Load and Resistance Factor Design (LRFD) （负载和阻力系数设计(LRFD)）.pdfVIP

53:134 Structural Design II Load and Resistance Factor Design (LRFD) Specifications and Building Codes: • Structural steel design of buildings in the US is principally based on the specifications of the American Institute of Steel Construction (AISC). -- Current Specifications: 1989 ASD and 1999 LRFD. -- 1989 AISC Specification for Structural Steel Buildings – Allowable Stress Design and Plastic Design. (ASD) -- 1999 AISC Load and Resistance Factor Design Specification for Structural Steel Buildings. (LRFD) -- LRFD Manual: Manual of Steel Construction, Load and Resistance Factor Design, 3rd Edition, 2001. -- Manual of Steel Construction, 13th Edition, 2005 (combined ASD and LRFD provisions). • Steel bridge design is in accordance with specifications of AASHTO: -- American Association of State Highway and Transportation Officials • Railroad bridge design is in accordance with specifications of AREA: -- American Railway Engineering Association. Design Philosophies: 1. Similar toplastic design, LRFD focuses on “limit state design”, where strength or failure condition is considered. 2. Factored load ≤ factored strength, or ∑ (Loads × load factors) ≤ resistance × resistance factors ( ) 3. In general, load factors 1 amplify loads, while resistance ( ) factors 1 reduce strength. Structural Safety Requirement: φ Resistance factor Rn The nominal resistance, or strength, of the component under consideration Qi A load effect (a force or a moment) J.S. Arora/Q. Wang 1 LoadandResistFactor.doc 53:134 Structural Design II γi A load factor φRn is the called the design strength ∑γ Q is the summation of all the load effects i i