Bearing and tearout of austenitic and duplex stainless steel bolted connections

Due to the unique material characteristics of stainless steel, the bearing and tearout behaviour of stainless steel bolted connections can be different from that of carbon steel bolted connections. Such difference has been gradually recognised in recent design provisions for stainless steel structures. However, it is noteworthy that the existing design methods were mainly developed for austenitic and ferritic stainless steel bolted connections. Their applicability to duplex stainless steel bolted connections is questionable. Moreover, comparing to the bearing failure of stainless steel connections, less attention has been paid to the tearout failure, as well as the combined bearing and tearout failure in multi-bolt connections. To fill these gaps, an experimental and numerical study is carried out on the bearing/tearout behaviour and design of stainless steel bolted connections. The experimental programme includes 22 connection specimens with either single-bolt or multi-bolt configurations, made of austenitic or duplex stainless steel. The experimental tests are supplemented by a comprehensive numerical parametric study with more than 200 individual models, performed based on a validated finite element modelling technique. The obtained test and numerical results are used to assess the effects of different design parameters, as well as the applicability of existing design methods. It is concluded that the ultimate bearing/tearout resistances of austenitic and duplex connections are not simply proportionate to the ultimate strengths of the two materials. Given the same geometric design, the bearing resistance of a duplex connection is considerably higher than that of an austenitic connection, despite the similar ultimate strengths of the two materials. This difference in bearing performance is attributed to the different strain-hardening characteristics of austenitic and duplex materials, as well as the premature shear cracking in austenitic connections that leads to insufficiently developed strain-hardening. In comparison, the tearout resistances of austenitic and duplex connections with the same geometry are much closer, since the smaller end distance leads to more uniform deformations and more completely developed strain-hardening. Moreover, the combined bearing and tearout resistance of multi-bolt connections is found to be lower than the sum of the respective resistances of individual bolts. Finally, an updated design method is proposed that can accurately predict the bearing/tearout resistance of both austenitic and duplex stainless steel bolted connections. Proper partial factors are determined for the proposed method based on a reliability analysis.