## 1 Introduction  
Through the segmental construction method was said firstly used in China on arch bridges in the 7 th century and was used in Europe until the 12 th century, the first segmental precast concrete bridge was Choisy-Le-Roi, built in 1962 by [PERSON] and [PERSON], crossed the Seine River in France [1; 2; 3]. After that, with the development of prestressing techniques, segmental precast bridges are used in highway bridges, urban viaducts, and some railway bridges more and more [4; 5; 6; 7]. In recent decades, due to the advantages of less traffic disturbance, low environmental pollution, and short construction period, segmental precast bridges are vigorously promoted in China, especially for the application in urban viaducts and transit railway [8; 9; 10]. Segmental precast bridges are defined as bridges consisted of discrete segments stressed together by prestressed tendons to form bridge superstructure and substructure [2; 11]. Connected through the mechanical interlocking of multiple keys in the web section of the segments, segmental precast bridges are expected to behave as a monolithic structure and maintain allowable stress state for the serviceability limit state. In AASHTO (American Association of State Highway and TransportationOfficials) bridge design specifications [12; 13; 14; 15], it is emphasized allowable compression and tension stresses for segmental precast bridges depending on the type of joint and the presence or absence of bonded reinforcing across the joints. Without epoxy and temporary post-tensioning, dry joints are designed with smaller reduction factor for the shear capability and higher residual compression. These may result in thicker web walls or greater amounts of post-tensioning steel. But compared with undesirable brittle failure in epoxied joints, segmental precast bridges with dry joints are more favorable, moreover, cost-saving in epoxy construction [15; 16; 17; 18]. Multiple keys distributed over the height of the web and flanges of the segments play important roles in the following three aspects, (1) aligning segments during erection, (2) transferring the shear force between segments during service, (3) ensuring durability by protecting the prestress tendons against corrosion where the tendons pass through the joints. According to AASHTO LRFD (Load Resistance Factor Design)-17 [12], shear keys between segments should be utilized to prevent relative sliding between adjacent segments in segmental precast bridges. In conclusion, the behavior of segmental precast bridges is dependent on the behavior of the joints between segments [19; 20]. Through experiments and finite element analysis, researchers have demonstrated that the prestress value, shape, and number of the keys, concrete strength, friction coefficient, etc., are all significant parameters affecting the shear capacity of the dry joints. Based on the research results, the different shearing capacity formula of dry joints were proposed and discussed. As early as in 1983, through experiments on different types of joints, including no keys, single large key, and multiple keys, [PERSON] and [PERSON] [21] investigated the shear transfer strength across these types of joints used between adjacent segments of segmental precast bridges. Experimental results showed that the failure mode of the dry joint specimen is a direct shear failure at the key root. According to the test results, the formula of the shear bearing capacity \(\mathbf{V}\) of dry joint was proposed, namely, \(\mathbf{V}\) is the sum of \(\mathbf{V_{f}}\), and \(\mathbf{V_{c}}\). Here, \(\mathbf{V_{f}}\) is the friction resistance of the keys, \(\mathbf{V_{c}}\) is the shear resistance at the concrete key root. The formula was later adopted by AASHTO [15]. 1990, [PERSON] [22] conducted direct shear tests on keyed joints, considering parameters, such as a number of keys, prestressing level, and the epoxy thickness.