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355787256-ETABS-Design-of-RC-Structures-to-EC2.pdf

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C h a p t e r VII Design for Eurocode 2 This chapter describes in detail the various aspects of the concrete design procedure that is used by ETABS when the user selects the 1992 Eurocode 2 (CEN 1992). Various notations used in this chapter are listed in Table VII-1. The design is based on user-specified loading combinations. However, the program provides a set of d
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  C h a p t e r  VII Design for Eurocode 2 Thischapterdescribesindetailthevariousaspectsoftheconcretedesignprocedurethat is used by ETABS when the user selects the  1992 Eurocode 2  (CEN 1992).Various notations used in this chapter are listed in Table VII-1.Thedesignisbasedonuser-specifiedloadingcombinations.However,theprogramprovides a set of default load combinations that should satisfy requirements for thedesign of most building type structures.English as well as SI and MKS metric units can be used for input. But the code isbased on Newton-Millimeter-Second units. For simplicity, all equations and de-scriptions presented in this chapter correspond to  Newton-Millimeter-Second units unless otherwise noted. Design Load Combinations The design loading combinations define the various factored combinations of theload cases for which the structure is to be checked. The design loading combina-tionsareobtainedbymultiplyingthecharacteristicloadsbyappropriatepartialfac-tors of safety. If a structure is subjected to dead load (DL) and live load (LL) only,the design will need only one loading combination, namely 1.35 DL + 1.5 LL. Design Load Combinations  129  ETABS Concrete Design Manual 130  Design Load Combinations  A c  Gross cross-sectional area of a frame member, mm 2  A cv  Area of section for shear resistance, mm 2  A s  Area of tension reinforcement in a beam, mm 2 Area of total longitudinal reinforcement in a column, mm 2  A s   Area of compression reinforcement, mm 2  A sw  Total cross-sectional area of links at the neutral axis, mm 2 a  Depth of compression block, mm b  Width or effective width of the section in the compression zone, mm b  f   Width or effective width of flange, mm b w  Average web width of a flanged beam, mm d   Effective depth of tension reinforcement, mm d    Effective depth of compression reinforcement, mm  E  c  Modulus of elasticity of concrete, MPa  E  s  Modulus of elasticity of reinforcement, assumed as 200000 MPa(EC2 4.2.2.3.2) e  Eccentricity of axial load in a column, mm e min  Minimum or nominal eccentricity, mm e tot   Total eccentricity for a braced column, mm  f  cd   Design concrete compressive strength =  f  ck  c   , MPa  f f  ck  c ,   Characteristic compressive cylinder strength of concrete at 28 days, MPa  f  cwd   Design concrete compressive strength for shear design =  f  cwk  c   , MPa  f f  cwk  cs ,   Characteristic compressive cylinder strength for shear design, MPa  f   yd   Design tensile yield strength of reinforcing steel =  f   yk  s   , MPa  f f   yk  y , Characteristic tensile yield strength of reinforcement, MPa  f  s   Stress in a beam compression steel, MPa  f   ywd   Design tensile strength of shear reinforcing steel =  f   ywk  s   , MPa  f f   ywk  ys , Characteristic tensile strength of shear reinforcement, MPa h  Overall depth of a section in the plane of bending, mm h  f   Flange thickness, mm l 0  Effective height of a column, mm l col  Clear height between end restraints, mm  M   Design moment at a section, N-mm Table VII-1  List of Symbols Used in the Eurocode 2  Design Load Combinations  131 Chapter VII Design for Eurocode 2  M M  1 2 , Smaller and larger end moments in a slender column, N-mm  M M   x y , Applied moments about the major and minor axes of a column, N-mm  M   Rd   Design moment of resistance of a section N-mm  M  Sd   Moment at a section obtained from analysis, N-mm m  Normalized design moment,  M bd f  cd  2    N   Ultimate axial load, N s v  Spacing of links, mm V   Rd  1  Design shear resistance from concrete alone, N V   Rd   2  Design limiting shear resistance of a cross-section, N V  Sd   Shear force at ultimate design load, N V V   x y , Shear force at ultimate design load in two directions, N V  wd   Shear force from reinforcement, N   Concrete strength reduction factor for sustained loading   Effective length factor,Enhancement factor of shear resistance for concentrated load    f   Partial safety factor for load   c  Partial safety factor for concrete strength, 1.5 by default   m  Partial safety factor for material strength   s  Partial safety factor for steel strength, 1.15 by default   Redistribution factor  c  Concrete strain  s  Strain in tension steel  s   Strain in compression steel   Effectiveness factor for shear resistance without concrete crushing,Out of plumbness factor   Tension reinforcement ratio,  A bd  s   cp  Effective average compressive stress in concrete column, MPa   Normalized tensile steel ratio,  A f f bd  s yd cd    Normalized compression steel ratio,  A f f bd  s yd cd      lim  Normalized limiting tensile steel ratio Table VII-1  List of Symbols Used in the Eurocode 2 (continued)  However, in addition to the dead load and live load, if the structure is subjected towind (WL) and earthquake (EL) forces, and considering that wind and earthquakeforces are subject to reversals, the following load combinations might have to beconsidered (EC2 2.3.3):1.35 DL1.35 DL + 1.50 LL (EC2 2.3.3)1.35 DL    1.50 WL1.00 DL    1.50 WL1.35 DL + 1.35 LL    1.35 WL (EC2 2.3.3)1.00 DL    1.00 EL1.00 DL + 1.5*0.3 LL    1.0 EL (EC2 2.3.3)These are the default load combinations. These default loading combinations areproduced for persistent and transient design situations (EC2 2.2.1.2) by combiningload due to dead, live, wind, and earthquake loads according to the simplified for-mula (EC2 2.3.3.1) for ultimate limit states.In addition to the above load combinations, the code requires that all buildingsshould be capable of resisting a notional design ultimate horizontal load applied ateach floor or roof level (EC2 2.5.1.3). It is recommended that the user define addi-tional load cases for considering the notional load in ETABS.Live load reduction factors, as allowed by some design codes, can be applied to themember forces of the live load condition on a member-by-member basis to reducethe contribution of the live load to the factored loading. Design Strength The design strength for concrete and steel are obtained by dividing the characteris-ticstrengthofthematerialsbyacorrespondingpartialfactorofsafetyasshownbe-low.  f f  cd ck  c    , (EC2 2.3.3.2)  f f  cwd cwk  c    , (EC2 2.3.3.2)  f f   yd yk  s    , (EC2 2.3.3.2)  f f   ywd ywk  s    , where (EC2 2.3.3.2) 132  Design StrengthETABS Concrete Design Manual
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