Influence of strain-hardening on the load-carrying behaviour of multi-bolt bearing type connections

This paper is concerned with the load-carrying behaviour of multi-bolt connections as a function of the underlying material grades, and accordingly studies the hole-bearing behaviour and the appropriate definition of resistance values for design on the basis of a series of experimental tests, covering diverse geometries and materials. The primary focus is on implementing a methodology to precisely identify the point on the loaddeformation curve where deformations shift from "acceptable" to "excessive". The developed methodology, termed INC1 in the paper, captures the corresponding resistance value at this critical juncture by differentiating between the different hardening characteristics of the various steel grades. More specifically, building on the authors' previous work for single-bolt connections, this paper extends the proposed approach to multi-bolt connections. In order to achieve this, a meticulous assessment of load distribution among individual bolts is conducted by closely monitoring bolt deformations during testing, refining the suggested design distribution accordingly. An accuracy study shows that the developed proposal has the potential to improve prediction accuracy and mechanical consistency of design predictions compared to the resistance model outlined in prEN1993-1-8. The incorporation of the f(u)/f(y) ratio into the proposed hole-bearing verification framework optimizes material utilization and contributes to resource conservation.