# On Flexural Performance of Girder-To-Girder Wet Joint for Lightweight Steel-UHPC Composite Bridge
## 4 Experimental Test of the Second Generation T-Shaped Joint
### Test Results
#### 4.2.2 Nominal Cracking Stress  
The nominal strength calculation method was identical to the comparative scheme. Considering that the crack width in the mid-span was extremely small, the yield value (1033.9 kN) was employed. The calculation results are listed in Table 5. The calculation sections are depicted in Figure 12.  
Figure 11: Test results: (**a**) load-deflection of mid-span; (**b**) load-crack width curve of joint interface.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Section Item** & **P\({}_{\text{cr}}\)/kN** & **M\({}_{\text{cr}}\)/kN-m** & **\(\sigma_{\text{cr}}\)/MPa** \\ \hline Section 2 (interface) & 196.6 & 124.3 & 7.39 \\ Section 4 (interface) & 143.5 & 90.8 & 5.40 \\ Section 1 (matrix) & 424.5 & 268.5 & 15.96 \\ Section 5 (matrix) & 336.5 & 212.8 & 12.66 \\ Section 3 (mid-span, pier top) & 1033.9 & 653.9 & 19.02 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Durability nominal stress of critical sections.  
Figure 12: Gauge and calculation sections layout.  
As shown in Table 5, when the crack width reaches 0.05 mm, the nominal stress of the T-shaped joint interface is in the range of 5.40-7.39 MPa, and the mean value is 6.4 MPa. Compared to the first generation T-shaped joint, even though the reinforcement ratio is slightly lower (i.e., the second scheme is 3.09%, the original is 3.37%), the nominal strength is higher (the original is 4.96 MPa). Furthermore, the strength of the joint center is significantly improved (148%). Combined with the construction advantages, the second generation T-shaped joint optimizes the original scheme significantly. However, as per the original design, the joint interface strength is still the key issue of the design.  
In previous research, [PERSON] [32] proposed five types of UHPC joints suitable for the prefabricated composite deck system. Axial tensile tests on UHPC panels and flexural tests on steel-UHPC composite girders were conducted. The reinforcement ratio was in the range of 3.84-10.54%, and the shape of the joint included: conventional wet joint, irregular joint shape, and steel plate-enhanced joint. The durability-based tensile strength varied from 7.9 to 15.7 MPa for axial tensile tests, and 8.9 to 14.2 MPa for flexural tests. [PERSON] [33] conducted two flexural tests on nine types of UHPC joints suitable for the lightweight steel-UHPC composite deck system. The reinforcement ratio was 4.52-7.92%, and the joint type included: dense reinforcement enhanced joint, steel plate enhanced joint, and welded reinforcement enhanced joint. The test results showed that the durability-based tensile strength was 11.0-26.5 MPa. Additionally, the joint allowable strength was significantly increased with the increasing of the reinforcement ratio.  
According to the test results in the above literature, it can be seen that the following methods can increase the joint strength significantly: (1) increasing the reinforcement ratio at the interface; (2) changing the conventional joint to an irregular shape; and (3) or setting up a reinforced steel plate at the joint bottom. Meanwhile, it is worth noting that the UHPC layer in the above literature is extremely thin (50 mm). On the one hand, the steel fiber distribution is more favorable in a thinner UHPC slab. On the other hand, the orthotropic steel deck located at the bottom can play the role of stiffener with a thinner UHPC layer. Both of them can produce higher tensile strength. While for the joint proposed in the present study, considering the complexity of construction and economic performance, increasing the reinforcement ratio seems to be one of the most preferred solutions to improve the joint interface strength.