Fatigue behavior of resin and steel reinforced resin used in IBCs

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Injection Bolts have been preferred for several reasons over other alternatives for the rehabilitation of old riveted steel bridges since 1970’s. More recently they have been used to obtain slip critical shear connections in new structures such as new bridges, large roofs, storm barriers and other structures exposed to cyclic loading. In addition, they are tested as a feasible alternative to traditional shear connectors in steel-concrete composite flooring systems, in combination with oversized holes in the flange of steel girder to allow reusability. On the grounds of this research a novel injection material was developed at T.U Delft, namely steel reinforced resin as an alternative to conventional resin allowed in the Netherlands for structural applications without compromising stiffness of connection. Due to limited research on fatigue of resins used in structural applications, in this study an initial attempt to investigate the cyclic behaviour of conventional and steel reinforced resin subjected to uniaxial compressive cyclic bearing stress, in confined conditions is performed. First, for this objective an experimental program using a tailor-made test setup was carried out, and the fatigue response in terms of slip over number of cycles for resin and steel reinforced resin in oversized holes of 6mm and 10mm was obtained. With this specimen configuration, is intended to reproduce as possible the stress state of double lap shear connection without endanger the fatigue cracking of steel parts. Frequency, stress ratio and other testing parameters that can influence the results have been chosen based on relative literature and assembly of setup. Three stress ranges used, with the maximum related to the recommended long term bearing stress for conventional resin, while the failure criterion was set at 0.3mm slip which is related to this long term bearing strength at the end of working life. Secondly, a numerical model of test set-up to investigate the static and quasi-static behaviour of specimens was developed and validated by the quasi static experimental results of initial stiffness of connection. Finally, through statistical treatment of test results fitted curves obtained, and characteristic curves with 95% probability of survival are proposed for both resin types and hole clearances based on probabilistic model of ASTM standard and probabilistic model proposed by Schneider and Maddox, using Student’s t distribution. On the basis of experimental results, large scattering was observed for both type of resins, and more prominent for the larger hole clearance and higher stress range. The reasons for this scatter are discussed and recommendations for future improvement of set-up are proposed. Due to scatter the results could not fully support the expectations that fatigue behaviour of steel reinforced resin is superior to that of conventional, as it is the case in static and creep behaviour. From a selection of specimens with limited scatter in 6mm oversized holes, a trend that connections with steel reinforced resin lead to less slip due to cyclic loads after 500.000 cycles was observed. From the numerical research on static models of specimens it was verified that the bearing stress state of resin layer is almost identical to that of the double lap shear connection of EN 1090-2 indicating a similar stress transfer mechanism. From the statistical evaluation of test data with ASTM probabilistic model the use of steel reinforced resin leads to higher fatigue endurance related to conventional resin in 10mm oversized hole, while the fatigue life of specimens with conventional resin decreased with larger hole clearance namely from 6 to 10mm.