# Fatigue Assessment of Prestressed Concrete Slab-Between-Girder Bridges
## 5 Conclusions  
A number of existing slab-between-girder bridges in the Netherlands do not fulfil the requirements of the newly introduced Eurocodes when these bridges are independently evaluated for punching (both static and for cycles of loading). The Eurocode model for determining the punching shear capacity is an empirical model, derived from the results of (mostly concentric) slab-column connection tests [44]. The structural behavior of the thin slabs in slab-between-girder bridges is different from that of slab-column connections. In particular, the development of compressive membrane action increases the capacity significantly. To study the structural behavior of slab-between-girder bridges, we selected as a case study the Van Brienenoord Bridge because it has the most critical slab geometry (largest span-to-depth ratio for the slabs) of this subset of bridges in the Dutch bridge stock. Based on the geometry of the case study bridge, we built two setups in the laboratory at a 1:2 scale and carried out static and dynamic tests. The outcome of the static tests could be used for assessing the static punching strength of the Van Brienenoord Bridge. Using the method given in the Eurocode for design by testing, a factor for converting mean values in the design values of 1.53 was derived. Using this approach, the resulting Unity Check for punching shear of the Van Brienenoord Bridge became 0.31. The outcome of the fatigue tests could be used to derive the Wohler curve for thin slabs in slab-between-girder bridges. Analyzing the fatigue live load model, we selected two critical loading cases for the fatigue assessment: the case with a single wheel load, and the case with two wheel loads (one of each axle). For both cases, we obtained the results of fatigue tests, and thus a Wohler curve. The assessment was then carried out based on a service life of 100 years, which led to 500 million cycles for the single wheel load, and 250 million cycles for the double wheel load. Considering the factor to convert the mean values to design values of 1.622 as derived from the static tests, we compared the applied load ratio to the load ratio resulting from the characteristic (5% lower bound) Wohler curve. Comparing these values gives a Unity Check of 0.39, for the case with a single wheel print, and of 0.37, for the case with a double wheel print. Evaluating the results of the Unity Checks, we could identify the most critical case, which was (by a small margin) the case of fatigue punching under a single wheel load. However, the resulting Unity Checks were much smaller than the limiting value of 1.0. As such, the conclusion is that the Van Brienenoord Bridge meets the Eurocode requirements for static punching and fatigue. Since the case study bridge was selected based on the most critical geometry, we could say that by extension, all other slab-between-girder bridges in the Netherlands meet the Eurocode requirements for static and fatigue punching. However, this final conclusion is only valid for bridges without deterioration and material degradation. Routine inspections remain an important bridge management tool to identify bridges that require further study. Conceptualization, C.v.d.V. and H.S. ; methodology, C.v.d.V., R.K., and E.O.L.L. ; validation, E.O.L.L. ; formal analysis, R.K. and E.O.L.L. ; investigation, R.K. and C.v.d.V. ; resources, H.S. ; data curation, E.O.L.L. and R.K.; writing--original draft preparation, E.O.L.L. ; writing--review and editing, R.K., C.v.d.V., and H.S. ; visualization, R.K. and E.O.L.L. ; supervision, C.v.d.V. and H.S. ; project administration, C.v.d.V. and H.S. ; funding acquisition, C.v.d.V. This research was funded by Rijkswatersstaat, Ministry of Infrastructure and the Environment. The APC was funded by the Delft University of Technology. The authors wish to express their gratitude and sincere appreciation to the Dutch Ministry of Infrastructure and the Environment (Rijkswatersstaat) for financing this research work.