coupling beam

Design of Shear Wall Coupling Design of Shear Wall Coupling Beams Using HighBeams Using High--PerformancePerformanceBeams Using HighBeams Using High--Performance Performance

FiberFiber--Reinforced ConcreteReinforced ConcreteJames K. WightJames K. Wight

F E Richart Jr ProfessorF E Richart Jr Professor of Civil Engof Civil Eng UniversityUniversityF.E. Richart, Jr. Professor F.E. Richart, Jr. Professor of Civil Engof Civil Eng. University . University of of MichiganMichigan

CoCo--Investigator: Prof. Gustavo ParraInvestigator: Prof. Gustavo Parra--Montesinos Montesinos Graduate Students: Remy Lequesne and Monthian SetkitGraduate Students: Remy Lequesne and Monthian Setkit

Presentation OutlinePresentation OutlinePresentation OutlinePresentation Outline

RC C l dRC C l d W ll S tW ll S t RC CoupledRC Coupled--Wall SystemsWall Systems Coupling Beams: Design RequirementsCoupling Beams: Design Requirements Use of diagonal reinforcementUse of diagonal reinforcement Design, detailing and construction issuesDesign, detailing and construction issues

Design Modifications and the use of Design Modifications and the use of HPFRCHPFRC

ConclusionsConclusions

RC CoupledRC Coupled--Wall SystemsWall SystemsRC CoupledRC Coupled--Wall SystemsWall Systems CoreCore--wall systems popular in moderate towall systems popular in moderate toCoreCore wall systems popular in moderate to wall systems popular in moderate to highhigh--rise structuresrise structures Architectural requirements lead to repeatedArchitectural requirements lead to repeated Architectural requirements lead to repeated Architectural requirements lead to repeated openings from floor to floor openings from floor to floor –– result is result is isolated walls connected by coupling beamsisolated walls connected by coupling beamsisolated walls connected by coupling beamsisolated walls connected by coupling beams

RC CoupledRC Coupled--Wall SystemsWall SystemsRC CoupledRC Coupled--Wall SystemsWall Systems

L t l tiff d t th f tL t l tiff d t th f t Lateral stiffness and strength of system Lateral stiffness and strength of system significantly influenced by design of coupling significantly influenced by design of coupling bbbeamsbeams Can be designed to spread plasticity over Can be designed to spread plasticity over height of systemheight of system Designed/detailed to retain strength and Designed/detailed to retain strength and g gg gsignificant percentage of stiffness during significant percentage of stiffness during large deformations into plastic range of large deformations into plastic range of g p gg p gbehavior.behavior.

Behavior of RC CouplingBehavior of RC CouplingBehavior of RC Coupling Behavior of RC Coupling BeamsBeams

Observed response of RC coupling beams Observed response of RC coupling beams during 1964 Alaska Earthquake was nonduring 1964 Alaska Earthquake was non--during 1964 Alaska Earthquake was nonduring 1964 Alaska Earthquake was nonductileductile

(http://www.nisee.org)

Use of Diagonal ReinforcementUse of Diagonal ReinforcementProposed by Thomas Paulay and others;Diagonals carry all shear and all flexure

Asd

Test Using Diagonal ReinforcementTest Using Diagonal Reinforcement

Construction Issues and Construction Issues and System Design ChangesSystem Design Changes

D i f di l i f t iD i f di l i f t i Design of diagonal reinforcement is easy Design of diagonal reinforcement is easy ––construction is NOTconstruction is NOT Trend in the USA is to use more slender Trend in the USA is to use more slender coupling beams, i.e. a larger length/depth ratiocoupling beams, i.e. a larger length/depth ratio Should we change our design approach?Should we change our design approach? Diagonal reinforcement is not as efficient at Diagonal reinforcement is not as efficient at gg

shallow angleshallow angle Use of HPFRC can reduce need for diagonal and Use of HPFRC can reduce need for diagonal and gg

confinement reinforcementconfinement reinforcement

Construction Issues

Coupling Beam Design:p g gMechanism Analysis of Coupling Beam

Vj Mpj

Mpj 2 pj j nM V

V

Mpj

or

pj j

j nVM

Vjn

or, 2pjM

*Assume, ( )( )p s yM A f jdp y

Coupling Beam Design:p g gFlexural Design of Coupling Beam

(assume combination of diagonal and longitudinal steel)( g g )

AssAsd

Coupling Beam Design:p g gFlexural Design of Coupling Beam

(assume combination of diagonal and longitudinal steel)( g g )

cos ( )(0.9 )p n s sd yM M A A f d p y

Solve for, cos(0 9 )

ps sd

MA A

f d

(0.9 )s sdyf d

Do not use capacity reduction factor Do not use capacity-reduction factor,

Coupling Beam Design:p g gShear Design of Coupling Beam

(Required strength V )(Required strength, Vn )

, where 0.85un

VV

,n

n c cf sd sV V V V V

n c cf sd s

For reinforced concrete, use 0cV

For fiber reinforced concrete, use 4 cf c wV f b d

Coupling Beam Design:p g gShear Design of Coupling Beam

(contribution from diagonal reinforcement)(contribution from diagonal reinforcement)

AsAAsd

2 iV A f 2 sinsd sd ytV A f

Coupling Beam Design:p g gShear Design of Coupling Beam

(contribution from vertical reinforcement)

AsAv

s

v ytA f dV

s

ysV

s

High Performance FiberHigh Performance Fiber--ggReinforced ConcretesReinforced Concretes

D fi iti f hi hD fi iti f hi h f fibf fib Definition of highDefinition of high--performance fiberperformance fiber--reinforced concrete typically means the reinforced concrete typically means the

t i l h t it i l h t i h d i b h i ih d i b h i imaterial has a strainmaterial has a strain--hardening behavior in hardening behavior in tension.tension.

Example of steel fibersExample of steel fibersExample of steel fibersExample of steel fibers

Tension Testing of Fiber ConcreteTension Testing of Fiber ConcreteRegular FRC HPFRC

Earthquake-Resistant Design Applications

The ductility, stiffness retention and fi i f HPFRCconfinement properties of HPFRC

members under inelastic load reversals k th ll t did t fmake them an excellent candidate for

use in earthquake-resistant design of i f d t b ildireinforced concrete buildings.

Research ObjectivesResearch Objectives

Investigate the use of precast HPFRC coupling beams in earthquake-resistant coupled wall systems

Reduce (eliminate) transverse and diagonal reinforcement requirements in coupling beams

Develop information on shear strength and damage tolerance of HPFRC members subjected to large displacement reversalssubjected to large displacement reversals

Cracking Pattern at Low Drift(Span/depth ratio of 1.2)SP-1 vs. SP-4 at 1.5% Drift

SP-1 SP-4

Shear Stress vs. Beam Drift ResponseSP 1 vs SP 4SP-1 vs. SP-4

10

4

6

8

a)

0

2

4

Stre

ss (M

Pa

-4

-2

Shea

r S

SP-1

-10

-8

-6 SP-4

-6 -4 -2 0 2 4 6

Drift(%)

Construction of Coupled Wall SystemConstruction of Coupled Wall System

CB-2 design (L/d = 1.75)g ( )Precast – shaded region

Precast Coupling BeamPrecast Coupling Beam

Component Test Setup

Actuator

W ll Bl k

Precast Coupling Beam

“Rigid” Links

Wall Block

Beam

Wall Block

CB-2 behaviorCB 2 behavior

CB-2 Testing ImagesCB 2 Testing Images

3% Drift

5.5% Drift

Four storyFour story coupled-wall

ispecimen

Precast Beam Casting

Coupled Wall Construction

Coupled Wall Construction

RC Wall Behavior

Additional Coupling Beam TestsAdditional Coupling Beam TestsAdditional Coupling Beam TestsAdditional Coupling Beam Tests Three beams, span/depth ratio of 2.75Three beams, span/depth ratio of 2.75

T h ACI li iT h ACI li i Target shear stress at ACI limitTarget shear stress at ACI limit

Specimen Diagonal Reinf.Material

2 YesHPFRC

4

6

Concrete

HPFRC

Yes

N6 HPFRC No

Reinforcement Pattern for Specimen 2Reinforcement Pattern for Specimen 2

Specimen 6HPFRC and No Diag Reinf

Specimen 2HPFRC and Diag Reinf HPFRC and No Diag. Reinf.HPFRC and Diag. Reinf.

ConclusionsConclusionsConclusionsConclusions For coupling beam span/depth ratios betweenFor coupling beam span/depth ratios between For coupling beam span/depth ratios between For coupling beam span/depth ratios between 2.0 and 4.0, the use of 2.0 and 4.0, the use of onlyonly diagonal reinforcement diagonal reinforcement is unreasonable is unreasonable –– Thus, use combination Thus, use combination of of ,,diagonal and longitudinal steel for flexural strengthdiagonal and longitudinal steel for flexural strength.. UUse se of HPFRC of HPFRC allowed allowed elimination of transverse elimination of transverse reinforcement requirements for diagonal bars reinforcement requirements for diagonal bars ––SSignificantly simplified ignificantly simplified the beam the beam construction.construction. We recommend to use a combination We recommend to use a combination of diagonal of diagonal reinforcement, reinforcement, vertical vertical stirrups, and HPFRC stirrups, and HPFRC for for h t thh t thshear strengthshear strength..

ConclusionsConclusionsConclusionsConclusions Coupling beams constructed with HPFRC showedCoupling beams constructed with HPFRC showed Coupling beams constructed with HPFRC showed Coupling beams constructed with HPFRC showed superior damage tolerance at low to moderate drift superior damage tolerance at low to moderate drift level compared to RC coupling beams.level compared to RC coupling beams.p p gp p g Supplemental diagonal reinforcement is required in Supplemental diagonal reinforcement is required in short coupling beams to achieve large drift short coupling beams to achieve large drift g gg gcapacities, stiffness retention and adequate energy capacities, stiffness retention and adequate energy dissipation.dissipation. Use Use of a precast coupling beam is a practical of a precast coupling beam is a practical alternativealternative..

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