## 3 Design of Different Girder-to-Deck Interface Connections
### The Different Girder-to-Deck Interface Connections  
Figure 6 illustrates the cross section of prefabricated composite girders with different girder-to-deck connections proposed in this study. There are four cases proposed. These cases differ in details of reinforcement, stud connector, and precast deck structure. Since the connection with multi-step casting concrete, the design of the girder-to-deck interface connection is different from that of a conventional composite connection. The design of the girder-to-deck interface connection strongly influences the structural performance of the prefabricated composite girder. It includes three critical interface types: (1) interface of monolithic grout, (2) interface between the field-cast haunch and the precast deck, and (3) interface between the field-cast haunch and the steel girder. This study focused on interface types (1) and (2) because of the diversity of these interface types with different girder-to-deck interface connections. It is necessary for in-depth analysis to ensure accurate calculation of connection details. Consequently, the structural performance of the prefabricated composite girder is ensured. The shear planes (interfaces) of different girder-to-deck interface connections are shown in Figure 7. In Figure 7, the mechanical connector is the reinforcement or stud connector. It should be noted that these are only potential shear planes. Based on the evaluation of the number of reinforcements crossing the shear plane at a cross section and shear plane type (monolithic shear plane or cold-joint shear plane),  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Interface Type** & \(c\) **(MPa)** & \(\mu\) & \(K_{1}\) & \(K_{2}\) **(MPa)** \\ \hline Concrete placed monolithtically & & & & \\ _For normal-weight concrete_ & 2.8 & 1.4 & 0.25 & 10.3 \\ _For lightweight concrete_ & 1.7 & 1 & 0.25 & 6.9 \\ \hline Cast-in-place concrete slab on clean concrete & & & & \\ girder surfaces, with surface roughened to an & & & & \\ amplitude of 6 mm & & & & \\ _For normal-weight concrete_ & 1.9 & 1 & 0.3 & 12.4 \\ _For lightweight concrete_ & 1.9 & 1 & 0.3 & 9 \\ \hline Concrete placed against a clean concrete surface, & & & & \\ with surface intentionally roughened to an & & & & \\ amplitude of 6 mm & & & & \\ _For normal-weight concrete_ & 1.7 & 1 & 0.25 & 10.3 \\ _For lightweight concrete_ & 1.7 & 1 & 0.25 & 6.9 \\ \hline Concrete placed against a clean concrete surface, & & & & \\ but not intentionally roughened & & & & \\ \hline Concrete anchored to as-rolled structural steel by & & & & \\ headed studs or by reinforcing bars where all steel & 0.17 & 0.7 & 0.2 & 5.5 \\ in contact with concrete is clean and free of paint & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Coefficients for different interface types.  
the shear planes governing the reinforcement detail of cases 01, 02, and 04 are usually shear planes 1.1, 2.1, and 4.1, respectively. Particularly for Case 03, it is necessary to have a comparison between shear planes 3.1, 3.2, and 3.3. Therefore, not all shear planes are calculated in Section 3.3. The design of the interface type (3) is similar to the design for a conventional composite girder, with reference to Article 6.10.10 of the AASHTO LRFD.  
Figure 6: Prefabricated composite girders with different girder-to-deck connections.  
Figure 7: Potential shear planes of different girder-to-deck interface connections.