2004 sept nbcc 2005 seismic changes combined presentation
DESCRIPTION
Seismic Design ChangesImpact on Insurance IndustryTRANSCRIPT
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2005 National Building Code of Canada
Seismic Design ChangesSeismic Design Changes
Impact on Insurance Industry
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NBCC 2005 Seismic Design Changes
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Gravity Element Failures
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Reinforced Concrete Column Confinement
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What Causes Earthquakes
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2002Plattsburgh
NY
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Population
NBCC communities
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Risk
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Cascadia Subduction Zone
1700 A.D.Magnitude 9
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Jan de Fuca Plate Slip
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2005 National Building Code of Canada Seismic Design
Basics of Seismic Design
Changes Incorporated in 2005 NBCC Seismic Loads New Hazard Map Structural Analysis
Rationale Behind the Changes
Changes in CSA A23.3 Design Of Concrete Structures Standard.
Implications for the Insurance Industry
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Factors Influencing Seismic Effects
EQ Magnitude Type of EQ Distance Soil Structure
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Ductility Dissipating Seismic Energy
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Structural Response To Earthquakes
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Acceleration Response Spectrum
V = m x a
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Natural Modes of Building Vibration
Seismic Motion
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Concrete Plastic Hinges
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Seismic Shake Table Testing
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Ductility - Shear Wall Structures
( a ) = 1 .5 ( b ) = 2 .0 ( c ) = 3 .5
0 .0 0 2 00 .0 0 1 5
5 0 0 m m3
0 .0 0 2 5
0 .0 0 2 5
5 0 0 m m
3
4 5 0 m m
0 .0 0 2 5
0 .0 0 2 5
T ie s @ 1 64 8
H o o p s @
2 4
6
/ 2
3 0 0 m m ( p la s t ic h in g e )
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Braced Steel Structures
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2005 NBCC - Uniform Hazard Spectrum
More uniform margin of collapse (NEHRP), 1997 and Building Seismic Safety Council, 1997)
Seismic hazard at a lower probability of exceedance, nearer probability of failure exceedance, nearer probability of failure
Maximum considered earthquake ground motion
2% in 50 year probability of exceedance (2500 year return period)
New seismic hazard maps
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2005 NBCC Seismic DesignBad News 1995 Seismic Risk Level
10% in 50 yrs => 1 / 475 yrs return period 2005 New Seismic Risk Level 2005 New Seismic Risk Level
2% in 50 yrs => 1 / 2400 yrs return period
Good News:500 x 5 2500
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Hazard
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Probabilistic seismic hazard
Double integration to give hazard
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Rates of activity, and sizes of the
biggest events biggest events were
underestimated
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Different rates,
different errors in errors in rates for
magnitude-recurrence
curves Mx
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Some data do
not appear to appear to
fit the simple model
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Highest value of:-
Full Robust Hazard Model
Highest value of:-Probabilistic H modelProbabilistic R model Deterministic Cascadia model Probabilistic Stable craton model
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Base Shear NBCC 1995 vs 2005
V =VER
U
VE = v S I F W
1995
V =S (Ta) Mv IE
Rd RoW
VE = v S I F W
2005
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Design Spectral Accelerationdefined by 4 spectral hazard parameters
and 2 site factors
( ) ( )( ) ( )
smaller, is whichever 20or 50
s 20for 20.SF.SF.T.SFTS
aaav
aa
=
=
( )( )( ) s 04for 202
s 02for 02 s 01for 01
s 50for smaller, is whichever
.T.SF.T.SF.T.SF
.T
av
av
av
===
==
=
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Influence Of Soil The Soil Factor Can change the characteristics of earthquake motions.
Poor - deep loose sand; silty clays; sand and gravel; and soft, saturated granular soils.
Amplify earthquake forces on water-saturated soils
Good - bedrock stiff soils.
Much less vibration is transferred through thefoundation to the structure above.
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Site Classification for Seismic Site Response A = hard rock B = rock C = dense soil or soft rock C = dense soil or soft rock D = stiff soil E = > 3 m of soft soil F = others (liquefiable, peat, etc.)
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Design Spectral Response Acceleration Class C Soil
0.2
0.4
0.6
0.8
1.0
S(T)
VancouverMontrealTorontoSaskatoon
0.0
0.2
0 1 2 3 4T, s
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Conversion factors have been derived to ensure all hazard values are for site Class C
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Uniform Hazard Spectra
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Uniform Hazard Spectra
probabilistic and and
Cascadia
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Deaggregation of hazardcontributions by magnitude and distance
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Deaggregation of hazard contributions by magnitude and
distance
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New probability level will lead to more uniform protection
500 x 5 2500
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Uniform Hazard Spectrum More uniform margin of collapse (NEHRP),
1997 and Building Seismic Safety Council, 1997)
Seismic hazard at a lower probability of exceedance, nearer probability of failure exceedance, nearer probability of failure
Maximum considered earthquake ground motion
2% in 50 year probability of exceedeance (2500 year return period)
New seismic hazard maps
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General Requirements NBCC 2005Seismic Structural Design
Design for clearly defined load paths Must have a clearly defined Seismic
Force Resisting System (SFRS)Force Resisting System (SFRS) Stiff elements not part of SFRS to be
separated from structural components or made part of SFRS and accounted for in analysis
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Base Shear NBCC 1995 vs 2005
V =VER
U
VE = v S I F W
1995
V =S (Ta) Mv IE
Rd RoW
=
2005
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Ro (Overstrength) Factor 1.3-1.7
V =S (Ta) Mv IE
Rd RoW
V = Ve W
R R RR R Ro yieldsize sh mech= Rd = Ductility 1.5 4.0
V = VeRd Ro
W
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Ro (Overstrength) Factor
Ro depends on the system :1.3 1.7
Mpb
Mpb Mpb
Mpb-
- -
+
-
(a) = 1.5 (b) = 2.0 (c) = 3.5
Rd= 1.5 - 4.0
0.00200.0015
500 mm3
0.0025
0.0025
500 mm
3
450 mm
0.0025
0.0025
Ties @ 1648
Hoops @
24
6
/2
300 mm (plastic hinge)
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(a) = 1.5 (b) = 2.5 (c) = 4.0
/2 /2 /2 /2
>>>
450 mm
/6
>>>
450 mm
/6
16
48
8
24
300 mm/2
8
24
300 mm/4
6
100 mm
confinement/4
8
24
300 mm/4
steel2 2 2 2 2 2
Rd
1
1
1
1
1
1
SECTION 2 - 2SECTION 1 - 1 SECTION 1 - 1 SECTION 1 - 1SECTION 2 - 2 SECTION 2 - 2
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(a) = 1.5 (b) = 2.0 (c) = 3.5, 4.0
stirrups@ /2
Beams Diagonalbars hoops
Beamsstirrups@ @ 6
24
100 mm
8
24
300 mm/4
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Ve=
R FactorsV
VeV V
RUe=1995:
V VR R
e
d o=
e
V = / R R d oVe
Ve / Rd
2005:
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Effect of R values
E
X
P
E
C
T
E
D
F
O
R
C
E
R
=
2
.
0
R
=
4
.
0
TARGET DISPLACEMENT
E
X
P
E
C
T
E
D
F
O
R
C
E
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Base shear comparisonR/C Ductile shear walls, Rd = 3.5Soil Class C
0.12
VAN - 2004MTL - 2004
0.0 1.0 2.0 3.0 4.0Period (s)
0.00
0.04
0.08
V
/
W
MTL - 2004TOR - 2004VAN - 1995MTL - 1995TOR - 1995
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Influence of RdRo (R/C SFRS)Montreal, Soil Class C
0.20
0.25 R/C SFRS - Montreal
Conv. ConstructionMD WallsD Walls
0.0 1.0 2.0 3.0 4.0Period (s)
0.00
0.05
0.10
0.15
V
/
W
D WallsD Partially coupled wallsD Coupled wallsMD MRFs D MRFs
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Influence of RdRo (R/C SFRS)Vancouver, Soil Class C
0.30
0.40 R/C SFRS - Vancouver
Conv. ConstructionMD WallsD Walls
0.0 1.0 2.0 3.0 4.0Period (s)
0.00
0.10
0.20
V
/
W
D WallsD Partially coupled wallsD Coupled wallsMD MRFs D MRFs
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2005 NBCC Seismic Analysis
Better consideration of irregularities Requires more dynamic analysis Better consideration of torsional sensitivity Lateral storey drift limit increased: 2% -> Lateral storey drift limit increased: 2% ->
2.5%. Relates to structural damage. Post-disaster buildings shall not have any
irregularity
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Types of structural irregularities
1 Vertical stiffness irregularity2 Weight (mass) irregularity3 Vertical geometric irregularity4 In-plane discontinuity4 In-plane discontinuity5 Out-of-plane offsets6 Discontinuity in capacity (weak storey)7 Torsional sensitivity8 Non-orthogonal systems
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Irregularity trigger
When:
IEFaSa(0.2) > 0.35
+ any one of the 8 irregularity types,+ any one of the 8 irregularity types,
the building is considered as irregular
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Types of Irregularities1 Vertical Stiffness
lateral stiffness of the SFRS in a storey:< 70% of that in any adjacent storey, or < 80% of the average stiffness of the 3
storeys above or below.storeys above or below.
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Types of Irregularities2 Weight (Mass)
weight of a storey > 150% of weight of anadjacent storey.(a roof lighter than a floor below is excluded) (a roof lighter than a floor below is excluded)
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Types of Irregularities3 Vertical Geometric
horizontal dimension of the SFRS in a storey > 130% of that in any adjacent storey.(one-storey penthouse excluded)(one-storey penthouse excluded)
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Types of Irregularities4 In-Plane Discontinuity
in-plane offset of an element of the SFRS,or
reduction in lateral stiffness of an element in reduction in lateral stiffness of an element in the storey below.
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Types of Irregularities5 Out-of-Plane Offsets
discontinuity of lateral force pathe.g., out-of-plane offsetsof the elements of the SFRS.of the elements of the SFRS.
Top FloorsBottom Floors
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Types of Irregularities6 Discontinuity in Capacity - Weak Storey
storey shear strength less thanthat in the storey above.(Storey shear strength = total of all elements of the (Storey shear strength = total of all elements of the SFRS in the direction considered)
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Types of Irregularities7 Torsional sensitivity
if the ratio B > 1.7.B = max / avg calculated for static loads applied at 0.10 D calculated for static loads applied at 0.10 Dn
Plan
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Types of Irregularities
8 Non-orthogonal systems
SFRS not oriented along a set of orthogonal axes.
Plan
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Seismic Importance Factor
Importance Category IELow 0.8Low 0.8Normal 1.0High 1.3Post Disaster 1.5
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Modern Design Codes
SEAOC 1988/NBC 1990 CSA A23.3 1984 Canadian Concrete
Design Code Introduced Capacity Design
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Concrete Plastic Hinges
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Overview of Clause 21 Changes Introduced a ductility limit
state for plastic hinges in walls and coupling beams
Rotational capacity Rotational demand
f ( R d R o -
w )
idic id
h
w
h
w
-
L
w
/
2
L
w
L
w
/
2
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Plastic Hinges to Absorb Energy
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NBCC Concrete Ductile Systems
SINGLE WALLRd = 2.0 Rd = 4.0
COUPLED WALLRd = 2.5
MOMENT FRAME
Rd = 3.5 Rd = 4.0Rd = 3.5
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Un-Classified Systems
OUTRIGGER WALLFRAME WALLWALL - COLUMNS BRACED FRAME
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Earthquake Design Factor of Safety
Earthquake Factored Load Design
Factored Load 0.15 to 0.5 x Expected LoadLoad
Factored Bending Resistance 0.17 to 0.6 x Expected Load
Factor of Safety 0.17 to 0.6
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Philosophical Underpinning Earthquakes are rare events, the design
event has a 2% probability of exceedance in 50 years. That is, in an assumed 50 year building life, there is a 98% chance year building life, there is a 98% chance that the building will not experience an earthquake of this magnitude in its design life.
Therefore design only for life safety, not asset protection, the building may be irreparable but no one dies.
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2005 NBCC Objective Based Format
Part 1 Objectives of the Code Part 2 Prescriptive Solutions to Objectives
1995 1995 Firewalls with a fire rating of 2 hrs or less shall
be constructed of concrete or masonry. 2005 Firewalls with a fire rating of 2 hrs or less not
explicitly required to be masonry or concrete.
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Further InformationCommentary J - NBCC 2005Canadian J. of Civil Engineering, April 2003:
- overview and background of changes- seismic hazard maps- ground amplification factors- ground amplification factors- equivalent static load method- force modification factors- torsion- dynamic analysis- foundation rocking- non-structural components
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Thank YouThank You