For the renovation of the Suurhoff bridge, Arup decided to design and propose a new, innovative strengthening scheme, which improves the fatigue performance of the bridge deck and extends the design life of the bridge by at least 15 years. In this strengthening scheme, a steel plate is placed on top of the existing deck plate with a layer of epoxy in between. Preloaded injection bolts are also used to connect the strengthening plate with the deck plate. This strengthening techniques has clear advantages over the current alternatives with regard to weight, execution time, risks and flexibility in the design.
In order to better understand the behaviour of the renovated bridge deck, verify the effectiveness of the strengthening scheme and check the accuracy of the numerical models, a monitoring scheme is desirable. This is an important step in the development and optimisation of the strengthening approach, especially when the goal is to apply the scheme more often on future bridge renovation projects. To achieve this, the two research questions of this thesis are formulated as follows:
What is the effectiveness of strengthening an orthotropic steel deck with a bonded & bolted strengthening plate?
How can the behaviour of the bridge be numerically modelled to accurately capture the improved fatigue resistance?
This question will be answered through a combination of monitoring and finite element modelling. First, a monitoring scheme is set up with 16 strain gauges that are installed on the deck plate, troughs and cross girder. Quasi-static load tests are executed using a truck with known weight, both before and after the application of the strengthening scheme.
The load tests were successfully and accurately carried out and the results show a large reduction in the stress cycle. Stresses in the troughs are alleviated by 45-55% and stresses in the deck plate are reduced by 85-90%. This is largely in line with what was expected during the design.
Furthermore, the used FE models are validated so that more confidence can be gained in the design decisions. The full influence line is simulated, with the truck positioned at more than 120 longitudinal locations. The numerical modelling was able to accurately predict the shape and magnitude of the influence line generated by the truck loading. A difference in peak value between experimental and numerical results of no more than 25% was observed. The largest differences are observed for local bending in the deck plate of the unstrengthened bridge, but this is largely explained by the large sensitivity to the exact wheel position. For the strengthened bridge, a very good match is obtained in almost all locations. A difference between numerical and experimental results of no more than 10% is observed when not considering the area close to the bolts.
Close to the bolted connection (±200 mm), no accurate results can be obtained with a simplified modelling approach that uses shear springs to model the bolts. However, the obtained numerical results are conservative compared to the experimental results. Some simple modelling adjustments have been applied but are unable to significantly improve the results. A detailed modelling approach has successfully been applied in which the bolt has been modelled fully in solid elements. The preload is implemented through a dynamic relaxation phase, so the bolt force is transferred through friction of the plates without any relevant increase in computation time. Therefore, this modelling technique can relatively easily be applied in a global FE model. This modelling technique is more accurate, and analyses have successfully managed to reduce the error by 50%. However, stresses close to the bolt are still overestimated even with this advanced modelling approach and more research is needed for a complete match in this area.
In conclusion, the largely matching results reinforce the decisions from the design report. More confidence is gained in the static and fatigue design life, acknowledging the potential of this new strengthening scheme for future applications.
As recommendations for future research, more testing and design work could be carried out to further optimise the design of the strengthening scheme. Furthermore, the temperature loading can be investigated through testing and monitoring in order to reduce this critical load case. Lastly, more detailed local FE modelling around the bolted connection can help understand the behaviour in this area. This can further increase the potential of the strengthening scheme when bolts are applied in close proximity of critical fatigue details.