ACI 550.3-13: Design Specification for Unbonded Post-Tensioned … · 2020. 5. 12. · column special moment frames in accordance with 21.1.1.8 of ACI 318-11. Before acceptance testing

ACI 550.3-13

Design Specification for Unbonded Post-Tensioned

Precast Concrete Special Moment Frames Satisfying ACI 374.1

(ACI 550.3-13) and CommentaryAn ACI Standard

Reported by Joint ACI-ASCE Committee 550

Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=University of Texas Revised Sub Account/5620001114, User=wer, weqwe

Not for Resale, 01/26/2015 02:08:42 MSTNo reproduction or networking permitted without license from IHS

--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com

http://www.daneshlink.com

First PrintingNovember 2013

Design Specification for Unbonded Post-Tensioned Precast Concrete Special Moment Frames Satisfying ACI 374.1 and Commentary

Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of ACI.

The technical committees responsible for ACI committee reports and standards strive to avoid ambiguities, omissions, and errors in these documents. In spite of these efforts, the users of ACI documents occasionally find information or requirements that may be subject to more than one interpretation or may be incomplete or incorrect. Users who have suggestions for the improvement of ACI documents are requested to contact ACI via the errata website at www.concrete.org/committees/errata.asp. Proper use of this document includes periodically checking for errata for the most up-to-date revisions.

ACI committee documents are intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. Individuals who use this publication in any way assume all risk and accept total responsibility for the ap-plication and use of this information.

All information in this publication is provided “as is” without warranty of any kind, either express or implied, includ-ing but not limited to, the implied warranties of merchantability, fitness for a particular purpose or non-infringement.

ACI and its members disclaim liability for damages of any kind, including any special, indirect, incidental, or con-sequential damages, including without limitation, lost revenues or lost profits, which may result from the use of this publication.

It is the responsibility of the user of this document to establish health and safety practices appropriate to the specific circumstances involved with its use. ACI does not make any representations with regard to health and safety issues and the use of this document. The user must determine the applicability of all regulatory limitations before applying the document and must comply with all applicable laws and regulations, including but not limited to, United States Occupational Safety and Health Administration (OSHA) health and safety standards.

Participation by governmental representatives in the work of the American Concrete Institute and in the develop-ment of Institute standards does not constitute governmental endorsement of ACI or the standards that it develops.

Order information: ACI documents are available in print, by download, on CD-ROM, through electronic subscription, or reprint and may be obtained by contacting ACI.

Most ACI standards and committee reports are gathered together in the annually revised ACI Manual of Concrete Practice (MCP).

American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701

www.concrete.org

ISBN: 978-0-87031-850-4

American Concrete Institute®

Advancing concrete knowledge



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

http://www.concrete.org/committees/errata.asp

http://www.concrete.org

www.daneshlink.com


ACI 550.3-13

Design Specification for Unbonded Post-Tensioned Precast Concrete Special Moment Frames Satisfying

ACI 374.1 (ACI 550.3-13) and CommentaryAn ACI Standard

Reported by Joint ACI-ASCE Committee 550

Harry A. Gleich, Chair Larbi M. Sennour, Secretary

Te-Lin ChungNed M. Cleland

Thomas J. D’ArcyWilliam K. Doughty

Alvin C. EricsonNeil M. Hawkins

Augusto H. HolmbergL. S. Paul JohalJason J. Krohn

Emily B. LorenzKenneth A. LuttrellVilas S. MujumdarFrank A. Nadeau

Clifford R. OhlwilerLance Osborne

Victor F. Pizano-ThomenJose I. Restrepo

Sami H. Rizkalla

Mario E. RodriguezJoseph C. Sanders

Edith G. SmithJohn F. StantonP. Jeffrey Wang

Cloyd E. WarnesSubcommittee Members

Satyendra GhoshSuzanne Dow Nakaki

This Standard defines requirements that may be used to design special hybrid moment frames composed of discretely jointed precast concrete beams post-tensioned to concrete columns. After a major earthquake, these hybrid moment frames should exhibit minimal damage in beam-column regions and negligible permanent displacements. Hybrid moment frames do not satisfy the prescriptive requirements of Chapter 21 of ACI 318-11 for frames of monolithic construction. According to 21.1.1.8 of ACI 318-11, their acceptance requires demonstration by experimental evidence and analysis that the frames have strength and toughness equal to or exceeding those provided by comparable monolithic reinforced concrete frames that satisfy the prescriptive requirements of Chapter 21. This Standard describes the requirements that the licenseddesign professional may use to demonstrate, through analysis, that such frames have strength and toughness at least equal to those of comparable monolithic frames. This Standard is a revision of the ACI T1.2 Standard.

In this Standard, consistent with the format of ACI 318, the word “Section” is not included before a reference to a section of ACI 318. To more clearly designate a section of this Standard, however, the word “Section” is used before any reference to a section of this Standard. Consistent with the format of ASCE/SEI 7, the word “Section” is also included before a reference to a section of ASCE/SEI 7.

Keywords: drift ratio; earthquake-resistant design; energy dissipation; moment frame; post-tensioning; precast concrete; prestressed concrete; test module; toughness.

CONTENTS

CHAPTER 1—GENERAL, p. 31.1—Introduction, p. 31.2—Scope, p. 41.3—Structural drawings, p. 61.4—Units, p. 6

CHAPTER 2—NOTATION AND DEFINITIONS, p. 72.1—Notation, p. 72.2—Definitions, p. 8

CHAPTER 3—REFERENCED STANDARDS, p. 10

CHAPTER 4—MATERIALS, p. 114.1—General, p. 114.2—Ducts, p. 114.3—Energy-dissipating reinforcement, p. 114.4—Prestressing strands and tendons, p. 11

1

ACI 550.3-13 supersedes T1.2-03, was adopted August 8, 2013, and was published November 2013.

Copyright © 2013, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by any

means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc-tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


R4—MATERIALS, p. 114.5—Interface grout, p. 124.6—Grout for anchorage of energy-dissipating reinforce-

ment, p. 12

CHAPTER 5—FRAMING SYSTEM REQUIREMENTS, p. 13

5.1—General, p. 135.2—Strength, p. 135.3—Drift, p. 135.4—Moment frame characteristics, p. 145.5—Distribution of moment frames within structures, p. 155.6—Moment frame-floor slab interactions, p. 16

CHAPTER 6—DESIGN REQUIREMENTS FOR BEAMS OF MOMENT FRAMES, p. 17

6.1—Prestress, p. 176.2—Beam design, p. 17

CHAPTER 7—REQUIREMENTS FOR BEAM-COLUMN INTERFACES OF MOMENT FRAMES, p. 19

7.1—General, p. 197.2—Prestress force, p. 197.3—Interface grout, p. 197.4—Energy-dissipating reinforcement, p. 207.5—Nominal flexural strength, p. 207.6—Probable flexural strength, p. 207.7—Anchorage of energy-dissipating reinforcement, p. 237.8—Distribution of flexural reinforcement, p. 25

CHAPTER 8—FRAME JOINTS, p. 268.1—General, p. 26

R9—COMMENTARY REFERENCES, p. 27Authored references, p. 27

American Concrete Institute Copyrighted Material—www.concrete.org

2 SPECIFICATION FOR UNBONDED PT PRECAST CONCRETE SPECIAL MOMENT FRAMES SATISFYNG ACI 374.1



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


CHAPTER 1—GENERAL

1.1—IntroductionFor regions of high seismicity, 21.1.1.8 of ACI 318-11

permits the use of structural systems that do not meet the prescriptive requirements of Chapter 21 if certain experimental evidence and analysis are provided. The intent of ACI 374.1 is to define the minimum evidence required when attempting to validate the use of weak-beam, strong-column special moment frames in accordance with 21.1.1.8 of ACI 318-11.

Before acceptance testing can be undertaken, ACI 374.1 requires that a design procedure be developed for prototype moment frames having the generic form for which acceptance is sought, and that procedure be used to proportion the test modules. ACI 550.3-13 defines the requirements to be used for one specific type of moment frame that does not fully satisfy the prescriptive requirements of Chapter 21 of ACI 318-11. This moment frame has been validated for use in regions of high seismicity under ACI 374.1 and ACI 318. The moment frame uses precast concrete beams that are post-tensioned to precast or cast-in-place concrete columns. The columns are continuous through the joints and the beams each span a single bay. This Standard describes the frame as hybrid because it combines post-tensioned and precast concrete construction and combines the use of deformed reinforcement that is designed to yield with unbonded post-tensioning tendons that are designed to remain essentially elastic during the design basis earthquake (DBE).

In this specific type of hybrid frame, the post-tensioning tendons are unbonded. Horizontal reinforcing bars grouted in ducts located in the columns and in the top and bottom of the beams, and described in this Standard as energy-dissipating reinforcement, provide additional continuity between the beams and the columns, and additional moment strength to the beams. Those bars dissipate energy as they yield alternately in tension and compression during an earthquake.

A key feature of this system is that the grouted bars are deliberately debonded for a short distance in the beam adjacent to the beam-column interface to reduce the high cyclic strains that would otherwise occur at that location. Consequently, during an earthquake, the beams and columns displace essentially as rigid bodies with deformations occurring primarily at the beam-column interface as the beam rocks against the column.

A second key feature is that post-tensioning allows the columns to be built without the permanent corbels normally found in precast concrete construction. The post-tensioning has two purposes. First, the friction induced by the post-tensioning transfers vertical shears at the interface between beam and column for both gravity and lateral loadings. Second, with the post-tensioning deliberately designed to remain essentially elastic during the DBE, the post-tensioning forces the moment frame to return to its undeformed position following the DBE.

R1—INTRODUCTION AND SCOPE

R1.1—IntroductionLaboratory studies (Stone et al. 1995; Hawkins and

Ishizuka 1988; Priestley 1996; Priestley and MacRae 1994; Palmieri et al. 1996; Nakaki et al. 1999; Priestley et al. 1999; Day 1999) have shown that precast or prestressed concrete moment frames can provide safety and serviceability levels, during and after an earthquake, that meet or exceed performance levels required by 21.1.1.8 of ACI 318-11. To achieve such performance levels, the precast or prestressed concrete moment frames should be carefully proportioned and detailed. This Standard is based on the studies reported by Stone et al. (1995), Hawkins and Ishizuka (1988), Priestley and MacRae (1994), Priestley (1996), Nakaki et al. (1999), Priestley et al. (1999), and Day (1999). It contains the minimum requirements for ensuring that one type of precast and prestressed concrete moment frame can sustain a series of oscillations into the inelastic range of response without critical decay in strength or excessive story drifts. Further, that frame should show only minimal or no damage in beam-column joint regions and no permanent displacements after the oscillations cease.

A typical interior frame for this seismic-force-resisting system is illustrated in Fig. R1.1. Details for a vertical longitudinal section of the beam as it passes through the column are shown in Fig. R1.1(b), and details for cross sections of the beam at the column face (Section B) and on the centerline of the column (Section C) are shown in Fig. R1.1(c). The frame is composed of multistory columns to which single-bay precast concrete beams are connected. Except for possible yielding at the column bases, the interfaces between the precast beams and the continuous columns are the only locations where yielding of the reinforcement (nonlinear action location) occurs in the frame during a major earthquake. Crossing each interface are three deliberately debonded reinforcement elements: post-tensioned strands that extend the full length of the frame in the direction of its plane; and top and bottom deformed bar energy-dissipating reinforcement that is anchored by grouting in ducts preformed in the beam and column. The length over which the energy-dissipating reinforcement is debonded in the beam adjacent to the connection is selected deliberately to provide the desired design level of overall performance. Cheok et al. (1996) describes the development of a rational basis for the design procedures for a frame with equal strength for the top and bottom partially debonded energy-dissipating reinforcement and central post-tensioning tendons that remain elastic during a major earthquake. Stanton and Nakaki (2002) describe design guidelines for the same frame system using an iterative step-by-step procedure and displacement-based design procedures. Hawileh et al. (2006) provide nondimensional, noniterative, simplified design procedures for that same system for either displacement-based or force-based design procedures. Where force-based design procedures are used,


SPECIFICATION FOR UNBONDED PT PRECAST CONCRETE SPECIAL MOMENT FRAMES SATISFYNG ACI 374.1 3

CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


Under earthquake loading, the special moment frames described in this Standard are intended to behave differently than monolithic frames. Most of the deformations of the frames occur from the opening and closing of the joint at the interface between the precast beam and the column. Consequently, with the detailing procedures described in this Standard, damage during a major earthquake is limited in extent, confined essentially to the joint filler material, and is readily repairable after the earthquake. By contrast, monolithic frames designed to Chapter 21 of ACI 318-11 can suffer significant cracking, crushing, and spalling in the plastic hinging regions of the beam, the beam-column joint, or both, and repair can be costly. Further, monolithic special moment frames designed to Chapter 21 of ACI 318-11 may show permanent lateral deformations following a DBE, whereas the special moment frames described in this Standard do not.

The preceding paragraphs define the key characteristics of hybrid frames. The detailing requirements described in this Standard are for one specific type of special hybrid moment frame with:

a) Equal moment strengths for the top and bottom energy-dissipating reinforcing bars that cross the interface between the precast beam and column;b) Post-tensioning tendons that are unbonded from anchor to anchor and concentrically located within the cross section of the beam.Special moment frames with unequal moment strengths for

the top and bottom energy-dissipating reinforcing bars, and with amounts, location, and bonding of the post-tensioning tendons that differ from those described in this Standard, can be proportioned to have performance characteristics similar to the frames described in this Standard. However, research investigations additional to those completed to date, and modifications of the requirements described in this Standard, are needed before prescriptive provisions for the design of such frames can be formulated.

1.2—Scope1.2.1 This Standard defines requirements for a certain

type of hybrid special moment frame composed of precast concrete beams jointed at their connections to columns that are continuous past those joints. Whereas these frames do not satisfy all of the prescriptive requirements of 21.5 through 21.7 of ACI 318-11, analyses, tests, and reporting requirements in accordance with ACI 374.1 have established dependable and predictable strength, energy dissipation, stiffness, and drift capacities for characteristic beam-column configurations of the frames described in this Standard. Such special moment frames are permitted for structures assigned to SDC D, E, or F in accordance with 21.8.4 of ACI 318-11.

1.2.2 The intended user of this Standard is a licensed design professional experienced in earthquake-resistant design and precast concrete design and construction.

ASCE/SEI 7 and ACI 318-11 in combination permit the use of R, Cd, and Wo values for special hybrid moment frames designed in accordance with this Standard, which are the same as the R, Cd, and Wo values for monolithic cast-in-place moment frames designed in accordance with 21.5 through 21.7 of ACI 318-11.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


Fig. R1.1—Typical moment frame composed from discretely jointed precast concrete members: (a) elevation of typical interior moment frame; (b) detail of connection—A; and (c) typical sections—B and C.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


1.2.3 The requirements of this Standard supplement those of ACI 318-11 and the general building code, and shall govern in all matters pertaining to the design and construction of the hybrid special moment frames described in this Standard, except wherever this Standard is in conflict with requirements of the legally adopted general building code.

1.2.4 The requirements described in this Standard are for hybrid special moment frames with:

1. Equal moment strengths for the top and bottom energy-dissipating bars that cross the interface between the precast beam and column; and2. Post-tensioning tendons that are unbonded from anchor to anchor and concentrically located within the cross section of the beam.

1.2.5 All precast and reinforced concrete components and systems for the moment frames, and the associated gravity load frames, shall be designed to satisfy the requirements of ACI 318-11 except as modified by this Standard.

1.2.6 The special inspection requirements of 1.3.5 of ACI 318-11 shall be satisfied for all precast and reinforced concrete components and systems for the special moment frames.

1.3—Structural drawingsStructural drawings of the moment frames shall show all

features of the work, including those details essential for satisfactory earthquake-resistant performance of the frame. Essential details include:

a) Debonding the energy-dissipating reinforcement that crosses beam-column interfaces;b) Anchoring the energy-dissipating reinforcement and tendons within beams and columns;c) Developing floor slab-frame interactions that conform to those assumed in the contract documents.

1.4—UnitsValues in this specification are stated are in inch-pound

units. A companion specification in SI units is also available.

R1.2.3 For the hybrid moment frames described in this Standard to be accepted as special moment frames, the special detailing of the frames should be properly executed through continuous inspection by properly qualified personnel.

R1.3—Structural drawingsBecause reinforcement details in the region where the

precast concrete beam is connected to the continuous column are essential to the satisfactory performance of the moment frame in a major earthquake, the details should be designed meticulously and fully documented on the structural drawings for each connection of the moment frame. For the energy-dissipating reinforcement, essential elements include the length that reinforcement is to be deliberately debonded, how it is to be debonded, and details of its anchorage in the adjacent precast beam and column. For the post-tensioning tendon, essential elements are how and where the tendon will be anchored, and how it will be ensured that the tendon remains debonded during the grouting of the joint between the precast beam and column. Further, because satisfactory performance of the hybrid moment frame requires that yielding be limited to the energy-dissipating reinforcement crossing the beam-column interfaces, floor slab details in that connection region should be planned and executed so that they do not adversely affect the effective strength or stiffness of the connection.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


CHAPTER 2—NOTATION AND DEFINITIONS

2.1—NotationAj = effective cross-sectional area within a joint, in.2;

21.7.4 .1 of ACI 318-11Aps = area of post-tensioning tendons crossing beam-

column interface, in.2

As = area of energy-dissipating top reinforcement crossing beam-column interface, in.2

As′ = area of energy-dissipating bottom reinforcement crossing beam-column interface, in.2

Avc = area of closed hoops or spirals within a distance svc, in.2

b = width of compression face of precast beam, in.C = compression force when probable flexural strength

Mpr acts at interface, lbc = distance from extreme compression fiber of grout

pad to neutral axis at beam-column interface, in.d = distance from extreme compression fiber of grout

pad at interface to centroid of energy-dissipating tension reinforcement, in.

db = bar diameter of energy-dissipating reinforcement, in.E = load effects of earthquakes, or related internal

moments and forcesfc′ = specified compressive strength of concrete, psifprs = stress in post-tensioning tendons when stress in

energy-dissipating reinforcement is fu, psifpu = specified tensile strength of post-tensioning

tendons, psifpy = specified yield strength of post-tensioning tendons,

psifse = effective stress in post-tensioning tendons (after

allowance for all prestress losses), psifu = specified tensile strength of energy-dissipating

reinforcement crossing beam-column interface, psifvcy = specified yield strength of closed hoops or spirals, psify = specified yield strength of energy-dissipating

reinforcement, psih = overall thickness of precast beam of a moment

frame, in.hp = dimension of a column in direction of post-

tensioning tendon, in.Lclear = clear span measured face-to-face of columns, in.Lu = length over which energy-dissipating reinforcement

crossing beam-column interface is deliberately debonded, in.

Lups = length associated with a given interface over which post-tensioning tendon is unbonded, in.

ld = development length in tension for a straight deformed reinforcing bar, in.

Mpr = probable flexural strength at a beam-column interface of a precast concrete beam of moment frame, in.-lb

Mprs = contribution of post-tensioning reinforcement to Mpr, in.-lb

R2—NOTATION AND DEFINITIONS

R2.1—NotationWhereas areas of the top and bottom energy-dissipating

reinforcement are designated as As and As′, respectively, those two areas are required to be equal for the special hybrid moment frames described in this Standard. Different symbols are used for the top and bottom reinforcement to facilitate discussion and not to imply that the two areas may differ.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


Ms = contribution of energy-dissipating reinforcement to Mpr, in.-lb

Mu = factored moment acting at beam-column interface of moment frame, in-lb

Nu = effective post-tensioning force Apsfse, lbsvc = spacing of transverse reinforcement surrounding

development length of energy-dissipating reinforcement, in.

Vc = nominal shear strength provided by concrete, lbVD = shear force due to unfactored dead load, lbVL = shear force due to unfactored live load, lbVn = nominal shear strength, lbVu = factored shear force at section, lbab = coefficient quantifying the effective additional

debonded length for energy-dissipating reinforcement at Mpr

b1 = factor defined in 10.2.7.3 of ACI 318-11Dprs = additional elongation of post-tensioning tendon at

Mpr, in.Ds = elongation of energy-dissipating reinforcement at

Mpr, in.ef = strain in energy-dissipating reinforcement at its

fractureeprs = strain in post-tensioning tendon when stress in

energy-dissipating reinforcement is fu

ese = strain in post-tensioning tendon due to effective prestress only (after allowance for all losses)

esu = strain in energy-dissipating reinforcement at elongation Ds

eu = strain in energy-dissipating reinforcement at its tensile strength fu

qL = drift angle, radiansqLdesign = drift angle at design displacement, radiansqLmax = drift angle capacity at Mpr, radiansf = strength reduction factorl = overstrength factor for columnm = coefficient of friction

2.2—DefinitionsACI provides a comprehensive list of definitions through

an online resource, “ACI Concrete Terminology,” http://terminology.concrete.org. Definitions provided herein complement that resource. These definitions are additional to those of 2.2 of ACI 318-11 and of ACI 374.1.

energy-dissipating reinforcement—reinforcement (nonprestressed) that crosses the interface between the precast beam and the column, is debonded for a specified length in the beam adjacent to the beam-column interface, conforms to Section 6.2, and is designed to yield in the DBE.

nonlinear action location—interface where end of precast beam of moment frame meets column face.

seismic reinforcement—reinforcement that conforms to 21.1.5 of ACI 318-11.

R2.2—DefinitionsFor consistent application of this Standard, it is necessary

that terms be defined where they have particular meanings in this Standard. The definitions given are for use in application of this Standard only and do not always correspond to ordinary usage. A glossary of most-used terms relating to cement manufacturing, concrete design and construction, and research in concrete is available through an online resource “ACI Concrete Terminology,” http://terminology.concrete.org.

The term “nonlinear action location,” which is introduced in the National Earthquake Hazard Reduction Program (NEHRP) of the Federal Emergency Management Agency (FEMA) (1997), prompts the licensed design professional to recognize differences between the behavior of hybrid moment frames formed from discretely jointed precast members and moment frames of monolithic construction. For strong-column, weak-beam monolithic construction,



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

http://terminology.concrete.org

http://terminology.concrete.org

www.daneshlink.com


inelastic rotations that occur where the beam intersects the column are distributed over a length of the beam approximately equal to its depth. The center of the nonlinear action location is at the center of that length. For the same construction with hybrid moment frames composed of discretely jointed precast members, designed in accordance with this Standard, the inelastic rotations are concentrated at the precast beam-column interface. That interface is the center of the nonlinear action location.

The definition of reinforcement in ACI 318-11 does not permit easy differentiation between the four types of reinforcement permitted in special moment frames that are designed in accordance with this Standard. The licensed design professional can choose deformed reinforcement for the precast beams because this Standard requires that those beams be designed to remain essentially elastic when moments Mpr act on their ends. By contrast, reinforcement in the column may be locally stressed inelastically when the beam develops Mpr. The licensed design professional then needs to use seismic reinforcement conforming to 21.1.5 of ACI 318-11 for the column. The reinforcement, other than the post-tensioning tendons crossing the beam-column interface, is designed to yield during a design basis earthquake (DBE) and can have properties deliberately chosen to differ from those for the column and beam reinforcement. Therefore, the term “energy-dissipating reinforcement” is used to describe those bars and their purpose.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


CHAPTER 3—REFERENCED STANDARDSAmerican Concrete Institute (ACI)ACI 318-11—Building Code Requirements for Structural

Concrete and CommentaryACI 374.1-05—Acceptance Criteria for Moment Frames

Based on Structural Testing and Commentary

American Society of Civil Engineers (ASCE)ASCE/SEI 7-10—Minimum Design Loads for Buildings

and Other Structures Including Supplement No.1

ASTM InternationalASTM A416/A416M-12a—Standard Specification for

Steel Strand, Uncoated Seven-Wire for Prestressed ConcreteASTM A706/A706M-09b—Standard Specification for

Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement

ASTM C1107/C1107M-13—Standard Specification for Packaged Dry, Hydraulic-Cement Grout (Nonshrink)

International Code Council (ICC)IBC 2009—International Building Code 2009



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

http://www.concrete.org/general/home.asp

http://www.asce.org/

http://www.astm.org

http://www.iccsafe.org/Pages/default.aspx

www.daneshlink.com


CHAPTER 4—MATERIALS

4.1—GeneralAll materials and material tests shall conform to the

requirements of ACI 318-11, except as specified in this Standard.

4.2—DuctsDucts, including those for energy-dissipating

reinforcement, shall conform to the requirements of 18.17 of ACI 318-11.

4.3—Energy-dissipating reinforcement4.3.1 Energy-dissipating reinforcement shall have

deformation heights, yield strength, and an ultimate elongation equal to or exceeding those required for ASTM A706/A706M Grade 60 reinforcement.

4.3.2 Unless specific test data on the stress-strain properties of the energy-dissipating reinforcement are obtained before design and construction, the stress-strain properties shall conform to ASTM A706/A706M Grade 60. For the latter case, the tensile strength shall be taken as the specified minimum tensile strength fu. The strain eu at the tensile strength shall be taken as a strain 0.02 less than the strain at the minimum elongation specified in ASTM A706/A706M for the given bar size.

4.3.3 Where properties are based on test data as permitted by Section 4.3.2, the stress-strain properties of the energy-dissipating reinforcement for each bar size used in the moment frame shall be obtained from tensile tests specified in ASTM A706/A706M. The average strain eu of that reinforcement at its average tensile strength fu shall be obtained. Averages shall be based on the results of a minimum of three tension tests for each bar size of each steel heat used for the moment frame.

4.4—Prestressing strands and tendons4.4.1 In moment frames meeting the requirements of this

Standard, post-tensioned prestressing strand tendons shall be used at nonlinear action locations, and pretensioned prestressing reinforcement shall be permitted in precast concrete flexural members.

R4—MATERIALS

R4.3—Energy-dissipating reinforcementStress-strain properties of the energy-dissipating

reinforcement need to be defined accurately. The strength of the beam-column connection and the displacement of the frame are controlled by the maximum strain developed in that energy-dissipating reinforcement and its effective debonded length. The maximum strain demand placed on that reinforcement during an earthquake should not exceed the strain eu at which the reinforcement reaches its tensile strength fu, where eu and fu have the meanings shown in Fig. R4.3. If ASTM A706/A706M Grade 60 reinforcing bars are specified for the energy-dissipating reinforcement and no testing has been performed specific to the reinforcement used in the frame, then the licensed design professional should use limiting strain values that are less than the minimum elongations specified for those bars. It is important to note that eu is less than the minimum elongation ef in Fig. R4.3, specified for the corresponding bar size in ASTM A706/A706M. The strain increase between eu and ef is due to local necking of the bar. The difference between those two values of strain increases as the bar size decreases. In the absence of specific test data for the difference between eu and ef, that value can be taken as 0.02 (2 percent) for ASTM A706/A706M Grade 60 reinforcing bars.

R4.4—Prestressing strands and tendonsR4.4.1 Using prestressing reinforcement in special

moment frames in regions of high seismic risk is specifically allowed by ACI 318-11. Using pretensioned prestressing tendons as the reinforcement in the precast beam is reasonable because those beams should remain within

Fig. R4.3—Typical stress-strain relationship for energy-dissipating reinforcement.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


4.4.2 Prestressing strands shall conform to ASTM A416/A416M.

4.4.3 Prestressing strands shall be permitted to resist earthquake-induced forces, provided the strain in the strands does not exceed 0.011 at the limiting design story drift angle qLdesign.

4.4.4 Anchorages of post-tensioning tendons resisting earthquake-induced forces shall satisfy 21.5.2.5(d) of ACI 318-11.

4.5—Interface groutNonshrink grout shall contain at least 0.1 percent steel

or polypropylene fibers by volume and conform to ASTM C1107/C1107M.

4.6—Grout for anchorage of energy-dissipating reinforcement

Grout used to anchor the energy-dissipating reinforcement shall conform to the requirements of 18.18 of ACI 318-11.

their elastic range of response in the DBE, except at the beam-column interfaces. Using unbonded post-tensioned tendons consisting of prestressing strands in the beams to tie the beams and columns together is an important feature of the hybrid frames covered by this Standard. The use of bars instead of strands at nonlinear action locations is not permitted due to the significant additional stresses at high displacements caused by kinking of the bars where they cross the beam-column interfaces.

R4.4.3 Normally, it is considered good practice during construction to jack prestressing tendons to the highest force consistent with not causing permanent deformations of the prestressing steel. For the strands crossing the beam-column interface, the maximum permissible jacking stress will often be constrained by the design and may be as low as 0.4fpu to ensure that the strand does not yield in a major earthquake. However, experience shows (Post-Tensioning Institute 2012) that to prevent strand slippage, either long term or during the DBE, it is necessary to initially set wedges with forces that create stresses of approximately 0.8fpu in the prestressing steel. This requirement is automatically met when post-tensioning tendons are jacked initially to 0.8fpu and before the jacking force reduced to the desired stress. If the effective stress in the prestressing steel is to be limited to as little as 0.4fpu, separate wedge blocking operations are then necessary. Hydraulic blocking devices can be used that block one strand at a time and transfer their reaction force to the anchorage rather than to the strand.

Because the prestress force is also to prevent sliding due to vertical shear forces at the beam-column interface, the accurate calculation of prestress losses becomes more essential when low prestress levels are used. Reasonably accurate estimates of prestress losses can be calculated using the recommendations of Zia et al. (1979).



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


CHAPTER 5—FRAMING SYSTEM REQUIREMENTS

5.1—GeneralDesigns shall provide:5.1.1 A continuous uninterrupted load path to the

foundation for all components for dead load, live load, wind, and earthquake forces.

5.1.2 Integrity of the entire load path when the structure, and every story in it, is subject to a story drift angle of 0.035.

5.2—Strength5.2.1 At all sections, nominal strengths calculated in

accordance with the requirements of ACI 318-11 and Chapter 7 of this Standard, multiplied by the strength reduction factors specified in ACI 318-11, shall equal or exceed the required strengths for all factored load combinations of 9.2 in ACI 318-11 involving the earthquake loading E.

5.2.2 Where required, load conditions necessitating use of the overstrength factor Wo shall be determined in accordance with ASCE/SEI 7.

5.3—Drift5.3.1 The total drift angle shall be calculated as the lateral

displacement at the top of the structure divided by its height.

5.3.2 The story drift angle shall be calculated as the story drift divided by the story height.

5.3.3 The design total drift angle qLdesign and design story angle for the structure, of which the frame is part, shall be calculated as required by Sections 12.8.6, 12.9.2, or 16.1 of ASCE/SEI 7-10. Foundation flexibility shall be considered and, where appropriate, included in the analysis. Calculations shall include consideration of the soil type on which the moment frame is located in accordance with Section 12.13.3 of ASCE/SEI 7-10.

5.3.4 The design total drift angle qLdesign and story drift angles at the governing load combination involving the earthquake loading E, calculated as required in Section 5.3.3, shall not exceed 0.024.

R5—FRAMING SYSTEM REQUIREMENTSThe frame design is controlled primarily by drift rather

than strength considerations. Performance requirements for the moment frame, the post-tensioning tendons, and the energy-dissipating reinforcement for any moment frame composed from discretely jointed precast concrete members connected by a combination of post-tensioning and energy-dissipating reinforcement are given in Section 5.1. Specific detailing requirements for a frame with concentric post-tensioning and equal top and bottom energy-dissipating reinforcement are given in Sections 6.1 and 7.1.

R5.1—GeneralThe integrity of the load path to the foundation for all

components should be examined for the position to which the structure deforms at a maximum anticipated drift angle of 0.035. This drift angle requirement can be satisfied by examining the integrity of the load path when each story is deformed to the limiting drift angle of 0.035. The maximum drift angle of 0.035 is the angle to which hybrid frames satisfying ACI 374.1 are tested. The reasons for selecting an angle of 0.035 are discussed in Section R7.4 of ACI 374.1.

R5.3—DriftThe moment frame has to satisfy both total and story

drift angle constraints. Generally, the latter control the design. Both the maximum drift angle and the story drift angle resulting from the design basis earthquake (DBE) and the corresponding design displacement are limited to a maximum value of 0.024.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


5.3.5 The drift angle demand and drift angle capacity for any joint shall be calculated as the sum of the components caused by the:

a) Inelastic deformations at the beam-column interfaces at the probable flexural strengths for those interfaces;b) Sum of the corresponding elastic deformations of the beams and columns framing into that joint and of the joint shear deformations.

5.3.6 The structure shall be designed to have maximum total drift angle capacity qLmax and story angle capacities, equal to or greater than 0.035.

5.3.7 The story drift angle capacity shall be the least drift angle capacity for any joint in that story.

5.4—Moment frame characteristicsThe precast concrete special moment frames described in

this Standard shall, in addition to satisfying the requirements of 21.5 through 21.7 of ACI 318-11, have characteristics meeting the requirements of Sections 5.4.1 through 5.4.5.

5.4.1 Single-bay precast concrete beams shall be used. Single and multistory precast concrete columns shall be permitted.

5.4.2 For the frames, the interfaces between the beams and the beam-column joints shall be the only nonlinear action locations, except for column-to-foundation connections.

5.4.3 For multistory precast columns, the lap splices of longitudinal bars in columns in any given story shall be permitted only within the middle third of the height between the top of the slab and the bottom of the beam, except at column-to-foundation connections. Type 2 mechanical splices, described in 21.1.6.1(b) of ACI 318-11, shall be permitted at any location within the column except within the beam-column joint.

5.4.4 Post-tensioning tendons in the beams shall be concentric and the force in the tendons shall have:

a) As required by Section 7.2.1, an effective prestress fse that provides a clamping force across the beam-column

R5.4—Moment frame characteristicsThe minimum structural characteristics required of the

moment frame, regardless of the details of its design, are specified in Section 5.4.

R5.4.2 For strong-column, weak-beam construction, the column overstrength factor l equal to the ratio of the nominal flexural strengths of the columns framing into a given beam-column joint, SMc, to the nominal flexural strengths of the beams framing into the same joint, SMg, needs, as specified in 21.6.2.2 of ACI 318-11, to be equal to or greater than 1.2. For this Standard, values for SMc and SMg are to be calculated as specified in ACI 318. The licensed design professional should, however, choose a value for l consistent with the performance of joints established in the acceptance tests (ACI Innovation Task Group 1 2001). That value should be no less than 1.2 increased by factors that account for differences in column axial loads, slab reinforcement, and concrete and reinforcement strengths, anticipated for the prototype building and not present in the modules for which testing is reported by Priestley et al. (1999) and Day (1999).

R5.4.3 Columns may be precast or cast-in-place, provided they are continuous through beam-column joints.

R5.4.4 It is necessary that the post-tensioning tendons are continuous through the interior column joints and that the beams of the moment frame satisfy the three conditions specified in Section 5.4.4. There should be no



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


interface sufficient to resist the shear caused by factored gravity loads;b) A maximum stress at qLdesign, as required by Section 7.6.5, that is less than the stress at a strain of 0.011 for the post-tensioning tendons;c) A maximum stress fprs at a story drift ratio of qLmax that is less than 0.95 of the specified tensile strength for the post-tensioning tendons, fpu.

5.4.5 The top and bottom energy-dissipating reinforcement in the beams shall have equal areas and equal strengths. This reinforcement shall be bonded through the column and debonded in the beam adjacent to the beam-column interface. This reinforcement shall have:

a) For both top and bottom bars, as required by Section 7.4.2, a strength that is both large enough to provide the relative energy dissipation ratio of not less than 1/8 required by ACI 374.1, and small enough that the effective prestress in the post-tensioning tendon closes any gap at the beam-column interface when earthquake motions cease;b) For the bottom energy-dissipating reinforcement, as required by Section 7.4.1, an area and yield strength sufficient to prevent collapse of the beam under unfactored gravity loads in the event of fracture of the post-tensioned reinforcement.

5.5—Distribution of moment frames within structures

In structures where moment frames are used in combination with precast concrete frames supporting gravity loads, the lateral-force-resisting system shall be well distributed throughout the structure, as required by Section 1908.1.12 of the International Business Code (IBC) 2009.

slip of the precast beam relative to the column, either under gravity loads or under the maximum expected forces in an earthquake. To ensure the preceding condition and that the frame will not show permanent displacements following a DBE, the post-tensioning tendons passing through the beam-column interface must remain essentially elastic throughout that earthquake. Further, the effective prestress force in the post-tensioning tendons needs to be sufficient to cause compressive yielding in the top and bottom energy-dissipating reinforcement. Only then will any gap between the beam and the column that develops during an earthquake close after oscillations cease, because the energy-dissipating reinforcement develops permanent elongations as those bars yield in tension. Further, for the maximum credible earthquake (MCE), the total drift angle and the story drift angle should not exceed the maximum drift of 0.035, for which the design has been validated by testing in accordance with ACI 374.1 and the stress in the prestressing steel should be less than the specified tensile strength of that steel. The maximum stress that can be applied to the prestressing steel is usually limited by the capacity of the wedges anchoring that steel, and the licensed design professional should ensure that the stress at the MCE is less than the stress for which the wedges specified are qualified.

R5.4.5 The energy-dissipating reinforcement crossing the interface fulfills two functions. First, it is the primary source of energy dissipation for the frame during an earthquake. For that function, the reinforcement needs, as required by ACI 374.1, to provide a relative energy dissipation ratio exceeding 1/8. Second, the energy-dissipating reinforcement acts as integrity reinforcement additional to that provided by the post-tensioning tendons. For that function, the energy-dissipating reinforcement is anchored in the column and the beam, and is designed to support the gravity loads acting on the precast beam in the unlikely event that a post-tensioning tendon fractures during an earthquake or due to some other cause.

R5.5—Distribution of moment frames within structures

Damage to precast concrete structures in recent earthquakes raised concerns about whether ACI 318-95 provisions were adequate to enable the inertial forces acting on structures with precast gravity load frames to be transmitted by the diaphragms to the lateral-force-resisting elements. Section 1908.1.12 of IBC 2009 contains provisions intended to provide improved performance of structures having precast concrete gravity-load-supporting systems. Those provisions should be satisfied for buildings containing moment frames conforming to this Standard. Using the second method governing design of the beam-to-column connections,



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


5.6—Moment frame-floor slab interactionsMoment frame-floor slab interactions shall satisfy the

requirements of Sections 5.6.1 and 5.6.2.

5.6.1 The floor slab shall be designed and detailed, and its connections to the precast beams made, in such a manner that relative displacements at interfaces between beams and columns of hybrid frames are consistent with the displacements anticipated at those interfaces based on the response characteristics established in the acceptance tests.

5.6.2 The opening of the joints at the beam-column interfaces of the moment frames under earthquake-induced actions shall not affect the performance of either the gravity load system or the diaphragm.

rather than the first method specified in those provisions, is recommended.

R5.6—Moment frame-floor slab interactionSpecial attention should be given to the detailing of the

connection of the floor slab to the column, to the precast beams, and to any gravity load beam framing into the same column of a given intersection in the moment frame. The presence of the floor slabs, or the gravity load beam, should not change the form of the moment-rotation relationship for an interface from that established in the acceptance tests on specimen characteristic of that intersection. For two slab systems, tests (Chagnon 1998) at the University of California, San Diego, have shown that condition can be met by placing a 1 in. thick layer of compressible filler along the complete length of the column-slab interface and attaching the slab to the precast beams only. One slab system consisted of a cast-in-place, two-way, unbonded, post-tensioned slab. Although a significant gap opened at one end of the post-tensioned beam-column interface at the maximum drift, the compressive strain in the beam on the opposite side of the column reduced the movement of the two beams relative to one another. The crack that opened in the slab on the column centerline had only 25 percent of the width of the gap at the beam-column interface at maximum drift, and closed on unloading.

The second slab system consisted of untopped, one-way, precast pretensioned hollow-core planks spanning both perpendicular and parallel to the beam of the post-tensioned moment frame. The floor system forces were transferred to the beam-column subassemblage by bond beams at each end that had reinforcing bars doweled into the peripheral beams. The floor planks themselves were not connected to the beam-column subassemblage. That system performed well with no modification of the moment-rotation characteristics for the interfaces and essentially no damage to the floor planks.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


CHAPTER 6—DESIGN REQUIREMENTS FOR BEAMS OF MOMENT FRAMES

6.1—PrestressPrestress effects shall conform to the requirements of

Chapter 18 of ACI 318-11, except that the provisions of:a) 18.4 shall not apply for the factored load combinations required by 9.2 of ACI 318-11;b) 18.9 of ACI 318-11 for minimum bonded reinforcement shall apply only in beam regions outside of the regions where the energy-dissipating reinforcement is required to be debonded.

6.2—Beam design6.2.1 Shear strength of the beam for zero drift shall be

calculated using Eq. (11-2) of ACI 318-11 with Vc calculated by Eq. (11-4) of ACI 318-11 and Nu taken as Apsfse.

R6—DESIGN REQUIREMENTS FOR BEAMS OF MOMENT FRAMES

In Chapters 6 and 7, requirements are given for the precast beams and the beam-column connections of the moment frame. Those requirements are intended to provide a performance for the frame consistent with Sections 5.1 through 5.4. The requirements call for equal amounts of top and bottom energy-dissipating reinforcement and concentrically located post-tensioning tendons crossing the beam-column interfaces. To date, performance characteristics have been validated by tests (Priestley et al. 1999; Day 1999) only for interfaces with those properties.

Connections with nonconcentric post-tensioning (as are likely when part of the gravity loads acting on the precast beam are balanced by post-tensioning tendon forces) or connections with unequal top and bottom reinforcement (as are likely when the post-tensioning is nonconcentric) can be designed to perform satisfactorily. Additional analysis and acceptance testing are necessary, however, to establish design procedures to augment those of Chapters 6 and 7.

R6.1—PrestressThe post-tensioning tendons fulfill three functions. They

provide a reliable clamping force to resist shears caused by gravity loads and earthquake forces. They provide additional moment strength at the beam-column interface to that provided by the energy-dissipating reinforcement. Finally, by remaining essentially elastic during a DBE, they can close any gap at the beam-column interface when motions cease and therefore return the frame to its initial, undeformed condition. Those considerations relate primarily to strength, rather than serviceability, so that stresses at service loads are generally not a concern.

The strength of the energy-dissipating reinforcement crossing the interface, in relation to the strength of the post-tensioning tendons crossing that same interface, is selected to provide the response characteristics specified in Section 5.4.5. Applying the minimum bonded reinforcement provisions of 18.9 of ACI 318-11 to the interface region of the precast beam is inappropriate. In the central region of the precast beam, however, outside the area where the energy-dissipating reinforcement is anchored, those minimum reinforcement provisions apply.

R6.2—Beam designR6.2.1 In the end region of the precast beam, the amount of

stirrup reinforcement required depends on the contribution of the shear strength of the concrete to the total shear strength of the member. Because the energy-dissipating reinforcement is partly debonded in that region, the cracking pattern that develops differs from that expected for a reinforced concrete member with bonded reinforcement. Conversely, if the section is treated as prestressed, it is not immediately clear which of the shear strength formulas of ACI 318-11 is appropriate. Correlating the performance of the end regions of test beams with ACI 318-11 requirements suggests that an



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


6.2.2 The requirements of 21.5.4.2 of ACI 318-11 for proportioning transverse reinforcement shall not apply to concrete in the beam adjacent to a beam-column interface.

6.2.3 At each location where the cross section of the beam changes, the shear strength shall be evaluated and adequate reinforcement shall be provided to resist the shears at those locations. Shear reinforcement shall be in the form of closed ties, welded wire reinforcement, or welded wire grids.

6.2.4 The ends of the precast beam shall be detailed to minimize the effects of crushing or spalling where concrete corners bear on the interface grout or the column. The details shall be indicated on the design drawings, or the project specifications shall require the development of such details.

6.2.5 The post-tensioning tendon anchorages and the energy-dissipating reinforcement, for the length over which it is debonded, shall be protected against corrosion in accordance with 18.16 of ACI 318-11. Post-tensioning anchorages shall be sealed to prevent water intrusion. Details of the protection methods shall be indicated in the contract documents.

appropriate approach is to consider the prestress force as an axial compression force acting on the gross area of the beam at the interface.

R6.2.3 The cross section of the precast beam changes at locations where an allowance is made for the insertion of the energy-dissipating reinforcement. Shear failures may occur at such locations if inclined cracking develops and there is inadequate shear reinforcement.

R6.2.4 Under severe displacement cycles, the corners of the precast beam are likely to crush or spall unless preventative measures are taken. Reinforcement spirals surrounding the ducts that contain the energy-dissipating reinforcement are desirable to prevent any loss of moment strength with crushing or spalling. In addition, there are at least two other possible approaches that can assist in minimizing the effects of crushing. Structural steel angles or other reinforcement, such as carbon-fiber or aramid sheets, can be used to confine the beam corners. The reinforcement should extend from the corner of the precast beam to the depth of the energy-dissipating reinforcement in the direction of the thickness of the beam and from the corner to at least twice that depth in the direction of the span of the beam. The reinforcement should have sufficient thickness and anchorage adequate to provide the required confinement at the strain levels anticipated in a major earthquake. Alternately, the beam corners can be chamfered and the presence of that chamfering should be considered in the design. The geometry for the grout pad created between the beam and the column needs to be consistent with the geometry for the reinforcement or chamfering used on the end of the beam.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


CHAPTER 7—REQUIREMENTS FOR BEAM-COLUMN INTERFACES OF MOMENT FRAMES

7.1—GeneralThe interfaces at connections between beams of moment

frames and columns shall satisfy the requirements of Sections 7.2 through 7.8.

7.2—Prestress force7.2.1 Minimum prestress force Apsfse shall be

( )1.2 1.6D L

ps se

V VA f

+=

fm (7.2.1)

where m is the coefficient of friction and equal to 0.6; and f is the strength reduction factor for shear specified in 9.3.2.3 of ACI 318-11.

7.2.2 At Mpr, the design vertical shear strength shall be equal to or greater than the vertical shear strength demand. Unless it is demonstrated by test and analysis that an alternative procedure is to be used, this requirement shall be satisfied as follows:

1. The vertical shear strength demand shall be calculated as specified in 21.5.4 of ACI 318-11.2. The design vertical shear strength at Mpr shall be taken as fmC, where C is the compressive force resisted by the concrete at the interface. In calculating C, the stress in the post-tensioning tendon shall be taken as fprs, the stress in the energy-dissipating reinforcement in tension shall be calculated from strains calculated in accordance with Section 7.6.3 and 7.6.4, and the stress in the energy-dissipating reinforcement in compression shall be taken as 1.25fy.

7.3—Interface grout7.3.1 The thickness of the nonshrink interface grout shall

not exceed 1.5 in.

7.3.2 The specified compressive strength of the grout shall be not less than the value of fc′ for the beam.

R7—REQUIREMENTS FOR BEAM-COLUMN INTERFACES OF MOMENT FRAMES

R7.2—Prestress forceR7.2.1 Because shear failure occurs through the grout in

the pad between the beam and column, the coefficient of friction is taken as 0.6. When the post-tensioning tendon remains elastic under the design drift angle demand, the use of Eq. (7.2.1) permits the performance requirement of Section 5.4.4(a) to be met.

R7.2.2 Under earthquake action, the shear demand at the beam-column interface is a function of both the gravity loads acting on the precast beam and the earthquake moments induced in it. In accordance with Fig. R21.5.4 of ACI 318-11, the design shear force Vu is given by

( ) ( )1 20.75 1.2 1.6 pr pru D L

clear

M MV V V

L

+= + + (R7.2.2a)

where Mpr1 and Mpr2 are the values of Mpr for opposite ends of the deforming precast beam, and Lclear is the face-to-face distance between columns.

When the coefficient of friction is 1.0, the nominal shear strength equals the compression force acting at the interface

fVn = fC (R7.2.2b)

where C = Asfu – As′1.25fy + Apsfprs.

R7.3—Interface groutThe performance of the joint between the beam and the

column directly depends on the toughness of the grout used in the interface. The interface is also the only location where erection tolerances can be provided. The grout in the joint should have adequate toughness to remain intact and not crush or fall out before the end of the precast beam starts spalling in an extreme earthquake event. Using fiber reinforcement in the grout is desirable to ensure adequate toughness. Fibers may be steel or polypropylene. Polypropylene fibers are desirable in exposed locations because joints with steel fibers can be susceptible to rusting.

If the joint is too wide, the grout can fail under a combination of shear and axial stress at stresses less than the compressive strength of the grout. The compressive strength of the grout should be approximately the same as the compressive strength of the precast beam. If the grout



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


7.4—Energy-dissipating reinforcement7.4.1 The yield force in the energy-dissipating

reinforcement shall satisfy the requirement

D Ls y

V VA f

+≥

f (7.4.1)

where f is the strength reduction factor for shear specified in 9.3.2.3 of ACI 318-11.

7.4.2 The ratio of the moment provided by the energy-dissipating reinforcement Ms to Mpr shall not exceed 0.5 for both positive and negative moments.

7.5—Nominal flexural strength7.5.1 At the beam-column interface design for flexural

strength shall be based on

fMn ≥ Mu (7.5.1)

where f is the strength reduction factor for flexure and equal to 0.9.

7.5.2 The design story drift angle at the design displacement, qLdesign, shall satisfy Section 5.3.4.

7.5.3 The nominal flexural strength at the beam-column interface at qLdesign shall be calculated based on satisfaction of applicable conditions of equilibrium and compatibility of deformations.

7.6—Probable flexural strength7.6.1 The probable flexural strength at a beam-column

interface for both positive and negative moments at a drift angle of 0.035 shall be calculated based on the assumptions given in Sections 7.6.2 through 7.6.6 of this Standard and

has a strength considerably greater than that of the beam, it can cause premature crushing of the concrete in the end of the beam at high strain levels. If the grout has a strength considerably less than that of the beam, it will crush first at high strain levels and cause a prestress loss, the effects of which will be difficult to offset during any subsequent repair operations. The grout thickness of 1.5 in. specified in Section 7.3.1 is the maximum thickness that can be tolerated in construction if the behavior of the beam-column interface is to be consistent with behavior calculated in accordance with Chapter 7. The grout thickness of 1/2 in. shown in Fig R1.1 is a recommended design thickness.

R7.4—Energy-dissipating reinforcementR7.4.1 Where the energy-dissipating reinforcement is

properly anchored in both the column and the precast beam, and the width of the joint at the interface is relatively small, the shearing yield strength of a reinforcing bar is approximately half its tensile yield strength. The performance requirement of Section 5.4.5(b) can be met by satisfying the condition

( )

2s y s y D L

s y

A f A f V VA f

+ ′ += =

f (R7.4.1)

where f equals 0.85 in accordance with 9.3.4(c) of ACI 318-11.

R7.4.2 As demonstrated by Cheok et al. (1996) and Stanton and Mole (1994), if the fraction of the flexural strength Mpr at the interface contributed by the energy-dissipating reinforcement is approximately 0.5, there will be an equivalent energy dissipation of at least 15 percent in the third repeat cycle to a drift ratio of 0.035, and the performance requirements of ACI 374.1 will be satisfied.

R7.6—Probable flexural strengthFigure R7.6 shows existing conditions at the beam-column

interface for negative bending rotations when the energy-dissipating reinforcement is stressed to its tensile strength fu. The width of the joint opening at the level of the energy-



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


10.2.5 through 10.2.7 of ACI 318-11, and satisfaction of applicable conditions of equilibrium and compatibility of deformations.

7.6.2 As the connection at the interface opens the elongation—Ds of the energy-dissipating reinforcement in tension, and the additional elongation—Dprs of the post-tensioning tendon, shall be assumed to be directly proportional to distance from the neutral axis.

dissipating reinforcement and the corresponding strain in the energy-dissipating reinforcement are given by Eq. (R7.6a). The effective debonded length of 5.5db, but not less than 2.0db additional to the deliberately debonded length of Lu, is based on an analysis of the crack widths measured in the tests reported by Cheok et al. (1996). Smaller additional effective debonded lengths were found in tests (Stanton et al. 2000) where anchorage conditions were different to those reported in Cheok et al. (1996). Because the compressive strength of the grout should equal or exceed the compressive strength of the beam, the grout thickness should not be included in the debonded length.

When the interface rotates about its neutral axis, located at a distance c from the compression face of the grout pad, the joint opening at the level of the post-tensioned strands is Dprs, where Dprs is given by

( )( )

/ 2sprs

h cd c

D − D =−

(R7.6a)

If Lups is the length over which the post-tensioning tendon is unbonded, the strain in the strands at the probable flexural strength can be calculated as

prsprs se

upsL D

e = + e

(R7.6b)

where ese is the effective prestrain. Because the tendon is unbonded anchorage to anchorage, Lups equals the anchorage-to-anchorage distance, and Dprs is the sum of the joint openings at the tendon level.

The probable flexural strength Mpr is the sum of the contributions from the energy-dissipating reinforcement Ms and the post-tensioned reinforcement Mprs. Those moments are given by

1 11.252 2s s u s yc c

M A f d A f db b = − − −′ ′

(R7.6c)

Fig. R7.6—Rotation at beam-column interface.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


7.6.3 The strain in the energy-dissipating reinforcement in tension, esu, shall be calculated as

( )s

suu b bL d

De =

+ a (7.6.3)

where Lu is the length over which the energy-dissipating reinforcement is deliberately debonded in the beam adjacent to the interface; Ds is the elongation corresponding to a story drift angle of 0.035; and ab is a coefficient quantifying the effective additional debonded length that develops in the energy-dissipating reinforcement at Mpr. The value of ab shall be determined from a set of tests and shall not be taken as greater than 5.5 or less than 2.0.

when the stress in compression in the energy-dissipating reinforcement is taken as 1.25fy and

1

2prs ps prsh c

M A f− b =

(R7.6d)

where

Mpr = Ms + Mprs (R7.6e)

and

( )1

1.250.85

ps prs s u s y

c

A f A f A fc

b f + − ′

b = ′ (R7.6f)

and fprs is the stress corresponding to eprs.For a DBE having a 10 percent probability of occurrence in

50 years, the design drift angle concept should be consistent with the design displacement concept specified in 2.2 of ACI 318-11. As discussed in ACI 374.1, the target design drift angle should be considerably less than the drift angle capacity of 0.035. A target design drift angle of approximately 0.020 is desirable for the DBE having a 10 percent probability of occurrence in 50 years, and that value should not exceed 0.024. For the Maximum Considered Earthquake (MCE) the drift angle must not exceed the value of 0.035 for which the frame has been qualified.

Equations (R7.6a) through (R7.6f) allow calculation of Mpr for a beam-column interface with a given geometry. However, the actual Mpr value that is likely to be achieved and, therefore, the drift that results will be influenced by the detailing of the concrete in the compression zones for the beam-column interface. The cover over the confining reinforcement for the energy-dissipating reinforcement is likely to spall at or shortly after the prestressing steel yields or a drift angle of 0.02 is achieved. The values for d and h in Eq. (R7.6a) through (R7.6f) should be adjusted accordingly for calculation of Mpr.

R7.6.3 It is desirable that the licensed design professional examine variations in the calculated response with variations in values for Lu and ab before settling on a design detail for the deliberately debonded region of the energy-dissipating reinforcement. As ab values vary from 2.0 to 5.5, values for Mpr increase slowly whereas values for drift increase more rapidly.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


R7.7—Anchorage of energy-dissipating reinforcement

R7.7.2 Bars anchored in concrete confined by metal ducts, such as the spirally wound light gage steel ducts used for grouted post-tensioned construction, require less embedment length than bars anchored in monolithic concrete (Stanton et al. 2000; Precast/Prestressed Concrete Institute (PCI) 2004). For a Grade 60 bars and a concrete with fc′ = 5000 psi, 21.7.5 of ACI 318-11 requires a 32.6db tension development length for a straight bar. Because of the presence of the metal duct and the large amount of transverse reinforcement required by Section 7.7.3, a shorter development length will be required for the energy-dissipating reinforcement than that specified in 21.7.5 of ACI 318-11. Analysis of available results shows that a length of 25db is appropriate (Day 1999; Stanton and Mole 1994; PCI 2004; Seible and Priestley 1994; Gamble et al. 1995; Cheok and Stone 1994) if no fibers are used in the grout, and even shorter tension development lengths are appropriate if fiber is used in the grout. In the end column of a given frame, the column thickness hp should be large enough to anchor the energy-dissipating reinforcement. For the interior column of a multi-bay frame, energy-dissipating reinforcement should pass through the column and be anchored in both precast beams as well as the column. In a major earthquake, the energy-dissipating reinforcement

7.6.4 The strain calculated from Eq. (7.6.3) shall be not greater than 0.9eu. Unless the steel stress corresponding to the esu calculated from Eq. (7.6.3) is determined from measured stress-strain properties for that steel, the stress in the energy-dissipating reinforcement at Mpr shall be taken as fu.

7.6.5 The strain in the prestressing reinforcement, eprs, due to rotations at the interface, shall be calculated as

prsprs se

upsL D

e = e +

(7.6.5)

where ese is the strain in the prestressing reinforcement at its effective prestress, and Lups is the unbonded length associated with one interface or the length associated with a given interface over which the post-tensioning tendon is unbonded. The stress fprs in the post-tensioning tendon at Mpr shall not exceed 0.95fpu.

7.6.6 Unless the stress in the energy-dissipating reinforcement in compression is calculated from deformation compatibility considerations for the compressed concrete and known stress-strain properties for the energy-dissipating reinforcement, the stress in that reinforcement at Mpr shall be assumed to be 1.25fy.

7.7—Anchorage of energy-dissipating reinforcement

7.7.1 The energy-dissipating reinforcement shall be anchored by grout in ducts located in the concrete of the members on either side of the interface.

7.7.2 Development length ld for energy-dissipating reinforcement anchored in ducts shall be taken as 25db unless a lesser value is established from a set of tests.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


passing through an interior column is subject to a compressive force at one face of the column and a tensile force at the other face. The minimum column thickness should exceed the minimum tension development length for the bar.

R7.7.3 These confinement requirements have been derived from the results of tests on lap splices used at the base of bridge columns (Seible and Priestley 1994; Gamble et al. 1995). For fully reversed cyclic loads, those tests showed that, with adequate confinement, stresses in splices with development lengths as small as 25db could reach the tensile strength of the bar. That condition was achieved even though all the longitudinal bars of the column were spliced at the base to the same number of dowel bars protruding out of the foundation. The confining reinforcement had to be adequate to prevent sliding on a potential splitting plane separating the column and dowel bars. The situation at the end of the precast beam is analogous to that at the base of a bridge column. The energy-dissipating reinforcement needs to be anchored in the precast beam. The transverse reinforcement needs to be adequate to splice the energy-dissipating reinforcement to the longitudinal reinforcement of the precast beam. Figure R7.7.3 shows the worst potential splitting plane for a precast beam with a cross section the same as that of the precast beams by Cheok and Stone (1994). In those beams, the energy-dissipating reinforcement was placed in a trough and lap-spliced to the longitudinal reinforcement of the beam, which was four No. 3 bars. Shown in Fig. R7.7.3 is the value for Avc for that worst plane and details of the shear reinforcement used in the tests reported in Cheok and Stone (1994). The location of the worst plane changes with the beam dimensions and the details of the shear reinforcement. The splitting plane shown in Fig. R7.7.3 is the worst plane because its length is less, and the reinforcement crossing that plane is less, than for any other plane separating the energy-dissipating reinforcement and the longitudinal reinforcement of the beam. The shear reinforcement used in the tests reported in Cheok and Stone (1994) was a proprietary product, a welded wire reinforcement grid, and for that grid the value of Avc would be larger than that shown on Fig. R7.7.3 due to the participation of the W3.5 inside vertical wires. However, the use of the proprietary product is not required, and with the use of conventional shear reinforcement, only the contribution of two W5.5 wires could be relied upon for providing Avc.

7.7.3 Anchorages for the top and bottom energy-dissipating reinforcement crossing the interface shall be spliced to the matching top and bottom reinforcement of the precast beam. Closed hoops, spirals, welded wire reinforcement, or welded wire grids shall be used to confine the anchorage regions. The confinement reinforcement shall be provided both horizontally and vertically and shall extend the length of the anchorage. The confinement reinforcement shall have a yield strength Avcfvcy, calculated as 0.7Asfusvc/lb for the top reinforcement and as 0.7As′fusvc/lb for the bottom reinforcement, where svc is the spacing of the transverse reinforcement.

7.7.4 The restrictions on using splices in 21.5.2.3 of ACI 318-11 shall not apply where load transfer from the energy-dissipating reinforcement to the longitudinal reinforcement of the precast beam bars conforms to Section 7.7.3.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


7.8—Distribution of flexural reinforcementThe provisions of 10.6 of ACI 318-11 on distribution

of flexural reinforcement shall not apply to the energy-dissipating reinforcement.

Fig. R7.7.3—Potential splitting planes for beam of Cheok and Stone (1994).



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


CHAPTER 8—FRAME JOINTS

8.1—General8.1.1 Frame joints shall be designed in accordance with

the requirements of 21.7 of ACI 318-11. Nominal shear strengths shall be calculated using effective joint areas Aj, for which effective widths on any given horizontal plane within the joint include deductions for widths of post-tensioning ducts and widths of ducts for energy-dissipating bars.

8.1.2 The design shear strength of the joint when moments Mpr act on opposite faces of the joint shall not be taken as greater than f times the value specified in 21.7.4.1 of ACI 318-11. A lesser value shall be used if the appearance of that joint following a major earthquake is of concern.

R8—FRAME JOINTS

R8.1—GeneralFactored shears acting on frame joints should be less than

the design shear strengths derived from 21.7.4.1 of ACI 318-11. Further, because the intention is to limit damage during a major earthquake to the joint filler material, conservative procedures should be used to calculate joint shear strengths. The effective area of the joint is reduced by the presence of the post-tensioning duct and the presence of the energy-dissipating reinforcement ducts. Whereas the latter should be filled with grout, their presence causes a discontinuity that should be considered in defining Aj. For the joint of an exterior column, there can be an offsetting effect resulting from the anchorage of the post-tensioning tendons at the face of the column remote from the beam. That anchorage provides a reaction for the compression strut that forms within the beam-column joint under lateral loads. The existence of that reaction reduces the vertical projection of that strut to considerably less than the full depth of the beam-column joint and, therefore, reduces confinement requirements for the joint. For the joint of an interior column, however, there is no such offsetting effect, and the reduction in effective joint area Aj, caused by the presence of the post-tensioning and energy-dissipating reinforcement ducts, is significant.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


R9—COMMENTARY REFERENCESCommentary documents are listed first by document

number and year of publication followed by authored documents listed alphabetically.

American Concrete Institute (ACI)318-95—Building Code Requirements for Structural

Concrete and Commentary318-11—Building Code Requirements for Structural

Concrete and Commentary374.1-05—Acceptance Criteria for Moment Frames

Based on Structural Testing and Commentary

American Society of Civil Engineers (ASCE)ASCE/SEI 7-10—Minimum Design Loads for Buildings

and Other Structures Including Supplement No.1

Authored referencesACI Innovation Task Group 1, 2001, “Acceptance Criteria

for Moment Frames Based on Structural Testing (ACI T1.1-01) and Commentary (ACI T1.1R-01),” American ConcreteInstitute, Farmington Hills, MI, 11 pp.

ACI Innovation Task Group 1 and Collaborators, 2003, “Special Hybrid Moment Frames Composed of Discretely Jointed Precast and Post-Tensioned Concrete Members (T1.2-03),” American Concrete Institute, Farmington Hills, MI, 15 pp.

Chagnon, M., 1998, “Precast Seismic Resisting Frames Using Unbonded Prestressing Tendons,” Report to the Precast/Prestressed Concrete Institute on Research in Progress at the University of California, San Diego, CA, private communication.

Cheok, G. S., and Stone, W. C., 1994, “Performance of 1/3-Scale Model Precast Concrete Beam-Column Connections Subjected to Cyclic Inelastic Loads,” Report No. 4, NISTIR 5436, National Institute of Standards and Technology, Gaithersburg, MD, 59 pp.

Cheok, G. S.; Stone, W. C.; and Nakaki, S. D., 1996, “Simplified Design Procedure for Hybrid Precast Concrete Connections,” NISTIR 5765, National Institute of Standards and Technology, Gaithersburg, MD, 81 pp.

Day, S., 1999, “Cyclic Load Testing of Precast Hybrid Moment Frame Connections,” MSCE thesis, Department of Civil Engineering, University of Washington, Seattle, WA.

Federal Emergency Management Agency (FEMA), 1997, “Recommended Provisions for Seismic Regulations for New Buildings and Other Structures,” Part 1—Provisions, FEMA 302, and Part 2—Commentary, FEMA 303, Washington, DC, Feb. 1998.

Gamble, W. L.; Hawkins, N. M.; and Kaspar, I. I., 1995, “Seismic Retrofitting of Bridge Pier Columns,” Proceedings of the National Seismic Conference on Bridges and Highways, San Diego, CA.

Hawileh, R.; Tabatabai, H.; Rahman, A.; and Amro, A., 2006, “Non-Dimensional Design Procedures for Precast,



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

http://www.concrete.org/general/home.asp

http://asce.org/

www.daneshlink.com


Prestressed Concrete Hybrid Frames,” PCI Journal, V. 51, No. 5, Sept.-Oct., pp. 110-130.

Hawkins, N. M., and Ishizuka, T., 1988, “Concrete Ductile Moment Resistant Frames,” Proceedings of the Ninth World Conference on Earthquake Engineering, V. VIII, International Association for Earthquake Engineering, Tokyo, Japan, pp. 659-664.

Nakaki, S.; Stanton, J. F.; and Sritharan, S., 1999, “An Overview of the PRESSS Five-Story Precast Test Building,” PCI Journal, V. 44, No. 2, pp. 26-39.

Palmieri, L.; Sagan, E.; French, C.; and Kreger, M., 1996, “Ductile Connections for Precast Frame Systems,” Mete A. Sozen Symposium, SP-162, J. K. Wight and M. E. Kreger, eds., American Concrete Institute, Farmington Hills, MI, pp. 313-355.

Post-Tensioning Institute (PTI), 2012, “Recommendations for Stay-Cable Design, Testing and Installation,” sixth edition, Farmington Hills, MI.

Precast/Prestressed Concrete Institute (PCI), 2004, “Anchorage in Grouted Conduit,” PCI Handbook, sixth edition, Chicago, IL, Chapter 6, p. 8.

Priestley, M. J. N., 1996, “The PRESSS Program’s Current Status and Proposed Plans for Phase III,” PCI Journal, V. 41, No. 2, pp. 22-40.

Priestley, M. J. N., and MacRae, G. A., 1994, “Precast Seismic Resisting Frames Using Unbonded Prestressing Tendons,” Report of 4th U.S. PRESSS Coordinating Meeting, San Rafael, CA, pp. 108-116.

Priestley, M. J. N.; Sritharan, S.; Conley, J. R.; and Pampanin, S., 1999, “Preliminary Results and Conclusions from the PRESSS Five-Story Precast Concrete Test Building,” PCI Journal, V. 44, No. 6, pp. 42-67.

Seible, F., and Priestley, M. J. N., 1994, “Strengthening of Rectangular Bridge Columns for Increased Ductility,” Proceedings of Third Annual Seismic Research Workshop, California Department of Transportation (CALTRANS), Sacramento, CA.

Stanton, J. F., and Mole, A., 1994, “A Hybrid Precast Prestressed Concrete Frame System,” Fourth Meeting of U.S.-Japan Joint Technical Coordinating Committee on PRESSS, Tsukuba, Japan, May, 24 pp.

Stanton, J. F., and Nakaki, S. D., 2002, “Design Guidelines for Precast Concrete Seismic Structural Systems,” PRESSS Report No. 01/03-09, UW Report No. SM 02-02, Department of Civil Engineering, University of Washington, Seattle, WA, Feb.

Stanton, J. F.; Raynor, D.; and Lehman, D. E., 2000, “Bond of Reinforcing Bars Grouted in Ducts,” Report to Charles Pankow Builders Ltd., Altadena, CA, Department of Civil Engineering, University of Washington, Seattle, WA.

Stone, W. C.; Cheok, G. S.; and Stanton, J. F., 1995, “Performance of Hybrid Moment-Resisting Precast Beam-Column Concrete Connections Subjected to Cyclic Loading,” ACI Structural Journal, V. 92, No. 2, Mar.-Apr., pp. 229-249.

Zia, P.; Kent, P. H.; Scott, N. L.; and Workman, E. B., 1979, “Estimating Prestress Losses,” Concrete International, V. 1, No. 6, June, pp. 32-38.



CODE COMMENTARY



--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com

www.daneshlink.com


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

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

· Spring and fall conventions to facilitate the work of its committees.

· Educational seminars that disseminate reliable information on concrete.

· Certification programs for personnel employed within the concrete industry.

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

· Sponsoring and co-sponsoring international conferences and symposia.

· Formal coordination with several international concrete related societies.

· 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. ACI members receive discounts of up to 40% on all ACI products and services, including documents, seminars and convention registration fees.

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

American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701

www.concrete.org





--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com


www.daneshlink.com


Design Specification for Unbonded Post-Tensioned Precast Concrete Special Moment Frames Satisfying ACI 374.1 and Commentary

The AMERICAN CONCRETE INSTITUTE

was founded in 1904 as a nonprofit membership organization dedicated to public service and representing the user interest in the field of concrete. ACI gathers and distributes information on the improvement of design, construction and maintenance of concrete products and structures. The work of ACI is conducted by individual ACI members and through volunteer committees composed of both members 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. Committee activities include the development of building codes and specifications; analysis of research and development results; presentation of construction and repair techniques; 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 is composed of engineers, architects, scientists, contractors, educators, and representatives from a variety of companies and organizations.

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

www.concrete.org





--`,`,,```,,`,```,`,`,```,``,,,,-`-`,,`,,`,`,,`---

daneshlink.com

Daneshlink.com


www.daneshlink.com


Documents

ACI 550.3-13: Design Specification for Unbonded Post-Tensioned … · 2020. 5. 12. · column special moment frames in accordance with 21.1.1.8 of ACI 318-11. Before acceptance testing