# Investigations on Interface Shear Fatigue of Semi-Precast Slabs with Lattice Girders
## 4 Fatigue Tests on Semi-Precast Slabs with Lattice Girders
### Fabrication of Test Specimens  
The precast slabs for the initial specimens of Series 0 with two rows of lattice girders were manufactured in the prefabrication plant Elskes in Kamp-Lintfort, Germany. The reinforcement in the precast slab was in accordance with Figure 13, but with a support overlay of 20 cm and additional stirrups along the slab's ends. The slabs were cast with a concrete C25/30 and a surface left as cast. After concrete hardening, the precast slabs were transported to the laboratory of IMB. Before applying the in situ concrete with a design concrete strength of C25/30, the interface of EG02 was additionally weakened by a bond breaker to prevent an adhesive bond and to achieve a very smooth surface quality. The specimens of the following Test Series 1 and 2 were manufactured at IMB. The precast slabs of Test Series 1 generally followed Series 0, but with a smaller support overlay of 15 cm and without edge stirrups to test a more adverse case for interface shear failure (Figure 13). The roughness of the interface was aspired to be \(R_{\rm t}\) = 0.9 mm for Specimens \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Series 0** & **Series 1** & **Series 2** \\ \hline dimensions & & & 420/85/36 \\ (\(l\)/\(b\)/\(h\)) (cm) & 190/85/16 & 180/85/16 & (EG10–13)390/85/33 \\ height precast slab/ & & & (EG14) \\ in situ concrete (cm) & 7/9 & 7/9 & 7/29 (EG10–13) \\ effective depth \(d\) (cm) & 13 & 13 & 7/26 (EG14) \\ distance load-support \(a\) (cm) & 50 & 50 & 130 \\ lattice girder type & KTS 100 & KTS 100 & EQ 30 \\ shear slenderness \(a\)/\(d\) & 4.0 & 4.0 & 4.0 \\ long. reinforcement \(\rho_{\rm l}\) (\%) & 2.0 & 2.0 & 2.0 \\ \hline \hline \end{tabular} \(l=\) total length; \(b=\) width; \(h=\) total height.  
\end{table} 
Table 3: Dimensions and geometrical parameters of test specimens. EG03-EG08 without mechanical post-treatment. Specimen EG09 had a rough surface by slightly roughening after concrete casting. In Test Series 1, two, three, and four rows of lattice girders were applied, and the concrete strength for both precast slab and in situ concrete varied between C25/30 and C50/60. For the specimens of Test Series 2 with a precast slab of 7 cm, the interface roughness was about \(R_{\text{t}}\) = 0.9 mm, in accordance with Series 1. The in situ concrete layer for EG10-EG13 was 29 cm. To determine the effect of the height of the concrete cover in the compression zone, the in situ concrete layer of Specimen EG14 was reduced to 26 cm. The interface reinforcement varied between two and four rows of lattice girders and the concrete strength was C25/30 and C50/60. Figure 13 exemplarily shows the dimensions and reinforcement detail of the Series 1 specimens with two rows of lattice girders (EG03, EG06, and EG09). The parameters and material properties of the test specimens are summarized in Table 4. The reinforcement details of the other specimens as well as the material properties of concrete and reinforcement are illustrated in [43]. According to the technical approvals of the lattice girders, the longitudinal reinforcement must be fully anchored at the support. Since extending the support overlay and applying additional stirrups along the support would have a positive effect on the interface shear resistance, the anchorage of the longitudinal bars was enhanced by screw-nuts. The transverse (t) reinforcement was determined to be 20% of the longitudinal reinforcement with \(\mathcal{O}_{\text{t}}\) = 10 mm bars and yield strength of \(f_{\text{y}}\) = 500 N/mm\({}^{2}\). To ensure a crack formation of flexural cracks in the area of the welded sections of the lattice girders, triangular crack inducers were placed at the bottom side of the concrete slab at the position of the welds to produce comparable conditions of flexural crack initiation and shear crack propagation.