# Experiment on Flexural Fatigue Performance of Precast Bridge Deck Joints with Loop Connections
## 1 Introduction  
With the promotion of Industry 4.0 and Made in China 2025, the industrial construction of bridges has been developed rapidly [1; 2; 3]. Prefabricated assembly technology has been widely used in bridge engineering [4; 5]. The connection quality between precast segments determines the strength and stability of the whole structure [6; 7; 8]. Therefore, the reliable connection between precast structures is the key to ensure the construction quality of prefabricated structures. In recent years, several research studies have been conducted on the structural form and mechanical properties of bridge deck joints [9; 10; 11]. Wet joints are the main structural form to realize the reliable connection between precast bridge decks. However, since the bridge deck directly bears the vehicle load, the joint structure becomes the weakest part of the bridge deck [12]. Under the cyclic action of vehicle load, the stress state of the wet joint of a bridge deck is always in alternating states [13]. And, a problem will occur due to different types of effects on the wet joint [14]. In response to this problem, [PERSON] et al. [15] have carried out research on the optimum shape of a concrete joint under flexural conditions. Based on the optimal shape and dimensions of the joint obtained using finite element analysis, 14 specimens were tested under flexural and shear conditions. It can be concluded form the test results that shear keys can prevent structural cracking and the joint depth can increase the stiffness of the joint. Furthermore, [PERSON] et al. [16] investigated the loop joint and proposed a modified strut-and-tie model based on the finite element simulation. In this model, the effective strength and the width of the concrete compressive strut were considered to fit the special-force mechanism of the loop joint. [PERSON] et al. [17]studied the influence of joint shape, reinforcement ratio, and some other parameters on the wet joint using simulation. They concluded that the performance of a joint can affect the flexural stiffness of the beam structure, and with the increase of the reinforcement ratio of the beam, the wet joint can perform as well as the integrate beam. The research mentioned above involves the shape of the joint, force transmission mechanism, and reinforcement structure of the joint. It ensures the reasonable utilization of the mechanical properties of wet joints. In addition, some research has also been carried out on the innovative application of joint connection materials. [PERSON] et al. [18] applied two kinds of hybrid fibers into the ultra-high-performance fiber-reinforced concrete. Parameters were studied, and the performance of concrete with the hybrid macro-micro steel and macro-steel-polypropylene fibers were also compared. [PERSON] et al. [19] reviewed the existing studies about the bonding behavior between fiber-reinforced concrete and engineering cementitious composites with reinforcing steel bars. It can be concluded from the review that the bonding strength can be improved with several factors, such as compressive strength of engineering cementitious composites, the cover thickness, etc. The joint with loop connections is generally the longitudinal loop bar overlapped in the joint segment, and the transverse steel bars are arranged in the overlapping area [20]. Then, the concrete at the joints is poured and the joint with loop connections is formed. Considering that the joint with loop connections is a relatively new structural form, the degradation characteristics of this kind of joint under a fatigue load are not clear. The main purpose of this study is to clarify the applicability of loop connection in different types of prefabricated structural joints. At the same time, the degradation of flexural fatigue performance of deck joints with loop connections is investigated as well.