An ACl Standard
Requirements for Design of a Special Unbonded Post- Tensioned Precast Shear Wall Satisfying ACl 550.6 (ACl 550.7) and Commentary
Reported by Innovation Task Group 5
550.6 (ACI 550.7) and Commentary
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RequirementsforDesignofaS SpecialUnbonded Post-TensionedPrecastShearWallSatisfying ACI 550.6 (ACl 550.7) and Commentary
An ACI Standard
ReportedbyACl InnovationTaskGroup5
Charles W. DolanChair
Coesalring member S.K. Ghosh
This zlandared defnes procedwres thet may be wred to derign speciel precast concrete shear walis coupled or mcoapled posed ofdiscretely joned precast pnels thar are vertically posr-fensined to h fodatin wth abonded tenos. Suct wlls are mitable for se isas yiy on pauis anos aof p Qrar yy fo sa desi categories. Aer α mjor ssmc eet rhese wlls ca be cpctdto eshbr l de the fexr gig regi ar te bse of the wall as well as ngligibe pemenr displacements. Such malls do notsatisfy the prescriptive requiremens of Chaper 18 ef ACI 318-14 for shear walls of mnlinc cosction. Accoling to I8.2.1.7 ef ACT 318J4 theirtht the wlls he sfength nd thes egm to or eceeding se ccepfmce reires demstrati by perimenl eviece an msisthe prescriptive reqirememts of Chpter 8. This shanard dercrbes she provided by prae mnolihic renforce cocete wls ar stisfyprocedues rher rhe designer may mse to demomstate rhrough masis ht fde pl es att rfcp ei if crei walls Th sanrd cosists f Desig Reirmt nd α Cmar:
eergy dirpti ineri tifess a stengt; d 2. Individel wals inclading siderations to enswre dsctilits
temrioning tendoms ond coupling devices in providing energy dissipatiom 3. Copled wolls incluing sideratioms of te roles ef the pos-od stenh mdsf coled w gree e of se prvie by r ced wlls aing a sepre ts.
rfACAC84 The Comemtary references docamentry evidence addirional to theDesign Reirements. l this stndnd oeve no parison made benee pefmnef pt smles tisfyg e presripreqirements of ACI 318 an modrles etirying these Desigw Reqrire- ments bt not satisfying ACI 318. Sach perisons both experimemland analytical are avuilable iae the cied references.
Allreferences to ACI 318 and ACI 318R in these Desige Raguirementsand Commentary refer to ACI 318-J4 swniess anorher edirion of ACI 318 ix specifically desigated. All references to ASCE/SEI 7 in these DesigeReqriremenzs and Commenary are to ASCE/SEI 7-J0 inclading third prinzing apdates.
“Section* (s not inchaded before a reference to α section of ACI 318-14. To In this standard consistent with the formet of ACI 318-34 the wondmore clesrly designate α section in rhis standand however the word “Section" is ased before ary reference ro α section of shis standard.Consistenr winh ahe format of ASCE/SEI 7-10 the wond “Section" (x incladed before α reference to a sectiomn of ASCE/SEI 7-10.
Among the sabjects covered in rhese Design Reqairement are requtre.ments for:
1. Materias inchding conideratiens for te coupling or conectiodece pd epryefgdispif
ACI Committe Reports Guides Manuals StandardPractices and Commentaries are intended for guidance in planning designing executing and inspecting construction.at om senptpu jo asn g pap si unp s petent to evaluate the significance and limitations of itscontent and remendations and who will accept responsibility for the application of the material it contains.The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall notbe liable for any loss or damage arising therefrom.
Keywords: couling devices; drift angle; energy dissipation; lateral resis-tanoc; post-tensioning: precast coecrete; prestressed concrete; seismic design:; special shear wall test module; toughness.
CONTENTS
Chapter1-General p.2
1.iIntroduction
documents. If items found in this document are desired by the Reference to this document shall not be made in contractshal be rstated in mandatory language for incorporation by Architect/Engineer to be a part of the contract documents theythe Architect/Engineer.
1.2-Scope1.3-Drawings
CHAPTER1-GENERAL
1.1-Introduction
For regions of high seismic risk where structures assignedto Seismic Design Category (SDC) D E or F shall be used 18.2.1.7 of ACI 318 permits the use of structural systems thatcertain experimental evidence and analysis are provided (all references to ACI 318 and ACI 318R in this standard refer toACI 318-14 unless another edition of ACI 318 is specificallyminimum experimental evidence that is deemed sufficient to designated). The intent of ACI 550.6 is to define thepermit the use of unbonded post-tensioned precast structural wall systems in accordance with 18.2.1.7 of ACI 318 whenthose systems do not satisfy fully the prescriptive require-ments for wall systems in Chapter 18 of ACI 318.
Chapter 2-Notation and definitions p. 5
2.i-Notation 2.2-Definitions
Chapter 3-Referenced standards and reports p.7
Chapter 4-Materials p. 8
4.1-General4.2-Ducts4.4-Concrete 4.3-Reinforcement4.5-Interface grout4.7--Corrosion protection of prestressing tendons 4.6-Coupling devices
Before validation testing can be undertaken ACI 550.6requires that a design procedure be developed for prototypeis sought and that design procedure is used to proportion the wall systems having the generic form for which acceptancea specific type of wall system that does not satisfy the test modules. This standard defines the design procedure forprescriptive requirements of Chapter 18 of ACI 318 but is550.6. The wall system uses precast concrete panels that are validated for use in regions of high seismicity under ACIpost-tensioned to the foundation and intended to rock n that foundation under seismic actions.
walls p. 9 Chapter 5-Structural system requirements for
5.2-Strength 5.1-General5.3-Drift5.5-Distribution of walls within structures 5.4-Wall characteristics5.6-Wall system-gravity load frame interactions
For coupled walls coupling devices located along thevertical boundaries of adjacent walls provide the required energy dissipation and energy-dissipating reinforcement thatcrosses the wall-foundation interface is unnecessary. During an earthquake the coupled walls displace as rigid bodies thatare tied together. Wall deformations occur primarily at thewith each wall rocking separately at that interface. interface between each individual wall and the foundation
wall systems p. 12 Chapter 6-Design requirements for uncoupled
6.1-Scope6.2-Materials 6.3-Prestress force6.4--Energy-dissipating reinforcement6.5-Shear strength 6.6-Flexural strength and drift limits 6.7-Detailing of lowermost wall panel6.8Interface grout
post-tensioning steel is deliberately designed to remain The unbonded post-tensioning has two purposes. First theessentially elastic during the design basis earthquake (DBE) defined in ASCE/SEI 7 so that it forces the walls to return to their undeformed positions following the event. Second the onthewall ranferstheorizontal sheardtlatralladings friction induced by the post-tensioning and gravity loadingat the interfaces between the wall and the foundation andbetween the precast panels of the wall.
Chapter 7-Design requirements for coupled wall systems p.16
7.1-Scope 7.2-Materials7.3-Coupling devices7.4-Prestress force 7.5Shear strength7.6-Flexural strength and drift limits7.7Lowermost panel 7.8-Interface grout
The detailing procedures described in this standard are forwall system coupled or uncoupled. Four statements define one specific type of unbonded post-tensioned precast shearkey characteristics of uncoupled and coupled unbondedpost-tensioned precast concrete cantilever shear walls that satisfy this standard:
the foundation to an anchor at the top of the wall and located (a) Post-tensioning tendons unbonded from an anchor inin a single duct on the vertical centerline of the wall or ifneeded in two or more ducts positioned symmetrically on either side of that vertical centerline and within 10% of the wall length from that centerline;
Chapter 8-Design requirements for coupling devices p.18
8.1-Scope 8.2-General8.3-Materials8.4Design methodology
(b) Precast panels one story or more in height; and
(c) For uncoupled walls two sets of energy-dissipating@Setsmireihforcing bars crossing the interface between the lower-
Chapter 9-Commentary references p.20
most precast panel of the wall and the foundation and withthe sets located symmetrically about the vertical centerlineof the wall; or
dcmage during α DBE event is limited in extent confinedessentially to the wall to foundotion joint filler material or tothe concrete cover over the boundlary element reinforcement αI the woll toes and can be readily repaired ofter the ecrth-quake. By confrast monolithic walls coupled and uncou- pled designed to Chapter 18 of ACI 318 can saffersignificant cracking crushing and spalling in the plastichinging regions at the base of the walls in the coupling beams or both and repair can be costly. Further mono-lithic special shear walls designed to Chapter 18 of ACI 318 may show permcnent lateral deformations following α DBEevent whereas the special shear walls described in this stan-dard should not.
(d) For coupled walls energy-dissipating coupling devicesfor a given vertical joint between coupled walls of equal strength at least two in number for each coupled edge of apanel in the wall and positioned so that the width of thevertical joint between panels remains approximately constant in width as the walls rock on their bases.
R1.1
Large-scale laboratory experiments (Borα et al. 2007:Perez et al. 2003; Priestley et al. 1999: Rahman nd Restrepo 2000; Suntcna 2005) have shown thur unbondedpost-tensioned precast concrete cantilever shear walls can provide safery and serviceability levels during and after cnearthquake that meet or exceed performcnce levels requiredby 18.2.1.7 of ACI 318 and ACI 550.6. Analytical studies (Kuram 2002: Perez et al. 2004o b; Rahman and Restrepo2000; Stcnfon and Nakaki 2002; Thomas and Sritharcan 2004: Srirharan et al. 2007) hcve shown thar to achieve sachperformance levels rhe shear wolls should be proportionedand detailed in accordance with specifc considerctions. This standord is developed from the aforementioned stucdiesrequiremens for ensuring that one rype of nbonded post- cnd reloted references. Tris standord contains the minimuIensioned precast concrete cantilever shecr wall system ancoupled or coupled can sustain α series of oscilarions into the inelastic rnge of response without critical decay in strengthor excessive story drifs. Further that shear wall should show only minimal or no dcmage to the wall and minimal or nopermnanent displacements after the osciflarions cease.
Precast shear wals with the following can be propor-tioned to have performance chcracterisrics similar to the walls described in this standard:
1. Unbonded tendons that cross the wall-foundarion inter-face at locations along the length of the wall that are more than 10% of the wall lengrh from its vertical centerline; or
characteristics differing from those for the energy-dissi- 2. Uncoupled walls with energy dissipation devices havingpating reinforcement described in Section I.1(c) and posi-tioned differently along the length of the wall; or
3. Coupled walls wizth coupling elements connectingvertical bouncdaries of adjacent walls and having character- istics for the coupling elements differing from those for thecoupling devices described in Secrion 1.1(d).
date cnd modifications of the procedures dlescribed in this Research irvestigations addirional to those pleted toSndrd eer needfore pepiv pvis for the design of such precast shear walls can be formuelated.
post-tensoning tendons are abonded and designed to remin In this specific rpe of coupled or uncoupled wll system theontal josbewen the precast pnes tht mke p αi- elastic daoring the DBE. Except at the foundarion rhe hori-lever woll are designed to remain closed during an earthquoke.
1.2-Scope
1.2.1 This standard defines design requirements for acertain class of unbonded post-tensioned precast concrete shear walls that can be used as special reinforced concrete shear walls for Bearing Wall and Building Frame SpecialReinforced Concrete Shear Wall Systems as defined in ASCE/SEI 7.
into ducts located in the wall panels abutring the foundation For uncoupled walls vertical reinforcing bars groutedcnd in the foundation cnd described in this stcndard asas they yield ltenately in tension nd pression dring energy-dissipating reinforcement provide energy dissipationcn earthquake. These bars also provide continuiry additional Io the post-tensioning berween the cantilever wall and thefoundation n dditionalmomen strengthforthe wallhe grouted bars are deliberately debonded for a specificdistance in the panel adjocent to the wall-foundarion interfaceIo reduce the high cyclic strains that would otherwise occur aI that location. Consequently during an earthquake thecantilever woll can displace essentiolly as a rigid body. Vertical deformarions occur primorily at the wal-foundationinterfoce as the wall rocks agcinst the foundation.
1.2.2 The requirements described in this standard are forspecial unbonded post-tensioned precast shear walls with:
no significant discontinuities in plan in vertical configuration 1. Essentially planar proportions in the vertical direction or in their lateral-force-resisting system and designed to have a single critical section for flexure and axial loads at thebase of the shear wall;
anchor and located in a single duct at the centroid of the 2. Post-tensioning tendons unbonded from anchor totransverse cross section of the wall or in an additional two or more ducts positioned symmetrically on either side of thatcentroid and within 10% of the shear wall length from thatcentroid; and
in this standard are intended to behave differently than Under seismic looding the special shear walls describedmonolithic shear wolls. Most of the deformations of the wallsbetweenh precastwals and hfoatin.Conseqty. occer from the opening and closing of the joint at the interface
3. Energy dissipation provided: a) for uncoupled walls byenergy-dissipating reinforcement that crosses the interfacebetween the base of the wall and the foundation; and b) for
