Prediction model for preloaded injected bolts in double-lapped connections

Preloaded and/or injected bolted connections are commonly used in steel bridges in The Netherlands. The injection of bolts became a good alternative for replacing riveted connections because the injected resin in the bolt-hole clearance increases the slip resistance of the connection. In the design model, according to the standard EN1993-1-8:2011 (1), it is assumed that the resistance of a preloaded and injected bolted connection is equal to the sum of the two separate resistances from preloading and injection. This research aims to check the above statement and thus investigate the resistance of a “slip-critical” double-lapped joint, including preloading and/or injection. The conclusion is based on experimental and numerical study, addressing three connection variations. In addition, the Eurocode approach of determining the short-term resistance is considered for two different preloading levels. Each experiment is based on this short-term testing method that complies with the described method of EN1090-2 (2). The numerical analysis is validated by the experimental results and then used to gain insight into the behaviour of the connection. Based on these results, it can not be concluded that it is safe to assume that the resistance of a preloaded and injected bolted connection is equal to the sum of the separate resistances obtained from preloading and injection. However, qualification of the conclusion depends on a criterion for measuring relative displacements at specific locations which is addressed in this paper.