LEGARCIA AC 318 08 Seismic Requirements[1]

7/27/2019 LEGARCIA AC 318 08 Seismic Requirements[1]

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ACI 318-08 - Seismic Requirements -- Luis E. Garcia

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Requirementsin ACI 318-08

Requirementsin ACI 318-08

By:

Luis Enrique GarcaPresident American Concrete Institute ACI 2008-2009

Partner Proyectos y Diseos Ltda. Consulting Engineers

Professor Universidad de los Andes

Bogot, Colombia

By:

Luis Enrique GarcaPresident American Concrete Institute ACI 2008-2009

Partner Proyectos y Diseos Ltda. Consulting Engineers

Professor Universidad de los Andes

Bogot, Colombia

General Requirements

General Requirements

Modifications in Modifications inScope

Terminology

Scope

Terminology

R1.1.9 Provisions forearthquake resistanceR1.1.9 Provisions forearthquake resistance

Commentary was expanded to:

Explain changes in terminology used

Commentary was expanded to:

Explain changes in terminology used

ACI 318-08 with model codes and otherdocuments

ACI 318-08 with model codes and otherdocuments

R1.1.9 Provisions forearthquake resistanceR1.1.9 Provisions forearthquake resistance

In this version of ACI 318 2008 for the first In this version of ACI 318 2008 for the first

time, earthquake resistance requirements aredefined in function of the Seismic DesignCategory SDC required for the structure andnot directly associated with the seismic riskzone.

time, earthquake resistance requirements aredefined in function of the Seismic DesignCategory SDC required for the structure andnot directly associated with the seismic riskzone.

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The minimum SDC to use is governed by thelegally adopted general building code of whichACI 318 forms a part.

The minimum SDC to use is governed by thelegally adopted general building code of whichACI 318 forms a part.


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TABLE R1.1.9.1 CORRELATION BETWEEN SEISMIC-RELATED

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; IBC 2000, 2003; 2006;

NFPA 5000, 2003, 2006; ASCE 7-

98, 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;

ASCE 7-93 7-95 NEHRP 1991

SPC

A, B

SPC

C

SPC

D; E

5

, ,1994

Uniform Building Code 1991,

1994, 1997

Seismic Zone

0, 1

Seismic Zone

2

Seismic Zone

3, 4

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

Chapter 2Notation and Definitions

Chapter 2Notation and Definitions

There were important changes innotation of the whole document and allindividual Chapter notation was movedto Chapter 2.

There were important changes innotation of the whole document and allindividual Chapter notation was movedto Chapter 2.

to Chapter 21. All definitions, old andnew, were moved to Chapter 2.

to Chapter 21. All definitions, old andnew, were moved to Chapter 2.

Chapter 21Earthquake-resistant

Chapter 21Earthquake-resistant

Chapter 21 was reorganized in function ofSeismic Design Categories (SDC) A, B, C,and D, E, and F in incremental order fromordinary to special:

Chapter 21 was reorganized in function ofSeismic Design Categories (SDC) A, B, C,and D, E, and F in incremental order fromordinary to special:

A B CD, E, FA B CD, E, F

Seismic Design Category andEnergy Dissipation Capacity

Seismic Design Category andEnergy Dissipation Capacity

SDC DenominationMust com l with i n

Seismic DesignCategory

(Energy dissipationcapacity)

ACI 318-08

A OrdinaryChapters 1 to 19 and 22

B Chapters 1 to 19, 22,and 21.2

C IntermediateChapters 1 to 19, 22,

and 21.3 y 21.4

D, E, F SpecialChapters 1 to 19, 22,

And 21.5 to 21.13


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Elastic vs. Nonlinear DemandElastic vs. Nonlinear Demand

1010

2020 linear elasticlinear elasticnonlinearnonlinear

-20-20

-10-10

00

00 11 22 33 44 55 66 77 88 99 101 0 1111 1 21 2 1 31 3 1 41 4 1 515

time (s)time (s)

(cm)(cm)

linear elasticlinear elastic

nonlinearnonlinear0.40.4

0.60.6

0.80.8

forceforce

-0.8-0.8

-0.6-0.6

-0.4-0.4

-0.2-0.2

00..

00 11 22 33 44 55 66 77 88 99 1010 1111 1 21 2 1 31 3 1 41 4 1 515

time (s)time (s)

(1/W)(1/W)

Current seismic design strategyCurrent seismic design strategy Given an energy dissipation capacity for the structural

material and structural system, defined through an R Given an energy dissipation capacity for the structural

material and structural system, defined through an R

horizontal seismic force is obtained from:

horizontal seismic force is obtained from:

ey

FF

R=

obtained using Newtons 2ndLaw:

obtained using Newtons 2ndLaw:

= e aF m ass S T ( , ) Acceleration response spectrumfrom the general building code

Acceleration response spectrumfrom the general building code

energy dissipation

capacity is notavailable?

energy dissipation

capacity is notavailable?


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Nonstructural wallpanel in contactwith the structure column

ACI 318-08 requires (21.1.2) that interaction between structural and

nonstructural elements that ma affect the res onse durin the earth uake

hNonstructural wall

panel separatedfrom the structure

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.

C.21.1 General RequirementsC.21.1 General Requirements

Compressive strength of concrete 21 MPa Compressive strength of concrete 21 MPacf v w

concrete 35 MPa

For computing the amount of confinement

reinforcement fyt700 MPa (= 100,000 psi = 7000kgf/cm2) Reinforcing steel must meet ASTM A706. If ASTM

A615 is used, it must meet:

v wconcrete 35 MPa

For computing the amount of confinement

reinforcement fyt700 MPa (= 100,000 psi = 7000kgf/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 fyby more than 125 MPa. The ratio of the actual tensile strength to the actual yield

strength is not less than1.25

The actual yield strength based on mill tests does notexceed fyby more than 125 MPa.

The ratio of the actual tensile strength to the actual yieldstrength is not less than1.25


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21.3 - Intermediate moment frames21.3 - Intermediate moment frames21.3 - Intermediate moment frames21.3 - Intermediate moment frames

Two-way slabs without beams (slab-column 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,

where must be calculated as defined in

Chapter 11 for prestressed and non prestressed

slabs.

At the critical sections for punching shear, shear

caused by factored gravity loads shall not exceed,

where must be calculated as defined in

Chapter 11 for prestressed and non prestressed

slabs.

cV0.4 cV

This requirement may be waived if the slab

complies with 21.13.6

This requirement may be waived if the slab

complies with 21.13.6

21.4 Intermediate precast structural walls21.4 Intermediate precast structural walls

Requirements of 21.4 apply to intermediate Requirements of 21.4 apply to intermediateprecas s ruc ura wa s orm ng par o eseismic-force resisting systems.

In connections between wall panels, orbetween wall panels and the foundation,yielding must be restricted to steel elementsor reinforcement..

precas s ruc ura wa s orm ng par o eseismic-force resisting systems.

In connections between wall panels, orbetween wall panels and the foundation,yielding must be restricted to steel elementsor reinforcement..

Elements of the connection that are notdesigned to yield must develop at least 1.5Sy.

Elements of the connection that are notdesigned to yield must develop at least 1.5Sy.

21.5 Flexural members of specialmoment frames


x a orce umus no exceeClear span of element n must be larger

than 4dRatio bw/h > 0.3

x a orce umus no excee

Clear span of element n must be larger

than 4dRatio bw/h > 0.3

c g.

w

bw> 250 mm

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

w

bw> 250 mm

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


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21.5 Flexural members of specialmoment frames21.5 Flexural members of specialmoment frames 21.5 Flexural members of specialmoment frames21.5 Flexural members of specialmoment frames

Lon itudinal reinforcementLon itudinal reinforcement

Steel ratio for negative and positivereinforcement must not be less than:

Steel ratio for negative and positivereinforcement must not be less than:

cf 1.4 but:

At least two bars continuous top and bottom.

but:

At least two bars continuous top and bottom.

y

0.025



Longitudinal reinforcementLongitudinal reinforcement

n n faceM M max.0.25nM

nM

n nM M0.5



Longitudinal reinforcementLongitudinal reinforcement

Lap splices are permitted if hoops are providedthroughout the splice length. Maximum hoop

spacing must not exceed d/4 or 100 mm.

No lap splices are permitted in joints or within 2hof column face or where inelastic action is

Lap splices are permitted if hoops are providedthroughout the splice length. Maximum hoop

spacing must not exceed d/4 or 100 mm.

No lap splices are permitted in joints or within 2hof column face or where inelastic action isexpec e .expec e .


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21.5 Flexural members of special

moment frames

21.5 Flexural members of special

moment framesHoops must be provided:Hoops must be provided:

50 mm50 mm 50 mm50 mms d/2s d/2

2h2h 2h2h

confinement

zones

confinement

zones

21.5 Flexural members of specialmoment frames21.5 Flexural members of specialmoment frames

Shear design:Shear design:

nn

VeVe

prM

prM+

pr prizq der e

n

M MV

. .+ + =

pr prizq der

e

n

M MV

. . ++ =

Mprcomputed using fypr= 1.25 fy and = 1.0Mprcomputed using fypr= 1.25 fy and = 1.0



Pu1Pu1 Pu2Pu2WuWu

(Vu)ver. right(Vu)ver. right(Vu)vert. left(Vu)vert. left

11

xx

Vu(x)Vu(x)

u u uver .izq. ver .der .n1V V P + (Vu)ver. left + Ve(Vu)ver. left + Ve

(Vu)ver. left-Ve(Vu)ver. left-Ve

shear

envelope

shear

envelope (Vu)ver. right+ Ve(Vu)ver. right+ Veu vert. right - eu vert. right - e

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

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

21.6 Special moment frame memberssubjected to bending and axial load


General

Axial force greater than

The least section dimension that passes

General

Axial force greater than

The least section dimension that passes

0.10 c gf Aroug e cen ro mus e grea er an

300 mm.

Ratio b/h > 0.4

roug e cen ro mus e grea er an300 mm.

Ratio b/h > 0.4


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21.6 Special moment frame memberssubjected to bending and axial load21.6 Special moment frame memberssubjected to bending and axial load

Column flexural strength must complywith:

Column flexural strength must complywith:

1.2nc nbM MMnc M

Mnb

Mnb

Mnc

nb

MnbMnc

Mnbnc

Mnc Mnb

Mnc

Mnc MnbMncMnbMnc

(a) (c)(b)

21.6 Special moment frame memberssubjected to bending and axial load21.6 Special moment frame memberssubjected to bending and axial load

Transverse reinforcement in confining zones must complyTransverse reinforcement in confining zones must complywith:

Spiral columns:

Columns with hoops:

with:

Spiral columns:

Columns with hoops:

0.3 As b f

0.12= cs

yt

f

f

= sh yt chf A0.09 = c csh

yt

s b fA

f



hx hx hx

xh mm350

joint transversejoint transverse

hx b

hc

b

b

s d long.

s0

/ 4

6

confinementzones

confinementzones

50 mm50 mm0

lap splices incentral zone

lap splices incentral zone

ren orcement asrequired by 21.7ren orcement asrequired by 21.7

n

h

h 60

b long6d .s50 mm50 mm

0joint transverse

reinforcement as

required by 21.7

joint transversereinforcement as

required by 21.7

450 mmx-100s

mm

mm

0

3

150

100

+ =

150 mm



Shear design Shear design MprMpr

Mprcorresponds to the maximum moment

strength for the axial load range on theelement (1.25fyand =1). Ve cannot beless than the one obtained from anal sis.

Mprcorresponds to the maximum momentstrength for the axial load range on theelement (1.25fyand =1). Ve cannot beless than the one obtained from anal sis.

hnhn VeVe

pr prarriba abajo

e

n

M MV

h

+=

For design Vc= 0 if Ve is more than 50%

of the required shear or the axial force

is less than 0.05fcAg

For design Vc= 0 if Ve is more than 50%

of the required shear or the axial force

is less than 0.05fcAgMprMpr


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21.7 Joints of special moment frames21.7 Joints of special moment frames

General requirementsGeneral requirements

When computing shear strength within the joint inspecial frames all longitudinal reinforcement must be

presumed to be stressed at 1.25fy.

Longitudinal reinforcement terminating at a joint mustbe extended to the far face of the column confined coreand anchored in tension.

When computing shear strength within the joint inspecial frames all longitudinal reinforcement must be

presumed to be stressed at 1.25fy.

Longitudinal reinforcement terminating at a joint mustbe extended to the far face of the column confined coreand anchored in tension.

en t e eam ong tu na re n orcement passesthrough the joint , the column dimension parallel to thereinforcement cannot be less than 20db largestlongitudinal bar, for normal weight concrete and 26dbfor lightweight concrete.

en t e eam ong tu na re n orcement passesthrough the joint , the column dimension parallel to thereinforcement cannot be less than 20db largestlongitudinal bar, for normal weight concrete and 26dbfor lightweight concrete.

21.7 Joints of special moment frames21.7 Joints of special moment frames Computation of the shear demand on the joint: Computation of the shear demand on the joint:

Mpr-cMpr-cVe-colVe-colplane to evaluate

shear Vu

plane to evaluate

shear Vucolumncolumn

beambeam

s y sT f A1.25

c s y sC T f A1.25=

c s y sC T f A1.25 =

s y sT f A1.25

Ve-colVe-colpr-cpr-c

u y s s eviga col V f A A V 1.25 + y s eviga col

u

y s eviga col

f A V

V

f A V

1.25

1.25

Beam in both sides:Beam in both sides: Beam in one side:Beam in one side:


Shear strengthShear strength

Joints confined in all four faces

Joints confined in three faces or in opposite faces

Joints confined in all four faces

Joints confined in three faces or in opposite faces

n c jV f A1.70 =

n c jV f A1.25 = Other joints Other joints

n c jV f A1.00 =


Definition of Aj Definition of Aj

Ajbwbw

bwbw

hh

Aj

bwbw

hh

x

w

w

b x

b h

2 +


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Development for hooks embedded in the Development for hooks embedded in theconfined coreconfined core

db

dh

critical

section

y bf d

= cf5.4

21.8 Special moment framesconstructed using precast concrete21.8 Special moment framesconstructed using precast concrete

The requirements of 21.8 apply for special The requirements of 21.8 apply for specialmoment frames built using precastconcrete forming part of the seismic-force-resistant system.

The detailing provisions in 21.8.2 and21.8.3 are intended to produce frames thatrespond to design displacementsessentiall like monolithic s ecial moment

moment frames built using precastconcrete forming part of the seismic-force-resistant system.

The detailing provisions in 21.8.2 and21.8.3 are intended to produce frames thatrespond to design displacementsessentiall like monolithic s ecial momentframes.

The provisions of 21.8.4 indicate that whennot satisfying 21.8.2 or 21.8.3 they mustsatisfy the requirements of ACI 374.1

frames.

The provisions of 21.8.4 indicate that whennot satisfying 21.8.2 or 21.8.3 they mustsatisfy the requirements of ACI 374.1

21.8 Special moment framesconstructed using precast concrete

21.8 Special moment framesconstructed using precast concrete

Special precast moment frames with ductile Special precast moment frames with ductileconnec ons mus comp y w arequirements for special cast-in-place framesand Vn should not be less than 2Ve.

Special precast moment frames with strongconnections are intended to experience

connec ons mus comp y w arequirements for special cast-in-place framesand Vn should not be less than 2Ve.

Special precast moment frames with strongconnections are intended to experience

.

These requirements are applicableindependently of any of these two situations.

.

These requirements are applicableindependently of any of these two situations.

21.9 Special structural wallsand coupling beams

21.9 Special structural wallsand coupling beams

Terminology Terminology

hh

VuVuww

hwhw


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Minimum steel ratioMinimum steel ratio

14.3.2 Minimum steel ratio of vertical reinforcement computed over gross section is:

14.3.2 Minimum steel ratio of vertical reinforcement computed over gross section is:

. or deformed bars not larger than N 5 (5/8) 16M(16 mm), withfy not less than 420 MPa.

0.0015 for other deformed bars.

0.0012 for welded wire reinforcement with diameter notlarger than16 mm.

14.3.3 - Minimum ratio of horizontal reinforcement area togross concrete area,t:

. or deformed bars not larger than N 5 (5/8) 16M(16 mm), withfy not less than 420 MPa.



14.3.3 - Minimum ratio of horizontal reinforcement area togross concrete area,t:

0.0020 for deformed bars not larger than N 5 (5/8) 16M(16 mm), withfy not less than 420 MPa.



0.0020 for deformed bars not larger than N 5 (5/8) 16M(16 mm), withfy not less than 420 MPa.



Difference between walland column

Difference between walland column

14.3.6 Vertical reinforcementneed not be enclosed by lateral tiesif vertical reinforcement area is notgreater than 0.01 times grossconcrete area, or where vertical

14.3.6 Vertical reinforcementneed not be enclosed by lateral tiesif vertical reinforcement area is notgreater than 0.01 times grossconcrete area, or where verticalreinforcement is not required ascompression reinforcement.reinforcement is not required ascompression reinforcement.

21.9 - Special structural walls andcoupling beams


eas wo cur a ns o re n orcemen

must be used in a wall if Vu

exceeds

(MPa) =

eas wo cur a ns o re n orcemen

must be used in a wall if Vu

exceeds

(MPa) =cv c0.17 A f cv c0.53 A f (kgf/cm2)(kgf/cm2)



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

where c is: where c is:n cv c c n y V A f f +

cc0.250.25

w

w

h

0.170.17

00 2.0 2.01.51.50.50.5 1.0 1.0 2.5 2.5


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Nonlinear response of wallNonlinear response of wall

Using Moment-area theorems it is possible to show that thelateral deflection caused by curvature up to yield (greenzone) is:

Using Moment-area theorems it is possible to show that thelateral deflection caused by curvature up to yield (greenzone) is:

bb

and the additional deflection caused by nonlinearrotation (orange zone) is:and the additional deflection caused by nonlinearrotation (orange zone) is:

Total lateral deflection is then:Total lateral deflection is then:

yyu y)u y)pp

uu

aa

Nonlinear wall deflectionNonlinear wall deflection

wwCurvature

at yieldDeflection

at yieldNonlineardeflection

Nonlinearcurvatureyy uy)uy)

hwhw

) )pp pp

The total deflection is:

We can solve for the ultimate curvaturedemand and obtain:

The total deflection is:

We can solve for the ultimate curvaturedemand and obtain:

yy u y)u y)

Moment-curvature diagram for wall sectionMoment-curvature diagram for wall section

MM

MnMn

Ultimate curvature

demand

Ultimate curvature

demand

McrMcr

00 crcr yy uunn

What happens at section?What happens at section?

cucuAt level ofdisplacementAt level ofdisplacement

ccs > ys > y

At level ofAt level of

At level of

nominalstrength

At level of

nominalstrength

demanddemandStrainStrain

c= 0.003c= 0.003

s = ys = y c< 0.003c< 0.003

uu

nnyy

ww

hh

yield in

tension of

extreme

reinforcement

yield in

tension of

extreme

reinforcement

yy


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ACI 318 08 Seismic Requirements Luis E Garcia


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Old (pre-1999) procedureOld (pre-1999) procedureBoundary elementsBoundary elements w

resisting all flexural

effect that include

seismic forces

resisting all flexural

effect that include

seismic forces

Pu

Mu

heb

u ucu w ebP MP 2 h= + u utu g w ebP MP 0A h= 0n c g st st yP [0.85 f (A A ) A f ] = + n(max) 0nP 0.80 P tn st yP A f =

21.9 - Special structural walls and

coupling beams

21.9 - Special structural walls and

coupling beamsBoundary elements Both proceduresBoundary elements Both procedures

procedures) these boundary elements must extendhorizontally from the maximum compression fiber adistance equal to the greater of : c-0.1w or c/2.

In section with flanges the boundary element must includethe effective flange width and must extend at least 300 mminto the web.

Transverse reinforcement must be that required for column,but there is no need to comply with equation 21-3.

procedures) these boundary elements must extendhorizontally from the maximum compression fiber adistance equal to the greater of : c-0.1w or c/2.

In section with flanges the boundary element must includethe effective flange width and must extend at least 300 mminto the web.

Transverse reinforcement must be that required for column,but there is no need to comply with equation 21-3.

Special transverse reinforcement in the boundary elementmust extend into the foundation element supporting thewall.

Wall horizontal transverse reinforcement must be anchoredinto the confined boundary element core.

Special transverse reinforcement in the boundary elementmust extend into the foundation element supporting thewall.

Wall horizontal transverse reinforcement must be anchoredinto the confined boundary element core.



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

In ACI 318-08, there are modifications inthe re uirements for cou lin beams inwalls.

walls.

Coupling beamsCoupling beams

ACI 318 08 Seismic Requirements Luis E Garcia


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21.10 Special structural wallsconstructed using precast concrete

21.10 Special structural wallsconstructed using precast concrete

Scope These requirements apply to special Scope These requirements apply to specials ruc ura wa s cons ruc e us ng precasconcrete forming part of the seismic-force-resisting system.

Special structural walls constructed usingprecast concrete shall satisfy all requirementsof special cast-in-place structural walls plusthose of section 21.10.

s ruc ura wa s cons ruc e us ng precasconcrete forming part of the seismic-force-resisting system.

Special structural walls constructed usingprecast concrete shall satisfy all requirementsof special cast-in-place structural walls plusthose of section 21.10.

Special structural walls constructed usingprecast concrete and unbonded post-tensioning tendons and not satisfying therequirements of 21.10.2 are permitted providedthey satisfy the requirements of ACI ITG-5.1.

Special structural walls constructed usingprecast concrete and unbonded post-tensioning tendons and not satisfying therequirements of 21.10.2 are permitted providedthey satisfy the requirements of ACI ITG-5.1.

21.11 Structural diaphragms and trusses21.11 Structural diaphragms and trusses

floor

diaphragm

floor

diaphragm

prescribedhorizontal

forces

prescribedhorizontal

forces

21.11 Structural diaphragms and trusses21.11 Structural diaphragms and trusses

This section contains:This section contains:

Requirements for slabs-on-grade , floor and roof slabswhen they are part of the seismic-force-resisting systemmust comply with this section.

Minimum thickness for diaphragms are given. Gives minimum reinforcement for diaphragms.

Indicates shear strength for these elements

Defines when boundar elements must be used in

Requirements for slabs-on-grade , floor and roof slabswhen they are part of the seismic-force-resisting systemmust comply with this section.

Minimum thickness for diaphragms are given. Gives minimum reinforcement for diaphragms.

Indicates shear strength for these elements

Defines when boundar elements must be used indiaphragms.

Includes requirements for construction joints within thediaphragm.

diaphragms.

Includes requirements for construction joints within thediaphragm.


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ACI 318-08 - Seismic Requirements -- Luis E Garcia


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ACI 318 08 Seismic Requirements Luis E. Garcia

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21.13 Members not designated as part of

the seismic-force-resisting system



Story drift cannot exceed the larger of:Story drift cannot exceed the larger of:

ug

c

or

V

V

0.005

0.035 0.05 where Vugis the factored gravity punchingshear demand and Vc is the punching shearstrength.

where Vugis the factored gravity punchingshear demand and Vc is the punching shearstrength.





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