cac handbook chapter 11 seismic design

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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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4

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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10

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

6

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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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60


21

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62


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Details of Ductile Beam

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Design of Interior Ductile Column

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66


23

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68


69


24

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Design of Interior Beam-Column Joint

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72


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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

cac handbook chapter 11 seismic design

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