# ASD vs LRFD_ForWebSite.ppt

1 Jun 2023
1 sur 107

### ASD vs LRFD_ForWebSite.ppt

• 1. 1 General Comparison between AISC LRFD and ASD Hamid Zand GT STRUDL Users Group Las Vegas, Nevada June 22-25, 2005
• 2. 2 AISC ASD and LRFD • AISC = American Institute of Steel Construction • ASD = Allowable Stress Design AISC Ninth Edition • LRFD = Load and Resistance Factor Design AISC Third Edition
• 3. 3 AISC Steel Design Manuals • 1963 AISC ASD 6th Edition • 1969 AISC ASD 7th Edition • 1978 AISC ASD 8th Edition • 1989 AISC ASD 9th Edition • 1986 AISC LRFD 1st Edition • 1993 AISC LRFD 2nd Edition • 1999 AISC LRFD 3rd Edition
• 4. 4 ASD and LRFD Major Differences • Load Combinations and load factors • ASD results are based on the stresses and LRFD results are based on the forces and moments capacity • Static analysis is acceptable for ASD but nonlinear geometric analysis is required for LRFD • Beams and flexural members • Cb computation
• 5. 5 ASD Load Combinations • 1.0D + 1.0L • 0.75D + 0.75L + 0.75W • 0.75D + 0.75L + 0.75E D = dead load L = live load W = wind load E = earthquake load
• 6. 6 ASD Load Combinations Or you can use following load combinations with the parameter ALSTRINC to account for the 1/3 allowable increase for the wind and seismic load 1. 1.0D + 1.0L 2. 1.0D + 1.0L + 1.0W 3. 1.0D + 1.0L + 1.0E • PARAMETER$ALSTRINC based on the % increase • ALSTRINC 33.333 LOADINGS 2 3 • 7. 7 LRFD Load Combinations • 1.4D • 1.2D + 1.6L • 1.2D + 1.6W + 0.5L • 1.2D ± 1.0E + 0.5L • 0.9D ± (1.6W or 1.0E) D = dead load L = live load W = wind load E = earthquake load • 8. 8 Deflection Load Combinations for ASD and LRFD • 1.0D + 1.0L • 1.0D + 1.0L + 1.0W • 1.0D + 1.0L + 1.0E D = dead load L = live load W = wind load E = earthquake load • 9. 9 Forces and Stresses • ASD = actual stress values are compared to the AISC allowable stress values • LRFD = actual forces and moments are compared to the AISC limiting forces and moments capacity • 10. 10 ASTM Steel Grade • Comparison is between Table 1 of the AISC ASD 9th Edition on Page 1-7 versus Table 2-1 of the AISC LRFD 3rd Edition on Page 2-24 • A529 Gr. 42 of ASD, not available in LRFD • A529 Gr. 50 and 55 are new in LRFD • A441 not available in LRFD • A572 Gr. 55 is new in LRFD • A618 Gr. I, II, & III are new in LRFD • A913 Gr. 50, 60, 65, & 70 are new in LRFD • A992 (Fy = 50, Fu = 65) is new in LRFD (new standard) • A847 is new in LRFD • 11. 11 Slenderness Ratio • Compression KL/r ≤ 200 • Tension L/r ≤ 300 • 12. 12 Tension Members • Check L/r ratio • Check Tensile Strength based on the cross- section’s Gross Area • Check Tensile Strength based on the cross- section’s Net Area • 13. 13 Tension Members ASD ft = FX/Ag ≤ Ft Gross Area ft = FX/Ae ≤ Ft Net Area LRFD Pu = FX ≤ ϕt Pn = ϕt Ag Fy ϕt = 0.9 for Gross Area Pu = FX ≤ ϕt Pn = ϕt Ae Fu ϕt = 0.75 for Net Area • 14. 14 Tension Members ASD (ASD Section D1) Gross Area Ft = 0.6Fy Net Area Ft = 0.5Fu LRFD (LRFD Section D1) Gross Area ϕt Pn = ϕt Fy Ag ϕt = 0.9 Net Area ϕt Pn = ϕt Fu Ae ϕt = 0.75 • 15. 15 Compare ASD to LRFD ASD 1.0D + 1.0L LRFD 1.2D + 1.6L 0.6Fy (ASD) × (1.5) = 0.9Fy (LRFD) 0.5Fu (ASD) × (1.5) = 0.75Fu (LRFD) ASD × (1.5) = LRFD • 16. 16 Tension Members X Y Z FIXED JOINT -400. o • 17. 17 Tension Members • Member is 15 feet long • Fixed at the top of the member and free at the bottom • Loadings are: • Self weight • 400 kips tension force at the free end • Load combinations based on the ASD and LRFD codes • Steel grade is A992 • Design based on the ASD and LRFD codes • 18. 18 Tension Members ASD W18x46 Actual/Allowable Ratio = 0.989 LRFD W10x49 Actual/Limiting Ratio = 0.989 • 19. 19 Tension Members ASD W18x46 Area = 13.5 in.2 FX = 400.688 kips Ratio = 0.989 LRFD W10x49 Area = 14.4 in.2 FX = 640.881 kips Ratio = 0.989 • 20. 20 Tension Members Load Factor difference between LRFD and ASD 640.881 / 400.688 = 1.599 Equation Factor difference between LRFD and ASD LRFD = (1.5) × ASD Estimate required cross-sectional area for LRFD LRFD W10x49 Area = 14.4 in.2 Area for LRFD      135 640881 400688 10 15 0989 0989 14 395 . . . . . . . . • 21. 21 Tension Members Code Check based on the ASD9 and using W10x49 FX = 400.734 kips Ratio = 0.928 Load Factor difference between LRFD and ASD 640.881 / 400.734 = 1.599 LRFD W10x49 Ratio = 0.989 LRFD Ratio computed fromASD     0928 640881 400734 10 15 0989 . . . . . . • 22. 22 Tension Members ASD Example # 1 Live Load = 400 kips W18x46 Actual/Allowable Ratio = 0.989 LRFD Example # 1 Live Load = 400 kips W10x49 Actual/Limiting Ratio = 0.989 Example # 2 Dead Load = 200 kips Live Load = 200 kips W14x43 Actual/Limiting Ratio = 0.989 Code check W14x43 based on the ASD9 W14x43 Actual/Allowable Ratio = 1.06 • 23. 23 Compression Members • Check KL/r ratio • Compute Flexural-Torsional Buckling and Equivalent (KL/r)e • Find Maximum of KL/r and (KL/r)e • Compute Qs and Qa based on the b/t and h/tw ratios • Based on the KL/r ratio, compute allowable stress in ASD or limiting force in LRFD • 24. 24 Compression Members ASD fa = FX/Ag ≤ Fa LRFD Pu = FX ≤ ϕc Pn = ϕc Ag Fcr Where ϕc = 0.85 • 25. 25 Limiting Width-Thickness Ratios for Compression Elements ASD b/t = h/tw = LRFD b/t = h/tw = 95 / Fy 056 . / E Fy 253 / Fy 149 . / E Fy • 26. 26 Limiting Width-Thickness Ratios for Compression Elements Assume E = 29000 ksi ASD b/t = h/tw = LRFD b/t = h/tw = 95 / Fy 9536 . / Fy 253 / Fy 25374 . / Fy • 27. 27 Compression Members ASD KL/r ≤ C′c (ASD E2-1 or A-B5-11) LRFD (LRFD A-E3-2)       F Q KL r C F KL r C KL r C a c y c c                1 2 5 3 3 8 8 2 2 3 3 / / /   F Q F cr Q y c  0658 2 .  Where   C E QF c y 2 2  Where   c y KL r F E  c Q  15 . • 28. 28 Compression Members ASD KL/r > C′c (ASD E2-2) LRFD (LRFD A-E3-3)   F E KL r a  12 23 2 2  / Where   C E QF c y 2 2  c Q  15 . F F cr c y        0877 2 .  Where   c y KL r F E  • 29. 29 Compression Members LRFD F F cr c y        0877 2 .  Where   c y KL r F E  F KL r F E F cr y y                          0877 2 .    F E KL r cr  0877 2 2 . /    F E KL r cr  20171 23 2 2 . /  • 30. 30 Compression Members ASD LRFD Fcr / Fa = 1.681 LRFD Fcr = ASD Fa × 1.681   F E KL r a  12 23 2 2  /   F E KL r cr  20171 23 2 2 . /  • 31. 31 Compression Members ASD (ASD C-E2-2) LRFD λc = Maximum of ( λcy , λcz , λe ) KL r K L r K L r KL r y Y y z z z e / , ,                Where KL r E F e e         • 32. 32 Compression Members LRFD Where:   cy y y y y K L r F E    cz z z z y K L r F E  e y e F F  • 33. 33 Compression Members Flexural-Torsional Buckling   F EC K L GJ I I e w x x y z             2 2 10 . • 34. 34 Qs Computation ASD LRFD When 95 195 / / / / / F k b t F k y c y c   Q b t F k s y c   1293 000309 . . ( / ) / When 056 103 . / / . / E F b t E F y y   Q b t F E s y   1415 074 . . ( / ) /   k h t h t k c c    4 05 70 10 0.46 . / / , . if otherwise • 35. 35 Qs Computation Assume E = 29000 ksi ASD LRFD When 95 195 / / / / / F k b t F k y c y c   Q b t F k s y c   1293 000309 . . ( / ) / When 9536 1754 . / / . / F b t F y y   Q b t F s y   1415 0004345 . . ( / ) • 36. 36 Qs Computation ASD LRFD When b t F k y c / / /  195     Q k F b t s c y  26200 2 / / When b t E Fy / . /  103     Q E F b t s y  069 2 . / / • 37. 37 Qs Computation Assume E = 29000 ksi ASD LRFD When b t F k y c / / /  195     Q k F b t s c y  26200 2 / / When b t Fy / . /  1754     Q F b t s y  20010 2 / / • 38. 38 Qa Computation ASD LRFD b t f b t f b e            253 1 44 3 . ( / ) b t E f b t E f b e          191 1 0 34 . . ( / ) Assume ksi E b t f b t f e            29000 32526 1 57 9 , . . ( / ) • 39. 39 Compression Members X Y Z FIXED JOINT -100. o • 40. 40 Compression Members • Member is 15 feet long • Fixed at the bottom of the column and free at the top • Loadings are: • Self weight • 100 kips compression force at the free end • Load combinations based on the ASD and LRFD codes • Steel grade is A992 • Design based on the ASD and LRFD codes • 41. 41 Compression Members ASD W10x49 Actual/Allowable Ratio = 0.941 LRFD W10x54 Actual/Limiting Ratio = 0.944 • 42. 42 Compression Members ASD W10x49 Area = 14.4 in.2 FX = 100.734 kips Ratio = 0.941 LRFD W10x54 Area = 15.8 in.2 FX = 160.967 kips Ratio = 0.944 • 43. 43 Compression Members Load Factor difference between LRFD and ASD 160.967 / 100.734 = 1.598 Equation Factor difference between LRFD and ASD LRFD Fcr = (1.681) × ASD Fa Estimate required cross-sectional area for LRFD LRFD W10x54 Area = 15.8 inch Area for LRFD       14 4 160967 100734 10 1681 10 085 0941 0944 1605 . . . . . . . . . . • 44. 44 Compression Members Code Check based on the ASD9 and use W10x54 FX = 100.806 kips Ratio = 0.845 Load Factor difference between LRFD and ASD 160.967 / 100.806 = 1.597 LRFD W10x54 Ratio = 0.944 LRFD Ratio computed fromASD      0845 160967 100806 10 1681 10 085 0944 . . . . . . . . • 45. 45 Compression Members ASD Example # 1 Live Load = 100 kips W10x49 Actual/Allowable Ratio = 0.941 LRFD Example # 1 Live Load = 100 kips W10x54 Actual/Limiting Ratio = 0.944 Example # 2 Dead Load = 50 kips Live Load = 50 kips W10x49 Actual/Limiting Ratio = 0.921 Code check W10x49 based on the ASD9 W10x49 Actual/Allowable Ratio = 0.941 • 46. 46 Flexural Members • Based on the b/t and h/tw ratios determine the compactness of the cross-section • Classify flexural members as Compact, Noncompact, or Slender • When noncompact section in ASD, allowable stress Fb is computed based on the l/rt ratio. l is the laterally unbraced length of the compression flange. Also, Cb has to be computed • When noncompact or slender section in LRFD, LTB, FLB, and WLB are checked • LTB for noncompact or slender sections is computed using Lb and Cb. Lb is the laterally unbraced length of the compression flange • 47. 47 Flexural Members ASD fb = MZ/SZ ≤ Fb LRFD Mu = MZ ≤ ϕb Mn Where ϕb = 0.9 • 48. 48 Limiting Width-Thickness Ratios for Compression Elements ASD LRFD Assume E = 29000 ksi d t F w y / /  640 b t E Fy / . /  038 h t E F w y / . /  376 b t Fy / /  65 b t Fy / . /  64 7 h t F w y / . /  640 3 • 49. 49 Flexural Members Compact Section ASD (ASD F1-1) Fb = 0.66Fy LRFD (LRFD A-F1-1) ϕb Mn = ϕb Mp = ϕb Fy ZZ ≤ 1.5Fy SZ Where ϕb = 0.9 • 50. 50 Flexural Members Compact Section X Y Z FIXED JOINT -15.00 -15.00 o o FIXED JOINT Braced at 1/3 Points • 51. 51 Flexural Members Compact Section • Member is 12 feet long • Fixed at both ends of the member • Loadings are: • Self weight • 15 kips/ft uniform load • Load combinations based on the ASD and LRFD codes • Steel grade is A992 • Braced at the 1/3 Points • Design based on the ASD and LRFD codes • 52. 52 Flexural Members Compact Section ASD W18x40 Actual/Allowable Ratio = 0.959 LRFD W18x40 Actual/Limiting Ratio = 0.982 • 53. 53 Flexural Members Compact Section ASD W18x40 Sz = 68.4 in.3 MZ = 2165.777 inch-kips Ratio = 0.959 LRFD W18x40 Zz = 78.4 in.3 MZ = 3462.933 inch-kips Ratio = 0.982 • 54. 54 Flexural Members Compact Section Load Factor difference between LRFD and ASD 3462.933 / 2165.777 = 1.5989 Equation Factor difference between LRFD and ASD LRFD = (0.66Sz)(1.5989) / (0.9Zz) × ASD Zz LRFD W18x40 Zz = 78.4 in.3 for LRFD      684 3462 933 2165777 066 09 0959 0982 783 . . . . . . . . • 55. 55 Flexural Members Compact Section Code Check based on the ASD9, Profile W18x40 MZ = 2165.777 inch-kips Ratio = 0.959 Load Factor difference between LRFD and ASD 3462.933 / 2165.777 = 1.5989 LRFD W18x40 Ratio = 0.982 LRFD Ratio computed fromASD      0959 3462 933 2165777 066 09 684 784 0981 . . . . . . . . • 56. 56 Flexural Members Compact Section ASD Example # 1 Live Load = 15 kips/ft W18x40 Actual/Allowable Ratio = 0.959 LRFD Example # 1 Live Load = 15 kips/ft W18x40 Actual/Limiting Ratio = 0.982 Example # 2 Dead Load = 7.5 kips/ft Live Load = 7.5 kips/ft W18x40 Actual/Limiting Ratio = 0.859 Code check W18x40 based on the ASD9 W18x40 Actual/Allowable Ratio = 0.959 • 57. 57 Flexural Members Noncompact Section ASD • Based on b/t, d/tw and h/tw determine if the section is noncompact • Compute Cb • Compute Qs • Based on the l/rt ratio, compute allowable stress Fb • Laterally unbraced length of the compression flange (l) has a direct effect on the equations of the noncompact section • 58. 58 Flexural Members Noncompact Section ASD fb = MZ/SZ ≤ Fb LRFD Mu = MZ ≤ ϕb Mn Where ϕb = 0.9 • 59. 59 Limiting Width-Thickness Ratios for Compression Elements ASD LRFD 65 95 F b t F y y   d t F w y  640 038 083 . / . E F b t E F y L   376 57 . . E F h t E F y w y   h t F w b  760 • 60. 60 Limiting Width-Thickness Ratios for Compression Elements Assume E = 29000 ksi ASD LRFD 65 95 F b t F y y   d t F w y  640 64 7 1413 . / / . / F b t F y L   6403 970 7 . / . / F h t F y w y   h t F w b  760 • 61. 61 Flexural Members Noncompact Section ASD (ASD F1-3) (ASD F1-2) ASD Equations F1-6, F1-7, and F1-8 must to be checked. F F b t F b y f f y           079 0002 2 . .   If minimum or L L b F d A F b c f y f y           76 20000 • 62. 62 Flexural Members Noncompact Section ASD When (ASD F1-6) 102 10 510 10 3 3     C F l r C F b y T b y   F F l r C F F Q b y T b y y s             2 3 1530 10 0 6 2 3 / . • 63. 63 Flexural Members Noncompact Section ASD When (ASD F1-7) l r C F T b y   510 103   F C l r F Q b b T y s    170 10 0 6 3 2 / . • 64. 64 Flexural Members Noncompact Section ASD For any value of l/rT (ASD F1-8) F C ld A F Q b b f y s    12 10 06 3 / . • 65. 65 Flexural Members Noncompact Section LRFD 1. LTB, Lateral-Torsional Buckling 2. FLB, Flange Local Buckling 3. WLB, Web Local Buckling • 66. 66 Flexural Members Noncompact Section LRFD – LTB • Compute Cb • Based on the Lb, compute limiting moment capacity. Lb is the lateral unbraced length of the compression flange, λ = Lb/ry • Lb has a direct effect on the LTB equations for noncompact and slender sections – FLB • Compute limiting moment capacity based on the b/t ratio of the flange, λ = b/t – WLB • Compute limiting moment capacity based on the h/tw ratio of the web, λ = h/tw • 67. 67 Flexural Members Noncompact Section LRFD LTB (Table A-F1.1) For λp < λ ≤ λr (LRFD A-F1-2) Where: Mp = Fy Zz ≤ 1.5Fy Sz Mr = FLSz FL = Smaller of (Fyf − Fr) or Fyw λ = Lb/ry λp =   M C M M M M n b p p r p r p p                           176 . E Fyf • 68. 68 Flexural Members Noncompact Section LRFD LTB (Table A-F1.1) Where: λr = X1 = X2 = X F X F L L 1 2 2 1 1    S EGJA z 2 4 2 C I S GJ w y z       • 69. 69 Flexural Members Noncompact Section LRFD FLB (Table A-F1.1) For λp < λ ≤ λr (LRFD A-F1-3) Where: Mp = Fy Zz ≤ 1.5Fy Sz Mr = FLSz FL = Smaller of (Fyf − Fr) or Fyw λ = b/t λp = λr =   M M M M n p p r p r p                          038 . E Fy 083 . E FL • 70. 70 Flexural Members Noncompact Section LRFD WLB (Table A-F1.1) For λp < λ ≤ λr (LRFD A-F1-3) Where: Mp = Fy Zz ≤ 1.5Fy Sz Mr = Re Fy Sz Re = 1.0 for non-hybrid girder   M M M M n p p r p r p                          • 71. 71 Flexural Members Noncompact Section LRFD WLB (Table A-F1.1) λ = h/tw λp = λr = 376 . E Fy 57 . E Fy • 72. 72 Flexural Members Noncompact Section ASD LRFD     C M M M M M M M M M C b b       175 105 03 2 3 10 1 2 1 2 2 1 2 1 2 . . . . , . max If between and C M M M M M M M M b A B C A B C         125 25 3 4 3 . . max max absolute value of moment at quarter point absolute value of moment at centerline absolute value of moment at three quarter point • 73. 73 Flexural Members Noncompact Section X Y Z Roller -12.00 -12.00 o o Pin • 74. 74 Flexural Members Noncompact Section • Member is 12 feet long • Pin at the start of the member • Roller at the end of the member • Cross-section is W12x65 • Loadings are: • Self weight • 12 kips/ft uniform load • Load combinations based on the ASD and LRFD codes • Steel grade is A992 • Check code based on the ASD and LRFD codes • 75. 75 Flexural Members Noncompact Section ASD W12x65 Cb = 1.0 Actual/Allowable Ratio = 0.988 LRFD W12x65 Cb = 1.136 Actual/Limiting Ratio = 0.971 Code check is controlled by FLB. Cb = 1.0 Actual/Limiting Ratio = 0.973 • 76. 76 Flexural Members Noncompact Section ASD Example # 1 Live Load = 12 kips/ft W12x65 Actual/Allowable Ratio = 0.988 LRFD Example # 1 Live Load = 12 kips/ft W12x65 Actual/Limiting Ratio = 0.971 Example # 2 Dead Load = 6 kips/ft Live Load = 6 kips/ft W12x65 Actual/Limiting Ratio = 0.85 Code check W12x65 based on the ASD9 W12x65 Actual/Allowable Ratio = 0.988 • 77. 77 Design for Shear ASD fv = FY/Aw ≤ Fv = 0.4Fy (ASD F4-1) LRFD Vu = FY ≤ ϕvVn = ϕv0.6Fyw Aw (LRFD F2-1) Where ϕv = 0.9 h t F w y /  380 h t E F w yw / . /  2 45 • 78. 78 Design for Shear Assume E = 29000 ksi ASD fv = FY/Aw ≤ Fv = 0.4Fy (ASD F4-1) LRFD Vu = FY ≤ ϕvVn = ϕv0.6Fyw Aw (LRFD F2-1) Where ϕv = 0.9 h t F w y /  380 h t F w yw / . /  417 2 • 79. 79 Design for Shear ASD fv = FY/Ay ≤ (ASD F4-2) LRFD Vu = FY ≤ ϕvVn = ϕv (LRFD F2-2) Where ϕv = 0.9 h t F w y /  380 2 45 307 . / / . / E F h t E F yw w yw     F F C F v y v y   2 89 0 4 . . 0 6 2 45 . . / / F A E F h t yw w yw w         • 80. 80 Design for Shear LRFD Vu = FY ≤ ϕvVn = ϕv (LRFD F2-3) Where ϕv = 0.9 307 260 . / / E F h t yw w     A E h t w w 452 2 . /         • 81. 81 Design for Shear X Y Z FIXED JOINT -15.00 -15.00 o o FIXED JOINT Braced at 1/3 Points • 82. 82 Design for Shear • Same as example # 3 which is used for design of flexural member with compact section • Member is 12 feet long • Fixed at both ends of the member • Loadings are: • Self weight • 15 kips/ft uniform load • Load combinations based on the ASD and LRFD codes • Steel grade is A992 • Braced at the 1/3 Points • Design based on the ASD and LRFD codes • 83. 83 Design for Shear ASD (Check shear at the end of the member, equation “F4-1 Y”) W18x40 Actual/Allowable Ratio = 0.8 LRFD (Check shear at the end of the member, equation “A-F2-1 Y”) W18x40 Actual/Limiting Ratio = 0.948 • 84. 84 Design for Shear ASD W18x40 Ay = 5.638 in.2 FY = 90.241 kips Ratio = 0.8 LRFD W18x40 Ay = 5.638 in.2 FY = 144.289 kips Ratio = 0.948 • 85. 85 Design for Shear Code Check based on the ASD9, Profile W18x40 FY = 90.241 kips Ratio = 0.8 Load Factor difference between LRFD and ASD 144.289 / 90.241 = 1.5989 Equation Factor difference between LRFD and ASD LRFD = (0.4)(1.5989) /(0.6)(0.9) × ASD LRFD W18x40 Ratio = 0.948 LRFD Ratio computed fromASD      08 144 289 90241 04 06 10 09 0948 . . . . . . . . • 86. 86 Design for Shear ASD Example # 1 Live Load = 15 kips/ft W18x40 Actual/Allowable Ratio = 0.8 LRFD Example # 1 Live Load = 15 kips/ft W18x40 Actual/Limiting Ratio = 0.948 Example # 2 Dead Load = 7.5 kips/ft Live Load = 7.5 kips/ft W18x40 Actual/Limiting Ratio = 0.83 Code check W18x40 based on the ASD9 W18x40 Actual/Allowable Ratio = 0.8 • 87. 87 Combined Forces ASD fa /Fa > 0.15 (ASD H1-1) (ASD H1-2) LRFD Pu /ϕPn ≥ 0.2 (LRFD H1-1a) f F C f f F F C f f F a a my by a ey by mz bz a ez                    1 1 10 . f F f F f F a y by by bz bz 06 10 . .    P P M M M M u n uy b ny uz b nz               8 9 10 . • 88. 88 Combined Forces ASD fa /Fa ≤ 0.15 (ASD H1-1) LRFD Pu /ϕPn < 0.2 (LRFD H1-1a) f F f F f F a a by by bz bz    10 . P P M M M M u n uy b ny uz b nz 2 10               . • 89. 89 Combined Forces X Y Z • 90. 90 Combined Forces • 3D Simple Frame • 3 Bays in X direction 3 @ 15 ft • 2 Bays in Z direction 2 @ 30 ft • 2 Floors in Y direction 2 @ 15 ft • Loadings • Self weight of the Steel • Self weight of the Slab 62.5 psf • Other dead loads 15.0 psf • Live load on second floor 50.0 psf • Live load on roof 20.0 psf • Wind load in the X direction 20.0 psf • Wind load in the Z direction 20.0 psf • 91. 91 Combined Forces ASD <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < Active Units Weight Unit = KIP Length Unit = INCH > < > < Steel Take Off Itemize Based on the PROFILE > < Total Length, Volume, Weight, and Number of Members > < > < Profile Names Total Length Total Volume Total Weight # of Members > < W10x33 2.1600E+03 2.0974E+04 5.9418E+00 12 > < W12x58 1.4400E+03 2.4480E+04 6.9352E+00 4 > < W12x65 1.4400E+03 2.7504E+04 7.7919E+00 4 > < W12x72 2.1600E+03 4.5576E+04 1.2912E+01 12 > < W6x9 3.2400E+03 8.6832E+03 2.4600E+00 18 > < W8x40 1.4400E+03 1.6848E+04 4.7730E+00 4 > < W8x48 1.4400E+03 2.0304E+04 5.7521E+00 4 > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < ACTIVE UNITS WEIGHT KIP LENGTH INCH > < > < TOTAL LENGTH, WEIGHT AND VOLUME FOR SPECIFIED MEMBERS > < > < LENGTH = 1.3320E+04 WEIGHT = 4.6566E+01 VOLUME = 1.6437E+05 > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> • 92. 92 Combined Forces LRFD <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < Active Units Weight Unit = KIP Length Unit = INCH > < > < Steel Take Off Itemize Based on the PROFILE > < Total Length, Volume, Weight, and Number of Members > < > < Profile Names Total Length Total Volume Total Weight # of Members > < W10x33 3.6000E+03 3.4956E+04 9.9030E+00 16 > < W10x39 1.4400E+03 1.6560E+04 4.6914E+00 4 > < W10x49 7.2000E+02 1.0368E+04 2.9373E+00 4 > < W12x45 1.4400E+03 1.9008E+04 5.3850E+00 4 > < W6x9 3.2400E+03 8.6832E+03 2.4600E+00 18 > < W8x31 1.4400E+03 1.3147E+04 3.7246E+00 4 > < W8x40 1.4400E+03 1.6848E+04 4.7730E+00 8 > < > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < ACTIVE UNITS WEIGHT KIP LENGTH INCH > < > < TOTAL LENGTH, WEIGHT AND VOLUME FOR SPECIFIED MEMBERS > < > < LENGTH = 1.3320E+04 WEIGHT = 3.3874E+01 VOLUME = 1.1957E+05 > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> • 93. 93 Combined Forces ASD WEIGHT = 46.566 kips LRFD WEIGHT = 33.874 kips • 94. 94 Deflection Design ASD <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < Active Units Weight Unit = KIP Length Unit = INCH > < > < Steel Take Off Itemize Based on the PROFILE > < Total Length, Volume, Weight, and Number of Members > < > < Profile Names Total Length Total Volume Total Weight # of Members > < W10x33 2.1600E+03 2.0974E+04 5.9418E+00 12 > < W12x58 1.4400E+03 2.4480E+04 6.9352E+00 4 > < W12x65 1.4400E+03 2.7504E+04 7.7919E+00 4 > < W12x72 2.1600E+03 4.5576E+04 1.2912E+01 12 > < W14x43 1.4400E+03 1.8144E+04 5.1402E+00 4 > < W14x48 1.4400E+03 2.0304E+04 5.7521E+00 4 > < W6x9 3.2400E+03 8.6832E+03 2.4600E+00 18 > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < ACTIVE UNITS WEIGHT KIP LENGTH INCH > < > < TOTAL LENGTH, WEIGHT AND VOLUME FOR SPECIFIED MEMBERS > < > < LENGTH = 1.3320E+04 WEIGHT = 4.6933E+01 VOLUME = 1.6566E+05 > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> • 95. 95 Deflection Design LRFD <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < Active Units Weight Unit = KIP Length Unit = INCH > < > < Steel Take Off Itemize Based on the PROFILE > < Total Length, Volume, Weight, and Number of Members > < > < Profile Names Total Length Total Volume Total Weight # of Members > < W10x33 2.1600E+03 2.0974E+04 5.9418E+00 12 > < W10x49 1.4400E+03 2.0736E+04 5.8745E+00 8 > < W10x54 7.2000E+02 1.1376E+04 3.2228E+00 4 > < W12x40 1.4400E+03 1.6992E+04 4.8138E+00 4 > < W14x43 2.8800E+03 3.6288E+04 1.0280E+01 8 > < W14x48 1.4400E+03 2.0304E+04 5.7521E+00 4 > < W6x9 3.2400E+03 8.6832E+03 2.4600E+00 18 > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> < ACTIVE UNITS WEIGHT KIP LENGTH INCH > < > < TOTAL LENGTH, WEIGHT AND VOLUME FOR SPECIFIED MEMBERS > < > < LENGTH = 1.3320E+04 WEIGHT = 3.8345E+01 VOLUME = 1.3535E+05 > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> • 96. 96 Deflection Design ASD WEIGHT = 46.933 kips LRFD WEIGHT = 38.345 kips • 97. 97 Compare Design without and with Deflection Design ASD Without Deflection Design WEIGHT = 46.566 kips With Deflection Design WEIGHT = 46.933 kips LRFD Without Deflection Design WEIGHT = 33.874 kips With Deflection Design WEIGHT = 38.345 kips • 98. 98 Design same example based on Cb = 1.0 Code and deflection design with Cb = 1.0 ASD Compute Cb WEIGHT = 46.933 kips Specify Cb = 1.0 WEIGHT = 51.752 kips LRFD Compute Cb WEIGHT = 38.345 kips Specify Cb = 1.0 WEIGHT = 48.421 kips • 99. 99 Design Similar example based on Cb = 1.0 and LL×5 • Code and deflection design with Cb = 1.0 and increase the live load by a factor of 5. • Area loads are distributed using two way option instead of one way • Also change the 2 bays in the Z direction from 30 ft to 15 ft. ASD WEIGHT = 25.677 kips LRFD WEIGHT = 22.636 kips Difference = 3.041 kips • 100. 100 Design Similar example based on Cb = 1.0 and LL×10 • Code and deflection design with Cb = 1.0 and increase the live load by a factor of 10. • Area loads are distributed using two way option instead of one way • Also change the 2 bays in the Z direction from 30 ft to 15 ft. ASD WEIGHT = 31.022 kips LRFD WEIGHT = 29.051 kips Difference = 1.971 kips • 101. 101 Stiffness Analysis versus Nonlinear Analysis • Stiffness Analysis – Load Combinations or Form Loads can be used. • Nonlinear Analysis – Form Loads must be used. Load Combinations are not valid. • Nonlinear Analysis – Specify type of Nonlinearity. • Nonlinear Analysis – Specify Maximum Number of Cycles. • Nonlinear Analysis – Specify Convergence Tolerance. • 102. 102 Nonlinear Analysis Commands • NONLINEAR EFFECT • TENSION ONLY • COMPRESSION ONLY • GEOMETRY AXIAL • MAXIMUM NUMBER OF CYCLES • CONVERGENCE TOLERANCE • NONLINEAR ANALYSIS • 103. 103 Design using Nonlinear Analysis Input File # 1 1. Geometry, Material Type, Properties, 2. Loading ‘SW’, ‘LL’, and ‘WL’ 3. FORM LOAD ‘A’ FROM ‘SW’ 1.4 4. FORM LOAD ‘B’ FROM ‘SW’ 1.2 ‘LL’ 1.6 5. FORM LOAD ‘C’ FROM ‘SW’ 1.2 ‘WL’ 1.6 ‘LL’ 0.5 6. FORM LOAD ‘D’ FROM ‘SW’ 0.9 ‘WL’ 1.6 7. DEFINE PHYSICAL MEMBERS 8. PARAMETERS 9. MEMBER CONSTRAINTS 10. LOAD LIST ‘A’ ‘B’ ‘C’ ‘D’$ Activate only the FORM loads 11. STIFFNESS ANALYSIS 12. SAVE
• 104. 104 Design using Nonlinear Analysis Input File # 2 1. RESTORE 2. LOAD LIST ‘A’ ‘B’ ‘C’ ‘D’ 3. SELECT MEMBERS 4. SMOOTH PHYSICAL MEMBERS 5. DELETE LOADINGS ‘A’ ‘B’ ‘C’ ‘D’ 6. SELF WEIGHT LOADING RECOMPUTE 7. FORM LOAD ‘A’ FROM ‘SW’ 1.4 8. FORM LOAD ‘B’ FROM ‘SW’ 1.2 ‘LL’ 1.6 9. FORM LOAD ‘C’ FROM ‘SW’ 1.2 ‘WL’ 1.6 ‘LL’ 0.5 10. FORM LOAD ‘D’ FROM ‘SW’ 0.9 ‘WL’ 1.6 11. LOAD LIST ‘A’ ‘B’ ‘C’ ‘D’ 12. STIFFNESS ANALYSIS 13. CHECK MEMBERS 14. STEEL TAKE OFF 15. SAVE
• 105. 105 Design using Nonlinear Analysis Input File # 3 1. RESTORE 2. LOAD LIST ‘A’ ‘B’ ‘C’ ‘D’ 3. SELECT MEMBERS 4. SMOOTH PHYSICAL MEMBERS 5. DELETE LOADINGS ‘A’ ‘B’ ‘C’ ‘D’ 6. SELF WEIGHT LOADING RECOMPUTE 7. FORM LOAD ‘A’ FROM ‘SW’ 1.4 8. FORM LOAD ‘B’ FROM ‘SW’ 1.2 ‘LL’ 1.6 9. FORM LOAD ‘C’ FROM ‘SW’ 1.2 ‘WL’ 1.6 ‘LL’ 0.5 10. FORM LOAD ‘D’ FROM ‘SW’ 0.9 ‘WL’ 1.6
• 106. 106 Design using Nonlinear Analysis Input File # 3 (continue) 1. NONLINEAR EFFECT 2. GEOMETRY ALL MEMBERS 3. MAXIMUM NUMBER OF CYCLES 4. CONVERGENCE TOLERANCE DISPLACEMENT 5. LOAD LIST ‘A’ ‘B’ ‘C’ ‘D’ 6. NONLINEAR ANALYSIS 7. CHECK MEMBERS 8. STEEL TAKE OFF 9. SAVE
• 107. 107 General Comparison between AISC LRFD and ASD Questions

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