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1C O N C R E T E D E S I G N H A N D B O O K T H I R D E D I T I O N
Seismic Design
Presented By: Denis Mitchell
Denis Mitchell and
Patrick Paultre
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NBCC 2005 - CANCEE CSA A23.3 Clause 21- Special Provisions
for Seismic Design Explanatory Notes on Clause 21
by Jim Mutrie and Perry Adebar
Handbook Chapter 11 Seismic Design by Denis Mitchell and Patrick Paultre
Seismic Design in Concrete Design Handbook
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General RequirementsNBCC 2005 Design for clearly defined load paths
Must have a clearly defined Seismic Force Resisting System (SFRS)
Stiff elements not part of SFRS to be separated from structural components or made part of SFRSand accounted for in analysis
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Uniform Hazard Spectrum More uniform margin of collapse (NHERP, 1997
and BSSC, 1997)
Seismic hazard at a lower probability of 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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Site Classification for Seismic Site Response
A = hard rock B = 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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Seismic Site Coefficients
Depend on site classification Depend on spectral response acceleration, Sa Fa is acceleration based site coefficient Fv is velocity based site coefficient
Site Class C: Fa = Fv = 1.0 for all values of Sa
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Design Spectral Response Acceleration, Site Class C
00.10.20.30.40.50.60.70.80.9
1
0 1 2 3 4
T
S(a)
VancouverMontrealOttawaTorontoLondon
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Base Shear, V NBCC 2005
V =S(Ta) Mv IE
Rd RoW
Spectral response acceleration
Higher mode effect factor
Importance factor
Ductility-related force modification factor
Overstrength-related force modification factor
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Factor for Higher Mode Effects, Mv
Equivalent static lateral force based on assumed single mode response
Depends on type of SFRS Depends on ratio Sa(0.2)/Sa(2.0) Depends on fundamental period of
structure, Ta
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Seismic Importance Factor
Importance Category IELow 0.8
Normal 1.0
High 1.3
Post Disaster 1.5
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Design and Detailing Provisions for Moment Resisting Frames
Design and Detailing Provisions Required for Different Reinforced Concrete Structural Systems and Corresponding Rd and R0 Factors
Type of SFRS Rd Ro Summary of design and detailing requirements in CSA A23.3-04
Ductile moment resisting frames
4.0 1.7 Beams capable of flexural hinging with shear failure and bar buckling avoided. Beams and columns must satisfy ductile detailing requirements. Columns properly confined and stronger than beams. Joints properly confined and stronger than beams.
Moderately ductile moment resisting frames
2.5 1.4 Beams and columns must satisfy detailing requirements for moderate ductility. Beams and columns to have minimum shear strengths. Joints must satisfy moderate ductility detailing requirements and must be capable of transmitting shears from beam hinging.
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Concrete Frames(a) = 1.5 (b) = 2.5 (c) = 4.0
/2 /2 /2 /2
>>>
450 mm
/6
>>>
450 mm
/6
1648
824
300 mm/2
824
300 mm/4
6100 mm
confinement/4
824
300 mm/4
steel2 2
1
1
2 2
1
1
2 2
1
1
SECTION 2 - 2SECTION 1 - 1 SECTION 1 - 1 SECTION 1 - 1SECTION 2 - 2 SECTION 2 - 2
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Design and Detailing Provisions for shearwallsDesign and Detailing Provisions Required for Different Reinforced Concrete Structural Systems and Corresponding Rd and R0 Factors
Type of SFRS Rd Ro Summary of design and detailing requirements in CSA A23.3-04
Ductile coupled walls
4.0 1.7 At least 66% of base overturning moment resisted by wall system must be carried by axial tension and compression in coupled walls. Coupling beams to have ductile detailing and be capable of flexural hinging or resist loads with diagonal reinforcement (shear failure and bar buckling avoided). Walls must have minimum resistance to permit attainment of nominal strength in coupling beams and minimum ductility level.
Ductile partially coupled walls
3.5 1.7 Coupling beams to have ductile detailing and be capable of flexural hinging or resist loads with diagonal reinforcement (shear failure and bar buckling avoided). Walls must have minimum resistance to permit attainment of nominal strength in coupling beams and minimum ductility level.
Ductile shearwalls
3.5 1.6 Walls must be capable of flexural yielding without local instability, shear failure or bar buckling. Walls must satisfy ductile detailing and ductility requirements.
Moderately ductile shearwalls
2.0 1.4 Walls must satisfy detailing and ductility requirements for moderate ductility. Walls must have minimum shear strength.
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Shearwalls
0 .0 0 2 00 .0 0 1 5
5 0 0 m m3
0 .0 0 2 50 .0 0 2 5
5 0 0 m m 3
4 5 0 m m
0 .0 0 2 50 .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 )
( a ) = 1 .5 ( b ) = 2 .0 ( c ) = 3 .5
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Coupled W alls( a ) = 1 .5 ( b ) = 2 .0 ( c ) = 3 .5 , 4 . 0
s t ir r u p s@ / 2
B e a m s D ia g o n a lb a r s h o o p s
B e a m ss t ir r u p s@ @ 6
2 41 0 0 m m
82 4
3 0 0 m m/ 4
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Types of structural irregularities
1. Vertical stiffness irregularity2. Weight (mass) irregularity3. Vertical geometric irregularity4. In-plane discontinuity5. Out-of-plane offsets6. Discontinuity in capacity (weak storey)7. Torsional sensitivity8. Non-orthogonal systems
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Conditions for IrregularitySFRS is irregular when: IEFaSa(0.2) > 0.35, and any one of the 8 irregularity types.
Irregularity type 6 (weak storey) not permitted except if IEFaSa(0.2) < 0.2 and V x 1.5.
Post-disaster buildings some irregularities not permitted
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Conventional ConstructionConventional ConstructionRRdd = 1.5 = 1.5 -- FRAMESFRAMESColumns ties shall comply with MD details
unless: Sum of Mr of columns at a joint is greater
than Mr of beams framing into joint Mr of column greater than elastic Mf
(RdRo = 1.0) IEFaSa(0.2) is less than 0.2
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Conventional ConstructionConventional ConstructionRRdd = 1.5 = 1.5 -- W ALLSW ALLS Walls designed according to Clause 14 Cannot apply reduction factor to lap splice
lengths Vr shall be greater than Vf but not less than
the smaller of: V corresponding to Mr at base of wall V corresponding to elastic shear (RdRo = 1.0)
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Conventional ConstructionConventional ConstructionRRdd = 1.5 = 1.5 -- W all ReinforcementW all Reinforcement Distributed reinforcement:
2 layers if thickness greater than 210 mm Min. area of horizontal steel = 0.0015Ag Min. area of vertical steel = 0.002Ag No ties required in compression zone if
total area of vertical steel less than 0.005Ag and bar size less than 20M
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Conventional ConstructionConventional ConstructionRRdd = 1.5 = 1.5 -- W all ReinforcementW all Reinforcement Concentrated vertical reinforcement:
Not less than 2 15M at each end Less than 0.04 Ag in boundary region If concentrated steel in excess of 2
20M then vertical bars to be tied (column ties)
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Shear Failure of Poorly Detailed Shear Failure of Poorly Detailed Shear W all Shear W all Kobe 1995Kobe 1995
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Precast Concrete FramesTwo types of connections:
Ductile connection: Experiences yielding Frame members designed for extra
strength Strong connection:
Remains elastic Factored resistances greater than
probable strength demand
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Failure of Connections in Failure of Connections in PrecastPrecastParking Structure Parking Structure Mexico 1985Mexico 1985
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Ductile Ductile PrecastPrecast Column with Column with Strong Connection Strong Connection -- Turkey 1999Turkey 1999
Diaphragmfailed
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Precast Concrete Shear W allsTwo types of walls: Ductile Shear Walls:
Must satisfy cast-in-place ductile wall requirements
Strong connections Shear Walls with Moderate Ductility:
Must satisfy cast-in-place MD wall requirements
Panel connections yielding restricted to steel elements
Adequate anchorage of wall panels to foundation
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Diaphragm Systems Provide complete load path Design chord forces Design collectors for transfer to SFRS
members Design as shear panels or use strut-and-tie
models Minimum slab reinforcement Reinforcement detailing requirements Limiting shear stresses in shear panels
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Diaphragm Failure in Diaphragm Failure in PrecastPrecastStructure Structure Northridge 1994Northridge 1994
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Members not Considered Part Members not Considered Part of SFRS of SFRS Flat Plate SystemsFlat Plate Systems
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Progressive Collapse of Flat Plate Progressive Collapse of Flat Plate Structure Structure Mexico City 1985Mexico City 1985
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Severe Drifts of Flat Plate Hospital Severe Drifts of Flat Plate Hospital Structure Structure Mexico City 1985Mexico City 1985
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Reduced Shear Stresses As a Reduced Shear Stresses As a Function of DriftFunction of DriftSlab-column
connections: Calculate gravity load
two-way shear stress (without seismic unbalanced moment)
Shear stress must be less than RE times the two-way shear strength
0.1005.085.0
=
iER
Interstorey drift cannot
exceed 0.025
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Frame Members not Considered Frame Members not Considered Part of SFRS (RPart of SFRS (Rdd = 2 or greater)= 2 or greater)
Frame members not considered part of the SFRS must be analyzed to determine forces induced due to the design displacement
If factored moments exceed nominal resistances then elements shall be designed to accommodate plastic hinging (detailing requirements provided)
Resistance must be sufficient to carry gravity load effects as well as axial and shear forces induced due to the design displacement
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Brittle Interior Brittle Interior Columns Columns Designed for Designed for Gravity Loads Gravity Loads OnlyOnly
Northridge 1994
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Limit on Concrete Limit on Concrete Compressive StrengthCompressive Strength Clause 21 of 1994 Standard limited
concrete compressive strength to 55 MPa 2004 Standard increased the limit to 80
MPa based on testing carried out at McGill and Sherbrooke on columns, walls, coupling beams, beam-column-slab sub-assemblages and a two-storey frame structure
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ColumnColumn Axial Load TestsAxial Load Tests--Sherbrooke and McGillSherbrooke and McGill
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Influence of ConfinementInfluence of Confinement
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Flexural and Axial Load Tests - Sherbrooke
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Flexure and Axial Load
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Flexure and Axial Load
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Two-Storey Frame Test -Sherbrooke
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BeamBeam--ColumnColumn--Slab SubSlab Sub--AssemblagesAssemblages-- McGillMcGill
Normal-strength concrete High-strength concrete
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Effects of Configuration and Effects of Configuration and Spacing of Hoops on ConfinementSpacing of Hoops on Confinement
Poor large s and nl = 4 Good small s and nl = 8
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Column Confinement, RColumn Confinement, Rdd = 4.0= 4.0
)2/( = lln nnk
cyh
csh shf
fA'
09.0 = cyh
c
ch
gpnsh hsf
fAA
kkA 2.0= '
ofp PPk /=
Gross area
Area confined
spacing
Core dimension
But not less than
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Ductility Demands Ductility Demands Ductile W allsDuctile W alls
id
( )004.0
2
=
ww
wfdofid
h
RRl
004.0
=w
dofid h
RR
Individual wall:
Segment of coupled wall:
Top deflection
Wall height
Wall overstrength factor
AdebarAdebar, , MutrieMutrie and and DeVallDeVall
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Ductility Capacities Ductility Capacities Ductile W allsDuctile W alls
( )ic u y pl =
0,0022cu w
iclc
=
2p wl l=
025.0002.02
=cwcu
icl
wy l/004.0=
025.02
maxmax =
=
w
swic l
l
Inelastic rotational capacity:
Max. concrete comp. strain
Depth of compression
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Ductility of Coupling BeamsDuctility of Coupling Beams
Inelastic rotational demand:
Inelastic rotational capacity:
0.04 for ductile diagonally reinforced coupling beams
0.02 for ductile conventionally reinforced coupling beams
u
cg
w
dfid h
RRl
l
= 0
Distance between wall centroids
Clear span of coupling beam
White and Adebar, 2004
L
Ln
wall
floorcb
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FullFull--Scale Testing of Coupling Scale Testing of Coupling Beams Beams -- McGillMcGill
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Influence of Concrete StrengthInfluence of Concrete Strength-- McGillMcGill
High Strength Coupling Beam
Normal Strength Coupling Beam
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Reversed Cyclic Loading Responses of Coupling Beams
-400
0
400
-80 0 80Deflection (mm)
Beam
She
ar (k
N)
- general yielding
- cover spalling
Specimen MR4
-400
0
400
-80 0 80Deflection (mm)
Beam
She
ar (k
N)
- general yielding
- cover spalling
Specimen NR4
Normal-Strength Concrete High-Strength Concrete
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Factored, Nominal and Probable Moment Resistance
Factored, Nominal and Probable Moment Resistances Type of flexural resistance
Calculated using
Where used Approximate relationships for flexure
rM = factored resistance
650.c = 850.s =
All members must satisfy fr MM
nM = nominal resistance
01.c = 01.s =
To ensure columns stronger than beams
rn M.M 21
pM = probable resistance
01.c = 01.s =
ys f.f 251=
rp M.M 471
Note: the relationship between nM and rM for the case of flexure and axial load depends on the level of axial load
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Factored Loading CasesPrincipal loads: 1.0D + 1.0E
And either of the following:1) For storage occupancies, equipment areas and
service rooms:1.0D + 1.0E + 1.0L + 0.25S
2) For other occupancies:1.0D + 1.0E + 0.5L + 0.25S
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Design Examples
Six-Storey Ductile Moment Resisting Frame in Vancouver
Ductile Core-Wall Structure in Montreal
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Rd = 4.0 and Ro = 1.7Site Classification C
(Fa & Fv = 1.0)Interior columns: 500 x 500 mm
Exterior columns: 450 x 450 mm
Slab: 110 mm thick
Beams (1-3rd floors): 400 x 600 mm
Beams (4-6th floors): 400 x 550 mm
Six-Storey Ductile Moment Resisting Frame in Vancouver
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Material PropertiesConcrete: normal density concrete with 30 MPaReinforcement: 400 MPaLive loadsFloor live loads:2.4 kN/m2 on typical office floors4.8 kN/m2 on 6 m wide corridor bayRoof load2.2 kN/m2 snow load, accounting for parapets and equipment projections1.6 kN/m2 mechanical services loading in 6 m wide strip over corridor bayDead loadsself-weight of reinforced concrete members calculated as 24 kN/m31.0 kN/m2 partition loading on all floors0.5 kN/m2 mechanical services loading on all floors0.5 kN/m2 roofingWind loading1.84 kN/m2 net lateral pressure for top 4 storeys1.75 kN/m2 net lateral pressure for bottom 2 storeysThe fire-resistance rating of the building is assumed to be 1 hour.
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Gravity Loading
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Design spectral responseacceleration E-W Direction
Empirical: Ta = 0.075 (hn)3/4 = 0.76 s
Dynamic: T = 1.35 s but not greater than 1.5Ta = 1.14s
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Design of Ductile Beam
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Design of Ductile Beam
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Design of Ductile Beam
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Design of Ductile Beam
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Design of Ductile Beam
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Details of Ductile Beam
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Design of Interior Ductile Column
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Design of Interior Ductile Column
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Design of Interior Ductile Column
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Design of Interior Ductile Column
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Design of Interior Ductile Column
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Design of Interior Ductile Column
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Design of Interior Beam-Column Joint
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Design of Interior Beam-Column Joint
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Design of Interior Beam-Column Joint
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Twelve-Storey Ductile Core Wall Structure in Montreal
E-W: Rd = 4.0 and Ro = 1.7N-S: Rd = 3.5 and Ro = 1.6Site Classification D (Fa = 1.124 & Fv = 1.360)
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Design spectral responseacceleration N-S Direction
Empirical: Ta = 0.05 (hn)3/4 = 0.87 s
Dynamic: T = 1.83 s but not greater than 2Ta = 1.74s
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Torsion of Core W all
Max BNS = 1.80Max BEW = 1.66
Max B > 1.7irregularity
type 7
avemaxx /B =
Torsional Sensitivity
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Seismic and W ind Loading
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Diagonally Reinforced Coupling Beam
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W all Reinforcement Details
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Factored Moment Resistance E-W
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Factored Moment Resistance N-S
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