Significant Changes in the 2005 ACI Code Including Changes Affecting Precast/Prestressed Concrete Part 1

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1 Significant Change in the 2005 ACI Code Including Change Affecting Precat/Pretreed Concrete Part 1 S. K. Ghoh, Ph.D., FPCI Preident S. K. Ghoh Aociate, Inc. Palatine, Illinoi Significant change made ince the publication of the 2002 ACI 318 Building Code, which are reflected in the upcoming 2005 edition of the Code, are ummarized. In addition to change impacting conventionally reinforced concrete, proviion affecting precat/pretreed concrete including pot-tenioned concrete are enumerated. Change in Appendix D, Anchoring to Concrete, are not dicued in thi Part 1 article. The 2005 edition of the American Concrete Intitute Building Code Requirement for Structural Concrete (ACI ) i in the final tage of preparation. The ignificant change from the previou edition of the ACI Code (ACI ) are ummarized in thi article. The complete change were publihed in the July 2004 iue of ACI Concrete International. 1 They were alo poted on the ACI webite until Augut 31, 2004, when the public comment period ended. Pertinent dicuion received by the deadline of Augut 31, 2004 will be publihed in a future iue of Concrete International. ACI Committee 318 i required to repond in writing to all the dicuion that i ubmitted. In the proce of reponding to public comment, the Committee may decide to make modification to the publihed change. However, major change are not anticipated at thi tage. The intent of thi article i to provide a ummary of ignificant change impacting conventionally reinforced concrete, precat concrete and pretreed concrete (including pot-tenioned concrete). Thi information hould be ueful to building official, deign engineer, practitioner and the academic community. ACI will be the reference document for concrete deign and contruction in the 2006 edition of the International Building Code, 2 Supplement No. 1 to the 2005 edition of the ASCE 7 Standard Minimum Deign Load for Building and Other Structure, 3 and the econd (2006) edition of the NFPA 5000 Building Contruction and Safety Code, 4 iued by the National Fire Protection Aociation. All ection number refer to the 2005 Code, unle otherwie noted. In the following paragraph, trike-out mark indicate deletion of exiting (ACI ) text, and underlining indicate addition of new text. Chapter 94 PCI JOURNAL

2 not dicued do not have any change in them. Change in Appendix D, Anchoring to Concrete, will be dicued in Part 2 of thi paper, to appear in the next iue of the PCI JOURNAL. Change of Notation Perhap the mot important change in ACI i a thorough clean-up of the notation ued in the Code. A Notation and Terminology Tak Group wa formed within ACI 318 under the leaderhip of Sharon Wood to review ACI and develop a unified et of notation. The feeling wa almot univeral that the Code will be eaier to ue if the notation i conitent throughout. The Tak Group identified ix pecific tak: 1. Conolidate imilar term a appropriate. 2. Eliminate unneceary term. 3. Provide a unique definition of each term ued in ACI Move precriptive requirement from the lit of notation into the Code. 5. Ue notation, rather than text, whenever poible in the Code. 6. Move the lit of notation from Appendix E to Chapter 2. The Tak Group effort reulted in the following change: 1. Notation ha been conolidated. Four hundred and ix term were included in Appendix E of ACI , while ACI include 305 term. 2. Duplicate definition of term are eliminated. In ome cae, the definition for term were lightly different in different chapter. In thoe cae, the mot general definition i given in the lit of notation and the definition i clarified in the Code, a needed. 3. All term related to tre in reinforcement are expreed in unit of pi. The applicable equation have been modified. 4. The lit of notation at the beginning of each chapter ha been deleted in ACI Mot of the notation-related change within the Code are editorial in nature and are motivated by the objective to ue notation, rather than text, within the Code proviion. 6. The Tak Group did not review the notation in the Commentary in detail, and the lit of Commentary notation i incomplete. However, a few change have been made to be conitent with the notation in the Code and to eliminate duplicate definition. Change in Terminology Welded wire fabric i now called welded wire reinforcement throughout the Code. Thi ha given rie to a large number of editorial change throughout ACI Chapter 2, Definition The definition of tructural lightweight concrete ha been revied o that it refer to equilibrium denity, a pecified in ASTM C , 5 and ue the correct title of C 567. The definition and required dimenion of a drop panel are currently given within Section 13.3 Slab Reinforcement. Uer of the Code cannot find thi definition eaily. The primary drop panel definition ha been moved to Chapter 2, where it i defined a a projection below the lab at leat onequarter the lab thickne beyond the drop. The additional dimenional requirement are given in Chapter 13, in a new Section Development length i now defined a length of embedded reinforcement, including pretenioned trand, required to develop... Tranfer length ha been newly defined a length of embedded pretenioned trand required to tranfer the effective pretre to the concrete. Chapter 3, Material A new paragraph ha been added at the beginning of Commentary Section pointing out that Fiber Reinforced Polymer (FRP) reinforcement i not addreed in thi Code and that ACI Committee 440 ha developed guideline for the ue of FRP Reinforcement. 6,7 The referenced tandard lited in Section have been updated. Section (Load Combination Including Flood Load) and (Load Combination Including Atmopheric Ice Load) of SEI/ASCE 7-02 Standard Minimum Deign Load for Building and Other Structure 3 are declared to be part of ACI The 17th, rather than the 16th, edition of AASHTO Standard Specification, dated 2002, 8 are partially adopted in Section The 2004, rather than the 2002, edition of ACI Qualification of Pot-Intalled Mechanical Anchor in Concrete 9 i adopted in Section The 2002, rather than the 2000 edition of AWS D1.1 Structural Welding Code Steel 10 ha been adopted in Section Chapter 5, Concrete Quality, Mixing, and Placing When an acceptable record of field tet reult i not available, concrete proportion etablihed from trial mixture meeting certain retriction are permitted in Section The firt retriction ha been modified to read: Combination of Material hall be thoe for propoed work. Thi i to clarify original intent. Chapter 6, Farmwork, Embedded Pipe, and Contruction Joint Section of ACI read: Contruction joint in floor hall be located within the middle third of pan of lab, beam, and girder. Joint in girder hall be offet a minimum ditance of two time the width of interecting beam. The two entence have now been placed in eparate Section and 6.4.5, o that Section (not 6.4.5) can be waived for pretreed concrete contruction in Chapter 18. Chapter 9, Strength and Serviceability Requirement Commentary Section R9.1 and R9.2 now make reference to SEI/ASCE 7-02, 3 rather than to ASCE Section ha been modified a follow: For If a tructure i in a flood zone, or i ubjected to force from atmopheric ice load, the flood or ice load and the appropriate load combination of SEI/ASCE 7 hall be ued. The expreion contained in Fig. R9.3.2 of ACI for interpolation of ϕ within ε t value of and did not produce accurate value, September-October

3 according to ome code uer. Editorial change have been made to modify the expreion to olve the inaccuracy. The ϕ of 0.75 in ACI for flexural ection in pretenioned member where trand embedment i le than the development length, a provided in Section , i now applicable from the end of the member to the end of the tranfer length. From the end of the tranfer length to the end of the development length, ϕ may be linearly increaed from 0.75 to 0.9. Where bonding of a trand doe not extend to the end of the member, trand embedment begin at the end of the debonded length. See alo Section and Fig. R (a). The following econd paragraph ha been added to Commentary Section R : Where bonding of one or more trand doe not extend to the end of the member, in lieu of a more rigorou analyi, ϕ may be conervatively taken a 0.75 from the end of the member to the end of the tranfer length of the trand with the larget debonded length. Beyond thi point, ϕ may be varied linearly to 0.9 at the location where all trand are developed, a hown in Fig. R (b). Alternatively, the contribution of the debonded trand may be ignored until they are fully developed. Embedment of debonded trand i conidered to begin at the termination of the debonding leeve. Beyond thi point, the proviion of Section are applicable. Confinement reinforcement often create congetion in reinforced concrete member. Reearch ha hown 11,12 that reinforcement with a yield trength up to 100,000 pi can be ued for confinement, without any detriment to member performance. Spiral reinforcement with pecified yield trength up to 100,000 pi i, therefore, permitted by Section of ACI Section 9.4 ha accordingly been modified a follow: The value of Deign hall not be baed on a yield trength of reinforcement f y and f yt ued in deign calculation hall not exceed in exce of 80,000 pi except for pretreing teel and for piral tranvere reinforcement in Chapter 10, Flexure and Axial Load The axial load limit of 0.10f c A g in Section i clarified to be a limit on factored axial compreion load. Commentary Section R ha been rewritten in place to provide editorial clarification. The maximum pacing of reinforcement cloet to the tenion force, for purpoe of crack control, i given by: = cc f 15 40, ,. 000 f with f in pi, wherea in ACI it wa given by: with f in ki unit. Thi change reflect the higher ervice tree that occur in flexural reinforcement with the ue of the load combination introduced in the 2002 Code. Note that f i permitted to be taken equal to (2/3) f y, rather than 60 percent of f y, a in ACI The crack control proviion were updated to reflect the higher ervice tree that occur in flexural reinforcement with the ue of the load combination introduced in ACI Section on kin reinforcement in deep member ha been modified a follow: If the effective depth d Where h of a beam or joit exceed 36 in., longitudinal kin reinforcement hall be uniformly ditributed along both ide face of the member. Skin reinforcement hall extend for a ditance d/2 nearet h/2 from the tenion face. nearet the flexural tenion reinforcement. The pacing the pacing k between longitudinal bar or wire of the kin reinforcement hall be a provided in , where c c i the leat ditance from the urface of the kin reinforcement or pretreing teel to the ide face. not exceed the leat of d/6, 12 in., and 1000A b /(d-30). It hall be permitted to include uch reinforcement in trength computation if a train compatibility analyi i made to determine tre in the individual bar or wire. The total area of longitudinal kin reinforcement in both face need not ex- 540 = 25. cc f f ceed one half of the required flexural tenile reinforcement. The change in Section are intended to implify the crack control proviion for kin reinforcement and make thee proviion conitent with thoe required for flexural tenion reinforcement. The ize of kin reinforcement i not pecified; reearch 13 ha indicated that the pacing rather than bar ize i of primary importance. A indicated earlier, Section ha been modified to permit the ue of piral reinforcement with pecified yield trength of up to 100,000 pi. For piral with f yt greater than 60,000 pi, only mechanical or welded plice may be ued. Section require that in addition to load combination involving lateral load, the trength and tability of the tructure a a whole under factored gravity head mut be conidered. In Item (a) and (b) of that ection, 1.4 dead load and 1.7 live load of ACI ha been replaced by factored dead and live load in ACI , thu upplying a much-needed clarification. Chapter 11, Shear and Torion A change of much ignificance to the precat concrete indutry i that an alternative deign procedure for torion deign ha been introduced in Section , which more realitically addree L-haped beam. Deign for torion now mut be in accordance with Section through , or The deign for torion in Section through i baed on a thin-walled tube, pace tru analogy. Section , titled Alternative deign for torion, tate: For torion deign of olid ection within the cope of the Code with an apect ratio, h/b t (h = overall thickne or height of member, b t = width of that part of cro ection containing the cloed tirrup reiting torion), of three or greater, it hall be permitted to ue another procedure, the adequacy of which ha been hown by analyi and ubtantial agreement with reult of comprehenive tet. Section (Detail of torional reinforcement) and (Spacing of torion rein- 96 PCI JOURNAL

4 forcement) apply. Commentary Section R tate that example of uch procedure are to be found in Reference 14, 15, and 16, which have been extenively and uccefully ued for deign of precat pretreed concrete beam with ledge. The procedure decribed in Reference 14 and 15 i an extenion to pretreed concrete ection of the torion deign procedure of pre-1995 edition of ACI 318. The fourth edition of the PCI Deign Handbook 17 decribe the procedure of Reference 14 and 15. The procedure wa experimentally verified by the tet decribed in Reference 18. Section , which require tranvere torional reinforcement to be anchored in way indicated by Item (a) or (b), ha had Item (a) modified a follow: (a) A 135-deg tandard hook or eimic hook, a defined in 21.1, around a longitudinal bar; Chapter 13, Two-Way Slab Sytem A new Section precribe the dimenional requirement for drop panel that were in ACI Section and , but make them applicable only when the drop panel i ued to reduce the amount of negative reinforcement over a column or minimum required lab thickne. A new Commentary Section R point out that drop panel with dimenion le than thoe pecified in may be ued to increae lab hear trength. Chapter 14, Wall The ϕ in Eq. (14-1), giving the deign axial load trength of a wall eligible to be deigned by the empirical deign method, wa 0.7 in ACI Now the ame ϕ mut correpond to compreion-controlled ection in accordance with Section Thi i for conitency with Chapter 9. For imilar reaon, under Section 14.8, Alternative deign of lender wall, the previou requirement that the reinforcement ratio hould not exceed 0.6ρ bal wa replaced by the requirement that the wall be tenioncontrolled, leading to approximately the ame reinforcement ratio. Chapter 15, Footing An important clarification of Section ha been provided by replacing Other pile cap hall atify one of 11.12, , or Appendix A with Other pile cap hall atify either Appendix A, or both and Section 15.5 deal with hear deign of footing. A new term, deign tory drift ratio, i defined a the relative difference of deign diplacement between the top and the bottom of a tory, divided by the tory height. Thi i part of a change in Section that i dicued later. A mentioned earlier, Section 9.4 and have been modified to allow the ue of piral reinforcement with pecified yield trength of up to 100,000 pi. A entence added to Section pecifically prohibit uch ue in member reiting earthquakeinduced force in tructure aigned to Seimic Deign Category D, E, or F. Thi i largely the reult of ome migiving that high trength piral reinforcement may be le ductile than conventional mild teel reinforcement and that piral failure ha in fact been oberved in earthquake. There are fairly convincing argument, however, againt uch pecific prohibition. Spiral failure, primarily oberved in bridge column, have invariably been the reult of inufficient piral reinforcement, rather than the lack of ductility of the piral reinforcement. Alo, pretreing teel, which i the only high-trength teel available on thi market, i at leat a ductile a welded wire reinforcement, which i allowed to be ued a tranvere reinforcement. Section modifie the development length requirement of Chapter 12 for longitudinal beam bar terminating at exterior beam-column joint of tructure aigned to high eimic deign categorie. But then Section of ACI required that all continuou reinforcement in tructural wall be anchored or pliced in accordance with the proviion for reinforcement in tenion in Section Section of ACI further required that all continuou reinforcement in diaphragm, true, tie, chord, and collector element be anchored or pliced in accordance with the proviion for reinforcement in tenion a pecified in Section Section and were very confuing to the uer, becaue Section i really not applicable to itua- Chapter 18, Pretreed Concrete Tendon of continuou pot-tenioned beam and lab are uually treed at a point along the pan where the tendon profile i at or near the centroid of the concrete cro ection. Therefore, interior contruction joint are uually located within the end third of the pan, rather than the middle third of the pan, a required by Section Thi ha had no known detrimental effect on the performance of uch beam. Thu, Section i now excluded from application to pretreed concrete. ACI required pretreed two-way lab ytem to be deigned a Cla U, which meant that f t could be up to 7.5 f c. ACI retrict f t in uch lab to 6 f c, thu limiting the permiible flexural tenile tre in two-way pretreed lab to the ame value a in ACI and prior code. Section ha been modified a follow: Where If h the effective depth of a beam exceed 36 in., the area of longitudinal kin reinforcement coniting of reinforcement or bonded tendon hall be provided a required by In Commentary Section R , the tatement that for tatitically indeterminate tructure, the moment due to reaction induced by pretreing force, referred to a econdary moment, are ignificant in both elatic and inelatic tate i now upported by three added reference The entence, When hinge and full reditribution of moment occur to create a tatically determinate tructure, econdary moment diappear. ha been deleted. Thi remove an unneceary and potentially confuing entence. Section no longer refer to normal live load, becaue it i largely meaningle. Chapter 21, Special Proviion for Seimic Deign September-October

5 tion covered by thoe ection. Thi problem exited with ACI 318 edition prior to 2002 a well. In a very ignificant and beneficial change, the requirement of Section were modified to remove the reference to beam-column joint in Section Becaue actual force in longitudinal reinforcement of tructural wall may exceed calculated force, it i now required that reinforcement in tructural wall be developed or pliced for f y in tenion in accordance with Chapter 12. The effective depth of member referenced in Section i permitted to be taken a 0.8l w for wall. Requirement of Section 12.11, 12.12, and need not be atified, becaue they addre iue related to beam and do not apply to wall. At location where yielding of longitudinal reinforcement i expected, 1.25f y i required to be developed in tenion, to account for the likelihood that the actual yield trength exceed the pecified yield trength, a well a the influence of train-hardening and cyclic load reveral. Where tranvere reinforcement i ued, development length for traight and hooked bar may be reduced a permitted in Section 12.2 and 12.5, repectively, becaue cloely paced tranvere reinforcement improve the performance of plice and hook ubjected to repeated cycle of inelatic deformation. The requirement that mechanical plice of reinforcement conform to Section , and welded plice to Section , ha now been placed in Section Conequently, Section (f) of of ACI have been deleted. In a companion change, Section now require that all continuou reinforcement in diaphragm, true, trut, tie, chord, and collector element be developed or pliced for f y in tenion. Structural tru element, trut, tie, diaphragm chord, and collector element with compreive tree exceeding 0.2f c at any ection are required to be pecially confined by Section The pecial tranvere reinforcement may be dicontinued at a ection where the calculated compreive tre i le than 0.15f c. Stree are calculated for factored force uing a linear elatic model and gro-ection propertie of the element conidered. In recent eimic code and tandard, collector element of diaphragm are required to be deigned for force amplified by a factor Ω 0, to account for the overtrength in the vertical element of the eimic-forcereiting ytem. The amplification factor Ω 0 range between 2 and 3 for concrete tructure, depending upon the document elected and on the type of eimic ytem. To account for thi, Section now additionally tate that where deign force have been amplified to account for the overtrength of the vertical element of the eimic-force-reiting ytem, the limit of 0.2f c and 0.15f c hall be increaed to 0.5f c and 0.4f c, repectively. In a very ignificant change, proviion for hear reinforcement at labcolumn joint have been added in a new Section , to reduce the likelihood of punching hear failure in two-way lab without beam. A precribed amount and detailing of hear reinforcement i required unle either Section (a) or (b) i atified. Section (a) require calculation of hear tre due to the factored hear force and induced moment according to Section The induced moment i the moment that i calculated to occur at the lab-column joint where ubjected to the deign diplacement defined in Section Section and the accompanying commentary provide guidance on the election of lab tiffne for the purpoe of thi calculation. Section (b) doe not require the calculation of induced moment, and i baed on reearch 22,23 that identifie the likelihood of punching hear failure conidering intertory drift and hear due to gravity load. The requirement i illutrated in the newly added Fig. R The requirement can be atified in everal way: adding lab hear reinforcement, increaing lab thickne, deigning a tructure with more lateral tiffne to decreae intertory drift, or a combination of two or more of thee factor. If column capital, drop panel, or other change in lab thickne are ued, the requirement of Section mut be evaluated at all potential critical ection. 98 PCI JOURNAL

6 REFERENCES 1. ACI Committee 318, Reviion to ACI Building Code Requirement for Structural Concrete and Commentary, Concrete International, V. 26, No. 7, July 2004, pp ICC, International Building Code, International Code Council, Fall Church, VA, 2003, 2006 (to be publihed). 3. ASCE, ASCE 7 Standard Minimum Deign Load for Building and Other Structure, Structural Engineering Intitute, American Society of Civil Engineer, Reton, VA, 1998, 2002, 2005 Including Supplement (to be publihed). 4. NFPA, NFPA 5000 Building Contruction and Safety Code, National Fire Protection Aociation, Quincy, MA, ASTM, Tet Method for Determining Denity of Structural Lightweight Concrete, 17th Edition, American Society for Teting and Material, Wahington, DC, ACI Committee 440, Guide for the Deign and Contruction of Concrete Reinforced with FRP Bar (ACI 440.1R-03), American Concrete Intitute, Farmington Hill, MI, 2003, 42 pp. 7. ACI Committee 440, Guide for the Deign and Contruction of Externally Bonded FRP Sytem for Strengthening of Concrete Structure (ACI 440.2R-02), American Concrete Intitute, Farmington Hill, MI, 2002, 45 pp. 8. AASHTO, Standard Specification for Highway Bridge, 17th Edition, American Aociation for State Highway and Tranportation Official, Wahington, DC, ACI, Qualification of Pot-Intalled Mechanical Anchor in Concrete (ACI ), American Concrete Intitute, Farmington Hill, MI, AWS, Structural Welding Code Steel, AWS D1.1/D1.1M, American Welding Society, Miami, FL, Saatcioglu, M., and Razvi, S. R., Diplacement-Baed Deign of Reinforced Concrete Column for Confinement, ACI Structural Journal, V. 99, No. 1, January-February 2002, pp Peiki S., Graybeal, B., and Mudlock, M., Propoed Deign of High-Strength Spiral Reinforcement in Compreion Member, ACI Structural Journal, V. 98, No. 6, November-December 2001, pp Froch, R. J., Modeling and Control of Side Face Beam Cracking, ACI Structural Journal, V. 99, No. 3, May-June 2002, pp Zia, P., and McGee, W. D., Torion Deign of Pretreed Concrete, PCI JOURNAL, V. 19, No. 2, March-April 1974, pp Zia, P., and Hu, T. T. C., Deign for Torion and Shear in Pretreed Concrete Flexural Member, PCI JOURNAL, V. 49, No. 3, May-June 2004, pp Collin, M. P., and Mitchell, D., Shear and Torion Deign of Pretreed and Non-Pretreed Concrete Beam, PCI JOURNAL, V. 25, No. 4, September-October 1980, pp PCI, PCI Deign Handbook Precat and Pretreed Concrete, Fourth Edition, Precat/Pretreed Intitute, Chicago, IL, Klein, G. J., Deign of Spandrel Beam, PCI Specially Funded Reearch Project No. 5, Precat/Pretreed Concrete Intitute, Chicago, IL, Bondy, K. B., Moment Reditribution: Principle and Practice Uing ACI , PTI Journal, V. 1, No. 1, Pot-Tenioning Intitute, Phoenix, AZ, January, 2003, pp Lin, T. Y., and Thornton, K., Secondary Moment and Moment-Reditribution in Continuou Pretreed Concrete Beam, PCI JOURNAL, V. 17, No. 1, January-February 1972, pp Collin, M. P., and Mitchell, D., Pretreed Concrete Structure, Repone Publication, Canada, 1997, pp Megally, S., and Ghali, A., Punching Shear Deign of Earthquake Reitant Slab-Column Connection, ACI Structural Journal, V. 97, No. 5, September-October 2000, pp Moehle, J. P., Seimic Deign Conideration for Flat Plate Contruction, Mete A. Sozen Sympoium: a Tribute From hi Student, ACI SP-162, J. K. Wight and M. E. Kreger, Editor, American Concrete Intitute, Farmington Hill, MI, 1996, pp September-October