Tài liệu General Comparison between AISC LRFD and ASD doc

General Comparison between AISC LRFD and ASD Hamid Zand GT STRUDL Users Group Las Vegas, Nevada June 22-25, 2005 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 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 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 ASD Load Combinations • 1.0D + 1.0L • 0.75D + 0.75L + 0.75W • 0.75D + 0.75L + 0.75E D L W E = = = = dead load live load wind load earthquake load 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 1.0D + 1.0L 1.0D + 1.0L + 1.0W 1.0D + 1.0L + 1.0E • PARAMETER $ ALSTRINC based on the % increase • ALSTRINC 33.333 LOADINGS 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 L W E = = = = dead load live load wind load earthquake load Deflection Load Combinations for ASD and LRFD • 1.0D + 1.0L • 1.0D + 1.0L + 1.0W • 1.0D + 1.0L + 1.0E D L W E = = = = dead load live load wind load earthquake load 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 ASTM Steel Grade • Comparison is between Table 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 10 ... 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 ASD and. . .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 AISC. .. the AISC allowable stress values • LRFD = actual forces and moments are compared to the AISC limiting forces and moments capacity ASTM Steel Grade • Comparison is between Table of the AISC ASD