5501R_09

mailto:[email protected]

ACI 550.1R-09

Reported by Joint ACI-ASCE Committee 550

Guide to Emulating Cast-in-PlaceDetailing for Seismic Design

of Precast Concrete Structures

Guide to Emulating Cast-in-Place Detailing for Seismic Designof Precast Concrete Structures

First PrintingFebruary 2009

ISBN 978-0-87031-319-6

American Concrete Institute®

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Guide to Emulating Cast-in-Place Detailingfor Seismic Design of Precast Concrete Structures

Reported by Joint ACI-ASCE Committee 550

ACI 550.1R-09

Te-Lin Chung Mohammad S. Habib Kenneth A. Luttrell* Mario E. Rodriguez

Ned M. Cleland* Neil M. Hawkins Vilas S. Mujumdar* Joseph C. Sanders

William K. Doughty Augusto H. Holmberg Frank A. Nadeau John F. Stanton*

Alvin C. Ericson† L. S. Paul Johal Clifford R. Ohlwiler P. Jeffrey Wang

Melvyn A. Galinat Jason J. Krohn Victor F. Pizano-Thomen Cloyd E. “Joe” Warnes*

Harry A. Gleich* Emily B. Lorenz Sami H. Rizkalla

*Member of the subcommittee that prepared this report.†Chair of the subcommittee that prepared this report.The committee would like to acknowledge Cloyd E. Warnes’ contribution for providing the initial information on emulation, and FDG, Inc., of Arvada, CO, for providinggraphics.

Thomas J. D’ArcyChair

ACI Committee Reports, Guides, Manuals, StandardPractices, and Commentaries are intended for guidance inplanning, designing, executing, and inspecting construction.This document is intended for the use of individuals who arecompetent to evaluate the significance and limitations of itscontent and recommendations and who will acceptresponsibility for the application of the material it contains.The American Concrete Institute disclaims any and allresponsibility for the stated principles. The Institute shall notbe liable for any loss or damage arising therefrom.

Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the contract documents, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.

This guide provides information for detailing precast concrete structuresthat should meet building code requirements for all seismic design categoriesby emulating cast-in-place reinforced concrete design. This guide alsoexplains how emulative precast concrete structures can address the provisionsof ACI 318-08, including those of Chapter 21, if special attention isdirected to detailing the joints and splices between precast components.

Keywords: ductility; elastic design; emulation; flexural strength; joint;precast concrete; precast detailing; reinforcement.

CONTENTSChapter 1—Introduction and scope, p. 550.1R-2

1.1—Introduction1.2—Scope

Chapter 2—Notation and definitions, p. 550.1R-22.1—Notation2.2—Definitions

550.

ACI 550.1R-09 supersedes ACI 550.1R-01 and was adopted and published February2009.Copyright © 2009, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by electronic ormechanical device, printed, written, or oral, or recording for sound or visual reproductionor for use in any knowledge or retrieval system or device, unless permission in writingis obtained from the copyright proprietors.

Chapter 3—General design procedures, p. 550.1R-23.1—Selecting a structural system3.2—Ductility and hinges3.3—Design and analysis procedures

Chapter 4—System components, p. 550.1R-7

Chapter 5—Connection of precast elements,p. 550.1R-8

5.1—Connections in wall systems5.2—Connections in frame systems5.3—Other connections: floor diaphragms5.4—Special materials and devices

Chapter 6—Guidelines for fabrication, transportation, erection, and inspection,p. 550.1R-15

Chapter 7—Examples of emulative precast concrete structures, p. 550.1R-16

Chapter 8—Summary and conclusions,p. 550.1R-16

Chapter 9—References, p. 550.1R-169.1—Referenced standards and reports9.2—Cited references

1R-1

550.1R-2 ACI COMMITTEE REPORT

CHAPTER 1—INTRODUCTION AND SCOPE1.1—Introduction

Emulative detailing is defined as the design of connectionsystems in a precast concrete structure so that its structuralperformance is equivalent to that of a conventionallydesigned, cast-in-place, monolithic concrete structure(Ericson and Warnes 1990).

Emulative detailing is distinct from jointed detailing,where precast elements are connected with special jointingdetails, such as welded or bolted plates, in that the bendingstiffness of the connections differs from that of the members.As commonly applied, “emulation” refers to the design ofthe vertical or horizontal elements of the gravity and lateral-force-resisting system of a building. Emulative detailing ofprecast concrete structures is applicable to any structuralsystem where monolithic structural concrete would also beappropriate, regardless of seismic design category (Precast/Prestressed Concrete Institute 1999).

Design practice in some countries with a high seismic risk,such as New Zealand and Japan, follows design codes thataddress precast concrete detailed by emulation of cast-in-place concrete design. Performance of joints and relateddetails of emulative precast concrete structural concepts hasbeen extensively tested in Japan. Because emulative precastconcrete structures have been constructed there for overthree decades, emulative methods for seismic design arewidely accepted.

Typical details showing proportional dimensions, as wellas reinforcing steel, are schematic only and are providedsolely to demonstrate the interactivity of the jointing essentials.All connection details are subject to structural analysis andcompliance with code requirements. Splicing reinforcingbars by welding or lapping is not permitted by ACI 318-08whenever the bars are subjected to stresses beyond the actualyield points of the reinforcing steel being used. Based ontests of mechanical splices reported by the CaliforniaDepartment of Transportation (Noureddine et al. 1996),concern was expressed about staggering of mechanicalsplices of reinforcing bars. Staggering is not required bycurrent codes.

Only essential reinforcing bars are shown in detail toprovide clarity. Other reinforcing steel that would typicallybe incorporated into a conventional design is not shown. Thespecification and delineation of reinforcing bars or strandsizes and locations, layers, types, and numbers are theresponsibility of the designer.

1.2—ScopeThe purpose of this guide is to give the reader a working

knowledge of emulation and emulative detailing to meetrequirements in current codes. The term “emulation” hasbecome a common concept for designers working withprecast concrete systems, but has also been misinterpreted inrelation to jointed systems. This guide shows a variety ofemulative details and describes how they are used. Design isbasically that of monolithic cast-in-place reinforced concreteconverted to precast members, so no special design knowledgeis required to use emulative details.

CHAPTER 2—NOTATION AND DEFINITIONS2.1—NotationAcv = gross area of concrete section bounded by web

thickness and depth of section in the direction ofshear force considered

fc′ = specified compressive strength of concreteMc = factored moment amplified for the effects of member

curvature used for design of compression memberMnb = nominal flexural strength of beam, including slab

where in tension, framing into jointMnc = nominal flexural strength of column framing into

joint, calculated for factored axial force, consistentwith the direction of lateral forces considered,resulting in lowest flexural strength

Mpr = probable flexural strength of members, with orwithout axial load, determined using the propertiesof the member at the joint faces assuming a tensilestress in the longitudinal bars of at least 1.25fy anda strength reduction factor φ of 1.0

Ω = dynamic amplification factor

2.2—Definitionselement—an individual part of the structure such as a

column, beam, wall, floor, or roof section that can be precastin other than its final location.

emulation—designing precast elements and their structuralconnections to perform as if the structure was a conventionalcast-in-place concrete structure.

emulative detail—a connection in which the structuralperformance is equivalent to that of a continuous member ora monolithic connection.

jointed detail—a connection where the bending stiffnessdiffers from that of the members and requires special designto collect, transfer, and redistribute forces from one memberto another through the connection.

member—an individual part of the structural system,synonymous with element, such as a column, beam, floor,roof, or wall.

structure—a building or bridge built with individualelements or members.

system—a collection of elements or members that form astructure.

CHAPTER 3—GENERAL DESIGN PROCEDURESA large body of technical information is available for the

design of cast-in-place reinforced concrete structures, andextensive research and development is ongoing for all typesof cast-in-place concrete technology. Numerous textbookshave been written about the behavior and design of cast-in-place reinforced concrete. Design procedures and examplesfor cast-in-place reinforced concrete are available (Cole/Yee/Schubert and Associates 1993). Building codes areregularly revised to reflect new research and technologydevelopments, and the results are incorporated into teachingand working practice (International Code Council 2006; ACI318-08). This knowledge for designing reinforced cast-in-place concrete structures is readily applicable to the designof emulative precast concrete.

EMULATING CAST-IN-PLACE DETAILING FOR SEISMIC DESIGN OF PRECAST CONCRETE STRUCTURES 550.1R-3

The analysis and design of cast-in-place reinforcedconcrete structures is based on the premise that the entiresystem behaves monolithically. A cast-in-place concretestructure is actually built member by member with jointsbetween concrete placements because of limitations inconcrete placing, construction procedures, or schedules. Dueto the continuity of the reinforcement and specific requirementsfor construction joints, the structure performs as a unit. Theprincipal element of emulative detailing of precast concreteis to detail a precast structure that will exhibit structuralbehavior similar to that of a cast-in-place structure.

Construction joints, whether in prefabricated or cast-in-place concrete structures, should be located and detailed toensure transmission of induced forces and loads in both theconcrete and reinforcing steel. For precast concrete, emulativeconstruction joints will likely occur at the same locations asdry joints in cast-in-place structural elements. Joints willusually be located at the ends of beams and columns, at both theends and sides of floor elements, and between wall elements.

The essential differences between cast-in-place reinforcedconcrete and emulative, reinforced, precast concrete relate tofield connections and assembly of the prefabricatedelements. Prefabricated elements have additional designrequirements for stripping, transportation, and erection loadsimposed on them, but the structural analysis and elementdesign is essentially the same for both types of construction.

Using emulative methods for connecting precast concreteelements, the detailing process follows three general steps:

1. The structural system for resisting gravity and lateralloads should be selected. A separate gravity-load-resistingframe can be combined with lateral-load-resisting shearwalls, or both functions can be accomplished with moment-resisting frames. System selection is often controlled by theheight of the building and the span of the components as wellas architectural requirements. Some code limitations mayalso apply (International Code Council 2006).

2. The structure should be designed and detailed to meetthe requirements of the applicable building code as if it wereto be constructed of monolithic cast-in-place reinforcedconcrete, keeping in mind that the structure will be dividedinto structural elements of sizes and shapes that:• Are suitable for plant fabrication;• Are capable of being transported; and• Can be erected by cranes available to the contractor.

3. The structure should be organized into precast elementsof appropriate sizes and shapes to meet the aforementionedcriteria. The appropriate connections should then bedesigned and detailed to satisfy the requirements of theapplicable building code to allow the precast elements to bereconnected in a way that emulates a monolithic system.

The manufacture and construction of precast structurestypically follows six steps:

1. The precast structural elements are manufactured withcode-compliant mechanisms for splicing the structuralreinforcing bars to provide continuity of the reinforcementthroughout the structure and in accordance with approved design;

2. The prefabricated elements are transported to theproject site when they are cast off-site;

3. Individual precast elements are erected and temporarilysecured;

4. The reinforcing bars are connected between the precastconcrete elements by completing the splices;

5. The precast concrete elements are connected with groutor concrete closures; and

6. Elements are reshored or braced as required to achievestability.

3.1—Selecting a structural systemSelecting an appropriate structural system, such as structural

walls, box structures, moment-resisting frames, and dualsystems for both lateral and gravity loads, can be the mostimportant step in achieving an economical, structurallysound design. Essentially, four types of structural elementsare used in combination to form complete building systems.Horizontal elements include beams and slabs. Verticalstructural elements include walls and columns or combinationsof both horizontal and vertical elements, such as cruciformelements. These elements can be combined in variousconfigurations to form commonly recognized lateral-load-resisting systems, such as structural walls and moment-resistingframes. Emulative detailing principles apply to all of them.

With precast concrete, the designer has the option to selectthose frames or walls necessary to resist lateral loads underthe code requirements. For seismic conditions, the elementsof the gravity load frame need only meet the requirements ofACI 318-08, Section 21.13.5 (frame members not propor-tioned to resist forces induced by earthquake motions) andthe requirement that each precast member be connected toadjacent members.

3.1.1 Structural walls—Structural walls resist lateralforces parallel to the plane of the wall. Because of the relativelylarge in-plane depth of the wall members, significant lateralstiffness is provided.

The International Building Code (IBC) (InternationalCode Council 2003), based on the National EarthquakeHazards Reduction Program (NEHRP) (Building SeismicSafety Council 1997) recommended provisions, recognizedtwo classifications of shear walls. First, “Ordinary ReinforcedConcrete Shear Walls” are walls designed in accordancewith ACI 318 Chapters 1 through 18. This includes Chapter 16on precast concrete, which includes provisions for structuralintegrity. Ordinary reinforced concrete shear walls arepermitted in buildings in seismic performance Categories A,B, and C. These requirements do not include the seismicdetailing provisions of Chapter 21 of ACI 318-08. Systemsbraced with ordinary reinforced concrete structural walls areassigned a response modification factor, or R factor, of 4.5for load-bearing wall systems, and 5 for structural wallsbracing a vertical frame. The IBC 2006 (International CodeCouncil 2006) makes the same references to the ACI 318, butchanges the term “shear wall” to “structural wall.” The IBC2006 refers to ASCE/SEI 7-05, which creates new categoriesfor precast concrete that are distinct from cast-in-placeconcrete, but engineers can also use emulative detailing tomeet the cast-in-place categories.


The second classification of shear walls in the IBC 2003(International Code Council 2003) was “Special ReinforcedConcrete Shear Walls.” IBC 2006 (International Code Council2006) again changed the terminology from “shear” to“structural.” These walls meet the requirements for ductiledetailing included in ACI 318-08, Section 21.8. ASCE/SEI 7-05assigns an R factor to the various structural systems. Systemsbraced with special reinforced concrete structural walls areassigned an R factor of 5.5 for load-bearing wall systems,and 6 for structural walls bracing a vertical frame. Specialreinforced concrete structural walls are used in buildings inseismic performance Categories D, E, and F. Special reinforcedconcrete structural walls may be used in these SeismicDesign Categories (SDCs) up to a maximum height of 160 ft(48.8 m) (100 ft [30.5 m] in the case of Category F).Although not required for regions of lower seismic risk,engineers can design special reinforced concrete structuralwalls for these regions for their increased integrity, strength,and ductility, and for the reduction of base shears afforded bythe higher R factors. The R factors can be further increasedwhere the walls are used in combination with momentframes. Used with intermediate moment frames, ordinaryreinforced concrete structural walls are assigned an R factor of5.5. Used with special moment frames, the R factor increasesto 7.0.

For ordinary structural walls, emulation does not providea specific benefit in increasing R factors. The level of strengthand ductility reflected by the R factors only requires that thestandard details be used with precast and tilt-up construction.ASCE/SEI 7-05 recognizes precast concrete walls with threelevels of detailing requirements. Ordinary Precast ConcreteShear Walls can be used only in buildings with low seismicrisk (Seismic Design Category B) and require only detailingfor structural integrity. These integrity requirements includeat least two base connections for each wall rated at a nominalforce of 10 kips (44.5 kN) and floor or roof anchorage basedon site acceleration with a minimum threshold force. Thesewalls are assigned an R factor that is lower by a value of 1than the comparable ordinary reinforced concrete shear thatis cast in place. For moderate seismic risk (Seismic DesignCategory C), precast walls must be Intermediate PrecastShear Walls, which have additional requirements for ductileconnections. These walls are assigned an R factor that is thesame as a comparable cast-in-place wall. In buildings classifiedwith high seismic risk (Seismic Design Categories D, E, and

Fig. 3.1—Dual building, ductile yielding of partially debondedbars between foundation and shear wall boundary elements.

F), shear walls must be Special Reinforced Concrete ShearWalls. In this case, there is no difference between monolithiccast-in-place and precast concrete walls. When precast, thesewalls must meet the detailing requirements for cast-in-placewalls in addition to the ductile detailing requirements appliedto Intermediate Precast Concrete Shear Walls. This may includeboundary elements with special confinement reinforcement atclose spacing that prevents the buckling of the main flexuralreinforcing after yielding under cyclic loading. For specialstructural walls, however, only those walls that meet the ACI318-08 Chapter 21 requirements have R factors. Precast wallscan then emulate the performance and detailing of monolithiccast-in-place walls using the rules that were developed forcast-in-place construction.

The only alternative to emulation for special structuralwalls is the general provision of ACI 318-08, Section21.1.1.8, which allows alternative systems if the proposedsystem is demonstrated by experimental evidence and analysisto have strength and toughness equal to or exceeding thoseprovided by a comparable monolithic reinforced concretestructure. There is also acceptance of walls that use unbondedpost-tensioning tendons in accordance with ACI ITG-5.1.For moment frames, the engineer can refer to ACI T1.1.This, however, is not considered emulation, but rather anewly developed jointed frame system.

Because a small rotation in a wall will create a largedemand for bar elongation, ductility at the base is important.Ductility can be increased significantly by debonding barsinto and out of the foundation so that they can deform inelas-tically over a longer length (Soudki et al. 1995), thusresulting in greater bar elongation and wall rotationalductility (Fig. 3.1). Reinforcing steel specified for specialstructural walls should be ductile and have controlledstrength properties. ACI 318-08, Section 21.1.5.2, requiresthat reinforcement resisting earthquake forces meet ASTMA706/A706M with some exceptions.

3.1.2 Box structures—Box structures are a type of structuralsystem that may fall under the category of walls. Familiarexamples of box or cellular structures, shown in Fig. 3.2 and
3.3, include stair cores, elevator cores, and some panel-type multistory residential buildings. The overlapping cornersshown in Fig. 3.3 provide a strong shear component whencompleted. In particular cases, when the boxes include inte-gral floors, ceilings, or both, they have been called cells.Even though a large number and variety of buildings fallingunder this category have been constructed in North America,it was the Architectural Institute of Japan (AIJ) that primarilyformalized the classification of box structures as a structuralsystem for earthquake-resistant buildings (Suenaga 1974).
A box is a three-dimensional cell. Monolithic cells can beemulated in precast construction with three-dimensionalmodules or by assembling with separately manufacturedfloor and wall panels using the emulative details shown inthis report (refer to Fig. 3.2, 5.4, and 5.8).

3.1.3 Moment-resisting frames—Moment-resisting frames(both steel and reinforced concrete) are used for buildingsover a wide range of heights.


Fig. 3.2—Precast shear tower using mechanical splices andcast-in-place closure connections between elements.

Fig. 3.3—Use of mechanical connections and interlockingprecast wall elements to create a monolithic shear tower.Note: Erection sequencing must be coordinated.

When structures are required to remain elastic, designprocedures require larger structural members to resist forcesresulting from earthquakes. This leads to increased materialcosts, higher lateral forces on nonstructural elements, andprobable loss of some floor and window opening space dueto bulkier columns. Under elastic design provisions, beamsmay require greater depth, resulting in increased storyheights and, consequently, taller buildings. In regions whererelatively minor earthquake loads are expected, design forelastic response can be appropriate when it may not beeconomical to detail for ductility. The NEHRP-based codeprovisions (Building Seismic Safety Council 1997) permitthe use of ordinary moment frames for SDCs A and B.

In June 1978, NEHRP was established. The “NationalEarthquake Hazard Reductions Program (NEHRP)Recommended Provisions for the Development of SeismicRegulations for New Buildings and Other Structures”(Building Seismic Safety Council 1997) was first publishedin 1985, and was subsequently updated. These provisionsincluded recommendations for the evaluation of loads andgeneral building details, and material-specific parameters anddetailing provisions that are consistent with those generalrecommendations.

The 1994 edition of the recommended provisions was usedin making major changes to the “Uniform Building Code”(UBC) (International Conference of Building Officials[ICBO] 1997). The IBC 2000 (International Code Council2000) was the culmination of the effort initiated by the Inter-national Code Council in 1997 to develop a comprehensiveset of regulations for building systems consistent with andinclusive of the scope of the existing model codes. The 2003and 2006 IBC (International Code Council 2003, 2006) areupdates to the 2000 IBC.

Ductility is an important consideration where concretemoment frames subjected to lateral loads are assumed tobehave inelastically. This is usually the case in SDCs D, E,and F as defined in IBC 2003 and 2006, Section 1616.3(International Code Council 2003, 2006). Special reinforcedconcrete moment frames may be used in these SDCs, as

intermediate reinforced concrete moment frames are onlypermitted to be used in SDCs A, B, and C. For a completedescription of permitted use of various systems, the reader isreferred to IBC 2006 (International Code Council 2006) andASCE/SEI 7-05 provisions.

Concrete frames can be readily designed to perform in aductile manner. Full-scale tests of reinforced concrete beam-column connections have shown that such connections areductile and can perform effectively under earthquake loading.Plastic hinging of beam-end connections is highly dependenton the type and amount of reinforcement used in the intendedductile hinge region, usually at or near beam ends.

Chapter 21 of ACI 318-08 provides prescriptive requirementsfor special moment frames intended to ensure strong-column/weak-beam behavior.

The “AIJ Structural Guidelines for Reinforced ConcreteBuildings” (Architectural Institute of Japan 1994), a designmanual for reinforced concrete frames, explains how todesign concrete structures to behave elastically for equivalentearthquake loads associated with horizontal structureaccelerations of up to 20% of gravity. The manual also providesfor the deliberate introduction of ductile (inelastic) hinges inthe beams near the beam-column junctures and at selectedlocations in the columns (Fig. 3.4 and 3.5). Sufficient strength
is designed into the hinge regions to accommodate lateralfloor accelerations up to 100% of gravity. The longitudinalreinforcement ratio of ductile hinges is intentionally limitedso that the bars are capable of being strained significantlybeyond their yield point, therefore inelastically elongatingthe bars. This mechanism absorbs and dissipates a substantialamount of seismic energy imparted to the frame.
3.1.4 Dual systems: frames and structural walls—Dualbuilding systems consist of a combination of structural wallsand moment frames. A dual system can be used when amoment-resisting frame alone does not provide sufficientlateral stiffness. Design attention should be directed to theprobable lack of deformation compatibility in both elasticand inelastic modes between frames and walls because theydo not experience compatible deformations in response to


Fig. 3.4—Planned yield hinges in a ductile moment frame.(Hinges in bottom of columns of foundations.)

Fig. 3.5—Planned yield hinges in a ductile moment frame.(Hinges in columns at top and bottom.)

normal as well as severe loads. Connections between framesand walls need to accommodate the different behavior of thetwo systems. Because the shape of the deformation ofcantilevered walls and moment-resisting frames is different,while a rigid diaphragm will impose the same story drift oneach system, there is likely to be forces transferring betweenthe wall and frame that must be considered in the design ofthe diaphragm and collector connections.

3.2—Ductility and hingesDuctility in reinforced concrete frames allows the structure to

accommodate large ground motions through energy dissipationat plastic hinge regions.

Ductility can be achieved in reinforced concrete membersby limiting the longitudinal steel ratio in high-moment (high-stress) regions while providing sufficient transverse reinforce-ment for concrete confinement.

These guidelines for structural design of reinforcedconcrete structures are used in the United States and in otherhighly active seismic regions of the world.

The AIJ standard requires a structure to have a minimumlateral-load-resisting capacity to limit the response deformationduring an earthquake. It also requires the formation of aductile yield mechanism to dissipate energy from the earth-quake; that is, a structural designer should plan a desirableyield mechanism (strong-column, weak-beam) for a structureexpected to undergo a design earthquake and then generatesuch a yield mechanism in the beams during a strongearthquake to permit controlled local damage, but also toprevent excessive system deformation or instability. Yieldmechanisms in moment frames should also be providedbetween foundations and the base of columns and, undercircumstances relating to the amount of acceptable damageto the roof system, at the tops of columns.

Under the AIJ approach, the designer first plans a desirableyield mechanism to give both the required strength to the

structure and sufficient ductility to the planned yield hinges(yield-mechanism design). Next, the designer provides non-yielding regions and members with sufficient elastic strengthto encourage the formation of the planned yield mechanism inthe intended location of the structure (yield-mechanism-assuring design). Another feature is an approach in sheardesign of members based on a plasticity theory in which shearis to be resisted by strut-and-tie mechanisms. This shear designmethod can be used for beams, columns, and structural walls.

The earthquake resistance of the AIJ design approachrelies on the energy-dissipation capacity at the planned yieldhinges, usually located in beams adjacent to the columnfaces and in columns and walls at the foundation. Therefore,application of this method is limited to those parts of structuresthat can develop clearly defined yield mechanisms.

Because ductility in nonprestressed reinforced concrete ismostly a function of the mild steel longitudinal reinforcement,the reinforcement stress at intended hinge locations needs toexceed the yield point of the steel. This is accomplished bylimiting the cross-sectional area As of the steel reinforcementin the intended hinge region, forcing inelastic deformation.

3.3—Design and analysis proceduresIn general, a building’s lateral-load-resisting system is

classified as a shear-wall structure, moment-frame, or dualsystem. Initial design loads including the equivalent lateralforces are calculated using the general formula for a buildingperiod, which is conservatively based on a lower bound formonolithic concrete buildings. If the building is of sufficientheight or flexibility, the final design may be improved bycalculating the period more accurately from deformationsdetermined by analysis. This more accurate calculation canbe made using Rayleigh’s method or directly within thestructural analysis program being used. A longer calculatedperiod can be used to recalculate a lower equivalent lateralforce subject to the limitations imposed by ASCE/SEI 7-05.

3.3.1 Moment frames—Structural analysis of an emulativeprecast concrete structure follows the same procedure as thatused for a cast-in-place reinforced concrete structure.

The required strength of the various components of alateral-force-resisting system is determined by the analysisof a linear elastic model of the system. For frames, elasticanalysis is used to determine the flexural strength required atthe ends of the beams where they frame into the column. Toensure ductile behavior, the steel reinforcement ratio withina ductile hinge region is limited by ACI 318-08 to a maximumof 0.025. The positive moment strength of the beam at thecolumn face has to be at least 50% of the negative momentstrength to resist reversals due to cyclic loading. The balanceof the design of the special moment frame is then based onmaking this area the weak link in the frame system.

Columns above and below a beam-column connection(joint) should have a total flexural strength Mnc that is 20%greater than the sum of the nominal flexural strength Mnb ofthe beams framing into the joint as provided by ACI 318-08,Section 21.6.2.2

ΣMnc ≥ (6/5)ΣMnb


The requirements for transverse reinforcement in bothbeams and columns are intended to ensure that the shearstrength does not limit the frame strength and that the areasof yielding are well confined for stable behavior beyondflexural yielding.

3.3.2 Shear walls—For walls, simplified analysis methodsthat rely on the relative shear and flexural stiffness of thewalls are available (Precast/Prestressed Concrete Institute1997). The analysis should consider the effects of sheardeformations for walls with aspect ratios lower than 3:1. Theeffects of the eccentricity of the center of mass differing fromthe center of stiffness of the wall system should be consideredalong with the ASCE/SEI 7-05 code requirement to include5% eccentricity for accidental torsion. For a more detaileddiscussion, the reader is referred to “Seismic Design ofPrecast/Prestressed Concrete Structures” (PCI MNL 140-07).For most precast systems, the stiffness contribution made byconnecting the floor to the walls is not large enough to createmoment reversals or fixity in the wall at the floors. Precastwalls, then—even those that emulate monolithic construction—should be designed as cantilevered from the foundation.

During an earthquake, the desired behavior of reinforcedconcrete structural walls emulating cast-in-place detailing isflexural yielding at the wall base (Fig. 3.6). Providing ductilityis the intent of the detailing requirements imposed by ACI318-08, Sections 21.4, 21.9, and 21.10. These include:

• A minimum web reinforcement ratio of 0.0025, unlessthe design shear force exceeds Acv (where Acv isthe gross area of concrete section bounded by webthickness and depth of section in the direction of shearforce considered, in.2; and fc′ is the specified compres-sive strength of concrete, psi). Even where the designshear force is Acv or less, the web steel should stillmeet the minimum requirements of Chapter 14 for walls;

• A maximum wall reinforcement spacing of 18 in.(457 mm);

• At least two layers of reinforcement should be used inthe wall and in the wall-to-foundation interface wherethe shear force exceeds 2Acv ;

• Continuous reinforcement crossing the wall’s horizontaljoint should be located at the ends of the element; and

• Continuous vertical reinforcement in walls should bedeveloped or spliced in tension.

fc′

fc′

fc′

Fig. 3.6—Dual building with rotation of the shear wall ateach floor.

CHAPTER 4—SYSTEM COMPONENTSPrecast concrete elements are usually produced in a

manufacturing plant and then transported to their assignedpositions in the building. When detailing the monolithicallydesigned structural system into discrete precast components,the designer should consider transportation and erectionlimitations. These limitations include weight (pavement andbridge ratings), height (bridge, tunnel, and underpass clearance),length (maneuverability and state laws), width (permits,escorts, and state laws), and available crane capacities.

For shear-wall structures, highway bridge clearancegenerally restricts panel dimensions. Clearance limitationsusually restrict box module heights to approximately onebuilding story. Floor planks and panels are usually narrowerthan wall panels, and a number of pieces can be shipped oneach truck.

Beams and columns can be quite long and are usuallytransported horizontally. H-shaped or cruciform combinationsof beam and column members as shown in Fig. 4.1 can beused to reduce the location and number of connections in aframe system. The bay size and story height, along withtransport size restrictions, will usually control the size of acruciform subassembly. Cruciform frame elements aresometimes referred to as punched shear walls. They are easyto erect because they can be freestanding and supported withsimple braces in one direction. All of the connections can bemade in regions of low moments.

Fig. 4.1—Typical types of precast concrete cruciform elements.


A key advantage of using cruciform elements is theypermit rapid erection and field assembly of the principalvertical and horizontal structural components of a building,usually with the connections between the precast elementsbeing located in the columns and beams in regions that willexperience lower forces.

Subdividing a structure into components can be achievedmost efficiently by working closely with an engineeringconsultant specializing in precast concrete technology or byconsulting with the technical staff of a precast concretemanufacturer. In both cases, the advice of an erector isinvaluable. Constraints on available form sizes as well asshipping and handling considerations should be verified withthe intended precast concrete manufacturer before proceedingwith the design.

CHAPTER 5—CONNECTIONOF PRECAST ELEMENTS

Methods to field-connect precast concrete elements shouldoptimize the safety and efficiency of crane and erection crewoperations. Because the unit cost of crane time and erectioncrew time is relatively high, erection scheduling and fieldconnections that use the least amount of time in fieldassembly can be cost effective. Where ductility is needed,the key to achieving successful emulation is selectingappropriate field connection details.

Splices for reinforcement used with precast systems thatemulate monolithic cast-in-place systems generally involvelapped bars (ACI 318-08, Sections 21.5.2.3 and 21.6.3.2),mechanical splices, and welded splices (ACI 318-08,Section 21.1.7). When lapped bars are used, the laps need toextend for significant lengths of cast-in-place concrete topermit the lap lengths and confinement hoops required byACI 318-08, Chapter 21. The cast-in-place section should beat least as long as the required splice length for the bars. InACI 318-08, mechanical splices are divided into two classi-fications: Type 1 and Type 2. Type 1 splices meet therequirements of ACI 318-08, Section 12.14.3.2. These splicescannot be used within a distance of two times the memberdepth from the column or beam face or from sections wherereinforcement yielding is anticipated. Type 2 splices arepermitted at any location within a member and have todevelop the specified tensile strength of the spliced bar. Thespecific requirements for these splices are discussed in thefollowing sections. Welded splices are limited in use, similarto Type 1 splices.

5.1—Connections in wall systemsThe critical connection in wall systems is usually the

connection between the precast panel and the cast-in-placefoundation system, because this is the location of maximumshear and moment caused by lateral loads. In tall buildings,other wall panel-to-panel connections can be as important.

Horizontal joints in panel-to-panel connections are usuallya combination of grout and spliced vertical reinforcing bars.The grout provides continuity for compressive forces acrossthe joints, and the bars provide continuity for tensile forces.Figures 5.1 to 5.3 illustrate joints where vertical reinforce-

Fig. 5.1—Lapped splices in large conduit. (Note: Overlappingbars in grout-filled conduit are extended full-height through thestructural element. Welded and lapped splices must belocated more than 2h [where h is floor thickness] from theface of wall. Mechanical splices must be Type 2 if less than 2hfrom face of the wall.)

Fig. 5.2—Vertical bars in conduit are spliced and the system isgrouted. (Procedures: (1) wall panel is erected, but held high;(2) loose vertical bars in the panel being erected are splicedto protruding bars from below; (3) panel is lowered to correctelevation; and (4) conduit is grouted by gravity flow from topor through optional grouting port from bottom of panel.)(Note: Welded and lapped splices must be located more than2h [where h is floor thickness] from the face of wall. Mechan-ical splices must be Type 2 if less than 2h from face of the wall.)

ment is made continuous with lapped bars in conduit or bysplicing bars with a threaded coupler. Rapid field erection ispermitted by the use of high-strength joints, such as thoseshown in Fig. 5.4, where the vertical reinforcement is splicedand grouted with specially designed and evaluation-service-accepted sleeve mechanical connectors. At the wall base andat other joints where bar yielding can occur, these splicesshould be Type 2 mechanical splices. Other connection detailscan be found in the PCI manual “Seismic Design of Precast/Prestressed Concrete Structures” (PCI MNL 140-07).

A cast-in-place connection can be used between adjacentwalls when tall vertical wall panels are used. Alternatives for


Fig. 5.4—Typical types of mechanical splices using high-strength nonshrink grout.

Fig. 5.3—Several types of mechanical splices for connection of various configurations ofprecast walls and floors. (Note: Welded and lapped splices must be located more than 2h[where h is floor thickness] from the face of wall. Mechanical splices must be Type 2 if lessthan 2h from face of the wall.)

completing the vertical connection are illustrated in Fig. 5.5.
They feature a cast-in-place closure strip with horizontalinterconnecting reinforcing steel spliced mechanically. Thesteel can also be lapped where the splice lap length can fitwithin the closure placement width and the lap splice is in aregion of the member permitted by code. Figure 5.5(a) isused when there is no architectural concern for appearance,such as in elevator shafts, or where the walls will be hidden.Figure 5.5(b) is used where an architectural concrete face isexposed, such as in airport control towers. Figure 5.5(c) canbe used in punched shear walls, such as those used forjoining ends of cruciform beams and headers when there isan architectural concrete consideration.
Connections between floor diaphragms and walls are criticalif floor inertial forces are to be successfully transferred to thewall systems. Regardless of the design approach used insizing and detailing the walls, some engineers believe thatthe floor diaphragm and its connections should be designedto remain elastic under seismic loading. Therefore, it isdesirable to provide a wall-to-floor connection strength thatis appropriate for the strength of the wall system. Sample detailsfor these connections are shown in Fig. 5.3, 5.6, and 5.7.

The technique of crossing the positive moment steelshown in Fig. 5.3 and 5.6 provides for structural reinforcementcontinuity of the diaphragm across the wall, and providesmuch of the shear reinforcement. During construction, the


Fig. 5.5—Variations of splices and cast-in-place closure placements to create verticaljoints between precast concrete elements.

Fig. 5.6—Floor slab-to-wall detail where diagonal dowelscross the wall joint into the opposite floor.

Fig. 5.7—End detail of a monolithic connection betweenprecast concrete floor element and a precast concrete wall.

floor slabs may be shored where they meet the walls. Therefore,when slabs are inadvertently not fabricated sufficiently longenough to bear on the walls, the placing of the cast-in-placeconcrete in the closure strip can accommodate the deficiency.

Figure 5.8 shows vertical wall joints used in high seismiczones in Japan. These joints make the walls monolithicthrough lapped hoop bars and a cast-in-place closure. This isa common detail in Japanese precast construction that might be

considered by the engineer as an alternative to the commonlyused welded or bolted connections, which are not emulative.

5.2—Connections in frame systemsIdeal locations for connections in frame systems are at

points where frame forces, particularly moments, are likelyto be at minimum levels. It is natural to select the inflectionpoints as points to break a monolithic system apart and toreconnect as an emulative precast system. The H-shaped andcruciform frame systems shown in Fig. 4.1 have connectionsnear where the inflection points are likely to occur underlateral loading. Figure 5.9 shows several horizontal connections
using mechanical couplers, butt welding and bars welded toa bolted plate to tie top and bottom reinforcing bars. The 1997


Fig. 5.8—(a) Plan view of typical grouted or cast-in-place vertical joints in shear-wallpanels reinforced for high seismic loading (refer to adjacent plan view for different configu-rations); and (b) variations of vertical wall-to-wall connections (plan views).

Fig. 5.9—Horizontal connections between beam or girderends at locations other than column faces.

NEHRP (Building Seismic Safety Council 1997) provisionsrequire that connections, even at nominal inflection points, bedesigned to provide a moment strength not less than 40% ofthe maximum moment.

Figure 5.10 shows a number of variations of framed
connection systems.
For the purposes of fabrication, erection, and transportation,a frame system is often divided into individual beam andcolumn components. Connections of these individualelements can be subjected to large forces and need to satisfythe requirement that the column strengths at joints shouldexceed beam strengths by a specified percentage. Bendingmoments are usually transferred through these connectionsby a force couple formed by compression in packed grout orcast-in-place concrete and tension in spliced reinforcingbars. Figures 5.11 and 5.12 illustrate types of emulative
beam and column joints that can be detailed to resistearthquake-generated loads and deformations. Architecturaldetails may require joint locations at floor level.
IBC 2000 (International Code Council 2000) introducedtwo methods for frames emulating the behavior of monolithicreinforced concrete. One method used strong connections(cast-in-place concrete or grout in splices) and complied withall the provisions of Chapter 21 of 318-99. The other methodpermitted precast systems that do not meet all the require-ments of ACI 318-99, Chapter 21. This method requires theuse of strong connections in the most highly stressed portionsof the joints that force nonlinear action to occur in the beamsaway from the joints by a prescribed distance. Section1908.1.9 of IBC 2000 modified ACI 318-99 by addingSection 21.2.8, which stipulates the following requirementsfor these systems:

1. The location of the intended nonlinear region is selectedto promote development of a strong-column/weak-beam

mechanism under seismic loading. The nonlinear responselocation can be no closer to the near face of the strongconnection than h/2;

2. Reinforcement in the nonlinear action region shall befully developed outside both the strong connection region


Fig. 5.10—Various configurations of precast frame elements.

Fig. 5.11—Column-to-column connection through conduitsinstalled in a beam. Conduit diameter should be two to fourtimes the bar diameter for tolerance in field erection.

Fig. 5.12—Connection at beams and columns with cast-in-place closure.

and the nonlinear action region. Noncontinuous anchoragereinforcement of the strong connection shall be fully developedbetween the connection and the beginning of the nonlinearaction region. Lapped splices are prohibited as connectionhardware adjacent to a joint, the general area where theconnection occurs;

3. The design strength (φ times nominal strength) of thestrong connections is greater than a dynamic amplificationfactor Ω times the moment, shear, or axial force at the connec-tion location based on the probable strength at the nonlinearresponse location. For column-to-column connections, Ω is1.4. At these columns, transverse reinforcement for columns atjoints is required full-height. If the column-to-column spliceis midheight, these requirements are subject to an exceptionthat permits the moment strength of the connection to be 0.4times the maximum probable flexural moment strength Mprand the design shear strength to meet the requirements ofACI 318-99, Section 21.4.5.1; and

4. A strong connection located outside the middle half ofa beam should be a wet connection (for example, emulative

using grout or concrete) unless the dry connection (forexample, welded or bolted) can be substantiated by test (ACI318-08, Section 21.1.1.8). A mechanical splice located withinsuch a column face strong connection (the connection at thesurface or face of the column as opposed to being further backin the beam) should be a Type 2 mechanical splice.

Other methods for seismic detailing of precast concrete arepermitted by IBC 2000 (International Code Council 2000),but do not qualify under the definition of emulation. IBC2003 and 2006 (International Code Council 2003, 2006) donot list these requirements because they are covered inSection 21.8 of ACI 318-08.

5.3—Other connections: floor diaphragmsSatisfactory floor diaphragm connections are essential for

obtaining acceptable diaphragm behavior and transferringthe building’s inertial forces to the lateral-load-resistingsystem. A floor diaphragm can be a cast-in-place toppingslab over precast floor elements or an interconnected systemof precast concrete floor elements. Figures 5.13 and 5.14
show a series of floor connections, between floor panels orbetween floors and supporting beams, that can be achievedby combining pour strips and spliced reinforcing bars.
Diaphragms using cast-in-place concrete topping arepermitted by ACI 318-08. This was a modification to ACI318-05, Chapter 21, made in Chapter 19 of IBC 2003 (Interna-tional Code Council 2003). The topping slab can be designedeither as composite or noncomposite. Where mechanicalsplices are used to connect reinforcement between thediaphragm and the lateral-force-resisting system, the spliceshould develop 1.4 times the specified yield strength of thereinforcement. Codes (ACI 318-08 and IBC 2000-2006) donot allow diaphragms composed of interconnected untoppedprecast elements in regions of high seismic risk due to a lackof testing of systems and connections.

The model building codes require the diaphragm to bedesigned for similar lateral forces as derived for verticalelements of the lateral-load-resisting system. Elastic behavioris desirable in diaphragms, as it prevents yielding and failure


Fig. 5.13—Typical end connections of precast concrete floor slab elements.

in the load path before the vertical elements experience theyielding forces or displacements they are intended to sustain.

Detailed studies of the behavior of precast concretediaphragms has been reported (Fleischman et al. 2002,2005a,b; Cleland and Ghosh 2002). For more details, see thePCI manual “Seismic Design of Precast/PrestressedConcrete Structures” (PCI MNL 140-07).

A significant difference between the cast-in-place slab andthe precast slab with cast-in-place topping is the jointing.The jointing in the precast slab supporting the diaphragmslab tends to reflect as cracks in the cast-in-place topping.This discrete cracking can place a high strain demand onwhatever reinforcement or connections cross these joints.ACI 318-08, Section 21.11.7 addresses this strain demand bysetting a minimum spacing for wires in welded-wire reinforce-ment in diaphragms of 10 in. (254 mm) for regions of highseismic risk. Similarly, mechanical connectors designed totransfer load across joints should be capable of sustainingtheir design capacity under the concentrated strains thatcan accumulate at a joint. Connections intended for sheartransfer only cannot be permitted to lose shear strength when

the joint widens as an effect of flexure. The flexural (chord)reinforcement in the diaphragm should control diaphragmdeformation not only to limit drift, but also to protect theseelements from yielding. Detailed design of precastdiaphragms is beyond the scope of this guide.

Connections in box systems can be similar to wall andfloor systems. In addition, where seismic conditions dictatea rigorous connection detail, those shown in Fig. 5.8 havebeen used. The overall concepts used in box systems areshown in Figs. 3.2 and 3.3. Details of the actual joint sectionscan be adopted as referenced in the figures.

5.4—Special materials and devicesIn reinforced concrete, building codes allow splicing of

reinforcing bars by means of lapping (except No. 14 and No. 18bars), welding, and by use of mechanical splices. Neitherwelding nor lapping is permitted within potential plastichinge regions. Reinforcing bars are made continuousthroughout the critical stress regions of precast concreteelements in much the same manner as they are for cast-in-place concrete and with the same restrictions as to type ofsplices permitted.


Fig. 5.14—Longitudinal joint between precast concrete partial-thickness slabs with cast-in-place topping.

Structural ductility depends on the inelastic strain character-istics of the reinforcing bars and the concrete integrity withinthe plastic hinge. ASTM A706/A706M bars or equivalentshould be specified when greater bar ductility is desiredbecause the elongation capacity is greater than that of A615/A615M steel.

Figure 5.15 shows the generally available mechanical
splices used in concrete construction. Some splices—forexample, grouted—are readily adaptable for use in connectingprecast concrete elements. Others—for example, threaded,swaged—are appropriate for splicing bars only in cast-in-place applications. Grout-filled splices are generally usedwith vertical reinforcing steel because they can be embeddedcompletely inside the precast element without the need foran opening to access the splice during erection. Other typesmay be used in horizontal applications with cast-in-placeclosure placements. Because most splices are proprietary, theengineer should investigate the requirements and tolerancesneeded for a product under consideration, as bars to be
connected may be embedded and thereby impossible to turnand difficult to bend.

Most mechanical splicing devices are recognized by amodel code through an evaluation service, and may haveformal conditions for acceptance in a structure. One of theseconditions may be a requirement for special inspection.

To maintain the integrity of an emulative structure, groutspecified as part of mechanical splicing devices should bemixed and installed according to the sleeve system recom-mendations. Grout or mortar used in sleeves, sheaths, conduit,bedding, and any other opening or void between or in thestructural concrete elements should be carefully prepared andinstalled, with full attention paid to achieving the strengthspecified by the designer. The grout venting system shouldensure complete placement throughout the connection.

Grouts or mortars used in the interfaces between precastconcrete elements should be engineered. Grout strengthshould be specified and confirmed by the design engineer.Interface grout should not be formulated at the job site by


Fig. 5.15—Typical types of reinforcing bar splices.

untrained persons or mixed by using hand tools such as a hoeand wheelbarrow.

Grout field sample specimens should be made and curedaccording to ASTM C109/C109M, C942, or both, and testedby a recognized testing laboratory to ensure that the specimensmeet specifications. For grout used in mechanical splices, aquality-control program that follows the recommendationsof the splice manufacturer should be developed.

Conventional concrete mixtures can be used in closureplacements to join precast concrete elements (refer to Fig. 5.5 to5.10 and 5.12 to 5.14). The strength of the concrete specifiedfor closures should be no less than the strength specified forthe precast elements. For more details, see the PCI manual“Seismic Design of Precast/Prestressed Concrete Structures”(PCI MNL 140-07).

For emulative purposes, most connections include someform of reinforcement splicing. ACI 318-08, Type 2mechanical splices need to develop the specified tensilestrength of the reinforcing bar, which translates to 150% ofthe specified yield strength. Research performed at theCalifornia Department of Transportation (Noureddine et al.1996) shows that a minimum stress in the inelastic range inexcess of 160% of the specified yield strength of the reinforcingbar is indicated to achieve 4% strain. Under the UBC 1997(International Conference of Building Officials 1997), forhighly active seismic regions, Type 2 mechanical splices inplastic hinging areas were required to develop at least 160%of the specified bar yield strength.

CHAPTER 6—GUIDELINES FOR FABRICATION, TRANSPORTATION, ERECTION, AND INSPECTION

Fabrication of precast concrete elements for use in emulativeprecast concrete structures is similar to that for most precaststructural products. The primary difference is the reinforcingbars at the connections should be made continuous throughjoints. To meet this requirement, bars may need to projectthrough a member’s end bulkheads, which requires modi-fication of the bulkhead forms

Transportation of emulative precast elements is similar tothat for traditional precast concrete elements.

The type of connections used can affect erection speed.When erection is carefully planned for maximum efficiency,total crane time for a complete cycle of picking a wall panel,raising it, fixing it in place, and returning the slings back forthe next element can be appreciably reduced. Precast cruciformelements were installed under optimum conditions at the upperstories of the 30-story MGM Grand Hotel in Las Vegas.

Inspection should focus on the connection system. Most ICCevaluation reports for splices require that they be installedaccording to the manufacturer’s instructions and under thespecial inspection requirement of the UBC. Design engineersshould check that regional building code acceptance numbershave been issued for proprietary splicing devices.

The American Concrete Institute publishes numerousguidelines for quality control, such as ACI 117. The Precast/Prestressed Concrete Institute (PCI) (1999) publishes a practicalmanual relating to erection practice (MNL-127-99).


CHAPTER 7—EXAMPLES OF EMULATIVE PRECAST CONCRETE STRUCTURES

Many precast concrete structures using emulative technologyhave been constructed in the United States and Japan.Several significant examples are provided in this chapter.

Because of its immense size and record-time assembly, the30-story MGM Grand Hotel in Las Vegas, completed in 1994,is an interesting example of the use of emulative detailing. Theexterior elements in the longitudinal frames were assembledfrom precast concrete frame cruciform members called trees.In the transverse direction, precast shear walls were used. Thefloors were precast, prestressed, untopped hollow coreelements (seismic detailing in slab not required).

The 37-story Ohkawabata residential tower in Tokyo wasconstructed of precast concrete cruciform frames (Warnes1990). Tokyo is located in one of the most severe seismicregions in the world. Simple beams and nonbearing partitionwalls between apartments were also fabricated of precastconcrete. Balconies and floors were also constructed withhalf-thickness precast elements and cast-in-place floortopping. This method not only eliminates the need to erectand shore forms, but also provides space for installing electricalconduit. More importantly, the topping ensures that a positivehorizontal diaphragm is provided for each floor. Floor instal-lation work proceeded directly behind the erection of frames,permitting follow-on trades to work on floors directly belowthe erection floor.

The standard design for Federal Aviation Administrationhigh-level (over 200 ft [61 m]) air traffic control towers usesprecast emulative detailing. Several of the towers are over 300 ft(91.5 m) tall, including those at airports in Miami, Denver, andDallas/Fort Worth. Towers were also built in Salt Lake Cityand Portland, OR, which are in higher seismic zones. Whilethey appear to be shear walls, the concept is actually a specialmoment-resisting frame that meets the 1997 UBC restrictions(160 ft [49 m]) on the height of shear-wall structures.

A report (Architectural Institute of Japan 1996) on theperformance of concrete structures during the Hyogoken-Nanbu (Kobe) earthquake in 1995 illustrated the effect ofimproved code requirements. A significant number of cast-in-place reinforced concrete frame structures constructedunder Japanese building code requirements in effect before1971 collapsed or were severely damaged. A Japanese codechange in 1971 significantly increased the amount of lateralreinforcement of columns by requiring additional columnties (hoops). None of the reinforced concrete building framestructures within the zone of strong motion influence of theKobe event constructed under the provisions of the 1971 AIJcode requirements collapsed, though there was severedamage (spalled concrete cover and cracking) to some.

A significant Japanese code change in 1981 introduced acode requirement for deliberately installing ductile hinges inbeams at beam-column joints. This was done to ensure thatplastic hinges would occur in beams at locations where theywere desired. None of the concrete frame buildings builtunder the 1981 code that were situated within the zone ofinfluence of the strong seismic forces at Kobe collapsed or

experienced significant damage beyond repair of spalledconcrete and minor cracking.

At Kobe, over 100 precast concrete box-frame (panel-type) structures located at 37 project sites within the zone ofstrong motion influence of the earthquake were notdamaged, and were approved for immediate occupancy afterthat seismic event (Ghosh 1995).

CHAPTER 8—SUMMARY AND CONCLUSIONSAll of the jointing details illustrated herein have been used

in the construction of emulative precast concrete structures.Many of these details, when experimental evidence ofperformance has been required by building officials as acondition for approval, have been tested for structuralperformance in laboratories in the United States and Japan.Building officials in Japan require that all proposed newjointing details be tested in a laboratory as a condition ofapproval. Some building officials in the United States alsorequire testing verification of new joint details before theyare approved for use.

Concrete structures using these connections can bedesigned according to contemporary standard reinforcedconcrete practice and current applicable building codes forreinforced concrete. Because the designs conform to therequirements of building codes for cast-in-place concrete,local building officials should recognize that emulativeprecast concrete structures satisfy building code require-ments for cast-in-place concrete.

CHAPTER 9—REFERENCES9.1—Referenced standards and reports

The standards and reports listed as follows were the latesteditions at the time this document was prepared. Becausethese documents are revised frequently, the reader is advisedto contact the proper sponsoring group if it is desired to referto the latest version.

American Concrete Institute117 Specifications for Tolerances for Concrete

Construction and Materials318 Building Code Requirements for Structural ConcreteT1.1 Acceptance Criteria for Moment Frames Based on

Structural Testing

American Society of Civil Engineers (ASCE)ASCE/SEI 7-05 Minimum Design Loads for Buildings

and Other Structures

ASTM InternationalA615/A615M Standard Specification for Deformed

and Plain Carbon-Steel Bars forConcrete Reinforcement

A706/A706M Standard Specification for Low-AlloySteel Deformed and Plain Bars forConcrete Reinforcement

C109/C109M Standard Test Method for CompressiveStrength of Hydraulic Cement Mortars(Using 2-in. [50-mm] Cube Specimens)


C942-99 Standard Test Method for CompressiveStrength of Grouts for Preplaced-Aggregate Concrete in the Laboratory

These publications may be obtained from the followingorganizations:

American Concrete InstituteP.O. Box 9094Farmington Hills, MI 48333-9094www.concrete.org

American Society of Civil Engineers1801 Alexander Bell Dr.Reston, VA 20191www.asce.org

ASTM International100 Barr Harbor Dr.West Conshohocken, PA 19428-2959www.astm.org

9.2—Cited referencesArchitectural Institute of Japan, 1994, “AIJ Structural

Guidelines for Reinforced Concrete Buildings,” Tokyo,Japan.

Architectural Institute of Japan, 1996, Preliminary Recon-naissance Report of the 1995 Hyogoken-Nanbu Earthquake(Kobe, Japan), Tokyo, Japan.

Building Seismic Safety Council, 1997, “National Earth-quake Hazard Reductions Program (NEHRP) Recom-mended Provisions for Seismic Regulations for NewBuildings and Other Structures,” National Institute ofBuilding Sciences, Washington, DC.

Cole/Yee/Schubert and Associates, 1993, “Seismic DesignExamples of Two 7-Story Reinforced Concrete Buildings inSeismic Zones 4 and 2A of the Uniform Building Code,”Concrete Reinforcing Steel Institute, Schaumburg, IL.

Cleland, N. M., and Ghosh, S. K., 2002, “UntoppedPrecast Concrete Diaphragms in High-Seismic Applications,”PCI Journal, V. 47, No. 6, Nov.-Dec., pp. 94-99.

Concrete Reinforcing Steel Institute, 1990, “Pacific ParkPlaza, Emeryville CA: A 30-Story Special Moment ResistantFrame Reinforced Concrete Building: Case History Report,”Bulletin No. 39-25, Schaumburg, IL.

Ericson, A. C., and Warnes, C. E., 1990, “Seismic Tech-nology for Precast Concrete Systems,” Concrete IndustryBulletin, Concrete Industry Board, Inc., Spring.

Fleischman, R. B.; Farrow, K. T.; and Eastman, K., 2002,“Seismic Performance of Perimeter Lateral-System Struc-tures with Highly Flexible Diaphragms,” EarthquakeSpectra, V. 18, No. 2, May.

Fleischman, R. B.; Naito, C.; Restrepo, J.; Sause, R.; andGhosh, S. K., 2005a, “Precast Diaphragm Seismic DesignMethodology Research Project, Part I: Design,” PCIJournal, V. 50, No. 5, Sept.-Oct., pp. 68-83.

Fleischman, R. B.; Naito, C.; Restrepo, J.; Sause, R.; andGhosh, S. K., 2005b, “Precast Diaphragm Seismic DesignMethodology Research Project, Part II,” PCI Journal, V. 50,No. 6, Nov.-Dec., pp. 14-31.

Ghosh, S. K., 1995, “Observations on the Performance ofStructures in the Kobe Earthquake of January 17, 1995,” PCIJournal, V. 40, No. 2, Mar.-Apr., pp. 14-22.

International Code Council, Inc., 2000, “InternationalBuilding Code,” International Code Council, Inc., FallsChurch, VA, 756 pp.



International Conference of Building Officials, 1997,“Uniform Building Code,” V. 2, Structural EngineeringDesign Provisions, International Conference of BuildingOfficials, Whittier, CA, 492 pp.

Iverson, J. K., and Hawkins, N. M., 1994, “Performance ofPrecast/Prestressed Concrete Building Structures DuringNorthridge Earthquake,” PCI Journal, V. 39, No. 2, Mar.-Apr., pp. 38-55.

Noureddine, I.; Richards, W.; and Grottkau, W., 1996,Plastic Energy Absorption Capacity of #18 Reinforcing BarSplices under Monotonic Loading, California Department ofTransportation, Division of New Technology, Materials andResearch, Office of Structural Materials.

Precast/Prestressed Concrete Institute, 1997, “Design forLateral Resistance with Precast Concrete Shear Walls,” PCIJournal, V. 42, No. 5, Sept.-Oct., pp. 44-64.

Precast/Prestressed Concrete Institute, 1999, ErectorsManual, MNL-127-99, Precast/Prestressed Concrete Insti-tute, Chicago, IL.

Precast/Prestressed Concrete Institute, 2007, “SeismicDesign of Precast/Prestressed Concrete Structures (MNL-140-07),” Precast/Prestressed Concrete Institute, Chicago, IL.

Soudki, K.; Rizkalla, S.; and LeBlanc, B., 1995, “Hori-zontal Connections for Precast Concrete Shear WallsSubjected to Cyclic Deformations—Part 1: Mild SteelConnections,” PCI Journal, V. 40, No. 3, pp. 78-96.

Suenaga, Y., 1974, Box-Frame-Type Precast ReinforcedConcrete Construction of Five, Six and Seven-Story ApartmentType Buildings, Yokohama National University, Yokohama,Japan.

Warnes, C. E., 1990, Precast Concrete Moment Frames,Seminar Presentation to Consulting Engineers, CanadianPrecast/Prestressed Concrete Institute, Ottawa, ON, Canada.

As ACI begins its second century of advancing concrete knowledge, its original chartered purposeremains “to provide a comradeship in finding the best ways to do concrete work of all kinds and inspreading knowledge.” In keeping with this purpose, ACI supports the following activities:

· Technical committees that produce consensus reports, guides, specifications, and codes.

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· Student programs such as scholarships, internships, and competitions.

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· Periodicals: the ACI Structural Journal and the ACI Materials Journal, and Concrete International.

Benefits of membership include a subscription to Concrete International and to an ACI Journal. ACImembers receive discounts of up to 40% on all ACI products and services, including documents, seminarsand convention registration fees.

As a member of ACI, you join thousands of practitioners and professionals worldwide who share acommitment to maintain the highest industry standards for concrete technology, construction, andpractices. In addition, ACI chapters provide opportunities for interaction of professionals and practitionersat a local level.

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www.concrete.org



The AMERICAN CONCRETE INSTITUTE

was founded in 1904 as a nonprofit membership organization dedicated to publicservice and representing the user interest in the field of concrete. ACI gathers anddistributes information on the improvement of design, construction andmaintenance of concrete products and structures. The work of ACI is conducted byindividual ACI members and through volunteer committees composed of bothmembers and non-members.

The committees, as well as ACI as a whole, operate under a consensus format,which assures all participants the right to have their views considered. Committeeactivities include the development of building codes and specifications; analysis ofresearch and development results; presentation of construction and repairtechniques; and education.

Individuals interested in the activities of ACI are encouraged to become a member.There are no educational or employment requirements. ACI’s membership iscomposed of engineers, architects, scientists, contractors, educators, andrepresentatives from a variety of companies and organizations.

Members are encouraged to participate in committee activities that relate to theirspecific areas of interest. For more information, contact ACI.

www.concrete.org

Guide to Emulating Cast-in-Place Detailing for Seismic Designof Precast Concrete Structures



Documents

5501R_09