## 1 Introduction
Consequently, the above works are no longer suitable for the reliability evaluation of existing simply supported T-beam bridges. Reinforcement steel corrosion can also cause stiffness changes in bridges. Moreover, load action is mainly calculated by the modified eccentric compression method, with stiffness as one of the main parameters. [PERSON] and [PERSON] et al. analyzed the relationship between steel corrosion degree and deflection and strain of bridges using laboratory-accelerated and static load tests. The results demonstrated that both structural resistance and stiffness would decrease when steel corrosion occurred [29; 30]. [PERSON] et al. proved that reinforcement corrosion increased the vulnerability of bridges while reducing stiffness [31]. Based on accelerated and fatigue load testing, [PERSON] et al. studied the flexural stiffness of a corroded beam under repeated loading [32]. It was found that if quantization between reinforcement corrosion and structural stiffness is established, it will be effective for the accurate reliability analysis of simply supported T-beam bridges considering the effect of steel corrosion on LLD. The American Concrete Association put forward the product of the elastic modulus of concrete and the effective moment of inertia to calculate the flexural stiffness of cracked concrete structures [33]. Based on the flexural mechanical experimental study of corroded reinforced concrete bridges, a modified model of structural stiffness was obtained by regression analysis [34]. On this basis, experimental results can be deeply exavated to obtain the LLD coefficient calculation method under the condition of steel corrosion, which improves the accuracy of load action analysis. In practical engineering, the corrosion process is accelerated under the action of vehicle load, which further aggravates the decrease in bridge stiffness [35]. When the stiffness of a simply supported T-beam bridge decreases, it will affect the reinforcement corrosion process with the load action redistributed. Hence, an iterative algorithm can be employed to deal with the interaction between vehicle load, chloride erosion process, and reinforcement corrosion. The chloride erosion process is directly related to the water/cement ratio of concrete [36]. In the Chinese concrete design code [37], the formula between water/cement ratio and concrete strength is proposed. Thus, the water/cement ratio computed by the measured data can be integrated into the iterative process mentioned above, which greatly improves the accuracy of bridge reliability analysis. Mid- and small-span bridges account for the largest proportion of the existing bridge structure system, among which simply supported T-beam bridges are widely used due to their reasonable structure, convenient construction, and economical efficiency. However, the variation of LLD caused by reinforcement corrosion has a great adverse influence on the reliability of simply supported T-beam bridges. To overcome this drawback, a reliability analysis method is established considering the variation of structural resistance and LLD influenced by reinforcement corrosion. In this paper, a calculation method for corrosion rate and degree of reinforcement is proposed based on the measured data of concrete strength and concrete cover thickness. Consequently, reinforcement corrosion analysis is improved by the proposed method, in which the relationship between reinforcement corrosion and water/cement ratio is innovatively derived by inspections of concrete strength. The LLD theory considering the effect of reinforcement corrosion is formed using a modified eccentric compression method and an iterative algorithm, of which the parameters are updated by Bayesian theory without prior information. Considering the influence of reinforcement corrosion on the LLD theory, the modified eccentric compression method is optimized by effective stiffness. This provides an effective method for the vehicle effect calculation of corroded reinforcement bridges.