OPG
guidelines are formatted to ensure that, as a minimum, the 2007 CDA and MNR 2011
dam safety guidelines are satisfied. Several OPG owned dams are located in areas
which are governed by different jurisdiction. In this case, additional analysis might be
required to ensure compliance with the governing criteria for those areas.
7.1
Quebec
Dams that are located in the province of Quebec must meet the criteria set out by the
Quebec Dam Safety Regulations. Load cases and methods of analysis shall be as
presented in the previous sections of this standard. Hazard classification and as a
result, the design flood, shall be determined in accordance with the Quebec Dam Safety
Regulations as described in OPG standard DS-STD-06, Classification of Dams and
Inflow Design Flood Selection. Selection of the design earthquake shall be made by
determining the k factor provided in the Quebec seismic reference maps as part of the
Quebec Dam Safety Regulations [Ref. 25]. Alternatively, a minimum earthquake return
period of 2,500 year shall be adopted.
7.2
Parks Canada
Dams that fall under the jurisdiction of Parks Canada must abide by the Directive for
Dam Safety Program of Parks Canada Dams and Water-Retaining Structures. Load
cases and methods of analysis shall be as presented in previous sections of this
standard. The dam classification system used in the Parks Canada regulation is
described in OPG standard DS-STD-06, Classification of Dams and Inflow Design Flood
Selection. This information is required to determine the appropriate IDF and Earthquake
magnitude. The IDF shall be selected in accordance with OPG standard DS-STD-06,
Classification of Dams and Inflow Design Flood Selection. The Design Basis
Earthquake shall be selected in accordance with the Directive for Dam Safety Program
of Parks Canada [Ref. 26] and OPG procedure DS-PRO-01, Procedures for
Determination of Design Seismic Ground Motion Parameters.
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References
1.
Dam Safety Program, Hydraulic Structures, Ice Pressures. Memo from P.Kalnins to
G.DiGiambattista, dated April 9/86. FILE: DSP-410.1-00-046
2.
”Task Report of Seismic and Hydraulic Loads and Load Combinations for Review of
Existing Dams”, Civil Design Department, Geotechnical and Hydraulic Engineering
Department, Ontario Hydro, April, 1987. FILE: DSP-410.1-00-001
3.
Ontario Power Generation, Dam Safety Program – “Procedures for Determination of
Design Seismic Ground Motion Parameters”, Document No. DS-PRO-01.
4.
Dam Safety Program, Design Seismic Ground Motions. Memo from J.H.K.Tang to
G.F.Smith dated February 10, 1988. FILE: DSP-410.1-00-005
5.
Ontario Power Generation, Dam Safety Program – “Classification of Dams and Inflow
Design Flood Selection”, Document No. DS-STD-06.
6.
Uplift Pressure Under Gravity Dam. Letter from Professor Evert Hoek to K.K.Tsui,
January 1989. FILE: DSP-200.01
7.
”Stability Analysis of Existing Concrete Structures”, J.O.H.Nunn, M.Pildysh, and
R.A.Keys, Proceedings Dam Safety Seminar, Edmonton, Alberta, September, 1986.
8.
”Design Criteria for Concrete Arch and Gravity Dams”, US Bureau of Reclamation,
Monograph No. 19.
9.
”Dam Safety Program, Factors of Safety for Review of Concrete Dams”. J.H.K.Tang,
Civil Design Department, Ontario Hydro, July 22, 1987. FILE: DSP-200.012
10.
”Tensile Strength of Concrete”, Jerome M.Raphael, ACI Journal, March-April, 1984.
11.
”Minutes of Meeting – Dam Safety Program, Analysis of Water and Earth Retaining
Structures”. September 22, 1987. FILE: DSP-200.01
12.
”Minutes of Meeting – Dam Safety Program, Seismic Loading, Tensile Strength at
Concrete/Rock Interface and Sliding Resistance”, October 19, 1987.
FILE: DSP-410.1-00.005
13.
”Engineering Technical Letter No. 1110-2-256, Engineering and Design – Sliding
Stability for Concrete Structures”, US Army Corps of Engineers, June 24, 1981.
14.
”Engineering Guidelines for the Evaluation of Hydro Power Projects”, Federal Energy
Regulatory Commission, July 1987.
15.
Dam Safety Assessment Program, Review of Ontario Hydro’s Standard and Criteria by
Harza Engineering Company Consulting Engineers, Chicago, Illinois, 1989.
FILE: DSP-200.01
Printed on 5 January, 2012. This document may have been revised since it was printed. The approved current version is posted on the Ontario Power
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Standards for Design Review of Concrete Gravity Dams
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16.
Dam Safety Assessment Program, Review of Ontario Hydro’s Standard and Criteria by
BC Hydro International Ltd., 1989. FILE: DSP-200.01
17.
Dam Safety Assessment Program, Review of Ontario Hydro’s Standard and Criteria by
Dr. K.Y.Lo, University of Western Ontario, 1989. FILE: DSP-200-012
18.
Dam Safety Assessment Program, Review of Ontario Hydro’s Standard and Criteria by
Dr.E.Hoek, University of Toronto, 1989. FILE: DSP-200-012
19.
Dam Safety Assessment Program, Review of Ontario Hydro’s Standard and Criteria by
Dr.N.Morgenstern, University of Alberta, 1989. FILE: DSP-200-012
20.
Sensitivity Study of Small Low Hazard Concrete Dam by Civil Analysis section, CEAD,
Ontario Hydro, File no. (Dated May, 1991).
21.
Ontario Power Generation – Dam Safety Assessment Program – “Determining Ice Loads
in the Assessment of Concrete Dams”, Document No. DS-PRO-08.
22.
Dam Safety Guidelines, Canadian Dam Association, 2007.
23.
Dam Safety Guidelines, Technical Bulletin 9: Structural Considerations for Dam Safety,
Canadian Dam Safety Association, 2007.
24.
Ontario Power Generation, Dam Safety Program, "Standards for the Assessment of
Mechanical and Electrical Equipment", Document no. DS-STD-04.
25.
Quebec Dam Safety Regulations, Ministere du Developpement durable, de
l’Environnement et des Parcs, July 2011.
26.
Directive for Dam Safety Program of Parks Canada Dams and Water-Retaining
Structures, Parks Canada, January 2009
27.
Static Ice Loads on Hydro-Electric Structures, CEA Technologies, CEATI Report No.
T002700-0206, August 2003.
28.
Structural Design and Factors of Safety, Technical Bulletin, Ontario Ministry of Natural
Resources, August 2011.
29.
Seismic Hazard Criteria, Technical Bulletin, Ontario Ministry of Natural Resources,
August 2011.
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TABLE 1
LOAD COMBINATIONS FOR SAFETY EVALUATION
OF CONCRETE GRAVITY DAMS
Load
Combination
1
(Fig 1)
NORMAL
UNUSUAL
EXTREME
(Earthquake)
PostEarthquake
Water Level
Headwater Level
(HWL)
max operating
(Fig 1-1)
winter (December to
March) max
operating
(Fig 1-2)
IDF level
(Fig 1-3)
Winter (December to
March) max
operating
Tailwater Level
(TWL)
min recorded or
min allowable
min recorded or
min allowable in
winter
IDF level
Min recorded or
min allowable in
winter
max operating
(Fig 1-5)
winter max operating
(Fig 1-6)
min recorded or
min allowable
min recorded or
min allowable in
winter
max operating
(Fig 1-1)
min recorded or
min allowable
winter (December to
March) max
operating
(Fig 1-2)
min recorded or
min allowable in
winter
Ice Load
Earthquake
--
--
Thermal Ice
Load from
CEATI Model
(min 75 kN/m)
--
--
Thermal &
Jacking Ice
Load from
CEATI Model
--
--
Same as in
Winter
condition for
NORMAL load
combination
DEice
Figures 2,
3, 4, 5, & 7
--
2
MDE
--
Same as in
Winter
condition for
NORMAL load
combination
Hydrostatic
Uplift
--
2
Includes
cracking
from MDE
Earthquake
case
Includes
cracking
from DEice
Earthquake
case
NOTES:
1 Other loads to be considered in all cases, but not shown in the above table, include dead, live,
snow, wind, drag, thermal loads and the effects of soil and silt deposits, where applicable.
2 MDE (Maximum Design Earthquake) & DEice (Design Earthquake with ice) are identified in Table
4(a) & 4(b).
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TABLE 2
MINIMUM FACTORS OF SAFETY
Load Combination
Factor of Safety for Sliding and Stresses
Analysis
With Cohesion
Based on Zero Based on Adequate
Based on Limited
Cohesion1
Test Data and
Information and
Analysis2
Test Data2
Normal
Unusual
Extreme
(Earthquake)
Post-Earthquake
1.5
1.3
1.1
2.0
1.5
1.3
3.0
2.0
1.5
1.1
N/A
N/A
Notes:
1 Cohesion refers to the shear strength or adhesion of material(s) when normal stress across the
prospective failure plane is zero. The failure plane under consideration can be either at the
bedrock-concrete interface or at a concrete joint within the structure. Cohesion is generally
determined by direct tension and/or triaxial compression tests and is measured in force per
square area [usually pounds per square inch, (psi)]. Cohesion represents a shear strength or
adhesion of the materials across the failure plane under investigation of [0 psi]. Analysis based
on zero cohesion shall be documented in all cases.
2
Test Data Refers to the laboratory tested strength parameters of structural or foundation
materials. Adequate test data refers to testing which has taken place at the site being assessed.
The higher factors of safety are reserved for sites where cohesion values are obtained based on
extrapolations from testing performed at nearby sites which are considered to be representative.
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TABLE 3
ACCEPTANCE CRITERIA
Load Case
Normal
Unusual
Extreme
Post-Earthquake
Position of resultant force
Middle third of the base (100%
3
compression)
Middle half of the base
Within the base
Within the base
Normal compression stress
<0.3 x f’c
1, 2
<0.5 x f’c
<0.9 x f’c
<0.5 x f’c
Notes:
1 Where f’c is the compression strength of concrete
2 The minimum between the provided value and the bearing strength of the foundation should be
used. Foundation bearing strength shall be calculated by dividing the ultimate compressive
strength of the foundation by the factors provided in Table 2.
3 Small portion of the base is allowed to be under zero compression for existing structures as long
as all other acceptance criteria is met.
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TABLE 4(a)
MAXIMUM DESIGN EARTHQUAKE FOR USE IN THE
ASSESSMENT OF CONCRTE DAMS (MNR 2011)
Hazard Potential
Classification
Low
Moderate
High
Very High
MAXIMUM DESIGN EARTHQUAKE (MDE)
(annual exceedance probability)
Life Safety
Property and
Environment
Loss of Life
None
1/500 year
None
1/500 to 1/1,000 year
10 or fewer
1/2,500 year
1/1,000 to
1/2,500 year
11 to 100
1/5,000 year
1/2,500 to
1/10,000 year
More than 100 1/10,000 year
Cultural – Built
Heritage
1/1,000 year
Notes:
1 The MDE levels are to be used for the “mean” rather than the “median” estimates. The mean is
the expected value given the epistemec uncertainties and for typical seismic hazard computations
th
th
in Canada, the mean hazard value typically lies between the 65 and 75 percentiles of the
th
hazard distribution. The median is at the 50 percentile.
2 Generally, a seismic hazard evaluation will not be required for Low or Moderate HPC dams
unless specifically requested by the Minister with supporting rational.
3 The MDE shall have a minimum value corresponding to a PGA = 5%g
4 DEice shall have and annual exceedance probability of 200 year or a PGA value of 2%g,
whichever is greater.
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TABLE 4(b)
MAXIMUM DESIGN EARTHQUAKE FOR USE IN THE
ASSESSMENT OF CONCRTE DAMS (CDA 2007)
Dam Class
CDA
Low
Significant
High
Very High
Extreme
MAXIMUM DESIGN EARTHQUAKE (MDE)
(annual exceedance probability)
OPG – ICC5
Very Low
Low
High6
Very High
1/500 year
1/1,000 year
1/2,500 year
1/5,000 year2
1/10,000 year2
Notes:
1 The MDE levels are to be used for the “mean” rather than the “median” estimates. The mean is
the expected value given the epistemec uncertainties and, for typical seismic hazard
th
th
computations in Canada, the mean hazard value typically lies between the 65 and 75
th
percentiles of the hazard distribution. The median is at the 50 percentile.
2 The MDE value must be justified to demonstrate conformance to societal norms of acceptable
risk. Justification can be provided with the help of failure modes analysis focused on the
particular modes that can contribute to failure initiated by a seismic event. If the justification
cannot be provided, the MDE should be 1/10,000 year.
3 The MDE shall have a minimum value corresponding to a PGA = 5%g
4 DEice shall have and annual exceedance probability of 200 year or a PGA value of 2%g,
whichever is greater.
5 Incremental Consequence Category (ICC) as determined by OPG standard DS-STD-06,
Classification of Dams and Inflow Design Flood Selection
6 For dams with a High ICC classification, the selected MDE shall have a probability of annual
exceedance between the 1/2,500 and 1/10,000 year. For dams with a consequence approaching
those of a Very High ICC dam, design earthquake of 1/10,000 shall also be checked in the
assessment. Results of such analysis shall be used as a safety margin study/evaluation, rather
than as an acceptance criteria.
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Criteria
1.0
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