A large part of the bridges in the Netherlands have been built in the 50s and 60s of the last century. These bridges have to be renovated because they are reaching the end of their designed lifespan and they are not designed for the more and heavier current traffic This is especially relevant for the steel bridges because this could lead to problems due to fatigue. A common method for renovating the bridge is by using a FRP bridge deck, which has a high strength to weight ratio and have good fatigue resistance. Since this is a relatively new method, a lot of research has been done for connection methods between the FRP bridge deck and the steel superstructure of the bridge. Two example of these connectors are the Lindapter Hollo bolted connector and the iSRR connector, which are both blind-bolted connectors. The iSRR connector uses steel reinforced resin to create an efficient, slip-resistant connection. This a relatively new connection method, therefore there is not a lot of knowledge about the long-term behavior of this connector. To investigate this, the iSRR connector has been installed alongside the Lindapter Hollo bolted connector at the Ulsderbrug in Groningen. These preloaded connectors are designed in such a manner that they only transfer tensile forces. These bolted connectors are monitored to compare both the short-term and long-term behavior. In addition to the monitoring a finite element model is made, to investigate to predictability of the bolt forces in the iSRR connector.
From the monitoring can be concluded that the iSRR connector shows less loss of preload over a period of 250 days, retaining 50.6% of the original preloading force. Compared to 42.7% for the Lindapter Hollo bolted connector. These losses of preload are significantly impacted by a rubber interlayer that is present between the clamping plate and the FRP bridge deck. Due to the relaxation of this rubber layer, only 77.5% of the applied preloading force is present one day after applying. The force variations, of up to 0.12 kN, due to traffic loads are relatively small and similar for both connector types. These forces are also affected by the rubber interlayer. Imperfections at these layers cause one bolt to experience force cycles up to 1.2 kN, which are ten times higher than for the other bolts. The influence of the stiffness of the rubber interlayer has been investigated using the finite element model. From this model can concluded that a lower stiffness of this layer leads to higher forces in the connectors. This model has been used to investigate the extrapolate the bolt forces for the most unfavorable stiffness of the rubber. Even for this conditions the lifespan of the bolts and the connectors is not affected by the forces due to traffic loading.
In conclusion, the results show that the iSRR bolts retains more of the applied preloading force over a long period than the Lindapter Hollo bolts. Short-term behavior has been similar between the bolts but has significantly been impacted by a rubber interlayer between the clamping plate and the FRP bridge deck. For further research it would be interesting to optimize the positioning of the rubber layer and investigate how this impacts the results.