Assessment of Reliability Levels and Adjustment of Load-resistance Factors Using Optimization for Gravitational Loads-governed Limit States of the AASHTO LRFD Bridge Design Specifications

• Published in: KSCE journal of civil engineering 2018, 22(9), , pp.3462-3472
• Main Authors: Lee, Hae Sung, Bae, Changhoon, Kim, Ji Hyeon
• Format: Article
• Language: English
• Subjects: Approximation; Bridge design; Bridge loads; Bridges; Civil Engineering; Composition; Dead loads; Design; Design specifications; Engineering; Geotechnical Engineering & Applied Earth Sciences; Gravitation; Gravity; Industrial Pollution Prevention; Limit state design; Limit states; Live loads; Load; Load resistance; Loads (forces); Mathematical analysis; Objective function; Optimization; Prestressed concrete; Reinforced concrete; Reinforcing steels; Reliability; Reliability analysis; Reliability aspects; Resistance factors; Specifications; Static loads; Steel; Structural Engineering; Yields; 토목공학
• ISSN: 1226-7988; 1976-3808
• DOI: 10.1007/s12205-017-0500-6

This paper presents the reliability levels provided by the load-resistance factors of the AASHTO LRFD Bridge Design Specifications for the Strength Limit State-I and -IV, and an optimization scheme for adjusting the load-resistance factors of the specifications. It is shown that the load-resistance factors of the specifications result in lower reliability indices than the target reliability index and widely varying reliability indices with the load composition for reinforced concrete, steel and pre-stressed concrete members. An optimization scheme is proposed to obtain a new set of the load-resistance factors that yield more uniform reliability levels and better approximation to the target reliability index in a wide range of load compositions. The objective function of the proposed optimization scheme is defined as the L 2 -norm of the error between the target and calculated reliability indices by load-resistance factors over a given interval of load composition. The results of the optimization show that the dead load factor for structural components should be increased by 0.1 for the Strength Limit State-I, and that the vehicular live load should be included in the Strength Limit State-IV. The use of exact figures up to the second decimal point is recommended for the resistance factors. A unified limit state for gravitational loads is proposed to replace the two limit states with a single limit state.