*4.2. Sensitivity Analysis*

The relationship between structural reliability and stochastic variables can be examined through sensitivity analysis [60]. The reliability index of the structure in the other two stochastic contexts (the stochastic structural resistance and stochastic loading condition) is shown in Figure 12. The reduction of the randomness of structural resistance or loading conditions can improve the reliability index, and the safety and stability of the structure also can be enhanced.

**Figure 12.** The reliability index in different stochastic contexts.

To study the impact of stochastic variables such as *d*, *f'c*, *fy*, and *SQ*, their multiples are changed and their relationship with the reliability index is shown in Figure 13. The reliability index can be improved effectively with the increase of *f'c* and *fy* or the decrease of *SQ*. However, there exists a complex relationship between slab depth *d* and reliability index; the reliability index is reduced when the multiple of *d* is between 1.15 and 1.35. The distribution of structural resistance with 1.3*d* is shown in Figure 14, which can be used to understand the reason for the reduction of the reliability index. The discontinuous distribution of structural resistance is existed, and the transition of failure modes from flexure to punching shear may exist, both through experimental and theoretical observations [22,61–63]. Therefore, the standard deviation of structural resistance is large, and the reliability index calculated by that is small.

**Figure 13.** Impact of stochastic variables with different multiples on reliability index.

**Figure 14.** Distribution of structural resistance with 1.3d.
