SEISMIC DESIGN REQUIREMENTS FOR REINFORCED CONCRETE BUILDINGSMODEL BUILDING CODES Amodelbuildingcodeisadocumentcontainingstandardized buildingrequirementsapplicablethroughouttheUnitedStates. ThethreemodelbuildingcodesintheUnitedStateswere:the UniformBuildingCode(predominantinthewest),theStandard BuildingCode(predominantinthesoutheast),andtheBOCA NationalBuildingCode(predominantinthenortheast),were initiated between 1927 and 1950. TheUSUniformBuildingCodewasthemostwidelyusedseismic code in the world, with its last edition published in 1997. Up to the year 2000, seismic design in the United States has been based on one these three model building codes. Representatives from the three model codes formed the InternationalCodeCouncil(ICC)in1994,andinApril2000,the ICCpublishedthefirsteditionoftheInternationalBuildingCode, IBC-2000. In 2003, 2006, 2009 and 2012, the second, third fourth and fifth editions of the IBC followed suit. Initiation Of The Equivalent Static Lateral Force Method The work done after the 1908 Reggio-Messina Earthquake in Sicily by a committeeappointedbytheItaliangovernmentmaybetheoriginof the equivalent static lateral force method, in which a seismic coefficient is applied to the mass of the structure, to produce the lateral force that isapproximatelyequivalentineffecttothedynamicloadingofthe expected earthquake. TheJapaneseengineerToshikataSanoindependentlydevelopedin 1915 the idea of a lateral design force V proportional to the buildings weight W. This relationship can be written asF = C W , where C is a lateralforcecoefficient,expressedassomepercentageofgravity.The first official implementation of Sanos criterion was the specification C = 10percentofgravity,issuedasapartofthe1924JapaneseUrban BuildingLawEnforcementRegulationsinresponsetothedestruction caused by the great 1923 Kanto earthquake. In California, the Santa Barbara earthquake of 1925 motivated several communities to adopt codes with C as high as 20 percent of gravity. Development Of The Equivalent Static Lateral Force Method The first edition of the U.S. Uniform Building Code (UBC) was published in1927bythePacificCoastbuildingOfficials(PCBO),containedan optional seismic appendix. The seismic design provisions remained in an appendix to the UBC until the publication of the 1961 UBC. In the 1997 edition of UBC the earthquake load (E) is a function of both the horizontal and vertical components of the ground motion. UBC/IBC Code sLateral ForceUBC 1927- UBC 1946 F = CW UBC 1949- UBC 1958 F = CW UBC 1961- UBC 1973 V = ZKCW UBC 1976- UBC 1979 V = ZIKCSW UBC 1982- UBC 1985 V = ZIKCSW UBC 1988- UBC 1994 V = ZICW/Rw UBC 1997 V = CvIW/RT IBC- 2000- IBC-2012 V = CsW Safety Concepts StructuresdesignedinaccordancewiththeUBCprovisions should generally be able to: 1. Resist minor earthquakes without damage. 2.Resistmoderateearthquakeswithoutstructuraldamage,but possibly some nonstructural damage. 3.Resistmajorearthquakeswithoutcollapse,butpossiblysome structural and nonstructural damage.

TheUBCintendedthatstructuresbedesignedforlife-safety intheeventofanearthquakewitha10-percentprobabilityof being exceeded in 50 years. The IBC intends design for collapse preventioninamuchlargerearthquake,witha2-percent probability of being exceeded in 50.Seismic Codes Are Based On Earthquake Historical Data The1925SantaBarbaraearthquakeledtothefirstintroductionof simpleNewtonianconceptsinthe1927UniformBuildingCode.Asthe levelofknowledgeanddatacollectedincreases,theseequationsare modified to better represent these forces. Inresponsetothe1985MexicoCityearthquake,afourthsoilprofile type,,forverydeepsoftsoilswasaddedtothe1988UBC,withthe factorequal to 2.0. The 1994 Northridge Earthquake resulted in addition of near-fault factor to base shear equation, and prohibition on highly irregular structures in near fault regions. Also, redundancy factor added to design forces. The 1997 UBC incorporated a number of important lessons learned from the1994Northridgeandthe1995Kobeearthquake,wherefoursite coefficientsuseintheearlier1994UBChasbeenextendedtosixsoil profiles,whicharedeterminedbyshearwavevelocity,standard penetration test, and undrained shear strength.

Based on R1.1.1.9.1 of ACI 318-08, for UBC 1991 through 1997, Seismic Zones 0 and 1 are classified as classified as zones of low seismic risk. Thus, provisions of chapters 1 through 19 and chapter 22 are considered sufficient for structures located in these zones. Seismic Zone 2 is classified as a zone of moderate seismic risk, and zones 3and4areclassifiedaszonesofhighseismicrisk.Structureslocatedin these zones are to be detailed as per chapter 21 of ACI 318-08 Code. ForSeismicDesignCategoriesAandBofIBC2000through2012, detailingisdoneaccordingtoprovisionsofchapters1through19and chapter22ofACI318-08.SeismicDesignCategoriesC,D,EandFare detailed as per the provisions of chapter 21.

Detailing Requirements of ACI 318-08 Code/StandardLevel of Seismic Risk LowModerateHigh IBC 2000-2012SDC A, BSDC CSDC D, E, F UBC 1991-1997zone 0, 1Zone 2Zone 3, 4

Major Changes from UBC 1994 (1) Soil Profile Types:The four Site Coefficients S1 to S4 of the UBC 1994, which are independent of the level of ground shaking, were expanded to six soil profile types, which are dependent on the seismic zone factors, in the 1997 UBC (SA to SF) based on previous earthquake records. The new soil profile types were based on soil characteristics for the top 30 m of the soil. The shear wave velocity, standard penetration test and undrained shear strength are used to identify the soil profile types. (2) Structural Framing Systems:In addition to the four basic framing systems (bearing wall, building frame, moment-resisting frame, and dual), two new structural system classifications were introduced: cantilevered column systems and shear wall-frame interaction systems. (3) Load Combinations:The 1997 UBC seismic design provisions are based on strength-level design rather than service-level design. (4) Earthquake Loads:In the 1997 UBC, the earthquake load (E) is a function of both the horizontal and vertical components of the ground motion. Seismic Design According To 1997 UBC The Static Lateral Force Procedure

Applicability The static lateral force procedure may be used for the following structures: All structures, regular or irregular (Table A1), in Seismic Zone no. 1 (Table A-2) and in Occupancy Categories 4 and 5 (Table A-3) in Seismic Zone 2. Regularstructuresunder73minheightwithlateralforceresistance provided by systems given in Table (A-4) except for structures located in soil profile type SF, that have a period greater than 0.70 sec. (seeTable A-5 for soil profiles). Irregular structures not more than five stories or 20 m in height. Structureshavingaflexibleupperportionsupportedonarigidlower portionwherebothportionsofthestructureconsideredseparatelycanbe classified as being regular, the average story stiffness of the lower portion is at least ten times the average stiffness of the upper portion and the period of theentirestructureisnotgreaterthan1.10timestheperiodoftheupper portion considered as a separate structure fixed at the base. Seismic Design According To 1997 UBC The Static Lateral Force Procedure Design Base Shear, V Thetotaldesignbaseshearinagivendirectionistobe determined from the following formula. The total design base shear need not exceed the following: Thetotaldesignbaseshearshallnotbelessthanthe following: Where V = total design lateral force or shear at the base. W = total seismic dead load In storage and warehouse occupancies, a minimum of 25 % of floor live load is to be considered. Total weight of permanent equipment is to be included. Where a partition load is used in floor design, a load of not less than 50 kg/m2 is to be included. I = Building importance factor given in Table (A-3). Z = Seismic Zone factor, shown in Table (A-2).R = response modification factor for lateral force resisting system, shown in Table (A-4). Ca = acceleration-dependent seismic coefficient, shown in Table (A-6).Cv= velocity-dependent seismic coefficient, shown in Table (A-7). T= elastic fundamental period of vibration, in seconds, of the structure in the direction under consideration evaluated from the following equations:For reinforced concrete moment-resisting frames, For other buildings, Alternatively, for shear walls,

Design Base Shear, V (Contd.) Wherehn= total height of building in meters Ac=combinedeffectivearea,inm2,oftheshearwallsinthefirststoryof the structure, given by De =the length, in meters, of each shear wall in the first story in the direction parallel to the applied forces. Ai=cross-sectionalareaofindividualshearwallsinthedirectionofloadsin m2

Design Base Shear, V (Contd.) Table (A-2): Seismic zone factor Z Note: The zone shall be determined from the seismic zone map (Graphs A-1 and A-2). Table (A-3):Occupancy Importance Factors

Tables And Graphs Zone 1 2A 2B 3 4 Z0.075 0.15 0.20 0.30 0.40Occupancy Category Seismic Importance Factor, I1-Essential facilities1.252-Hazardous facilities1.253-Special occupancy structures1.004-Standard occupancy structures 1.005-Miscellaneous structures 1.00Table (A-4): Structural Systems

Tables And Graphs (Contd.) Lateral-force resistingsystem description RHeight limit Zones 3&4. (meters) Bearing WallConcreteshear walls 4.548 Building FrameConcreteshear walls 5.573 Moment-Resisting Frame SMRF IMRF OMRF 8.5 5.5 3.5 N.L ---- ---- Dual Shearwall+ SMRF Shearwall+ IMRF 8.5 6.5 N.L 48 CantileveredColumn BuildingCantilevered column elements 2.210 Shear-wallFrame Interaction 5.548 Table (A-5):Soil Profiles Table (A-6): Seismic coefficient Ca Footnote: Site-specific geotechnical investigation and dynamic response analysis shall be performed to determine seismic coefficients for soil Profile Type .

Tables And Graphs (Contd.) Soil Profile TypeSeismic Zone Factor, Z Z =0.075Z = 0.15Z = 0.2Z = 0.3 SA 0.060.120.160.24 SB 0.080.150.200.30 SC 0.090.180.240.33 SD 0.120.220.280.36 SE 0.190.300.340.36 SFSee Footnote Table (A-7): Seismic coefficient Cv Graph (A-1): Palestines seismic zone factors (Source: International Handbook of Earthquake Engineering , Mario Paz)

Tables And Graphs (Contd.) Graph (A-2): Palestines seismic zone factors (Source: Annajah National University)

Tables And Graphs (Contd.) Vertical Distribution of Force: The base shear which is evaluated from the following equation, is distributed over the height of the building. Where: The shear force at each story is given The overturning moment is given by

Vertical Distribution of Forces Horizontal Distribution of Force: The design story shear in any direction, is distributed to the various elements of the lateral force-resisting system in proportion to their rigidities. Horizontal Torsional Moment: Thetorsionaldesignmomentatagivenstoryisgivenbymomentresulting from eccentricities between applied design lateral forces applied through each storys center of mass at levels above the story and the center of stiffness of theverticalelementsofthestory,inadditiontotheaccidentaltorsion (calculatedbydisplacingthecalculatedcenterofmassineachdirectiona distance equal to 5 % of the building dimension at that level perpendicular to the direction of the force under consideration). Interactions of Shear Walls with Each Other: Inthefollowingfiguretheslabsactashorizontaldiaphragmsextending between cantilever walls and they are expected to ensure that the positions of thewalls,relativetoeachother,don'tchangeduringlateraldisplacementof thefloors.Theflexuralresistanceofrectangularwallswithrespecttotheir weak axes may be neglected in lateral load analysis.

Horizontal Distribution of Forces The distribution of the total seismic load Fx, or Fy among all cantilever walls may be approximated by the following expressions: Fix = Fix + Fix and Fiy = Fiy + Fiy Where Fix= load induced in wall byinter-story translation only, in x-direction Fiy= load induced in wall by inter-story translation only, in y-direction Fix = load induced in wallby inter-story torsion only, in x-direction Fiy = load induced in wall by inter-story torsion only, in y-direction

Horizontal Distribution of Forces (Contd.) The force resisted by wall i due to inter-story translation, in x-direction, is given by The force resisted by wall i due to inter-story translation , in y-direction, is given by The force resisted by wall i due to inter-story torsion, in x-direction, is given by The force resisted by wall i due to inter-story torsion, in y-direction, is given by Where: xi = x-coordinate of a wall w.r.t the C.R of the lateral load resisting system yi = y-coordinate of a wall w.r.t the C.R of the lateral load resisting system ex = eccentricity resulting from non-coincidence of center of gravity C.G and center of rigidity C.R, in x-direction ey= eccentricity resulting from non-coincidence of center of gravity C.G and center of rigidity C.R, in y-direction Fx = total external load to be resisted by all walls, in x-direction Fy = total external load to be resisted by all walls, in y-direction Iix = second moment of area of a wall about x-axis Iiy = second moment of area of a wall about y-axis

Horizontal Distribution of Forces (Contd.) AccordingtoChapters2and21ofACI318-02,structuralwallsaredefinedasbeingwalls proportionedtoresistcombinationsofshears,moments,andaxialforcesinducedbyearthquake motions.Ashearwallisastructuralwall.Reinforcedconcretestructuralwallsarecategorizedas follows:

Ordinaryreinforcedconcretestructuralwalls,whicharewallscomplyingwiththerequirementsof Chapters 1 through 18.

Specialreinforcedconcretestructuralwalls,whicharecast-in-placewallscomplyingwiththe requirementsof21.2and21.7inadditiontotherequirementsforordinaryreinforcedconcrete structural walls.Special Provisions For Earthquake Resistance

According to Clause 1.1.8.3 of ACI 318-02, the seismic risk level of a region is regulated by the legally adopted general building code of which ACI 318-02 forms a part, or determined by local authority. AccordingtoClauses1.1.8.1and21.2.1.2ofACI318-02inregionsoflowseismicrisk,provisionsof Chapter 21are to be applied (chapters 1 through 18 are applicable). AccordingtoClause1.1.8.2ofACI318-02,inregionsofmoderateorhighseismicrisk,provisionsof Chapter 21 are to be satisfied. In regions of moderate seismic risk, ordinary or special shear walls are tobeusedforresistingforcesinducedbyearthquakemotionsasspecifiedinClause21.2.1.3ofthe code. AccordingtoClause21.2.1.4ofACI318-02,inregionsohhighseismicrisk,specialstructuralwalls complying with 21.2 through 21.10 are to be used for resisting forces induced by earthquake motions.

Classification of Structural Walls

Building Frame System: Based on section 1627 of UBC-1997, it is essentially a complete space frame that provides support for gravity loads. Moment Frames:BasedonACI2.1,21.1and21.2,aredefinedasframesinwhichmembers andjointsresistforcesthroughflexure,shear,andaxialforce.Moment frames are categorized as follows: Ordinary Moment Frames: ConcreteframescomplyingwiththerequirementsofChapters1through18 of the ACI Code. They are used in regions of low-seismic risk. Intermediate Moment Frames: Concreteframescomplyingwiththerequirementsof21.2.2.3and21.12in additiontotherequirementsforordinarymomentframes.Theyareusedin regions of moderate-seismic risk. Special Moment Frames: Concrete frames complying with the requirements of21.2through21.5,inadditiontotherequirementsforordinarymoment frames. They are used in regions of moderate and high-seismic risks.

Classification of Moment Resisting Frames

Earthquake Loads

Based on UBC 1630.1.1, horizontal earthquake loads to be used in the above-stated load combinations are determined as follows: Where: E=earthquakeloadresultingfromthecombinationofthehorizontalcomponent,andthevertical component,

Eh = the earthquake load due to the base shear, V

Ev = the load effects resulting from the vertical component of the earthquake ground motion and is equal to the addition of to the dead load effects D = redundancy factor, to increase the effects of earthquake loads on structures with few lateral force resisting elements (taken as 1.0 where z =0, 1 or 2)

Load Combinations LoadsACI 818-02UBC-1997 Dead (D) and Live (L) 1.2 D + 1.6 L1.32 D + 1.1 L Dead(D),Live(L) and Earthquake (E) 1.2 D + 1.0 L + 1.0 E1.2 D + 1.0 L + 1.1 E Theshearwallisdesignedasacantileverbeamfixedatthebase,totransferloadtothefoundation. Shear force, bending moment, and axial load are maximum at the base of the wall. Types of Reinforcement

To control cracking, shear reinforcement is required in the horizontal and vertical directions, to resist in plane shear forces. Theverticalreinforcementinthewallservesasflexuralreinforcement.Iflargemomentcapacityis required,additionalreinforcementcanbeplacedattheendsofthewallwithinthesectionitself,or withinenlargementsattheends.Theheavilyreinforcedorenlargedsectionsarecalledboundary elements.

Design of Ordinary Shear Walls Shear Design

According to ACI 11.1.1, nominal shear strength Vn is given as Where Vc is nominal shear strength provided by concrete and Vs is nominal shear strength provided by the reinforcement. Based on ACI 11.10.3, Vn is limited by the following equation. The shear strength provided by concreteVc is given by any of the following equations, as applicable. h= thickness of wall d= effective depth in the direction of bending, may be taken as 0.8 lw, as stated in ACI 11.10.4 Ag = gross area of wall thickness Nu = factored axial load

Design of Ordinary Shear Walls Shear Reinforcement

When the factored shear force exceeds Vc/2, -Horizontal reinforcement ration h is not to be less than 0.0025. Spacing of this reinforcement S2 is not to exceed the smallest of lw/5, 3h and 45 cm. - Vertical reinforcement ratio n is not to be taken less than Nor 0.0025. AccordingtoACI11.10.9.1,whenthefactoredshearforceVuexceedsVc,horizontalshear reinforcement must be provided according to the following equation. Spacing of this reinforcement S1 is not to exceed the smallest of lw/3, 3h and 45 cm.

Where: Av = Area of horizontal shear reinforcement within a distance S2. h = ratio of horizontal shear reinforcement area to gross concrete area of vertical section. n = ratio of vertical shear reinforcement area to gross concrete area of horizontal section.

Design of Ordinary Shear Walls Flexural Design

The wall must be designed to resist the bending moment at the base and the axial force produced by the wall weight or the vertical loads it carries. Thus, it is considered as a beam-column. Forrectangularshearwallscontaininguniformlydistributedverticalreinforcementandsubjectedto anaxialloadsmallerthanthatproducingbalancedfailure,thefollowingequation,developedby CardenasandMagurainACISP-36in1973,canbeusedtodeterminetheapproximatemoment capacity of the wall. Where: C = distance from the extreme compression fiber to the neutral axis lw = horizontal length of wall Pu = factored axial compressive load fy = yield strength of reinforcement = strength reduction factor

Design of Ordinary Shear Walls (Contd.) Reinforcement

Design of Ordinary Shear Walls (Contd.) Thank You For Your Patience!