# Investigations on Interface Shear Fatigue of Semi-Precast Slabs with Lattice Girders
## 4 Fatigue Tests on Semi-Precast Slabs with Lattice Girders
### Test Setup and Test Execution  
For the first sub-tests, the single span slabs were tested in four-point bending. The load from the test cylinder was transferred by a steel girder so that the shear spans (regions between load application and support) were one-third of the total span. A schematic depiction is given in Figure 11a. Figure 15a,b show the experiments within the IMB laboratory. In such test setup, shear is constant along both shear spans, while it is zero at the midspan between both points of load application, where the distribution of the bending moment is constant and has maximum. After fatigue failure within the shear span of the weaker slab end in the first sub-tests, a second sub-test was performed in which the setup was rearranged to three-point bending by moving the support from the fractured side to the previous load application and strengthening the fractured end of the specimens by external steel profiles. This testing procedure allowed the continuance of the cyclic testing of the shear span at the stronger slab end with identical loading conditions (with regard to shear and bending moment distribution) until fatigue failure (Figures 11b and 15c,d). The fatigue tests in Series 0 were started by deformation-controlled monotonic loading with 0.5 mm/min until flexural cracks reached the interface. This load level was defined as maximum load for the cyclic loading. For Test Series 1 and 2, the maximum loads were  
Figure 15: Test setup for fatigue tests: Sub-Test I for Test Series 0/1 (**a**), Sub-Test I for Test Series 2 (**b**), Sub-Test II for Test Series 0/1 (**c**), and Sub-Test II for Test Series 2 (**d**). previously defined to be 60% to 80% of the calculated static interface resistance according to [29]. For specimens with an interface roughness of \(R_{\text{t}}\approx 0.9\) mm, the interface resistance of a rough interface was considered. The reference value for specimens with high interface reinforcement ratios was the calculated static shear resistance. After applying the initial maximum load, the load range was defined to be between 30% to 75% of the maximum load. Thereby, the calculated stress ranges in the lattice girders were designed to be about \(\Delta\sigma_{\text{s}}=200\)\(\text{N}/\text{mm}^{2}\). The fatigue load was applied in a force-controlled manner, starting with a frequency of \(f=0.1\) Hz with continuous measurements of strain gauges and displacement transducers. After 100 load cycles, the frequency was increased to \(f=2.8\)-\(5.8\) Hz, depending on the deflection of the specimens. The displacement and strain measurements were monitored in periods after 1000 or 2000 load cycles. Depending on the reached number of load cycles, crack distribution, and displacement and strain measurements, the load range was increased in the first instance followed by increasing the maximum load. After failure at one side of the specimen in the first sub-test, the other side (shear span without failure) was subjected to the ultimate load levels of the first sub-test. If the state of fracture did not allow proceeding with the fatigue test, the second side was monotonically loaded until failure. The implemented maximum shear and shear ranges of the initial fatigue loading and the fatigue loading when failure occurred are summarized in Table 5. The authors of [43] give a comprehensive overview of the applied load history for each specimen.