Effects of material toughness and plate thickness on brittle fracture of steel members

Extensive research efforts have been devoted to clarifying the causes and their physical relationships of the brittle fracture of steel structures which were observed at the disasters of 1994 Northridge Earthquake and 1995 Hyogoken-Nanbu Earthquake. This paper reports the results of a full-scale fracture test to identify the effects of material toughness and plate thickness on the plastic deformation capacity governed by brittle fracture. Two innovative methods, which are called the artificial hot spot method and multiple critical point method, were employed for the experiment in order to simulate brittle fracture in steel members undergoing plastic deformation and to obtain reliable data from a small number of specimens. The artificial hot spot method was found with absolutely certainty to originate brittle fracture at an intended location, and the multiple critical point method provided a satisfactory consistency in the statistical estimation of prefracture ductility. The test results demonstrated that material toughness in terms of Charpy impact energy has a substantial influence on the ductility governed by brittle fracture, while the plate thickness is of less importance within the test range greater than an inch. It is suggested from this fact that Charpy values of structural steels, which are not specified or specified only to be greater than a single low level in current material standards, should be classified into multiple grades in accordance with the necessary performance levels of ductility required in earthquake resistant design.