## 1 Introduction  
Prefabricated concrete beams have been widely used in short- and medium-span highway bridges in China since the 1970s. A large portion of these beams are made up of hollow slab girders due to their advantages such as high production quality, installation convenience, high bridge clearance, and low construction cost [1]. Considering the bearing capacity and design width of the highway bridges, concrete hollow slabs are commonly arranged side by side with the span being less than 30 m. The load in the transverse direction can be transferred by tie bars [2] and hinge joints [3]. As such, an integrated beam structure is formed for the hollow slabs. However, only the hinge joints are employed in the design of the hollow slab bridges in China to reduce the cost, which leads to severe hinge joint damage during the bridge service life in the highway system [4]. The damage process generally includes two periods. In the first period, cracking occurs inside the hinge joint under the traffic loads. Longitudinal cracks on macroscale gradually form, and some cracks may extend to the bridge overlays. In the second period, concrete cracks continue to develop. Humid air and water will permeate into the joints along the cracks, leading to the concrete spalling and corrosion of the rebars [5]. With the increase of the hinge joint damage, transverse connections between the girders are weakened, and hollow slabs may behave individually under the non-uniform distributed load. The mechanical performance of the bridge will also deteriorate, and the bridge service life is shortened. To ensure the safety of the highway bridges, it is important to accurately evaluate the transverse connectivity of the hinge joints and the durability of the hollow slab girders. Visual inspection is a common method for checking the damage condition of concrete bridges [6; 7; 8]. For the hollow slab bridges, the condition of the hinge joints or the girders can be qualitatively assessed by visual inspectors. When the features such as the cracks along the joint region or the water seepage at the bottom of the joints are found, the joints may be considered as severely damaged [9]. The girders are recognized as unsafe or severely deteriorated if obvious cracking and spalling or the rebar corrosion is observed [10]. However, the status judgements are subjective for some features, and the reliability of the assessment depends on the inspectors' education level and experience [11]. In addition, a quantitative evaluation of the joints or girders cannot be realized based on the visual information. To obtain the change of the transverse connectivity after the joint damage, load tests are usually performed, and damage index of the hinge joints are proposed by the girder responses [4; 12]. Modal parameters are also employed by many scholars [13; 14] as the certain modal shape or shape difference index is sensitive to the joint damage. As for the durability evaluation of the concrete bridges, multiple parameters are required in the field test such as the concrete strength, corrosion degree of the rebars, and carbonation depth of concrete [15], and an analytic hierarchy process (AHP) is commonly employed considering the involved parameters. A key component of the evaluation of bridges' condition and their components is the establishment of a relationship between the evaluation results and bridge parameters. With the rapid development of machine learning, much effort has been invested in the application of artificial neutral networks (ANN) in bridge engineering [16; 17; 18; 19; 20]. [PERSON] and [PERSON] [16] found that neural networks were successfully trained and used in rating conditions of reinforced concrete bridge based on bridge type, span length, and other parameters. [PERSON] et al. [17] evaluated the bridge performance using an ANN and measured strains at different locations. [PERSON] et al. [18] used an ANN to accurately predict the grouting compactness in concrete beams with a number of detection parameters.