recommendations for design of beam-column joints in ... recommendation… · aci352r-91 (reapproved...

ACI352R-91(Reapproved 1997)

Recommendations for Design of Beam-Column Joints inMonolithic Reinforced Concrete Structures

Reported by ACI-ASCE Committee 352

Clarkson W. PinkhamChairman

J. D. ArtstizibalVitelmo V. BertcroMarvin E. CriswellAhmad J. DurramMohammad R. EhsaniEdward S. Hoffman

Norman W. HansonSecretary

James K. WightSubcommtttee Chairman

David A. HunterJames 0. JimaCary KopczynskiDonald F. MeinheitJohn J. OtrembiakRobert Park

Committee members voting on the 1991 revisions:

James K. Wight Mohammad R. EhsaniChairman Secretary

Ahmad J. DurraniChairman, Editorial Subcommittee

James R. CagleyMarvin E. CriswellLuis E. GarciaCary S. KopczynskiMichael E. Kreger

Donald F. MeinheitJack P. MoehleClarkson W. PinkhamMehdi SaiidtMustafa Seckin

These recommendations an a revision of earlier recommendations from

this committee. Recommendations are given for member proportions and

reinforcement dctaiL requind for satisfactory confiement of the column

core i n the joint region. adequate joint shear strength, the proper ratio of

column-moment strength versus beam-moment strength at the joint, and

development of reinforcing bars either terminating in or passing through

the joint. Commentary is provided to amplify the recommendations and

identify available reference material.

The recommendations are based on laboratory testing as well as field

studies and provide a state-of-the-art summary of current information.

Amas needing research aw identified. Design examples are presented to

i l lustrate the USC of the design ncommcndations.

Keywords: beam-column joints, anchorage (structural); beams (sup-porta); bond (concrete to reinforcement); columns (supports); confined

AC1 Commtttee Reports, Gurdes, Standard Practtces, and Commentarmsate intended for guidance in planning, designing, executing, and inspectingconstruction. This document is intended for the use of individuals whoare competent to evaluate the significance and limitations of its con-tent and recommendations and who will accept responsibility for theapplication of the material it contains. The American Concrete Institutedisclaims any and all responsibility for the stated principles. The Instituteshall not be liable for any loss or damage arising therefrom.

Reference to this document shall not be made in contract documents. Ifitems found in this document are desired by the Architect/Engineer to bea part of the contract documents, they shall be restated in mandatory lan-guage for incorporation by the Architect/Engineer. -..-.A-________

Mehdi SaiidiDonald R. StrandS. M. UzumeriSudhakar P. VermaLormg A. Wyl l ie , J r .Liandc Zhang

Gene R. StevensDonald R. StrandS. M. UzumeriSudhakar P. VermaLoring A. Wyl l ie , J r .

concrete; connections; earthquake resistant structures; hooked reinforce-ment; joints (junctions); reinforced concrete; reinforcmg steels; shearstrength; stresses; structural design; structures.

CONTENTS

Chapter l-Introduction and scope, p. 352R-21. l-Introduction1.2-Scope for concrete1.3-Scope for Type 2 joints

Chapter 2-Classification of beam-column joints, p.352R-2

2. l-General2.2~Definition

AC1 352R-91 became effectwe June I. 1991 and vqer\ede\ ACI 152R-85 Numer-out edmwal and m~ncr nw,\,cm\ were made to the report Reference\ have teenadded and updated

Copyrnght 8 1997, Amencan Concrete InWuteAll right\ raewed mcludmg rights of reproduction and we !n any form or by any

means. mcludmg the makmg of copes by any photo proce\\, or by electrow ormechanical &we, printed. written. or oral, or recordmg for wund or w\uaI reproduc-tmn or for u\e I” any knowledge or retrieval \y\tem or dewce. unle\\ perm,\\mn ,nwrung IF obtanud from the copyright proprietor+

352R-1

352R-2 MANUAL OF CONCRETE PRACTICE

(a) Exterior (b) Interior

‘Fig. I.l-Typical beam-to-column connections

Chapter 3-Design considerations, p. 352R-33. l-Critical sections3.2-Forces3.3-Serviceability3.4-Strength considerations

Chapter A--Nominal strength considerations, p. 352144. I-Compression4.2-Transverse reinforcement4.3~Shear for Type 1 and Type 2 joints4.4-Flexure4.5-Development of reinforcement

Chapter 5-Notation, p. 352R-9

Chapter &References, p. 352R-10

Appendix A-Areas needing research, p. 352R-12

Appendix B-Design examples, p, 3521-13

CHAPTER l-INTRODUCTION AND SCOPE*

l.l-IntroductionThese recommendations are for determining joint propor-

tions and design of the longitudinal and transverse reinforce-ment at the intersection of beams and columns in cast-in-place concrete frame construction. The recommendationsare written to satisfy strength and ductility requirements re-lated to the function of the joint,

In the past, the design of joints in monolirhic reinforcedconcrete srrucrures was primarily limited to satisfying an-chorage requirements for rhe reinforcement. Because of theuse of high-strength materials (concrete and steel), smallermember sections, and larger reinforcing bars, special atten-tion to rhe design and detailing of the joint has become moreimportant. In many designs, column sizes may be defined bythe requirements of joint detail design. Attention is focusedon the joint to ensure proper structural performance underall loading conditions that may reasonably be expec&d looccur and to alert the designer to possible congestion of re-inforcement.

*Design recommendations of Committee 352 are set in standard type: commentaryand explanations follow each section in italic type.

This report considers typical beam-column joints in cast-in-place reinforced concrete structures, as shown in Fig. 1.1.Specifically excluded from these recommendations are slab-column joints and precast structures where connections aremade near the beam-to-column intersection. Design exam-ples illustrating the use of these recommendations are givenin Appendix B.

The material presented here is an update of a previous re-port from ACI-ASCE Committee 352.49 A partial listing ofresearch information available to the committee at that timeis given in References l-38. Research information availablein References 39-66 and Chapter 2 1 of AC1 3 18 have beenreceived during the updating of these provisions. This reportaddresses joints in both seismic and nonseismic regions,whereas Chapter 2 1 of AC1 3 18 addresses only joints in seis-mic regions.

l&-Scope for concreteThese recommendations apply only to structures using

normal weight concrete in the joints.

1.3-4cope for Type 2 jointsFor Type 2 joints as defined in Section 2.1, only joints in

which the column width is equal to or greater than the beamwidth are covered by these recommendations.

For Type 2 joints, the recommendations provide guidanceonly in cases where the beam bars are located within the col-umn core. All currently available research results are forconnections where the beam width is less than or equal to thecolumn width and the beam centerline passes through rhecolumn centroid. Connecrions where the beam centerlinedoes norpass through the column centroid are included ifallbeam bars are anchored in or pass through rhe column core.However, the torsion resulting from this eccentricity shouldbe considered. Connections where the beam bars pass out-side the column core are excluded for Type 2 joints becauseof a lack of research data on rhe anchorage of such bars un-der large load reversals.

CHAPTJXR 2-CLASSIFICATION OFBEAM-COLUMN JOINTS

2.1-GeneralStructural joints are classified into two categories, Type 1

and Type 2, based on the loading conditions for the joint andthe anticipated deformations of the joint when resisting lat-eral loads.

2.1.1 Type I - A Type 1 joint connects members de-signed to satisfy AC1 318 strength requirements and inwhich no significant inelastic deformations are anticipated.

2.1.2 Type 2 - A Type 2 joint connects members desig-nated to have sustained strength under deformation reversalsinto the inelastic range.

The requirements forjoints are dependent on the deforma-tions at the joint implied by rhe design loading conditions.Typical examples of each joint type are:

Type 1 is a joint in a continuous moment resisting struc-ture designed on the basis of strength without considering

BEAM-COLUMN JOINTS 352R-3

special ductility requirements. Any joint in a typical framedesigned to resist gravity and normal wind loads would fallinto this category.

Type 2 is a joint that connects members that are requiredto dissipate energy through reversals of deformation into theinelastic range. Joints in moment resisting frame structuresdesigned to resist earthquake motions, very high winds, orblast effects are of this category.

2.2-DefinitionA joint is defined as that portion of the column within the

depth of the beam(s), including the slab, that frame into thecolumn.

CHAPTER 3-DESIGN CONSIDERATIONS

3.1-Critical sectionsA beam-column joint should be profirtioned to resist the

forces specified in Section 3.2 at the critical sections. Thecritical sections for transfer of member forces to the joint areat the joint-member interfaces. Critical sections for shearforces within the joint are defined in Section 4.3.1. Criticalsections for bars anchored in the joint are defined in Section4.51.

Design recommendations are based on the assumptionthat the critical sections are immediately adjacent to thejoint. Exceptions are made for joint shear and reinforcementanchorage. Fig. 3.1 shows the joint as a free body with forc-es acting on the critical sections.

3.2-Forces3.2.1-The joint should be designed for the interaction of

the multidirectional forces which the members transfer to thejoint including axial loads, bending, torsion, and shear.These forces are a consequence of the effects of externallyapplied loads as well as those resulting from creep, shrink-age, temperature, or settlement.

The joint should resist all forces that may be transferredby adjacent members, using those combinations that pro-duce the most severe force distribution at the joint, includingthe effect of any member eccentricity. Forces produced bydeformations resultingftom time-dependent effects and tem-perature should be taken into account. For Type 2 joints thedesign forces that the members transfer to the joint are notlimited to the forces determinedfrom a conventional analy-sis, but should be determinedfrom the nominal strengths ofthe members as defined in Section 3.2.2. Strength reductionfators are not used.

33.2-At every joint, consideration should be given to de-termine which members will reach initial flexural yieldingdue to gravity loads, lateral loads, and secondary effects, andthe design forces in the flexural reinforcement at the mem-ber-joint interfaces should be determined using the stress a&where fy is the specified yield strength of the reinforcing barsand a is a stress multiplier

ForType 1 a;l 1.0

Ccl TCl

(a) Due to Gravity Loads (bl Due to Loteml Loads

Fig. 3.I-Planarjointforces. T = tension force, C = com-pression force, V = shear force, subscript b for beam andsubscript c for column

ForType a;r 1.25

The analysis of the forces acting on a Type 1 or Type 2joint is identical. For Type 2 joints for which the sum of thecolumn flexural capacities exceed the sum of the beamflex-Ural capacities along any principal plane, the forces in Fig.3. I(b) representing tension and compressionfrom the beamsshould be based on the area of steel provided and the speci-jIed yield stress modiJied by a. The corresponding columnforces are then a function of the column axial load and themoments and shears required to keep the connection in equi-librium. For Type I joints [represented in Fig. 3.1(a)], thesame approach is used unless the column sections reachtheir capacities before the beam sections. In the latter case,the columns are assumed to be at their flexural capacities,with due consideration of column axial load, and the beammoments and shears have magnitudes required to keep thejoint in equilibrium.

The factor a is intended to account for the following: (a)the actual yield stress of a typical reinforcing bar is com-monly 10 to 25 percent higher than the nominal value, and(b) the reinforcing bars will strain harden at member dis-placements only slightly larger than the yield rotation. A re-search studyS demonstrates typical laboratory results for astatically determinate test specimen. The results, which werediscussed in detail in a previous committee report” show asignificant increase in steel stress above the actual yieldstress attributable to strain hardening when plastic hingingoccurs. A value of a = 1.0 is permitted for Type I joints be-cause only limited ductility is required in members adjacentto this type of joint. As pointed out in the previous committeereport,” a value of a = 1.25 should be regarded as a mini-mum for Type 2 joints. For reinforcing steels whose proper-ties are not controlled properly, a value of a larger than therecommended minimum may be appropriate.

3.3-ServiceabilityCracking and concentrated rotation are to be expected near

the joint faces where bending moments usually reach theirmaximum values. The section proportions of the framingmembers at the joint should satisfy the requirements of AC13 18 for cracking and deflection under service loads.

MANUAL OF CONCRETE PRACTICE

(0) Plon view of ’ iti with

BIy g~;~uSJingkomsinbo xondy

1A”

SCY

~t -7-T

byr0.75hy

XbY hY

AlJ4”

(b) ~onmvJ tf j$syE

providing c&f inement

Fig. 4.l-Dejnition of adequate lateral confining members

Serviceability requirements are intended primarily formembers meeting at a joint. No additional requirements overthose given in ACI 318 are specified. However, the designershould consider the possible ejfect of joint rotations oncracking and defection.

3.4-Strength considerationsAll joints should be designed, according to Chapter 4, to

resist the most critical combination of forces as defined inSection 3.2.

CHAPTER ANOMINAL STRENGTHREQUIREMENTS

4.l-Compression4.1.1-Transmission of the column axial load through the

joint region requires adequate lateral confinement of the con-crete in the column core by a combination of longitudinalcolumn reinforcement plus either transverse members fram-ing into the column or transverse reinforcement, as definedin Section 4.2, or both.

4.1.2-Longitudinal column reinforcement passingthrough the joint should satisfy Sections 10.9.1 and 10.9.2,ofAC1 318.

For Type 1 joints, longitudinal column bars may be offsetwithin the joint. The provisions of AC1 3 18 for offset barsshould be followed.

For Type 2 joints, longitudinal column bars extendingthrough the joint should not be offset at the joint and the area

of column reinforcement should be distributed around all pe-rimeter faces of the column core. Further, the center-to-cen-ter spacing between adjacent longitudinal bars should notexceed the larger of either 8 in. (200 mm) or one-third of thecolumn diameter or cross section dimension in the directionthe spacing is being considered. In no case should the spac-ing exceed 12 in. (300 mm).

Research on c01umn~‘~~~~ 2s*29*31 subjected to severe loadreversals has shown that a uniform distribution of the col-umn longitudinal reinforcement area improves confinementof the column core. The requirements of this section are in-tended to insure a relatively uniform distribution of the lon-gitudinal bars in Type 2 joints.

4.2-Transverse reinforcement4.2.1-Type 1 joints

4.2.1.1-Transverse reinforcement, as defined in Sec-tion 4.2.1.3, should be provided through the total depth of thejoint except for locations or in directions as defined in Sec-tion 4.2.1.2.

4.2.1.2-Within the depth of the shallowest memberframing into the joint, the following exceptions to Section4.2.1.3 are permitted:

a) Where beams frame into all four sides of the joint andwhere each beam width is at least three-quarters of thecolumn width and does not leave more than 4 in. (100mm) of the column width uncovered on either side ofthe beams, Section 4.2.1.3 does not need to be satis-fied.

b) Where beams frame into only two opposite sides of thejoint and the beam widths are at least three-quarters ofthe column width and no more than 4 in. (100 mm) ofthe column width remains uncovered on either side ofthe beams. Section 4.2.1.3 does not need to.be satisfiedin the direction perpendicular to the two sides of thejoint into which the beams frame. Transverse rein-forcement satisfying Section 4.2.1.3 should be pro-vided in the direction parallel to those two sides.

The primary junction of ties in a tied column is to preventthe outward buckling of the .column longitudinal bars and toprovide some confinement to the column core. For Type 1joints, ties may be omitted within the joint ifthere are trans-verse membersframing into the joint that are of a sulficientsize to effectively replace the cot@ement provided by ties.Some typical cases are shown in Fig. 4.1.

4.2.1.3-Transverse reinforcement should satisfy Sec-tion 7.10 of AC1 3 18 as modified in this section. At least twolayers of transverse reinforcement should be provided be-tween the top and bottom levels of beam longitudinal rein-forcement of the deepest member framing into the joint. Thecenter-to-center spacing should not exceed 12 in. (300 mm).If the beam-column joint is part of the primary system for re-sisting nonseismic lateral loads, the center-to-center spacingof the transverse reinforcement should not exceed 6 in. (150mm). To facilitate placement of transverse reinforcement inType 1 joints, cap or split ties may be used provided the laplength is sufficient to develop the tie strength.


When required, ties in the joint should satisfy the require-ments of ACI 318 for tied columns plus additional recom-mendations which confSte the column bars through the joint.When ties are recommended in a joint which is part of theprimary system for resisting nonseismic lateral loads, therecommended spacing is limited to 6 in. (150 mm), center tocenter, to provide additional confinement to the joint.

4.2.2-Type 2 joints4.2.2.1-When spiral transverse reinforcement is used,

the volumetric ratio P,~ should be

(4.1)

but should not be less than that required by AC1 3 18.4.2.2.2-Where rectangular hoop and crosstie trans-

verse reinforcement as defined in Chapter 2 1 of AC1 3 18 isused, the total cross-sectional area in each direction of a sin-gle hoop, overlapping hoops, or hoops with crossties of thesame size should be at least equal to

s,,h”f,’A,, = 0.3? (A/A, - 1) (4.2)

Jyh

but should not be less than

A, = 0.09s,,h”f,’-

f . (4.3)Jyh

The speci$ed reinforcement is expected to provide ade-quate conf%tement to the joint during anticipated earthquakeloading and displacement demands. The provided confine-ment is also expected to be sufficient for necessary forcetransfers within the joint. Eq. (4.1) and (4.2) are the same asthose given in Chapter 21 of ACI 318. The coefficient 0.09 inEq. (4.3) was selected based on the observed improved be-havior of tied columnP*29*31 which have properly detailedhoops and crossties.

4.2.2.LLFor joints connecting members which are partof the primary system for resisting seismic lateral loads, thecenter-to-center spacing between layers of transverse rein-forcement (hoops or hoops and crossties) sh should not ex-ceed the least of one-quarter of the minimum columndimension, six times the diameter of longitudinal columnbars to be restrained, or 6 in. (150 mm). Crossties, when re-quired, shall be provided at each layer of transverse rein-forcement. The lateral center-to-center spacing betweencrossties or legs of overlapping hoops should not be morethan 12 in. (300 mm) and each end of a crosstie should en-gage a peripheral longitudinal reinforcing bar.

4.2.2,AIf a joint connects members which are not partof the primary system for resisting seismic lateral loads, butthe members must be designed to sustain reversals of defor-mation in the inelastic range for deflection compatibilitywith the primary system for resisting seismic lateral loads,

the vertical center-to-center spacing between layers of trans-verse reinforcement s,, should not exceed the smaller of one-third of the minimum column dimension or 8 in. (200 mm).

In the design of building systems resisting earthquakeforces, it is assumed that loads have been reduced to a levelwherein member forces are determined by elastic theory.The inelastic response that is expected at the anticipated lev-el of earthquake excitation is provided for by the special de-tailing of the members and joints which comprise theprimary system for resisting seismic lateral loads. Memberswhich are not included in this system should also be capableof undergoing the same deformations as the primary systemwithout a loss of vertical load strength. Thus, memberswhich are not part of the primary system should be eitherflexible enough to respond elastically to the anticipatedground motion (not the reduced seismic design lateral forc-es) or else the nominal hooping recommended in Section4.2.2.4 should be provided to minimize joint deterioration.

The limitations on size and spacing of transverse rein-forcement given in this section, when combined with the lim-itations of Section 4.1,2 for spacing of longitudinal bars inType 2 joints, are intended to create a steel gridwork capa-ble of adequately confining the column core. Crossties arerequired to maintain the stiffness of the sides of the grid-work.

4.2.2.5-Transverse reinforcement, as defined in Sec-tions 4.2.2.1 and 4.2.2.2, should be provided unless the jointis confined on all sides by structural members which satisfySection 4.2.1.2(a), in which case the reinforcement shouldnot be less than half that required in Sections 4.2.2.1 and4.2.2.2. Spacing limitations of Sections 4.2.2.3 and 4.2.2.4apply regardless of confinement conditions.

Recent research result$8*32*33~46*48*56~62 have shown thatsmallerpercentages of transverse reinforcement can be usedwhen adequately sized transverse members are present.

4.2.2.6-All hoops should be closed with hooks of notless than 135 deg at their ends and 6 bar-diameter extensions.Single leg crossties should have a 135 deg bend with a 6 bar-diameter extension on one end and the other end may have astandard tie hook, as defined in Section 7.1 of AC1 318. Ifused, the 90 deg ends should be alternated on opposite facesof the column. In exterior and comer joints, the crosstiesshould be arranged such that the 135 deg bend is at the exte-rior face of the joint.

Recommended shapes of closed hoops and single legcrossties are shown in Fig. 4.2. The preferred shape for asingle leg crosstie would have a 135 deg bend at both ends.However, installation of such crossties usually is dift?cult. Astandard 90 deg tie hook is permitted, but does not provideeffective anchorage because the extension beyond the bendruns along the outside edge of the confined column core.Further, a shorter extension is permitted for the 90 deg bendbecause increasing the extension would offer only a slightimprovement. Thus it is recommended that when a 90 degbend is used it should be alternated on opposite faces alongthe column. However, in the case of exterior and comerjoints, where the loss of cover could affect the anchorage of


b

(0) Closed Hoop

(b) Single Leg Cross TieFig. 4.2-Requited dimensions oftmnsverse reinforcement

cross ties at the 90 deg be& it is recommended that only 135deg bend be used at the exterior face of the joint.

4.2.2.7-Transverse reinforcement layers required inthe joint should be extended into the columns above and be-low the joint as required by Chapter 21 of AC1 318. Trans-verse reinforcement as required by Chapter 21 of ACI 318should also be provided in the beams adjacent to the column.

Minimum distances for extending the joint transverse re-inforcement into the columns to provide confinement to thecolumn core above and below a joint are given in Section21.4.4.4 of AC1 3 18. The committee has reservations aboutthe adequacy of the specified extensions,26 such as at the topstory or at the base of a first story column, where the poten-tial flexural hinging zone may extend further into the storyheight than the minimum distances specified. In such casesthe joint transverse reinforcement should be extended to cov-er the entire potential flexural hinging zone.

4.3-Shear for Type 1 and Type 2 joints4.3.1-For joints with beams framing in from two perpen-

dicular directions, the horizontal shear in the joint should bechecked independently in each direction. The design shearforce V,, should be computed on a horizontal plane at themidheight of the joint by considering the shear forces on theboundaries of the free body of the joint and the normal ten-sion and compression forces in the members framing into thejoint as specified in Section 3.2.2. The following equationshould be satisfied

Table l-Values of y for beam-to-column joints

Joint type

Joint classificaton

(a) Interior 1 (b) Exter ior 1 (c)Caner

1 24 20 I52 2 0 I 1 5 1 2

(4.4)

where + = 0.85 and V,, the nominal shear strength of the jointis

V” = ‘YE (psi) bj h

vn = 0.083~8 (MPa) bj h (4.5)

where b, is the effective joint width and h is the thickness ofthe column in the direction of load being considered.

The effective joint width bj should be taken as

U+, + bc)bj= 2 (4.6)

but not greater than column width b, or greater than beamwidth bb plus half the column depth h on each side of thebeam. The term b* is the width of the beam in the ditectionof loading. Where beams of different width frame into oppo-site sides of the column in the direction of loading, bb shouldbe taken as the average of the two widths.

The constant y for Eq. (4.5) is given in Table 1 and de-pends on the joint classification, as defined in Section 4.3.2.and joint type, as defined in Chapter 2. The value for thecompressive strength f,’ in Eq. (4.5) should not be larger than6000 psi (42 MPa).

4.3~An interior joint has horizontal members framinginto all four sides of the joint. However, to be classified as aninterior joint for Table 1, the horizontal frame membersshould cover at least three-quarters of the width of the col-umn and the total depth of the most shallow horizontal mem-ber should not be less than three-quarters of the total depthof the deepest horizontal member framing into the joint. Ifthe four horizontal members do not satisfy this requirement,then the y value for this joint should be selected from Col-umn (b) of Table 1.

An exterior joint has at least two horizontal membersframing into opposite sides of the joint. However, to be clas-sified as an exterior joint for Table 1, the widths of the hori-zontal frame members on the two opposite faces of the jointshould cover at least three-quarters of the width of the col-umn and the total depth of these two members should be notless than three-quarters of the total depth of the deepestmember framing into the joint. If the two horizontal framemembers do not satisfy this requirement, then the 7 value forthis joint should be selected from Column (c) of Table 1.

All other joints should be classified as comer joints whenselecting a value for yin Table 1.


The geometric descriptions of interior, exterior, and cor-ner joints are given in Fig. 4.3.

Not all joints which have horizontal membersframing intoall four sides of the joint can be classified as interior jointswhen using Table I. If the dimensions of the horizontal mem-bers do not satisfy the given requirements, then a lower val-ue of y ir specified. Similarly, not all joints which havehorizontal members framing into two opposite sides of thejoint can be classified as exterior joints when using Table 1.Again, if the dimensions of the horizontal members do notsatisfy the given requirements, then a lower value of y isspecified.

Although the joint may be designed to resist shear in twoperpendicular horizontal directions, only one classificationis made for a joint. That is, only one value for y is selectedfrom Table I for the joint, and that value is used when check-ing the joint shear capacity in both directions.

The concrete compressive strength in Eq. (4.5) is limitedto 6OOOpsi (42 MPa) because only limited research data areavailable on the behavior of connections constructed usinghigher strength concrete.38

The normal procedure for calculating the horizontal de-sign shear in an interior and an exterior joint is shown inFig. 4.4. The procedure for determining the joint width incases when the beam width is less than the column width isshown in Fig. 4.5.

In cases where the beam centerline does not pass throughthe column centroid, torsion may occur. At the present time,there is insufficient research on eccentric .connections to de-velop specific design recommendations, but such eccentrici-ties have resulted in apparent increased earthquakedamage.” The designer should consider the possible conse-quences of member eccentricities on jointperformance whendesigning and detailing the joint.

The design philosophy embodied in Eq. (4.5) is that duringanticipated earthquake loading and displacement demands,the joint can carry the specified shearforces if the concretewithin the joint is adequately confined. To provide this con-

finement, Sections 4.1 and 4.2 contain recommended detailsfor column longitudinal and transverse reinforcement in thejoint region.

Some researchers2°.43 have pointed out the need to consid-er also vertical shear forces in the joint. It is expected thatthe recommendations for the distribution of the column lon-gitudinal reinforcement given in Section 4.1.2 will provideadequate vertical reinforcement in the joint to carry thatcomponent of joint shear.

The shear provisions adopted by Committee 352 are in-tended for limited displacement and rotation levels and alsoanticipate the beneficial effects of load redistribution in a re-dundantframe structure. Committee 352 has also addressedthe construction problems resulting frDm congestion of rein-forcement in beam-column joints.

4.AFlexure4.4.1-Flexural design of members at the joint should be

based on the provisions of AC1 3 18.

Column

+

ams

(a 1 Interior

(b.! I Exterior

Column

+

Beams

(c. t 1 Corner

(b. 2) Exterior

Column Beam

I-(c.2) Corner

Fig. 4.3-Geometric description of joints

h=%lfCbL-%

A22

I tJoint Elevation Beom Section

Fig. 4.4-Evaluation of horizontal joint shear

Plan Views

Fig. 4..5-Determination of effective joint width b,


Fig. rC.&Critical section for development of beam rein-forcement terminating in the joint

4.4.2-For Type 2 joints which are part of the primary sys-tem for resisting seismic lateral loads, the sum of the nomi-nal moment strengths of the column sections above andbelow the joint, calculated using the axial load which givesthe minimum column-moment strength, should not be lessthan 1.4 times the sum of the nominal moment strengths ofthe beam sections at the joint. For joints with beams framingin from two perpendicular directions, this ratio should bechecked independently in each direction.

4.4.3-For Type 2 joints which are not part of the primarysystem resisting seismic lateral loads, the ratio of column tobeam moment strengths should be greater than 1.0. If thisprovision is not met, transverse reinforcement as specified inSection 4.2.2.5 should be used both above and below thejoint and should extend a distance at least equal to twice theeffective depth of the column cross section, both above andbelow the joint boundaries.

The requirement that the sum of the nominal momentstrengths of the column sections above and below a Type 2joint be 40 percent greater than the nominal momentstrengths of the beam sections framing into the joint is in-tended to produceflexural hinging in the beams rather thanin the columns, as is normally preferred in the seismic designof moment resisting reinforced concrete frame structures.Therefore, the 1.4 factor is a minimum value and a highervalue could be necessary to develop beam hinging in struc-tures with heavily reinforced slabs. Appropriate slab widthshould be included in calculating the beam momentstrengths. Recent studiesf 7.42-44.~,48.Y-S~S8.8.60.62.63 hve shownthe presence of a slab to have a significant e@ect on the per-formance of connections. The committee continues to reviewthis data. However, at this time there is no clear consensuson the effective width of slab to use in determining the beamflexural strength.

For portions of the structure which are not part of the pri-mary system resisting seismic lateral loads, column hingmgdue to a severe earthquake is not critical as long .as propertransverse reinforcement is used. In certain cases, framesare designed with deep long-span beams and relatively smallcolumns. It is recommended that such frames not be part ofthe primary system resisting seismic lateral loads.

4X-Development of reinforcement4.5.1 Critical sections for development of beam reinforce-

ment-The critical section for development of reinforce-ment should be taken at the face of the column for Type 1joints and at the outside edge of the column core for Type 2joints.

During intense seismic loading, moment reversals are tobe expected at beam-to-column joints which cause stress re-versals in the beam and column longitudinal reinforcementat the connection. Research results” have shown that theconcrete cover over the column bars quickly becomes inef-fective for bar development in Type 2 joints. Thus, the criti-cal section for development is taken at the face of theconfined column core (see Fig. 4.6).

4.5.2 Hooked bars terminating in the joint4.5.2.1 Bar sizes should not exceed No. 11 and hooks

should be located as far from the critical section as possible.The minimum development length I,,,,, as defined in the fol-lowing sections, should not be less than 8db or 6 in. (150mm>.

4.5.2.2 For Type 1 joints, the development length l& ofa bar terminating in a standard hook should be computed asfollows

‘dh =f,Wd,

SOR(psi)

1 dh =fyNWd,

4.2K(MPa)(4.7)

a) For No. 11 and smaller bars, if side cover normal to theplane of the hook is not less than 2V2 in, (65 mm) andcover on the bar extension beyond the hook is not lessthan 2 in. (50 mm), lclhr as given in Eq. (4.3, may bemultiplied by 0.7.

b) For No. 11 and smaller bars, if the hook is enclosed ver-tically or horizontally within ties or stirrupties whichare provided along the full development length at aspacing not greater than 3d,, where db is the diameterof the hooked bar, then l,,, as given in Eq. (4.7). maybe multiplied by 0.8.

c) Where reinforcement in the flexural member is pro-vided in excess of that required for flexural strengthand anchorage for fy is not specifically required, ldA, asgiven in Eq. (4.7), may be reduced by the ratioA,(required)/A,(provided).

4.5.2.3-For Type 2 joints, all terminating bars shouldbe hooked within the transverse reinforcement of the jointusing a 90 deg standard hook, The development length, mea-sured from the critical section as defined in Section 4.5.1,should be computed as follows

‘dh =I

75 fi(psi)

‘dh =

afr (MPW,6.2fl(MPa)

(4.8) h (co1 1 ,-----jI

4.5.2.AIf transverse joint reinforcement is provided ata spacing less than or equal to three times the diameter of thebar being developed l,,,, as given in Eq. (4.8), may be multi-plied by 0.8.

4.5.2.5-For multiple layers of reinforcement, the barsin each layer must satisfy the given criteria.

For most Type 1 and all Type 2 exterior connections, barsterminating at a connection will be anchored using a stan-dard hook as defined by ACI 318. The tail extension of thehooks should project toward, and usually through, the mid-height of the connection. The required development length isgiven by Eq. (4.7) and (4.8), which were derivedfrom workdone by A CI Committee 408.22.

Eq. (4.7) is a combination of the provision in ACZ 318,Sections 12.5.2 and 12.5.3.1. Sections 4.5.2.2(a), (b), and(c)are identical to Section 12.5.3.2, 12.5.3.3, and 12.5.3.4 ofAC1 318. The differences between Eq. (4.7) and (4.8) reflectseveral factors including: (I) the hook in a Type 2 joint mustbe enclosed, within the confined core so the 0.7 factor of Sec-tion 4.5.2.2(a) is included, (2) an increase in length is fac-tored into the equation to reflect the detrimental effects ofload reversals,” and (3) the increase in stress under largedeformations is included with the fator 01. Section 4.5.2.4reflects the beneficial effects of very closely spaced trans-verse reinforcement. In most cases, the spacing of transversereinforcement will be greater than specified in Section4.5.2.4 to avoid congestion problems.

4.5.3-Straight bars terminating in Type 1 joints4.5.3.1-Straight bars should be No. 11 or smaller and

the development length for a straight bar terminating in theconnection should be taken as

ld

= fYWAt,( in.*)

25 &(psi)

(4.9)

but not less than

OLMBkfd;(psi) [O.O58d,(mm)&(MPa)]

Eq. (4.9) assumes the bar is contained within the core ofthe column. Any portion of the straight embedment lengthnot within the confined core should be increased by 30 per-cent.

a) If the depth of concrete cast in one lift beneath the barexceeds 12 in(300 mm), l,, should be increased by 30percent.

b) Where reinforcement in the flexural member is pro-vided in excess of that required for flexural strengthand anchorage for fY is not specifically required, I,+ maybe reduced by the ratio A,(required)/A,(provided).

Fig. 4.7-Bond stress on straight bar passing through thejoint

4.5.4 Beam and column bars passing through the joint-For Type 1 joints, no recommendations are made.

For Type 2 joints, all straight beam and column bars pass-ing through the joint should be selected such that

h(column)/d&ieam bars) 2 20

h(beam)/d,(column bars) 2 20

Various researchers14~19~3~33*~~s1@ have shown that straightbeam and column bars may slip within the beam-columnjoint during a series of large moment reversals. As shown inFig. 4.7, the bond stresses on these straight bars may be verylarge. The purpose of the recommended value for h/d, is tolimit slippage of the beam and column bars through the con-nection. Slip of reinforcing bars is not usually accounted forin normal design. However, when modeling a frame struc-ture for inelastic dynamic analysis, this slippage should beconsidered. To reduce the bond stresses to a value lowenough to prevent bar slippage under large load reversalswould require very large connections. A thorough treatmentof this topic is found in Reference 38.

CHAPTER r--NOTATION

A, =A, =

A, =

Ash =

b, =b, =b) =

db =

f,’ =

area of individual bararea of column core measured from outside edge tooutside edge of either spiral or hoop reinforcementsgross area of column sectiontotal cross-sectional area of all legs of hoop rein-forcement, including crossties, crossing a sectionhaving a core dimension h”design width of beamwidth of column transverse to the direction of sheareffective width of joint transverse to the direction ofshearnominal diameter of barspecified compressive strength of concrete in thejoint

= specified yield strength of reinforcement;h = specified yield strength of hoop and crosstie rein-

forcement& = specified yield strength of spiral reinforcementh = full deoth of column or full deuth of beam

ht, = core dimension of tied column, outside to outsideedge of bar, perpendicular to the transverse rein-forcement area A,* being designed

ld = development length for a straight barldh = development length for a hooked bar, measured

from the critical section to the outside end of thehook

WI = nominal moment capacity of section4’ = increased moment capacity of section when using a

> 1.0sh = center-to-center spacing of hoops or hoops plus

crosstiesVii = nominal shear strength of jointVU = design shear force in jointa = stress multiplier for flexural reinforcement at joint-

member interfaceY = shear strength factor reflecting confinement of joint

by lateral membersPS = ratio of volume of spiral reinforcement to total vol-

ume of core (out-to-out of spirals)4 = strength reduction factor

CHAPTER 6-REFERENCE!3

Referenced standardAC1 Committee 318, “Building Code Requirements for

Reinforced Concrete (AC1 3 18-89),” American Concrete In-stitute, Detroit, 1989,353 pp.

Cited references1. Hanson, Norman W., and Connor, Harold W., “Seismic

Resistance of Reinforced Concrete Beam-Column Joints,”Proceedings, ASCE V. 93, STJ, Oct. 1967, pp. 533-560.

2. Higashi, Y ., and Ohwada, Y., “Failing Behaviors of Re-inforced Concrete Beam-Column Connections Subjected toLateral Loads,” Memoirs No. 19, Faculty of Technology,Tokyo Metropolitan University, 1%9, pp. 91- 101.

3. Ohno, K., and Shibata, T., “On the Damage to the Ha-kodate College by the Tokachioki Earthquake, 1968,” Pro-ceedings, U.S.-Japan Seminar of Earthquake Engineeringwith Emphasis on the Safety of School Buildings, Sendai,Sept. 1970, pp. 129-144.

4. Hanson, Norman W., “Seismic Resistance of ConcreteFrames with Grade 60 Reinforcement,” Proceedings, ASCE,V. 97, ST6, June 1971, pp. 1685-1700.

5. Megget, L. M., and Park, R., “Reinforced Concrete Ex-terior Beam-Column Joint Under Seismic Loading,” NewZeulund Engineering (Wellington), V. 26, No. 11, Nov. 15,1971, pp. 341-353.

6. Renton, G.W., ‘The Behavior of Reinforced ConcreteBeam-Column Joints under Cyclic Loading,” ME thesis,University of Canterbury, Christchurch, 1972. ~

7. Park, R., and Sampson, Richard A., “Ductility of Rein-forced Concrete Column Sections in Seismic DesTgn,” AC1JOURNAL, Proceedings V. 69, No. 9, Sept. 1972, pp. 543-55 1.

8. Wight, J. K., and Sozen, M. A., “Shear Strength Decayin Reinforced Concrete Columns Subjected to Large Deflec-tion Reversals,” Report No. SRS 403, Department of Civil

Engineering, University of Illinois, Urbana-Champaign,Aug. 1973,290 pp.

9. Uzumeri, S. M., and Se&in M., “Behavior of Rein-forced Concrete Beam-Column Joints Subjected to SlowLoad Reversals,” Publication No. 74-05, Department ofCivil Engineering, University of Toronto, Mar. 1974,84 pp.

10. Park, R., and Thompson, K. J., “Behavior of Pre-stressed, Partially Prestressed, and Reinforced Concrete In-terior Beam-Column Assemblies under Cyclic Loading:Test Results of Units 1 to 7,” Research Report No. 74-9, De-partment of Civil Engineering, University of Canterbury,Christchurch, 1974.42 pp.

11. Hawkins, N. M., Kobayashi, A. S., and Fourney, M.E., “Revetsed Cyclic Loading Bond Deterioration Tests,”Structures and Mechanics Report No. SM 75-5, Departmentof Civil Engineering, University of Washington, Seattle,Nov. 1975.

12, Priestly, M. J. N., “Testing of Two Reinforced Con-crete Beam-Column Assemblies under Simulated SeismicLoading,” Report No. 5-7511, New Zealand Ministry ofWorks and Development, Wellington, 1975.

13. ACI-ASCE Committee 352, “Recommendations forDesign of Beam-Column Joints in Monolithic ReinforcedConcrete Structures,” AC1 JOURNAL, Proceedings V, 73, No.7, July 1976, pp. 375-393.

14. Meinheit, D. F., and Jirsa, J. 0.. ‘The Shear Strengthof Reinforced Concrete Beam-Column Joints,” Report No.77- 1, Department of Civil Engineering, Structures ResearchLaboratory, University of Texas at Austin, Jan. 1977.

15. Fenwick, R. C., and Irvine, H. M., “Reinforced Con-crete Beam-Column Joints for Seismic Loading,‘* ReportNo. 142, University of Auckland, Mar. 1977.

16. Lee, Duane L. N., Wight, James K., and Hanson, Rob-ert D., ‘RC Beam-Column Joints under Large Load Rever-sals,” Proceedings, ASCE, V. 103, ST12, Dee, 1977, pp.2337-2350.

17. Uzumeri, S. M., “Strength and Ductility of Cast-In-Place Beam-Column Joints,” Reinforced Concrete Srruc-rures in Seismic Zones, SP-53, American Concrete Institute,Detroit, 1977, pp. 293,350.

18. Vallenas, J., Bertero, V. V., and Popov, E. P., “Con-crete Confined by Rectangular Hoops Subjected to AxialLoads,” Repot7 No. UCB/EERC-77/13, Earthquake Engi-neering Research Center, University of California, Berkeley,Aug. 1977,114 pp.

19. Briss, G. R., Paulay, T., and Park R., “The Elastic Be-havior of Earthquake Resistant R. C. Interior Beam-ColumnJoints,” Report No. 78-13, Department of Civil Engineering,University of Canterbury, Christchurch, Feb. 1978.

20, Paulay, T., Park, R., and Priestly, M. J. N., “ReinforcedConcrete Beam-Column Joints Under Seismic bActions,”AC1 JOURNAL, Proceedings V. 75. No. 11, Nov. 1978, pp. 585-593.

21. Gill, W. D., Park, R., and Priestly, M. J. N., “Ductilityof Rectangular Reinforced Concrete Columns With AxialLoad,” Research Report No. 79- 1, Department of Civil En-gineering, University of Canterbury, Christchurch, Feb.1979, 136 pp.

BEAM-COLUMN JOINTS 352i?-11

22. AC1 Committee 408, “Suggested Development,Splice, and Standard Hook Provisions for Deformed Bars inTension, (AC1 408.1R-79),” American Concrete Institute,Detroit, 1979,3 pp.

23. She&h, S. A., and Uzumeri, S. M., “Properties of Con-crete Confined by Rectangular Ties,” AICAP-CEB Sympo-sium on Structural Concrete Under Seismic Actions (Rome,May 1979), Bullefin d’lnfortnution No. 132, Comite Euro-In-ternational du Deton, Paris, Apr. 1979, pp. 53-60.

24. Bertero, V. V., Popov, E. P., and Forzani, B., “SeismicBehavior of Lightweight Concrete Beam-Column Subas-semblages,” AC1 JOURNAL, Proceedings V. 77, No. 1, Jan-Feb. 1980, pp. 44-52.

25. Sheikh, Shamim A., and Uzumeri, S. M., “Strengthand Ductility of Tied Concrete Columns,” Proceedings,ASCE, V. 106, ST5, May 1980, pp. 1079-1102.

26. Selna, L., Martin, I., Park, R., and Wyllie, L., “Strongand Tough Concrete Columns for Seismic Forces,” Proceed-ings, ASCE, V. 106, ST& Aug. 1980,~~. 1717-1734.

27. Scott, B. D., Park, R., and Priestly, M. J. N., “Stress-Strain Relationships for Confined Concrete,” Research Re-port No. 80-6, Department of Civil Engineering, Universityof Canterbury, Christchurch, 1980, 106 pp.

28. Meinheit, Donald F., and Jirsa, James 0, “ShearStrength of R/C Beam-Column Connections,” Proceedings,ASCE, V. 107, ST1 1, Nov. 1982, pp. 2227-2244.

29. Scott, B. D., Park, R., and Priestly, M. J. M., “Stress-Strain Behavior of Concrete Confined by OverlappingHoops at Low and High Strain Rates,” AC1 JOURNAL, Pro-ceedings V. 79, No. 1, Jan-Feb. 1982, pp. 13-27.

30. Zhang, Liande, and Jirsa, J. O., “A Study of Shear Be-havior of Reinforced Concrete Beam-Column Joints,” PMF-SEL Report No. 82-1, University of Texas at Austin, Feb.1982.

31. Park, Robert, Priestly, M. J. Nigel, and Gill, Wayne D.,“Ductility of Square-Confined Concrete Columns,” Pro-ceedings, ASCE, V. 108, ST4, Apr. 1982, pp. 929-950.

32. Ehsani, M. R., and Wight, J. K., “Behavior of ExteriorReinforced Concrete Beam to Column Connections Subject-ed to Earthquake Type Loading,” Report No. UMEE 82R5,Department of Civil Engineering, University of Michigan,AM Arbor, July 1982,243 pp.

33. Durrani, A. J., and Wight, J. K., “Experimental Ana-lytical Study of Internal Beam to Column Connections Sub-jected to Reversed Cyclic Loadings,” Report No. UMEE82R3, Department of Civil Engineering, University of Mich-igan, Ann Arbor, 1982,275 pp.

34. Rabbat, B. G., Daniel, J. I., Weinmaun, T. L. and Han-son, N. W., “Seismic Behavior of Lightweight Concrete Col-umns,” PCA Construction Technology Laboratory/NationalScience Foundation, Washington, D.C., Sept. 1982. (Avail-able as PB83-204 891 from NTIS.)

35. “Code of Practice for the Design of Concrete Struc-tures,” (NZS 3101, Part 1:1982), Standards Association ofNew Zealand, Wellington, 1982, 127 pp.

36. “Commentary on The Design of Concrete Structures,”(NZS 3101, Part 2:1982), Standards Association of NewZealand, Wellington, 1982, 156 pp.

37. Suzuki, N., Otani, S., and Aoyama, H., “The EffectiveWidth of Slabs in Reinforced Concrete Structures,” Truns-action of the Japan Concrete Institute, V. 5, 1983, pp. 309-316.

38. Zhu, Sosngchao, and Jirsa, James O., “A Study ofBond Deterioration in Reinforced Concrete Beam-ColumnJoints,” PMFSEL Report No. 83- 1, Department of Civil En-gineering, University of Texas at Austin, July 1983.

39. Aoyama, H. “Overview of the Japanese Building CodeRequirements for Reinforced Concrete Beam-Column Jointsand Design Examples,” Paper prepared for the U.S.-N.Z.-Ja-pan Seminar on the Design of Reinforced Concrete Beam-Column Joints, Monterey, California, July 30-Aug. 1, 1984.

40. Kanada, K., Kondo, G., Fujii, S., and Morita, S., “Re-lation Between Beam Bar Anchorage and Shear Resistanceat Exterior Beam-Column Joints,” Transaction of the JapanConcrete Institute, V. 6, 1984, pp. 433440.

41. Kanada, K., Fujii, S., and Morita, S., “Effect of JointShear Reinforcement on Behaviors of Exterior Beam-Col-umn Joints under Reversed Cyclic Loadings,” Transactionof the Japan Concrete Institute, V. 7, 1985, pp. 559-566.

42. Aoyama, H., “Problems Associated with ‘Weak-Beam’ Design of Reinforced Concrete Frames,” Journul ofthe Faculty of Engineering, The University of Tokyo (B), V.38, No. 2, 1985, pp. 75-105.

43. Paulay, T., and Park, R., “Joints in Reinforced Con-crete Frames Designed for Earthquake Resistance,” Re-search Report 84-9, Department of Civil Engineering,University of Canterbury, Christchurch, New Zealand, June1984.

44. Leon, R. T., “The Effect of Floor Member Size on theBehavior of Reinforced Concrete Beam-Column Joints,”Proceedings, 8th World Conference on Earthquake Engi-neering, San Francisco, July 1984, pp. 445-452.

45. Yoshimura, M., and Kurose, Y., “Inelastic Behavior ofthe Building,” Earthquake Effects on Reinforced ConcreteStructures, U.S.-Japan Research, SP-84, American Con-crete Institute, Detroit, 1985, pp. 163-201.

46. Joglekar, M., Murry, P., Jirsa, J., and Klingner, R.,“Full Scale Tests of Beam-Column Joints,” Earthquake Ef-fects on Reinforced Concrete Structures, U.S.-Japan Re-search, SP-84, American Concrete Institute, Detroit 1985,pp. 271-304.

47. Zerbe, H, E., and Durrani, A. J., “Effect of a Slab onthe Behavior of Exterior Beam to Column Connections,” Re-port No. 30, Department of Civil Engineering, Rice Univer-sity, Houston, Texas, March 1985.

48. Ehsani, M. R., and Wight, J. K., “Effect of TransverseBeam and Slab on the Behavior of Reinforced ConcreteBeam-to-Column Connections,” AC1 JOURNAL, V. 82, NO. 2,March-April 1985, pp. 188- 195.

49. ACI-ASCE Committee 352, “Recommendations forDesign of Beam-Column Joints in Monolithic ReinforcedConcrete Structures,” AC1 JOURNAL, V. 82, No. 3, May-June1985, pp. 266-283.

50. Sattary-Javid, V., and Wight, J. K., “‘Earthquake Loadon R/C Beams: Building Versus Single Beam,” Journal ofStructurull Engineering, ASCE, V. 112, No. 7, July 1986, pp.

352~.12 MANUAL OF CONCRETE PRACTICE

14;13-1508.5 1. Otani, S., Kitayama, K., and Aoyama, H., “Beam Bar

Bond Requirements for Interior Beam-Column Connec-tions,” Proceedings of the International Symposium on Fun-damental Theory of Reinforced and Prestressed Concrete,Nanjing Institute of Technology, China, Sept. 1986.

52. Abdel-Fattah, B. and Wight, J. K., “Study of MovingBeam Plastic Hinging Zones for Earthquake-Resistant De-sign of R/C Buildings,*’ ACI Structural Journal, V. 84, No.1, Jan.-Feb. 1987, pp. 3 l-39.

53. Ehsani, M. R., Moussa, A. E., and Vallenilla, C. R,,“Comparison of Inelastic Behavior of Reinforced Grdinary-and High-Strength Concrete Frames,” AC1 JOURNAL, V. 84,No. 2, March-April 1987, pp. 161-169.

54. Fujii, S., and Morita, S., “Behavior of Exterior Rein-forced Concrete Beam-Column-Slab Subassemblages underBi-Directional Loading,” Paper Prepared for the U.S.-N.Z.-Japan-China Seminar on the Design of R.C. Beam-ColumnJoints for Earthquake Resistance, University of Canterbury,Christchurch, New Zealand, Aug. 198’7.

55. Kitayama, K., Otani, S., and Aoyama, H., “Behavior ofReinforced Concrete Beam-Column Connections withSlabs,” Paper Prepared for the U.S.-N.Z.-Japan-China Sem-inar on the Design of R.C. Beam-Column Joints for Earth-quake Resistance, University of Canterbury, Christchurch,New Zealand, Aug. 1987.

56. Durrani, A. J., and Wight. J. K., ‘Earthquake Resis-tance of Reinforced Concrete Interior Connections Includinga Floor Slab,” ACI Structural Journal. V. 84, No. 5, Sept.-Oct. 1987, pp. 400-406.

57. Aktan, A. E., and Bertero, V. V., “Evaluation of Seis-mic Response of RC Buildings Loaded to Failure,” JournalofStructural Engineering, ASCE, V. 113, No. 5, May 1987,pp. 1092-l 108.

58. Durrani, A. J., and Zerbe, H. E., “Seismic Resistanceof R/C Exterior Connections with Floor Slab,” Journal ofStructural Engineering, ASCE, V. 113, No. 8, Aug. 1987,pp. 1850-1864.

59. Otani, S., Li, S., and Aoyama, H., “‘Moment-Red&i-bution in Earthquake Resistant Design of Ductile ReinforcedConcrete Frames,” Transaction of the Japan Concrete Insti-tute, V. 9, 1987, pp. 581-588.

60. Pantazopoulou, S. J., Moehle, J. P., and Shahrooz, B.M., “Simple Analytical Model for T-Beam in Flexure,”Journal of Structural Engineering, ASCE, V. 114, No. 7,July 1988. pp. 1507-1523.

61. Kokusho, S., Hayashi, S., Wada, A., and Sakata, H.,“Elastic and Plastic Behavior of Reinforced Concrete Beamin Consideration of Axial Restriction Effect of Deforma-tion,” Report of the Research Laboratory of EngineeringMaterials, Tokyo Institute of Technology, No. 13, 1988, Na-gatsuta, Yokohama 227, Japan, pp. 253-270. w

62. French, C. W., and Boroojerdi, A., ‘%ontribution ofR/C Floor Slab in Resisting Lateral Loads,” Jdumal ofStructural Engineering, ASCE, V. 115, No. 1, Jan, 1989. pp.1 - 1 8 .

63. Ammerman, 0. V., and French, C. W., “R/C Beam-Column-Slab Subassemblages Subjected to Lateral Loads,”

Journal of Structural Engineering, ASCE, V. 115, No. 6,June 1989, pp. 1298-1308.

64. Leon, R.T., “Interior Joints with Variable AnchorageLength,” Journal of Structural Engineering, ASCE, V. 115,No. 9, Sept. 1989, pp. 2261-2275.

65. Zerbe, H.E., and Durrani, A.J., “Seismic Response ofConnections in Two-Bay R/C Frame Subassemblies,” Jour-nal of Structural Engineering, ASCE, V. 115, No. 11, Nov.1989, pp. 2829-2844.

66. Pat&e, P. et al.,“Seismic Response of ReinforcedConcrete Frame Subassemblages - A Canadian Perspec-tive,” Canadian Journal of Civil Engineering, V. 16, No. 5,1989, pp. 627-649.

APPENDIX A-AREAS NJIEDING RESEARCH

To help identify areas where research is needed, the com-mittee contacted some 60 design firms asking their views onneeded research topics. The following list is based on theopinion of the committee members and designers. The orderof the items listed is arbitrary.

AJ-Connections with beams wider than columnsThe current recommendations are based on results of tests

of connections where the column width is equal to or greaterthan the beam width. This allows all of the beam longitudinalreinforcement to be located within the column longitudinalreinforcement. Information is needed on the behavior of con-nections where beams are wider than columns and beam lon-gitudinal reinforcement cannot be placed within columnlongitudinal reinforcement.

AZ-Effect of eccentric beamsAll connections tested to date have included concentric

beams where the axes of the cohunn and beams are coinci-dent. Connections in which beam axes are eccentric to thecolumn axis are also common. This type of connection is fre-quently used in exterior frames of buildings where beamsframe into columns such that the outside faces of beams andcolumns are flush. It is not clear to what extent the presenceof torsion and the increase of associated stresses will affectthe capacity of these connections.

A&-Biaxially loaded jointsOnly limited research44*46J3 is available on the effects of

biaxial loading on joint behavior. This research indicates thatfor small columns the loss of section due to comer spallingcombined with the loss of bond and slip of the higheststrained bars can lead to premature column failure. Researchis needed to clarify biaxial joint behavior, particularly withreference to larger column sizes, different beam geometries,effects of floor slabs, and different anchorage lengths forboth beam and column bars.

A.&Relocation of plastic hinges away from the jointLimited resultsS2 are available for the capacity of joints

where the hinging region has been moved away from thejoint. Guidelines are needed for proper detailing to move

BEAM-COLUMN JOINTS 332~.13

plastic hinges away from the face of the column and for eval-uating the capacity of the connection when such details areused.

AS-Fiber reinforcement in the jointUsing fiber reinforcement may be an effective way to re-

duce the required confinement steel in the joint or to increasethe maximum allowable shear capacity of the beam-columnjoint. Experimental data are needed to quantify these effects.

A.&High strength concrete in the jointCurrent limitations on allowable joint shear stresses are

based on tests of normal weight and typical strength con-crete. The compressive strength of the concrete used in testspecimens varied from 3500 psi (24 MPa) to approximately5500 psi (38 MPa). In recent years high-strength concrete,with compressive strengths up to 19,000 psi (130 MPa), hasbeen used in construction of columns, Clearly, these recom-mendations were not developed for such high-strength con-cretes. Research is needed to evaluate the behavior andcapacity of high-strength concrete joints.53

A.7-Knee jointsThe majority of beam-column joint studies reported are

limited to connections in which the column continues aboveand below the joint. Knee joints, which are usually present atthe roof level of a building, require special attention becauseboth column and beam longitudinal reinforcement may ter-minate at that point and usually are anchored in the joint. Ex-perimental data are particularly needed for cyclically loadedspecimens.

A.g-Behavior of indeterminate systemsExperimental results for beam-column joints have been

primarily obtained from tests of statically determinate jointassemblies. There is a need to establish the effect of force re-distribution and joint deformation on the behavior of statical-ly indeterminate structural systems.65

A.9-Lightweight aggregate concreteAdditional studies are needed to evaluate all aspects of

joint behavior where various types of lightweight aggregateconcrete is used.+”

A.l&Effect of slabsThe contribution of the slab to stiffness and strength of

connections has been investigated in a number of recentstUdies.37,4244,47,48~5*~~~62,63~~ However, no definitive con-clusions have been developed on how the presence of a slabaffects the requirements for confinement and the moment ca-pacities of the beams.

A.ll-Steei congestionType 2 connections in many structures require a signifi-

cant amount of steel, thus making the construction processvery difficult. Means to reduce steel congestion need to bestudied and recommendations need to be made.

A.12-Distribution of plastic hingesNot all the joints within a structure located in an area with

high seismicity will experience significant inelastic defor-mations. Guidelines are needed to identify “Type 2” jointswithin a structure without having to do a comprehensive in-elastic analysis.

A.13-Limit on joint shearThe current limits on joint shear are overly conservative in

the opinion of many designers for certain combinations ofconfigurations, size of members, material strengths, etc.More experimental studies are needed to determine if theselimits can be raised.

A.14-Joints in existing structuresJoints in structures built prior to the development of cur-

rent design guidelines do not conform to the cumnt require-ments. These joints need to be studied in detail to establishtheir adequacy.

APPENDIX B-DESIGN EXAMPLES

Four design examples are presented. Each example pre-sents given member sizes and reinforcement and demon-strates the application of the committee’s joint designrecommendations. In all of the examples, it is assumed thatthe joints are part of the primary structural system for resist-ing lateral loads, that is, wind loads for Type 1 joints andearthquake loads for Type 2 joints. The examples are similarto those used in the first committee report. I3 A short discus-sion of how the changes in the committees recommendationsaffected the design of these joints is given at the end of thisappendix.

DESIGN EXAMPLE l-EXTERIOR TYPE 1 JOINT

umn, 24”X 24” with 12 No. tl ban

spondfel Bmm, IS” x 30”with 3 No. 10 bon, top.

I \Normol Boom. Ol”X26”with 4 No. t I bon, top

PLAN VIEWOF CONNECTION

Nomol Bwm

352~.14 MANUAL OF CONCRETE PRACTICE

Column longitudinal reinforcement (Section 41.2) Joint shear strengthThe indicated arrangement of twelve No, 11 bars is accept-

able.This is an exterior Type 1 joint which meets the geometry

restrictions of Section 4.3.2. Therefore, use y = 20 from Ta-ble 1.

Transverse reinforcement (Section 4.2.1)A permissible arrangement of No. 4 ties is shown. Spacing

between sets of ties should be less than or equal to 6 in. (Sec-tion 4.2.1.3).

Joint shear force (Section 43.1)Shear is not a problem in the transverse (spandrel) direc-

tion because large unbalanced moments are not anticipatedin this direction. For shear in the normal direction, the max-imum possible joint shear is a function of the flexural capac-ity of the beam normal to the connection.

bi = (24 in. + 21 in.)/2 = 21.5 in.

vri = 20 8 bj h(c01)

vrl = 20 &%&i (22.5 in-)(24 in.)

V” = 683,000 lb = 683 kips

cbvn = 0.85 (683 kips) = 581 kips > 315 kips (OK)

Hooked bar anchorage (Section 4.5.2.1)

T12’

-mi --

1,

a =

Iu, = 8490 k-in. = 708 k-ftv =co1 M&eam)/l2 ft = 59.0 kips

Joint shear

A,afy= 4 1.56 in.* ( I .O)‘ (60 ksi)0.85f,‘b 0.85 (4 ksi) (21 in.)

5.24 in.4( 1.56 in.*)( 1.0)(60 ksi)

Vu (joint)T u = A, a& = 374 kipsV,(ioint) = T,, - Vcor = 3 15 kips

The reduction factor of Section 4.5.2.2(a) applies, so

mod I& = (26.8 in.)(0.7) = 18.7 in.

Available space = 24 in. - 1.5 in. (back cover) - 0.5 in. (tiediameter)

= 22 in. (OK)

DESIGN EXAMPLE 2-INTERIOR TYPE 1 JOINT

,C&unn, 24” X 24” dth 8 Ma I4 bofs

r; ’ 4000 ps’

fy*eo kslham, 12” X 24*

with 3 No. IO bars, top,and 3 No. 9 tars. battun

PLAN VIEWOF CONNECTION

Longitudinal &am

Column longitudinal reinforcement (Section 4.1.2)The arrangement of eight No. 14 bars shown above is ac-

ceptable.

Transverse reinforcement (Section 4.2.1)Neither beam covers three-quarters of the column width.

Therefore, typical transverse reinforcement is required. Apermissible arrangement of No. 4 ties is shown. Spacing be-tween sets of ties should be less than or equal to 6 in. (Sec-tion 4.2.1.3).

Shea+-Shear is not a problem because large unbalancedmoments are not anticipated in either direction.


Anchorage-Top beam bars should be continuous throughthe joint. It is recommended that bottom bars also be contin-uous through the joint because the joint is part of the primarysystem for resisting lateral loads.

Before starting the examples for Type 2 joints, it is impor-tant to point out that to satisfy the anchorage and shear re-quirement.& a designer will probably have to use largercolumn sections than have previously been required. Widerbeam sections will be necessary to cover the column facesand thus allow the use of higher shear stress values.

Table B. 1 is based on anchorage requirements for bars ter-minating in a joint (Section 4.5.2). Table B.2 is based on re-quirements for the ratio of joint dimensions (actually beamand column dimensions) to the diameter of beam and columnbars (Section 4.5.4). These tables should be useful for select-ing main reinforcing bar diameters and joint dimensions.Values for Cd,, were calculated from Eq. (4.8) using 01= 1.25,fY = 60 ksi and& = 4000 psi. In Table B. 1, an extra 3$ in.has been added to Idh to determine the minimum column di-mension required to anchor a given bar. The quantity 3$ in.comes from two times the clear cover (typically lYz in. frontand back) plus one tie-bar diameter. The 20 percent reduc-tion factor for close spacing of transverse reinforcement isincluded in Column 5 of Table B. 1.

Table B.1Minhnum column depth for ‘Qpe 2 jointsbased on anchorage of terminating beam longitudinalreinforcement

h(min) for column

syz db in. &,, in.No. (i) (2)

For column hoops at a For column hoops at a(3) spacing > 3db. in. (4) spacing 5 3db in. (5)

6 0.750 11.9 15.4 13.07 0.875 13.8 17.3 14.68 1.00 15.8 19.3 1 6 . 19 1.13 17.8 21.3 1 7 . 8

10 1.27 20.1 23.6 19.61 1 1 .41 22.3 25.8 21.3

‘lhble B.2-IMmhnum column or beam depth for ‘Qpe 2joints based on size of longitudinal reinforcement

h(min) for column based on size of heamlongitudinal reinforcement of h(min) for heam

Bar size. No. dt,. in.based on size of column longitudinal

reinforcement. in.

6 0 750 15.07 0:875 1 7 . 58 1.00 20.09 1.13 22.6

1 0 I .27 25.411 1 .41 28.21 4 1.69 33.9

DESIGN EXAMPLE ?-EXTERIOR TYPE 2 JOINT

Preliminary design

f,’ = 4ooo psify = 60 ksi

Column, 24” X 24” with 12 No. I I &S

Spandrel Beam, 18” X 30”with 3 No. 10 bars, topand 3 No. 8 ban, bottom

\Normol Beam, 21” X 28”with 5 No. 10 bars, topond 3 No. 10 bon, bottom

Anticipated change-Change the top reinforcement in thespandrel beam from three No. 10 to four No. 9 to satisfy Se&tion 4.5.4 (Table B.2).

PLAN VIEW OFTHE JOINT

No. 4 tias~=6*

\ fjatisfks oil of tharaquimmanfs ofsaetion 4.2.2.3

i-+Spondd f3aam

saonl

Column longitudinal reinforcement (Section 4.1.2)The arrangement of twelve No. 11 bars acceptable.

Transverse reinforcement (Section 4.2.2)Provided

Ash = 4 legs (0.20 in?/leg)A sh = 0.80 in.2 (each direction)

from Eq. (4.2)

A sh

sr=03(6in.) (21in.) (4ksi) (24in.)2A .

60ksi [(21 in.j2-‘l

Ash = 0.771 in.2 < 0.80 in.2 (OK)

from Eq. (4.3)

As,,h”f,’

s h= o.og- =

f0.756 in? < 0.80 in.2 (OK)

yh

Shear (Section 4.3)For the bending analysis which follows, ignore the effect

of compression reinforcement and assume, in most loca-tions, d = h - 2.7 in. In locations where there is interferencebetween bars from the normal and spandrel beams, assume d= h - 3.7 in. in the spandrel beam.


Normal direction Spandrel direction

1 \ Assumed

M,‘(beam) = Asa&( d - 4)

a= Asort;5 1 . 2 7 in.* ( 1 . 2 5 ) ( 6 0 k s i )

OMf,‘b - 0.85 (4 ksi) (21 in.)

a = 6.67 in.M,,‘(beam) = (6.35 in.*)( 1.25)(60 ksi)

(25.3 in. - 6.67 inA)M,‘(beam) = 10,500 k-in. = 872 k-ftVCO1 = M,‘(beam)ll2 ft = 72.6 kips

Joint shear

~kE:c%t21

rlc Points inthe Cobmn

%i = As,afy

Aslafy 4 1.00 in.* ( 1.25) (60 ksi)aI = 0.85f,‘b= 0.85 (4 ksi) ( 18 in.)

41 = 4.90 in.

Ki = (4.00 in.*)( 1.25)(60 ksi) 26.3 in. - ‘T

Ki = 7 160 k-in. = 596 k-ft

Similarly

ThenMni = 4590 k-in. = 383 k-ft

0 “col.Joint shear

V,/=(M”; +M,;/12ft=81.6kips

Vu (joint)T,, = A, c$, = 476 kips

V,(joint) = T,, - Vco, = 404 kips

Joint shear strength-The spandrel beam dimensions aresufficient for classifying this as an exterior joint, so use y =15 (Table 1).

bj = (bb + bc)/2 < bb + 2[h(CO1)/21

= (21 in. + 24 in.)/2 = 22.5 in. (governs)

V, = Y &m bj h(COl)

= 15 dm (22.5 in.)(24 in.)

= 512,000 lb = 512 kips$V,= 0.85 (5 12 kips) = 435 kips > 404 kips (OK)

F Vu (joint)

TUl = (4.00 in.*)( 1.25)(60 ksi) = 300 kipsc u2 = Tl42 = (2.37 in.*)( 1.25)(60 ksi) = 178 kipsV,(joint> = T,, + Cu2 - Vco, = 3% kips

In this direction, bj = (18 in. + 24 in.)/2 = 21.0 in. (gov-ems), and

+V, = (0.85)( 15) Am (21 in.)(24 in.) ab

= 406 kips > 396 kips (OK)


Flexural strength ratio (Section 4.4.2) Preliminary designWhen determining the column flexural strength, the axial

load was assumed to be zero (conservative for this check).Also, a was set equal to 1 .O for this calculation. Using theseassumptions, M,, = 848 k-ft.

The beam flexural strengths have been found earlier usinga = 1.25. Those beam strengths will be divided by 1.25 toobtain an approximate value for the beam flexural strength ifa = 1.0. If the strength ratio is close to the allowable value,a more accurate determination of the beam flexural strengthfor a = 1 .O could be made.

Normal direction

M,, I 872 k-ft/l.25 = 698 k-ft

Spandrel direction

M,,, z 596 k-ft/1.2.5 = 477 k-ftMn2 z 383 k-ft/l.25 = 306 k-ft

Strength ratio checkNormal direction

I;M, (col) 2(848)q 0-d

= - = 2.43 > 1.4 (OK)698

Spandrel directionCM, (col) 2(848)=f, (b-) = 477+306

= 2.17 > 1.4 (OK)

Hooked bars terminating in a joint (Section 4.5.2)Only the No. 10 bars for the normal beam need to be

checked. Referring to Table B. 1, the required column dimen-sion is 23.6 in., which is less than the provided dimension of24 in.

Beam and column bars passing through the joint (Sec-tion 4.5.4)

The No. 9 bars in the spandrel beam govern the columnsize

h(co1) > 20 (1.13 in.) = 22.6 in. < 24 in. (OK)

The total beam depths are governed by the column bars

h(beams) > 20 (1.41 in.) = 28.2 in. = 28 in. (say OK)

DESIGN EXAMPLE 4-INTERIOR TYPE 2 JOINT

Column, 24*X 24” with 6 No. 14 hors

Transverse Beam, 12” X 24”with 3 No. 10 bars, topond 3 No. 9 bars, bottom

Beam, t6” X 26”with 4 No. Ii bars, top

4 No. 10 hors, bottom

Anticipated changes1. Change column to 28 x 28 in. and use twelve No. 11

bars. The dimension increase is required to satisfy shear andbar development requirements. The increase in the numberof longitudinal bars is required to give a more uniform distri-bution of longitudinal steel.

2. Change longitudinal beams to 21 x 30 in. and use fiveNo. 10 bars as top reinforcement. The beam width is in-creased to help satisfy confinement and shear requirements.The beam bar diameters are decreased to satisfy Section4.5.4 and the beam depth is increased to satisfy Section 4.5.4for the column bars.

3. Change transverse beams to 21 x 28 in. and use the samereinforcement. The width is increased to help satisfy con-finement and shear requirements and the beam depth is in-creased to satisfy Section 4.5.4 for the column bars. Thedepth of the transverse beams is set differently than the depthof the longitudinal beams to avoid reinforcing bar interfer-ence.

Tlormu” 6ooq 21-x 25PLAN VIEW OF with 3 No. IO bars. tOP

REVISED JOINT No. 9 bon. bottc4n

NO. 4

c’4’6

!j&fi;din all themqulmmonl ofwcWm 4.2.2.3

udiml born, 2rx30-5 No. IO ban. IDO

and 4 No. IO bms, bona

Column longitudinal reinforcement (Section 4.1.2)The indicated arrangement of twelve No. 11 bars is accept-

able.

Transverse reinforcement (Section 4.2.2)Provided A,, = 4 legs (0.20 in.*/leg) = 0.80 in.* (each di-

rection).Because beam dimensions satisfy Section 4.2.2.5, the val-

ue for Ash obtained from Eq. (4.2) and (4.3) may be reducedby 50 percent in the joint.

From EZq. (4.2)

352%18 MANUAL OF CONCRETE PRACTICE

A = 03(6”) (25”) (4bi) (28)* 1 = 0763in2sh - [ 1- -

60ksi (25)* * *

From Eq. (4.3)

A = 009(6”) (25”) (4W = 0900in2sh * 60ksi

Required As,, = 0.5 (0.90 in?) = 0.45 in.2 c 0.80 in2 (OK)Thus, for this joint the maximum allowable spacing (6 in.)

and the minimum tie size for a No. 11 bar govern the design.

Shear (Section 4.3)Clearly the longitudinal direction is critical because of the

larger beam steel area and the larger beam depth. Using thesame assumptions for the flexural analysis as were made inthe previous example.

M,; =

A4,; =M,,; =

lu,; =Vco1 =

5( 1.27 in?)( 1.25)(60 ksi) 27.3 - 9 >

11,400 k-in. = 951 k-ft4( 1.27 in?)( 1.25)(60 ksi)( 27.3 in. - q)

9380 k-in. =782 k-ft(Mn{ + M,i )/12 ft = 144 kips

/ “co1

cu27“” STTU,

A Vu (joint)TIll = 5 (1.27 in.2)( 1.25)(60 ksi) = 476 kipsc = Tu* = 4 (1.27 in.*)( 1.25)(60 ksi) = 38 1 kipsV$oint) = T,,, + C,,z - Vcol = 713 kips

Vn = Y ,&’ bj h(COl)

The beams have been made wide enough to classify this asan interior joint, so y = 20 (Table 1)

bi = (28 + 21 in.)/2 = 24.5 in. c bb + 2[h(col)L?]

wfl = (0.85)(20) ../m (24.5 inJ(28 in.)sb

= 738 kips > 713 kips (OK)

Flexural strength ratio (Section 4.4.2)Using the same assumptions used in Example 3, the col-

umn flexural strength is M, = 1070 k/ft.Beam flexural strengths for a = 1.0 am approximated as

was done in Example 3. Only the longitudinal beams need tobe considered because they are stronger than the transversebeams

&I,,, 5951 k-ftA.25 = 761 k-ftMn* z 782 k-ftD.25 = 626 k-ft

Flexural strength ratio =ZM,, (col) 2 (1070)

“M,, (bei- = 761 + 626

= 1.5 > 1.4 (OK)

Beam and column bars passing through the joint (Sec-tion 43.4)

The column dimension is governed by the largest beambar

h(co1) > 20 (1.27 in.) = 25.4 in. < 28 in. (OK)

Beam depths are controlled by the column bars

h(beam) > 20 (1.41 in.) = 28.2 in. I 28 in. (say OK)

Comparison to the results of the previous committee re-pod

For Type 1 joints, use of the new committee design recom-mendations led to no changes from the prior committeereportI for these design examples. For the Type 2 joint ex-amples there were some significant differences. Changeswere required in the column (joint) size for Example 4, andfor Examples 3 and 4 there was a large decrease in the re-quired amount of transverse reinforcement in the joint.These changes clearly reflect the committee’s current philos-ophy of requiring larger columns (joints) and less transversereinforcement. Other significant changes were the increasesin beam widths to better confine the joint and decreases inbeam bar sizes to reduce the tendency of bars to slip throughthe joint during earthquake-type loading.

SI METRIC TABLES AND EXAMPLE

Tables B. 1 (metric) and B.2 (metric) are given to aid in theselection of joint dimensions when using standard metric

BEAM-COLUMN JOINTS 3!52&19

bars. In Column 4 of Table B. 1 (metric), an extra 95 mm hasbeen added to 1, when determining the minimum columndimension required to anchor a given bar. This quantity rep-resents two times the clear cover (typically 40 mm) plus onetie bar diameter ( 15 mm). The 20 percent reduction factor forclose spacing of transverse reinforcement is included in Col-umn 5 of*Table B.l (metric).

Table B.l (metric)-Minimum column depth for ‘Qpe 2joints based on anchorage of terminating beam bars

IBarsize.No.(1)

db. &h(min) for column

mm mm For column hoops at a For column hoops at a(2) ( 3 ) swing > 34, (mm) (4) spacing 5 3db. (mm) (5)

1 5 16.0 236 3 3 1 32020 19.5 287 382 32525 25.2 3 7 1 466 39230 29.9 440 535 4473 5 35.7 526 6 2 1 516

Table B.2 (metric)-Minimum column or beam depthfor ‘Qpe 2 joints based on size of longitudinalreinforcement

h(min) for column based on size of beamlongitudinal reinforcement or h(min) for

Bar size, No. d,,, m mbeam based on size of column longitudinal

reinforcement, mm15 16.0 32020 19.5 39025 25.2 50430 29.9 5983 5 35.7 71445 43.7 874

Design example 3 (metric) is included to show the use ofmetric dimensions and units for beam-column joint design.This example is very similar to Example 3.

DESIGN EXAMPLE 3 (METRIC)-EXTERIORTYPE 2 JOINT

f:=3ohlPa I/Column, 600mm X 6OOmm, with 8

No. 35 bors

Spandrel beam, 450mm X 750mm.with 4 No. 30 bars, topand 3 No. 25 bars, bottom

Normal beom, 5OOmm X 750mm,wi th 6 No. 30 bars, topo n d 4 No. 30 hors, bottom

PLAN VIEW O F JOINT

No. (5at 150

Notes on joint geometry--Dimensions of the spandrel andnormal beams, when compared to the column dimensions,allow this joint to be classified as an exterior joint. The rein-forcement in the normal beam satisfies the requirements ofSection 4.5.2.3 [Column 4 of Table B.l (metric)]. The rein-fofcement in the spandrel beams satisfies the requirements ofSection 4.5.4 [Table B.2 (metric)].

Transverse reinforcement (Section 4.2.2)The arrangement of twelve No. 35 bars is acceptable.

Column longitudinal reinforcement (Section 4.1.2)

ProvidedAsh = 4 legs (200 mm2ileg)Ash = 800 mm2

From Eq. (4.2)

A = 03(150) (520) (30) (600)2 1 =582=2sh * 4 0 0 [ 1- -

(520) *

< 800 mm2 (OK)From JZq. (4.3)

= 527 mm2 < 800 mm2 (OK)

Shear (Section 4.3)For the bending analysis, ignore the effect of compression

reinforcement and in most locations assume d = h - 70 mm.In locations where there is interference between bars fromthe normal and spandrel beams, assume d = h - 100 mm inthe spandrel beam.

Normal Direction*

InflectionPoint

\

TI

“co13.5 m

1

1 MA

“colInflectionPoint(Assumed)

l 1 MPa = 1 N/mm’

2!52R-20 MANUAL OF CONCRETE PRACTICE

M,,‘(bem)=A,afy (d-i)

a Asafy=0.85f,‘b=

6 700 mm2 ( 1.25) (400 MPa)0.85 (30 MPa) (500 mm)

= 165mmM,‘(beam) = (4200 mm2)( 1.25)(400 MPa)

( 680 mm-y)

M,,‘(beam)=1.25x109N~mm=1250kN~mVco1 = Mn’(beanQl3.5 m = 359 kN

Joint shear

0 “col.

VTuVu (joint)

T,=A,af,=21OOkNV,,(joint) = T,, - Vcor = 1740 kN

Joint shear srrengrh-As previously determined, this is anexterior joint, so use y = 15 (Table 1)

bi = (bb + bJ2 < bb + 2[h(co1)/2]

= (500 mm + 600 mm)/2 = 550 mm (governs)

v, =O.O83 Y off bjh(COl)

= 0.083 (15) &if%ii% (550 mm)(600 mm)

=2250x 103N=2250kN

W” = 0.85 (2250 kN) = 1910 kN > 1743 kN (OK)

Spandrel direction

InflectionPoint \

T3.5m

1

Joint shear

Vu (joint)

Qlbafy

=0.85f,‘b=4 700 mm2 (1.25) (400 MPa)

0.85 (30 MPa) (450 mm)

= 122mm= (2800 mm2)( 1.25)

122 mm(400 MPa)( 650 mm - -2

a2= 3 500mm2 (1.25) (400MPa) =654mm

0.85 (30 MPa) (450 mm) *

wli = (1500mm2)(1.25)

65.4 mm(4OOMPa)(650mm--2 >

=463x106N.mm=463kN.mVCO1 = (M,,; + M,; )/3.5 m = 368 kNTIll = (2800 mm2)( 1.25)(400 MPa) = 1400 kNCu2 = Tu2 = (1500 mm2)( 1.25)(400 MPa) = 750 kNV,(joint) = T,,, + Cu2 - Vcor = 1780 kN

In this direction, bj = (450 IIUII + 600 mm)/2 = 525 IYUII(governs), and

$V, = (0.85)(0.083)( 15) d%%l% (525 mm)(600 mm)=2150x 103N=2150kN> 1780kN(OK)

Flexural strength ratio (section 4.43)When determining the column flexural strength, the axial

load was assumed to be zero (conservative for this check),and a was set equal to 1.0 for this calculation. Using theseassumptions, M, = 1075 kN . m.

The beam flexural strengths have been found earlier usinga = 1.25. Those beam strengths will be divided by 1.25 toobtain an approximate value for the beam flexural strengthswhen a = 1 .O.

Normal directionlnf lectiohPaint M,1125OkN.rn/1.25= 1OOOkN~m


Spandrel direction

M,,, z 867 kN . m/l.25 = 694 kN . m

Mn~~485~.m/1.25=388kN.m

Strength ratio check

Normal direction

CM,, (col)

=f,, (b=W= 2 YE) = 2.15 > 1.4 (OK)

Spandrel direction

CM” (col)CM, (t-4

= ;gyy;;8 = 1.99 > 1.4 (OK)

Hooked bars terminating in the joint and beam and col-umu bars passing through the joint (Sections 4.5.2 and4.5.4)

As mentioned previously, the joint dimensions were se-lected to satisfy these requirements which are summarized inTables B.l (metric) and B.2 (metric).

This report was submitted to letter ballot of the committee and approved in accor-dance with Institute procedures.

recommendations for design of beam-column joints in ... recommendation… · aci352r-91 (reapproved...

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