# Study on New Bolted T-Stub Connection with Inserted Plates under Axial and Cyclic Loads
## 4 Test Observations, Results and Analysis
### Compression Test
#### 4.2.2 Test Data Validation  
The test results in Figure 7 also provide the basis for verifying the mechanical model of compressive bearing capacity proposed in Section 2. In order to confirm the feature points on the test curve, including the yield point and the ultimate bearing point, a classical solution was adopted that can be summarized as follows: firstly, the secant stiffness of the elastic stage of the curve is defined as the initial stiffness \(K_{i}\), and the characteristic stiffness \(K_{st}\) is determined through the mean value of stiffness in the strain hardening stage of the curve. Secondly, two lines \(OA\) and \(AB\) are drawn with slopes equal to the stiffness values of \(K_{i}\) and \(K_{st}\), respectively, which pass through the intersection point of lines \(AB\) and \(OA\). A third line perpendicular to the \(X\) axis will intersect the monotonic curve at point \(C\), which is the yield characteristic point. The corresponding coordinate values are the yield force \(P_{y}\) and displacement \(\Delta_{y}\). Similarly, the intersection point between line \(AB\) and the curve is the ultimate bearing point, allowing the ultimate load \(P_{u}\) and the displacement \(\Delta_{u}\) to be fixed according to the coordinate values, as shown in Figure 8.  
Applying the approach of defining feature points to this study, the yield strength \(P_{y}\) of specimens was figured out using a monotonic compressive test that combined the calculation values based on the design equations proposed above (the comparison results are listed in Table 2). The theoretical bearing capacity of specimens in groups TC and WA was derived from Equation (3), while that of the specimens in group WB was calculated using Equation (5) in Section 2. The deviations between the test values and the theoretical values were quite reasonable, and in most situations the latter was less than the former, which indicates the design formulas were conservative. It is noteworthy that the strength of the weld could not be fully considered in this study, which is another reason for the lower theoretical value in groups WA and WB. The negative difference that occurred in specimen WB-P-75-52-C lied in the overall strength loss from the local buckling of web during the test. The thick flange and wide plate together resulted in a very limited deformation capacity and flange space, meaning that the web  
Figure 8: Definition of characteristic points.  
Figure 7: Relation curves between axial force and displacement measured in a monotonic compressive test, representing specimens in groups (**a**) TC, (**b**) WA and (**c**) WB.  
buckling occurred as a phenomenon of the compression of the classical T-stub connection, rather than the bolts yielding as expected in the theoretical prediction. This demonstrates that Equation (5) is not applicable when the T-stub strength is greater than that of the bolts and the plate width exceeds a certain range (which this paper later determines). The corresponding configuration is also not recommended in practice. The experimental results prove the good reliability of the mechanical model this paper put forward in general.