27 publications from this institution
This study was aimed to propose appropriate failure criteria for bolt fracture prediction in shear when threads are excluded from the shear plane. In this regard, the finite element methods for such prediction were divided into two main categories and for each category the available methods were discussed. Then, using finite element modeling and available experimental results of previous researchers, three methods here referred to as MTD1, MTD2 and MTD3 were proposed. MTD1 and MTD2 were based on the monitoring of the level of stress and strain at the critical elements of the bolt shank, while MTD3 was based on the extended finite element method and consisted of two main steps including defining crack initiation and crack evolution. Analytical results indicated that MTD1 and MTD3 were reasonably acceptable for prediction of the bolt fracture in shear with negligible amount of error. Method MTD1 is a suitable method when a progressive collapse analysis is not of interest and only the capacity of the system at the onset of the first bolt fracture is required. However, MTD3 can be used in a progressive collapse analysis where the amount of reduction in a system strength by fracturing of each component is of interest. However, in comparison to MTD1, MTD3 is remarkably time consuming.
Examination of Northridge fractured connections has revealed that the materials and the manufacturing parameters associated with the fracture behaviour of these connections are random. Hence, the fracture resistance and ductility of these connections are also random. In this study, most of the parameters which are believed to contribute to the fracture behaviour of Northridge connections are analysed with respect to previous research in the field. Then one of the pre-tested post-Northridge connections is modelled, using finite-element analysis and the results are used as typical examples to illustrate the effect of each parameter on the behaviour of these connections. Experimental fracture moment and ductility data of a set of previously conducted tests on the pre-and post-Northridge design are used to obtain suitable cumulative distribution functions of the normalised fracture moment and plastic rotation of these types of connections. Statistical results show that, despite all the modifications applied to the pre-Northridge connections, the magnitude of the minimum plastic rotation and the strength are still less than what is required by the seismic codes. Therefore, both pre- and post-Northridge connections do not have enough strength and ductility and consequently they are not reliable and should be further modified when used in seismic regions.
