Fracture Assessment Procedure for Steel Structures Subjected to Large Cyclic and Dynamic Strain – Based on WES TR 2808

Abstract

With a lesson leaned from the Kobe Great Earthquake, an engineering method, WES TR 2808, has been developed in Japan for evaluating the structural integrity under the seismic condition. This paper presents a main story of WES TR 2808, which is characterized by two key ideas. One is a reference temperature concept for fracture toughness evaluation. The material fracture toughness under the seismic condition is replaced by the static fracture toughness without prestrain at a reference temperature of T − ΔTPD, where T and ΔTPD are the service temperature and the temperature shift of fracture toughness by prestraining and dynamic loading, respectively. WES TR 2808 gives ΔTPD as a function of the elevation of flow stress in the seismic condition. Another idea is a correction of constraint loss in structural components. A large amount of plastic deformation causes a loss of constraint in structural components, which leads to a significant difference in the fracture driving force of the components and fracture toughness specimen. In WES TR 2808, the CTOD ratio β = δ3P.Equiv/δStruc was defined on the basis of the Weibull stress criterion, where δStruc is the CTOD of the structural component and δ3P.Equiv is an equivalent CTOD of the fracture toughness specimen at which the toughness specimen presents a compatible Weibull stress with the structural component. The CTOD ratio β is apparently less than 1 in a large-scale yielding condition, and roughly 0.4 for the wide plate component with a surface crack. It was shown that WES TR 2808 is applicable to the fracture performance assessment of column-to-beam connections subjected to large cyclic and dynamic strain. The discussion was given on the engineering judgement in WES TR 2808, which was adopted to make the procedures as simple as possible.