ACI 318 08 Seismic Requirements L E Garcia

ACI 318-08 318-08 - Seismic Seismic Require Requiremen ments ts -- Luis E. Garcia Garcia

Requirements in ACI 318-08

General Requirements z

By:

Luis Enrique García President American Concrete Concrete Institute – ACI – 2008-2009 Partner Proyectos y Diseños Ltda. Consulting Engineers Professor Universidad de los Andes Bogotá, Colombia

R1.1.9 – Pro R1.1.9 Provisi visions ons for for earthquake resistance z

z

Explain changes in terminology used

ACI 318-08 with model codes and other documents



Scope



Terminology

R1.1.9 – Pro R1.1.9 Provis visions ions for for earthquake resistance

Commentary was expanded to: 

Modifications in

z

In this version of ACI 318 2008 , for the first time ti me,, ea eart rth hqu quak ake e re resi sist stan ance ce re requ quir irem emen ents ts ar are e defined in function of the Seismic Design Cat ate egory — SDC req equ uired for the st strruc uctture and not directly associated with the seismic risk zone. The minimum SDC to use is governed by the lega le gall lly y ad adop opte ted d ge gen ner eral al bu buil ildi ding ng co code de of whi hich ch ACI 318 forms a part.

4

1


TABLE TA BLE R1.1.9.1 — CORRELATION BETWEEN SEISMIC-RELA SEISMIC-RELATED TED TERMINOLOGY IN MODEL CODES

Code, standard, or resource document and edition

Level of seismic risk or assigned seismic performance or design categories as

ACI 318-08; 318-08; IBC 2000, 2003; 2006; NFPA 5000, 2003, 2006; ASCE 798, 7-02, 7-05; NEHRP 1997, 2000, 2003

SCD* A, B

SCS C

SCD D, E, F

BOCA National Building Code 1993, 1996, 1999; Standard Building Code 1994, 1997, 1999; AS CE CE 7 -9 -9 3, 7 -9 -9 5 N EH EH RP RP 1 99 99 1, 1994

SPC† A, B

SPC C

SPC D; E

Uniform Building Code 1991, 1994, 1997

Seismic Zone 0, 1

Seismic Zone 2

Seismic Zone 3, 4

*SDC

†SPC

Chapter 2 Notation and Definitions z

There were important changes in notation of the whole document and all individual Chapter notation was moved to Chapter 2. to Chapter 21. All definitions, old and new, were moved to Chapter 2.

= Seismic Design Category as defined in code, standard, or resource document. = Seismic Performance Category as defined in code, standard, or resource document

5

Chapter 21 Earthquake-resistant

Seismic Design Category and Energy Dissipation Capacity SDC Seismic Design Category

z

Chapter 21 was reorganized in function of Seismic Design Categories (SDC) A, B, C, and D, E, and F in incremental order from ordinary to special: A → B → C → D, E, F

A B

Denomination (Energy dissipation capacity)

Must com l with i n ACI 318-08

Chapters 1 to 19 and 22

Ordinary

Chapters 1 to 19, 22, and 21.2

C

Intermediate

Chapters 1 to 19, 22, and 21.3 y 21.4

D, E, F

Special

Chapters 1 to 19, 22, And 21.5 to 21.13

2


Elastic vs. Nonlinear Demand linear elastic nonlinear

20

z

10 0

(cm)

-10

0 0

1

2 2

3 3

4 4

5 5

6 6

-20

7 7

8 8

9 9

0.4

Given an energy dissipation capacity for the structural material and structural system, defined through an R va ue ep epen ng o e e a ng sc eme e es es gn horizontal seismic force is obtained from:

F y

linear elastic

0.6

(1/W)

12 1 13 3 1 14 4 1 15 5

time (s)

0.8

force

1 10 0 11

Current seismic design strategy

F e R

nonlinear

.

obtained using Newton’s 2 nd Law:

0 -0.2 0 0 -0.4

1

2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9

10 10 11 1 2 1 13 3 1 14 4 1 15 5

Fe

-0.6 -0.8

time (s)

m ass

S a (T , )

Acceleration response spectrum spectrum from the general building code

energy dissipation capacity is not available?

4


C.21.1 – Genera Generall Requireme Requirements nts Nonstructural wall panel in contact with the structure

Nonstructural wall panel separated from the structure

column

h

ACI 318-08 requires (21.1.2) that interaction that interaction between structural and nonstructural elements th that at ma af affe fect ct th the e res res on onse se dur durin in th the e ear earth th ua uake ke Must be taken into account. Rigid members assumed not to be a part of the seismic-force-resisting system are permitted provided their effect on the response of the system is considered and accommodated in the structural design. Consequences of failure of structural and nonstructural members that are not a part of the seismic-force-resisting system shall be considered.

z

z

z

Compressive strength of concrete f c 21 MPa pec e compress ve s reng o g we g concrete ≤ 35 MPa For computing the amount of confinement reinforcement f yt ≤ 700 MPa (= 100,000 psi = 7000 kgf/cm2 ) Reinforcing steel must meet ASTM A706. If ASTM A615 is used, it must meet: 



The actual yield strength based on mill tests does not exceed f y by more than 125 MPa. MPa. The ratio of the actual tensile strength to the actual yield strength is not less than1.25 than1.25

5


21.3 - Inter Intermedi mediate ate moment moment frames

21.3 - Inte Intermedi rmediate ate moment moment frames

Two-way slabs without beams (slab-column frames)

At the critical sections for punching shear, shear caused by factored gravity loads shall not exceed, 0.4 V c where V c must be calculated as defined in Chapter 11 for prestressed and non prestressed slabs.

z

This requirement may be waived if the slab complies with 21.13.6

z

21.4 — Interm Intermediat ediate e precast structural structural walls z

z

z

Requirements of 21.4 apply to intermediate precas s ruc ura wa s orm ng par o e seismic-force resisting systems. In connections between wall panels, or between wall panels and the foundation, yielding must be restricted to steel elements or reinforcement.. Elements of the connection that are not designed to yield must develop at least 1.5S least 1.5S y.

21.5 — Flexural members of special special moment frames x a orce

u mus

no excee

Clear span of element than 4d

z

.

c

g

n must be larger

/h / h > 0.3 Ratio bw

z

w 

bw > 250 mm



larger than the width of the supporting element plus 3h /4 at each side

8


21.5 — Flexu Flexural ral members members of special special moment frames

21.5 — Flexural members of special special moment frames Lon itud itudina inall rei reinfor nforcem cement ent Steel ratio for negative and positive reinforcement must not be less than:

f c y

1.4 y

but:

0.025 At least two bars continuous top and bottom.

21.5 — Flexural members of special special moment frames Longitudinal reinforcement

M n

M n Mn

Mn

0.25

M n

max.face

21.5 — Flexural members of special special moment frames Longitudinal reinforcement Lap splices are permitted if hoops are provided throughout the splice length. Maximum hoop /4 or spacing must not exceed d or 100 100 mm. mm. No lap splices are permitted in joints or within 2h of column face or where inelastic action is expected.

0.5M n

9


21.5 — Flexural members of special special moment frames

21.5 — Flexural members of special special moment frames

Hoops must be provided:

Shear design:

Ve

50 5 0 mm mm

5 50 0 mm mm

s d/2

M pr V e

2h 2h

M pr

2 2h h

Wu

der .

V e

M pr

der .

= 1.0

21.6 — Speci Special al moment moment frame members members subjected to bending and axial load

(Vu)ver. right

Pu2

M pr

izq . n

M pr computed using f ypr = 1.25 f y and

21.5 — Flexu Flexural ral members members of special special moment frames Pu1

M pr

izq . n

confinement zones

(Vu)vert. left

M pr

n

General (Vu)ver. left + Ve

Vu(x)

1

(Vu)ver. left- Ve

Vu

ver .i.iz q. q.

Vu

Pu

ver .d .der .

1 z

n

x

z u vert. right -

shear envelope

e

300 mm.

(Vu)ver. right+ Ve

For design, Vc = 0 if Ve is more than 50% of required shear strength, or axial force is less than 0.05f’ cAg

Axial force greater than 0.10 fc Ag The least section dimension that passes t roug t e centro must e greater t an

z

h > 0.4 /h Ratio b /

10


21.6 — Speci Special al moment moment frame members members subjected to bending and axial load z

21.6 — Speci Special al moment moment frame members members subjected to bending and axial load Transverse reinforcement in confining zones must comply with: z Spiral columns: f

Column flexural strength must comply with:

s

Mnc M nc M nb M nb M nc

M

nc

M nb M nc

M nb M nc M nc

M nc

nb

(a)

1.2

M nb

z

h x

0.3 s b M nb M nc

(b)

M nb M nc

M nb

(c)

Ash

350 mm

h x

joint transverse ren or orce ceme men n as required by 21.7 0

h x

50 mm b / 4

confinement lap splices in central zone zones

hc

100 s0

s

6d b long. s0

h

- x 3

150 mm 100 mm

0

hn 6

s

450 45 0 mm 0

joint transverse reinforcement as required by 21.7

6d b

long .

150 15 0 mm

50 mm

fyt

A Ach

0.09 s bc f c f yt

Mpr

Shear design

V e

b

f

21.6 — Speci Special al moment moment frame members members subjected to bending and axial load z

h x

c

f yt

Columns with hoops:

sh

21.6 — Speci Special al moment moment frame members members subjected to bending and axial load h x

0.12

M pr

M pr

arriba

abajo

hn

Mpr corresponds to the maximum moment strength for the axial load range on the 1.25f y and =1 ). V e cannot be element ( 1.25 less le ss th than an th the e on one e ob obta tain ined ed fr from om an anal al si sis. s.

For design V c = 0 if if V V e is more than 50% of the required shear or the axial force is less than 0.05f’ c Ag

hn

Ve

Mpr

11


21.7 — Join Joints ts of special moment moment frames frames

21.7 — Join Joints ts of special moment moment frames frames Computation of the shear demand on the joint:

z

General requirements

V e-col

plane to evaluate

M pr-c

shear Vu z

z

z

When computing shear strength within the joint in special frames all longitudinal reinforcement must be presumed to be stressed at 1.25 at 1.25f f y . Longitudinal reinforcement terminating at a joint must be extended to the far face of the column confined core and anchored in tension. When the beam longitudinal reinforcement passes through the joint , the column dimension parallel to the reinforcement cannot be less than 20 20d d b largest longitudinal bar, for normal weight concrete and 26 26d d b for lightweight concrete.

21.7 — Join Joints ts of special moment moment frames frames Shear strength z

1.25fy As

Cc

Ts

1.25fy As

Ts

Ts

1.25fy As

1.25fy As beam

V e-col

pr-c

Beam B eam iin n both both sides: sides: Vu

1.25fy As

As

viga

Beam Beam in in one one side: side: 1.25fy As viga Ve

V e

c ol

V e

c ol

V u

c ol

1.25fy As

v ig a

21.7 — Join Joints ts of special moment moment frames frames z

1.70

Definition of A j

fc Aj

Joints confined in three faces or in opposite faces

Vn z

Ts

Joints confined in all four faces

Vn z

Cc

column

1.25

fc A j

1.00

fc Aj

h A j

bw bw

Other joints h

Vn

bw

x

A j bw

2 x

bw

h

12


21.7 — Join Joints ts of special moment moment frames frames z

Development for hooks embedded in the confined core

21.8 — Spec Special ial moment moment frames frames constructed using precast concrete z

critical section dh

fy d b

z

db

5.4 f c z

21.8 — Spe Special cial moment moment frames frames constructed using precast concrete z

Special precast moment frames with ductile con onn nec ons mus comp y w a requirements for special cast-in-place frames and V n should not be less than 2V e.

z

Special precast moment frames with strong connections are intended to experience . These requirements are applicable independently of any of these two situations. situations .

The requirements of 21.8 apply for special moment frames built using precast concrete forming part of the seismic-force- resistant system. The detailing provisions in 21.8.2 and 21.8.3 are intended to produce frames that respond to design displacements essent ess ential ialll lik like e monol monolith ithic ic s eci ecial al mom moment ent frames. The provisions of 21.8.4 indicate that when not satisfying satisfying 21.8.2 or 21.8.3 they must satisfy the requirements of ACI 374.1

21.9 — Spec Special ial structur structural al walls and coupling beams z

Terminology

h

hw w

Vu

13


Minimum steel ratio z

14. 4.3. 3.2 2 – Min inim imum um ste teel el ra rati tio o of ver erti tica call re rein info forc rcem emen entt comput com puted ed ove overr gros gross s sec sectio tion n is:

. f or or de fo for me me d ba rs rs n ot ot l ar ar ge ge r t ha ha n Nº 5 ( 5/ 5/ 8” 8” ) ó 16M (16 (1 6 mm mm), ), wit with h f y no nott le less ss th than an 42 420 0 MP MPa. a.

z

Difference between wall and column



other er def deform ormed ed bar bars. s. 0.0015 for oth



0.0012

z

f or or w el el de ded w ir ir e re in inf or or ce ce me me nt nt w it it h di am am et et er er n ot ot larger lar ger tha than16 n16 mm.

14.3.3 14.3 .3 - Mi Mini nimu mum m ra rati tio o of ho hori rizo zont ntal al re rein info forc rcem emen entt ar area ea to gross gro ss con concre crete te are area, a, ρt: 

0.0020



other er def deform ormed ed bar bars. s. 0.0025 for oth



0.0020

f or or de fo for me me d b ar ar s n ot ot l ar ar ge ge r t ha han Nº 5 ( 5/ 5/ 8” 8” ) ó 16 M (16 (1 6 mm mm), ), wit with h f y no nott le less ss th than an 42 420 0 MP MPa. a.

14.3.6 — Vertical reinforcement need not be enclosed by lateral ties if vertical reinforcement area is not greater than 0.01 times gross concrete area, or where vertical reinforcement is not required as compression reinforcement.

f or or w el el de ded w ir ir e re in inf or or ce ce me me nt nt w it it h di am am et et er er n ot ot larger lar ger tha than16 n16 mm.

21.9 - Special structura structurall walls and coupling beams

eas wo cur a ns o re n orcemen

21.9 - Special structur structural al walls and coupling beams z

Nominal Nom inal shear shear stren stren th must must not exceed: exceed:

Vn

must be used in a wall if Vu exceeds 0.17 Acv fc (MPa) = 0.53 A cv fc

(kgf/cm2)

z

where

c

is:

Acv

c

fc

n fy

c 0.25 0.17

hw 0 0

0.5 1.0 1.5 0.5

2 2.0 .0 2.5 2.5

w

15


Nonlinear response of wall Using Moment-area theorems it is possible to show that the lateral deflection caused by curvature up to yield (green zone) is:

Nonlinear wall deflection Curvature at yield

Deflection at yield

Nonlinear curvature

Nonlinear deflection

w u

y

b

y

hw

and the additional deflection caused by nonlinear rotation (orange zone) is: p y

The total total deflection is:

Total lateral deflection is then:

p u

y

p

a u

y)

y

We can solve for the ultimate curvature demand and obtain:

u

Moment-curvature diagram for wall section M

What happens at section?

Ultimate curvature demand At level of displacement demand

Mn

At level of nominal strength

Mcr

0 cr

y

n

u

cu u

Strain

s

y

s At le leve vell of yield in tension of extreme reinforcement

y

c

= 0.003

c

< 0.003

n

c y y

h w

17


21.9 - Speci Special al structural structural walls walls and coupling beams

Old (pre-1999) procedure

Boundary Boundar y elements – Both procedures procedures

Boundary elements res s ng a

w

exura

effect that include

heb

seismic forces Pu

Mu

Pu

Ptu

Ag Ptn

Mu w

heb

A st f y

0

Pcu

Pu

Mu

2

w

h eb

P0n

[0.85 fc (A (A g

Pn(max)

0.80

A st )

P0n

21.9 - Speci Special al structural structural walls walls and coupling beams z

A st f y]

procedures) these these boundary boundary elements must extend extend horizontally from the maximum compression fiber a distance equal to the greater of : c-0.1 w or c/2. boundary ry element must include z In section with flanges the bounda the effective flange width and must extend at least 300 mm into the web. reinforcement must be that required for column, z Transverse reinforcement but there is no need to comply with equation 21-3. z Special transverse reinforcement in the boundary element must extend into the foundation element supporting the wall. z Wall horizontal transverse reinforcement must be anchored into the confined boundary element core.

Coupling beams

In ACI 318-08, there are modifications in the re uirements for cou lin beams in walls.

20


21.10 — Spe Special cial structur structural al walls constructed using precast concrete

21.11 — Struct Structural ural diaphragms diaphragms and trusses

z

Scope— These requirements requirements apply to special structural walls constructed using precast concrete forming part of the seismic-force- resisting system.

z

Special structural walls constructed using precast concrete shall satisfy all requireme nts of special cast-in-place structural walls plus those of section 21.10.

z

Special structural walls constructed using precast concrete and unbonded post- tensioning tendons and not satisfying the requirements of 21.10.2 are permitted provided they satisfy the requirements of ACI ITG-5.1.

21.11 — Struc Structural tural diaphragms diaphragms and trusses trusses This section contains:

prescribed horizontal forces

z

z z

floor diaphragm

z z z

Requirements for slabs-on-grade , floor and roof slabs when they are part of the seismic-force-resisting system must comply with this section. Minimum thickness for diaphragms are given. Gives minimum reinforcement for diaphragms diaphragms.. Indicates shear strength for these elements Defi De fine nes s wh when en bo boun unda darr el elem emen ents ts mu must st be us used ed in diaphragms. Includes requirements for construction joints within the diaphragm.

21


21.13 — Membe Members rs not designated designated as part of the seismic-force-resisting system

21.13 — Member Members s not designated designated as part of the seismic-force-resisting system

Story drift cannot exceed the larger of:

0.005 or 0.035

0.05

V ug V c

where V ug is the factored gravity punching shear demand and V c is the punching shear strength.

The End

23

ACI 318 08 Seismic Requirements L E Garcia

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