# Fatigue Assessment of Prestressed Concrete Slab-Between-Girder Bridges
## 4 Discussion  
In the previous two paragraphs, we calculated the Unity Checks for static punching (\(UC\) = 0.31), for fatigue punching of one wheel load after 500 million cycles of the single load (\(UC\) = 0.391), and for fatigue punching of two wheel loads after 250 million cycles of the axle (\(UC\) = 0.37). Comparing these Unity Checks leads to the conclusion that the most critical case is punching fatigue for a single wheel load. However, the difference between the punching fatigue Unity Checks for one and two wheel loads was negligible. In addition, the Unity Checks were small, and significantly smaller than the limiting value of 1.0. This analysis shows the beneficial effect of considering compressive membrane action.  
All resulting Unity Checks were smaller than the limiting value of 1.0. This result means that the code requirements for static and fatigue punching were met for the case study bridge. This outcome directly shows the benefit of testing a scaled version of the Van Brienenoord Bridge in the laboratory.  
In addition to the conclusion that the Van Brienenoord Bridge met the code requirements for static and fatigue punching, we need to recall that this case study bridge was selected since it had the most critical geometry (largest span to depth ratio for the slab) of the existing slab-between-girder bridges in the Netherlands. As such, the conclusion becomes that all slab-between-girder bridges in the Netherlands, which form a well-defined subset of bridges in the Dutch bridge stock, fulfil the Eurocode requirements. Drawing this conclusion is valid, since these bridges were all built in the same time period, with the same materials, and using the same execution techniques--and are thus all very similar, with only small variations in the geometry and material properties.  
However, a side note that we should place with the conclusion that all slab-between-girder bridges in the Netherlands meet the requirements for static and fatigue punching, is that this conclusion is only valid for bridges without material degradation or other forms of damage. To ensure this premise, routine inspections remain necessary. Inspections are an important tool within the bridge management toolbox. If during an inspection indications of material degradation or damage are found, the bridge requires further analysis, and it should be evaluated to check that the conclusion that was based on an undamaged structure is still valid.  
For this research, the outcome was twofold: (1) the small resulting Unity Checks based on the experimental results, and (2) the fact that with this approach, the existing slab-between-girder bridges have been shown to fulfil the code requirements. This result also shows that constructing the 1:2 scale setups in the laboratory has been beneficial in the assessment of existing slab-between-girder bridges. Whilst building a 1:2 scale bridge in the laboratory may be considered expensive and time-consuming, testing such a setup gives unique insights on the overall structural behavior of a structural system. Testing at the component level cannot provide such insights. Therefore, the cost-benefit analysis of these experiments is in favor of testing a structural system. Taking this approach is not common, but it may be become an interesting approach for ministries or departments of transportation when they are confronted with a problem for an entire category of bridges.