This paper concerns the applicability of the Weibull stress method to predict a brittle fracture at beam-to-diaphragm connections based on experimental and analytical results from four-point shear tests under mixed-mode loading conditions and a beam-to-diaphragm specimen that simulates a beam-to-diaphragm connection.
The influence factor on RI, which is the mixing ratio of modes, was examined from the four-point shear tests. From the beam-to-diaphragm specimens, a correlation was found between the RI and the prediction accuracy derived from the experimental and analytical results.
The 1994 Northridge earthquake and the 1995 Kobe earthquake caused damage in the steel moment frames due to brittle fractures. A brittle fracture is a failure in which a crack propagates instantaneously across the entire cross-section of members and is fatal to the structure, so it must be avoided. For example, singularities that are subjected to the toes of a cope hole, due to the difference in geometry, can cause a fracture. At singularities, ductile cracks are initiated at the point of strain concentration, causing the crack to propagate and potentially leading to the failure of the structure.
Fracture parameters for evaluating brittle fracture of structural members include stress intensity factor K, J-integral value, crack tip opening displacement (CTOD), and energy release rate g. However, these do not apply to cases of progressive plastic deformation, and plastic constraints are different between material specimens used in experiments and actual structural defects (Iwashita et al. 2016, Toyoda et al. 1993).
In the local approach, the Weibull stress was proposed by Beremin as a new fracture evaluation parameter (Beremin et al., 1983). The critical value based on the Weibull stress is expected to be independent of specimen size, or crack length. Previous studies have investigated the applicability of the Weibull stress to building structures and have shown that prediction by the Weibull stress can improve the accuracy of brittle fracture prediction (Azuma et al. 2016). The Weibull stress can be applied to brittle fracture evaluation as a parameter that can be used after large-scale yielding. However, the Weibull stress assumes that Mode I act dominantly on the crack (Riesch-Opperman et al. 2002). Therefore, the Weibull stress does not consider the effect of Mode II and Mode III. Recent studies have shown that the Weibull stress approach cannot directly apply to connections under mixed-mode loading (Shimizu et al. 2014). A fracture evaluation method is needed regarding the effects of mixed modes.